#1 Ease of Use of Bottles and Jars for
Users with Arthritis
A study of ease of use issues and potential
design solutions for designers and consumers.
W. Bradley Fain, Ph.D.
Keith A. Kline, M.S.
May 2009
Preface
This monograph documents the methods and results of research conducted in the
Accessibility Evaluation Facility (AEF) of the Georgia Tech Research Institute. The
AEF has performed a series of ease of use evaluations for the Arthritis Foundation, the
Arthritis Society of Canada, and industry customers. Although information about the
outcome of specific evaluations has been withheld, the data and recommendations
presented in this monograph are based upon general outcomes and lessons learned from
research and product evaluations conducted at the Georgia Tech Research Institute.
For additional information about this monograph please contact:
Dr. Brad Fain
Georgia Tech Research Institute
ELSYS/HSID/HSEB Mail Code 0837
Atlanta, GA 30332-0837
Voice (404) 407-7261
Fax (404) 407-9261
brad.fain@gtri.gatech.edu
ii
Table of Contents
Preface................................................................................................................................. ii
Table of Contents ............................................................................................................... iii
List of Tables ...................................................................................................................... v
List of Figures .................................................................................................................... vi
Introduction ......................................................................................................................... 1
Impact of Container Design on People with Arthritis .................................................... 1
Tasks Associated with Container Usage ......................................................................... 2
Container Components and Variations ........................................................................... 4
Container Body ........................................................................................................... 5
Cap .............................................................................................................................. 5
Outer Safety Seal ........................................................................................................ 6
Inner Safety Seal ......................................................................................................... 7
Instructions and Labels ............................................................................................... 8
User Characteristics .......................................................................................................... 10
Types of Arthritis .......................................................................................................... 11
Osteoarthritis ............................................................................................................. 11
Rheumatoid Arthritis ................................................................................................ 12
Evaluation Methodologies ................................................................................................ 13
Ease of Use Issues and Potential Solutions....................................................................... 16
What are the common issues associated with the body of the container? .................... 17
The container may be too large to be gripped comfortably with adequate force. .... 17
The container may slip in the user’s hand. ............................................................... 21
What are the common issues associated with removing a twist-off cap? ..................... 23
Removing a factory sealed cap may require too much force. ................................... 23
Removing a cap may be difficult after it has been tightened by a user. ................... 25
The cap may slip in the user’s hand as he or she attempts to twist it. ...................... 26
Caps with a large diameter prevent a strong grasp. .................................................. 29
Short caps prevent a strong grasp. ............................................................................ 30
The amount of angular rotation required to remove the cap may be too great. ........ 31
What are the issues associated with opening a pop-open cap? ..................................... 32
The amount of force required to pop open the cap is too great. ............................... 32
The surface of the push tab is too small or too sharp................................................ 34
What are the issues associated with removing the outer safety seal or packaging? ..... 35
Removal of some outer safety seals requires the use of a tool. ................................ 35
The outer safety seal is intended to be broken as the product is initially opened, but
the force requirement may be too great. ................................................................... 38
The packaging box does not have a flap or tab for the user to pull. ......................... 40
What are the issues associated with removing the inner safety seal? ........................... 42
The user cannot peel the seal from the container. ..................................................... 42
The user cannot puncture the seal with a finger. ...................................................... 44
What are the issues associated with instructions and labeling? .................................... 45
The text or graphics are difficult to see. ................................................................... 45
The text is difficult to find. ....................................................................................... 46
The expiration date is difficult to find, read, or interpret. ......................................... 47
iii
Design Guidelines ............................................................................................................. 49
References ......................................................................................................................... 55
iv
List of Tables
Table 1: Tasks associated with container usage. ................................................................ 2
Table 2: Hand anthropometry of non-disabled individuals (Sources: [11, 13, 23]). ........ 10
Table 3: Maximum grip diameters of individuals with and without dexterity disabilities
(Source: [11]). ................................................................................................................... 11
Table 4: Maximum grip diameters of individuals with and without dexterity disabilities
(Source: [11]). ................................................................................................................... 19
Table 5: Relationships between maximum grip diameter and cylinder diameter for
maximum grip force. ......................................................................................................... 19
Table 6: Ease of use guidelines for container design. ....................................................... 49
v
List of Figures
Figure 1: An assortment of containers. ............................................................................... 1
Figure 2: Container components. ........................................................................................ 5
Figure 3: A cylindrical plastic container wrapped in a paper label. ................................... 5
Figure 4: An assortment of caps. ........................................................................................ 6
Figure 5: Outer safety seals include (a) packaging boxes, (b) plastic wrappings on the
cap, and (c) rings that bind the cap to the bottle. ................................................................ 7
Figure 6: Outer safety seal design featuring a thin strip of plastic connecting the cap to
the lower ring. ..................................................................................................................... 7
Figure 7: Inner safety seals. ................................................................................................ 8
Figure 8: Example of an expiration date that is difficult to read. ....................................... 9
Figure 9: Joints of the hand ............................................................................................... 12
Figure 10: Rheumatoid arthritis can cause deformation of the joints, resulting in stiffness
and restricted range of motion. ......................................................................................... 13
Figure 11: A user's grip strength (left) and pinch strength (right) are measured. ............. 15
Figure 12: The Wong-Baker FACES Pain Rating Scale. ................................................. 15
Figure 13: Indentions in a container allow a smaller grip diameter. ................................ 18
Figure 14: Indentions in the side of a large container provide good grasping points. ...... 18
Figure 15: A non-cylindrical container is easier for users to grasp. ................................. 21
Figure 16: Containers with shallow threading (left) and steep threading (right). ............. 25
Figure 17: A rubber coating on the cap increases surface friction and decreases required
grip force. .......................................................................................................................... 26
Figure 18: A smooth knob (left) and knurled knob (right) (Source: [10])........................ 26
Figure 19: Average torque generated on round and knurled caps by individuals with
arthritis. ............................................................................................................................. 27
Figure 20: Smoothly contoured knurls. ............................................................................ 27
Figure 21: Widely spaced, smooth knurls......................................................................... 28
Figure 22: Three styles of pop-open caps: the entire cap pops open (left), part of the cap
pops open (center), and a button causes part of the cap to pop open (right). ................... 32
Figure 23: A push tab that is too small and has a sharp edge. .......................................... 34
Figure 24: The indentation on this flip cap is large and smooth. ...................................... 34
Figure 25: The perforations on this outer seal are clearly visible. .................................... 36
Figure 26: The outer seal is broken when the user first twists the cap. ............................ 38
Figure 27: A box with a perforated strip. .......................................................................... 40
Figure 28: A box that provides a large tab under which the user can insert a finger. ...... 40
Figure 29: The inner seal is easy to remove because of the large tab on the edge. .......... 42
Figure 30: An expiration date that is difficult to read. ...................................................... 47
Figure 31: An expiration date that is easy to read. ........................................................... 47
vi
Introduction
According to the CDC’s Morbidity and Mortality Weekly Report, over 46 million
American adults have been diagnosed with arthritis by a doctor [5]. Of these, 19 million
Americans report that arthritis limits their daily activities in some way [6], and nearly 9
million Americans are disabled as a result of arthritis making it the most common cause
of disability in the United States [4]. By 2030, it is expected that arthritis will affect an
estimated 67 million American adults [5].
Many individuals with arthritis experience difficulty performing a variety of everyday
tasks, such as opening and using product containers. The products under consideration in
this monograph include jars, beverage bottles, and non-child resistant pill bottles, which
are collectively referred to as “containers” (see Figure 1). These products vary in size,
weight, shape, texture, safety seal design, and operating force requirements. Each of
these design components affects a user’s experience with the product, especially users
who suffer from the symptoms of arthritis. As a result, users with arthritis may be unable
to use certain products, or may experience considerable pain and difficulty during use.
This monograph discusses aspects of container design that affect ease of use for
individuals with arthritis.
Figure 1: An assortment of containers.
There are two primary reasons why a company may choose to design products that are
considered arthritis-friendly. First, a considerable portion of the market share is
composed of individuals with arthritis, which is the most common cause of functional
physical limitations in the United States. For users with arthritis, ease of use can become
a key market discriminator in a group of similar, competing products. Second, products
that are easy to use for individuals with arthritis will also be easy to use for most of the
general population.
Impact of Container Design on People with Arthritis
Users with arthritis may frequently experience difficulty and pain when attempting to
perform routine tasks such as opening containers. Beyond difficulty and pain, users may
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also feel a sense of helplessness and a loss of independence. These negative feelings are
likely to be directly associated with the product, and may reduce the chance that the
product will be purchased again. Instead, the user may seek a competing product that
appears to be easier to use. A tarnished product image may be extended to all products of
the same brand. That is, a user might assume that all products of a given brand are
equally difficult to use.
Whereas those products that are difficult to use may generate avoidance, products that are
easy to use may generate loyalty to the product and brand. Such products may stand out
in the user’s mind as notable exceptions to the daily frustrations of living with arthritis
and may help to restore a sense of independence.
Tasks Associated with Container Usage
To assess ease of use, the interaction between the user and the product should not be
thought of as a single operation. Instead, the interaction should be decomposed into
distinct operations. In this manner, the ease or difficulty of each operation can be
assessed individually, and specific recommendations for improvement can be provided.
Tasks are identified in a structured analysis of all the users’ actions associated with
product usage. This may be accomplished by observing individuals as they use the
product in a naturalistic setting. It is often beneficial to observe more than one user,
because some users might skip operations or perform them differently than other users.
For example, some users might neglect a container’s instructions for opening. Task
analysis results for container usage are shown in Table 1.
Table 1: Tasks associated with container usage.
1. Grasp and lift the container
2. Review product labeling and instructions
3. Remove the outer safety seal, or open the outer packaging
4. Open the cap
5. Remove the inner seal
6. Dispense contents of the container (extract a pill, pour or drink from
the bottle, or scoop contents from the jar)
7. Close the container
Each of the tasks in Table 1 may present difficulty for users with arthritis. In order to
make a product that is truly easy to use, it is not sufficient to make most tasks easy, while
neglecting one or more tasks. A single, difficult task can represent a significant barrier to
overall ease of use. Hence, designers should carefully consider the ease of all tasks,
rather than focusing on a single task that may seem more salient than others. Below is a
2
description of each task and a brief introduction of the associated container characteristics
that impact task performance.
Grasp and lift the container. For usage and transportation, a container must be grasped
and lifted. In most cases this is a single handed operation, and the other hand is free to
open the container or execute other related tasks. Grasping and lifting a container may be
difficult if the container is heavy, large, or does not provide a good gripping surface.
Individuals with arthritis may experience difficulty due to limited strength, dexterity, and
range of motion. They may also experience pain as they attempt to extend inflamed
joints beyond comfortable positions. As a result, some individuals with arthritis may be
unable to use the product as intended by the manufacturer, or they may risk dropping the
container.
Review product labeling and instructions. In order to safely and effectively use many
products, users must be able to read safety information, expiration dates, and dosage
instructions. This critical information must be noticeable and readable for all users.
Older adults, many of whom have age-related arthritis symptoms, typically have
decreased visual acuity. Therefore, older adults may have difficulty reading product
labeling and instructions that are printed in small font or with poor contrast. Although
this difficulty is not directly related to arthritis, it is an important consideration for a
product’s overall ease of use. Failure to read instructions and labels might have notable
consequences. For example, a user might misread an expiration date that is printed in
small font, and then proceed to consume a product that is no longer safe, efficacious, or
fresh. This could obviously lead to a tarnished brand image, or worse.
Remove the outer safety seal, or open the outer packaging. Outer packaging typically
consists of a box that encloses the container, or a tamper-evident plastic wrapping on the
cap of the container. Users can open a box by tearing it, peeling it open at a flap, or
tearing away a serrated strip. These actions may be difficult for individuals with arthritis
if excessive force is required and if the gripping surface is not adequate. The outer
plastic wrapping on a container can sometimes be removed by tearing or by twisting the
cap to break the plastic. Again, the forces required for these actions influence ease of
use. If the outer seal consists of a non-serrated plastic sheet, most individuals with
arthritis can be expected to experience difficulty. Although these tasks are only
performed once for each product, they can represent significant barriers to overall ease of
use. They also might establish a poor first impression of the product. A user might be
unlikely to purchase the product in the future if the experience is difficult or painful, or if
he or she must resort to using a tool (e.g., scissors).
Open the cap. Traditional cap design requires the user to tightly grasp the cap while
twisting it. Individuals with arthritis often have difficulty performing simultaneous
actions like grasping and twisting. This is particularly true if either one of the actions
requires substantial strength. Factory sealed caps may require more torque than some
individuals with arthritis can exert. A poor gripping surface on the cap or bottle can
compound the problem by forcing the user to exert excessive gripping force. Certain
containers may simply be impossible to open for some individuals with arthritis.
3
Remove the inner seal. Many containers, such as pill bottles, feature an inner safety seal
beneath the cap. The user must remove or puncture the seal in order to access the
container’s contents. Users might attempt to remove most or all of the seal from the
opening by either peeling the seal away from the opening or puncturing and tearing it.
The act of peeling may be difficult for individuals with arthritis if the seal does not
provide a sufficient gripping surface, or if the seal is bound too tightly to the opening.
The act of puncturing a seal may difficult if the required force exceeds that which the
user can exert with a fingertip. Users might resort to using a tool to puncture the seal,
which would not be considered easy usage.
Dispense contents of the container. The act of dispensing a container’s contents might
consist of extracting a pill, pouring or drinking from a bottle, scooping contents from a
jar, or some similar action. The potential difficulties associated with these actions are
similar to those associated with grasping and lifting a container. Individuals with arthritis
may encounter difficulties if the container is too large or heavy, or if the gripping surface
is poor. In addition, difficulty might be encountered if dexterous movements are required
(e.g., scooping contents from a small opening). An inability to correctly perform these
actions may result in spills.
Close the container. After using a product, the consumer must screw the cap onto the
bottle or snap the cap closed. The act of screwing a cap onto a container sometimes
requires a bit of dexterity in order to align the cap threading with the bottle threading.
Due to dexterity limitations, this action might be difficult for some individuals with
arthritis if the cap is short and has a small diameter.
Container Components and Variations
Most containers consist of five principal components (see Figure 2). These include the
container body, cap, labeling, outer safety seal, and inner safety seal. Each of these may
impede easy usage by individuals with arthritis. The following sections describe the
components and their common design variations.
4
Figure 2: Container components.
Container Body
Containers differ from each other by virtue of their material composition, shape, surface
texture, size, and weight. The material composition may be of a hard plastic, glass,
metal, or of a malleable plastic that conforms slightly to the hand. The shape of most
containers is cylindrical, but some are rectangular or elliptical. Some bottles have
vertical indentations that are indented to facilitate grip, or horizontal indentations that
allow a narrower grip. Finally, the container may be wrapped with a plastic or paper
label (see Figure 3).
Figure 3: A cylindrical plastic container wrapped in a paper label.
Cap
Caps (see Figure 4) vary by diameter, height, shape, surface texture, material, operating
force requirements, and opening mechanism. Twist-off caps simply unscrew from the
5
container; these vary with respect to the extent of rotation that is needed to remove the
cap from the container. Flip-top caps are hinged and can be pulled or lifted up, allowing
the product to be dispensed without fully removing the cap. Pop-off caps are those that
can be completely removed from the bottle by pulling or lifting without twisting. Some
caps are hybrids of the aforementioned types. One example is a twist-off cap with a tab
that pops open, so that the container’s contents can be accessed by either fully
unscrewing the cap or by popping open the tab.
Figure 4: An assortment of caps.
Caps can be composed of plastic, metal, or rubber; the composition partially determines
malleability and grip. More malleable materials may yield more readily to certain
operations, such as popping open. More malleable materials may also conform slightly
to the hand, thereby distributing the force and enhancing grip. However, note that if a
cap flexes too much as a user squeezes it then friction will be generated between the cap
and the bottle, making rotation more difficult.
Surface texture is another important factor that affects the ease with which users can grip
caps. Knurled and serrated surfaces generally provide better grip. However, extreme
knurling or sharp serrations can cause discomfort in the joints and skin, respectively.
This is especially true for users with arthritis who may have inflamed finger joints.
Caps may also feature a safety mechanism that prevents tampering or accidental opening.
For example, some pop-off caps, such as gallon milk containers, are bound to the bottle
by a plastic ring that must be peeled away before usage. Some twist-off caps incorporate
a ring that is attached to the lower rim of the cap (e.g., a soft drink bottle). Upon first
opening, the ring breaks away from the cap. The amount of force required to break the
seal varies dramatically between products. Some pop-off caps, such as those used on
certain pain reliever bottles, feature a safety locking mechanism that prevents the cap
from opening unless markings are aligned on the cap and cap.
Outer Safety Seal
Broadly defined, the outer safety seal may be either a box in which the bottle is packaged,
a tamper-evident wrapping on the bottle or cap, or a ring that binds the cap to the bottle
(see Figure 5). Rings that bind the cap to the bottle are discussed in the section on caps.
6
Figure 5: Outer safety seals include (a) packaging boxes, (b) plastic wrappings on the cap, and (c)
rings that bind the cap to the bottle.
A common type of outer safety seal consists of a thin plastic or paper wrapping that
encircles the cap and a portion of the bottle (see Figure 5b). Some plastic seals are
perforated, and may peel away or break loose when the cap is twisted. Others must be
cut or torn before removing the cap. The properties of paper seals are similar to those of
plastic seals. The thickness of the material and the presence of perforations will
determine whether users can easily break the seal by turning the cap, or whether they
must first remove the seal.
A different safety seal design is used on some bottles with flip-top caps. A thin strip of
plastic bridges the gap between the cap and the ring that attaches the cap to the bottle (see
Figure 6). When the strip of plastic is peeled away, the cap is free to flip up.
Figure 6: Outer safety seal design featuring a thin strip of plastic connecting the cap to the lower
ring.
Inner Safety Seal
Many containers feature an inner safety seal that protects product safety and freshness.
This type of seal usually features a tab that a user can grasp and pull either from the edge
of the seal or from a tab that flips up from the center of the seal (see Figure 7).
7
Figure 7: Inner safety seals.
The sizes and operating forces of tabs vary among products. Other seals do not provide a
tab and must be punctured and torn from the closure. The amount of force required to
puncture the seal varies among products.
Instructions and Labels
Instructions and labels may be required for safe and proper usage of a product.
Instructions include opening instructions, dosage information, and instructions for
consumption (e.g., “take with food”). Labels include warnings, such as drug interaction
precautions, and expiration dates.
Instructions for opening the cap are often placed directly on the cap, and are either
engraved or printed. Engraved text and graphics yield poor contrast with the background
surface, and may therefore be difficult to read, particularly in unfavorable lighting
conditions.
Dosage information and instructions for consumption are particularly important for
proper and safe usage of a product. Recommended doses can be displayed in either
paragraph or table format. Typically this information is made easier to find by using a
prominent title and by placing it apart from other text on the container.
Expiration dates are also important for safe and proper usage of a product. A user who
fails to notice an expiration date on an expired product may proceed to consume a
product that no longer meets the manufacturer’s standards, or may even be unsafe for
consumption. Expiration dates are often placed in obscure locations where users are
unlikely to see them, even if actively searching. Moreover, the text is often small,
blurred, and printed with poor contrast to the background. The format of the date may
also be important for identification and comprehension – for example, the meaning of “12
2010” is quite unclear in comparison with “Dec 2010.” The date can be preceded by the
words “use by” or “best before” or “expiration.” Notice that a date without such a prefix
might be interpreted as a “sell by” date.
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Figure 8: Example of an expiration date that is difficult to read.
Finally, warning labels alert users of the dangers associated with a product. Similar to
dosage information, warnings can be set apart by spacing and prominent titles in order to
make the information easier to find.
Common to all instructions and labels, the issues of font size and contrast are important.
Small font and poor contrast can make it difficult for users to find and read information.
A common example is an expiration date printed in black letters on the body of a dark
bottle.
9
User Characteristics
The design of products that are intended for individuals with arthritis should be guided by
anthropometric data and by an understanding of the functional limitations associated with
arthritis. Arthritis is a term used to describe painful inflammation of the joint or joints.
The disability has many causes, and there are over 100 types of arthritis. Inflammation
causes a reduction in tactile sensation and range of movement with a corresponding loss
of dexterity and mobility. Arthritis is the greatest contributor to mobility and dexterity
limitations, the largest category of functional limitations. As noted by TIA Access
(1996) [27], “Individuals have difficulty reaching things and doing complex or compound
manipulations such as pushing while turning or pressing several buttons simultaneously.
Twisting motions may be especially difficult. For individuals with arthritis, controls that
require pinching or rotating are difficult to operate. In addition, individuals who are
functionally limited are unable to exert as much force on controls as individuals without
functional limitations. Individuals with poor muscle control may find it difficult to make
fine motor movements with their fingers and may be restricted to gross movements with
their hand(s).”
Anthropometric data might provide useful guidance for the design of containers for users
with arthritis. There exists only a limited amount of anthropometric data on individuals
with arthritis. However, hand dimensions may not differ significantly between
individuals with and without arthritis [15], except for instances in which arthritis causes
deformation of the bones and joints (e.g., rheumatoid arthritis). These deformities may
prevent a user’s hand from fully encircling a cap or bottle. Table 2 shows anthropometric
data for individuals without arthritis. The data were compiled from several sources [10,
13, 24]. These include measurements from British adults aged 19-65 years [13], and
from British adults of unspecified age [10, 24].
Table 2: Hand anthropometry of non-disabled individuals (Sources: [10, 13, 24]).
Dimension
Gender 5th percentile (mm) 50th percentile (mm) 95th percentile (mm)
Male
173-175
178-189
205-209
Hand length
Female
159-160
167-174
189-191
Male
98
107
116
Palm length
Female
89
97
105
Male
44
51
58
Thumb length
Female
40
47
53
Male
11-12
23
26-27
Thumb breadth
Female
10-14
20-21
24
Male
64
72
79
Index finger length
Female
60
67
74
Male
78
87
95
Hand breadth
Female
69
76
83-85
10
Table 3 shows maximum grip diameters for individuals with and without dexterity
disabilities [10]. Maximum grip diameter is defined as the maximum diameter of a
cylinder that a person can grasp with contact between the thumb and middle finger.
Table 3: Maximum grip diameters of individuals with and without dexterity disabilities (Source:
[10]).
Gender 5th percentile (mm) 50th percentile (mm) 95th percentile (mm)
Male
45
52
59
Non-disabled
Female
43
48
53
Male
34
40
47
Dexterity-disabled
Female
34
40
48
Maximum grip diameter is of particular importance for usage of containers. Users with
arthritis may experience considerable pain when forcibly grasping an object with a wide
grip, in great excess of their maximum grip diameter. Hand breadth should also be taken
into consideration when designing the height of a container. If the container spans the
entire breadth of the hand (or more), then the user can distribute gripping force across the
whole palm and all four fingers.
Types of Arthritis
The term “arthritis” is used to refer to over 100 different diseases that affect the joints of
the body and the areas surrounding the joints. The most common types of arthritis are
osteoarthritis and rheumatoid arthritis. Osteoarthritis is typically associated with the wear
and tear of affected joints and is most prevalent in older adults. Rheumatoid arthritis can
affect younger adults and even children, and is associated with inflammation of the lining
of the joints. Other types of arthritis include fibromyalgia, gout, ankylosing spondylitis,
and scleroderma.
Osteoarthritis
Osteoarthritis (OA) is characterized by the deterioration of cartilage in the joints.
Healthy cartilage cushions adjacent bones and allows for easy joint movement. Thus, the
deterioration of cartilage causes bones to rub against each other, leading to stiffness,
swelling, pain, and restricted range of motion. In the final stages of OA, bits of bone may
float freely within the joint, and the lining of the joint (synovium) becomes inflamed [1].
Symptoms of osteoarthritis are more common in some joints than others. The base of the
thumb and the distal finger joints (see Figure 9) are most commonly affected [1]. These
joints are used in many interactions with containers. Distal finger joints are heavily
involved in certain pinch grips, such as that used to pinch a tab on a container’s safety
seal. They may also be used when puncturing an inner seal with the tip of the finger, or
when grasping a large container or cap. The thumb is involved with all grip types, and
nearly all manual interactions with containers. When gripping large containers or caps,
users may experience pain in the base of the thumb as they adopt a wide grip. However,
pain may also be experienced with smaller grips, such as those used to pinch a safety seal
or to twist a small cap.
11
Figure 9: Joints of the hand
Symptoms are less common in the proximal interphalangeal joints (middle joint;
approximately 35% of individuals with OA), and even less common in the
metacarpophalangeal joints (base of the fingers; approximately 15%) [1]. These joints
are involved in pinching tabs and gripping containers and caps.
Wrists, which are affected in 20% of men with OA and only 5% of women [1], are
involved in lifting and twisting actions. Symptoms are typically symmetric, meaning that
symptoms in one hand are often accompanied by symptoms in the other hand [8]. Thus,
many users may not be able to avoid pain by simply switching hands. A particularly
problematic action for individuals with arthritis in the wrists is the act of twisting open a
tightly secured cap. This can be painful for some users and simply impossible for others.
Rheumatoid Arthritis
Rheumatoid arthritis (RA) is characterized by inflammation and swelling of the joints,
accompanied by pain and restricted range of motion [2]. More advanced RA causes
deformation of the joints, which can prevent natural movements such as straightening the
fingers (see Figure 10). Stiffness and restricted range of motion may cause individuals to
adopt different strategies when using a product. For example, restricted wrist movement
may force users to use many repeated small movements to twist open a cap rather than
one or two large movements. Also, deformation of the finger joints may force users to
adopt different grips (e.g., a lateral “key” pinch rather than a finger tip pinch).
12
Figure 10: Rheumatoid arthritis can cause deformation of the joints, resulting in stiffness and
restricted range of motion.
Symptoms of rheumatoid arthritis commonly appear first in the smaller joints of the body
[2]. RA often affects the wrist joints and the finger joints closest to the hand (the
metacarpophalangeal joints). Pain and swelling in these joints interferes with the ability
to grip and twist objects, especially those that are large. Like OA, symptoms of RA are
often symmetric, affecting the same joints on both sides of the body [2, 20]. Thus, many
users may not be able to simply switch hands to avoid pain.
Evaluation Methodologies
There are two basic methods of acquiring information about human performance: direct
measurement and derived assessment. If the goal is to evaluate the ability of a specific
individual to use a product, then he or she is given a series of tasks to complete, and an
evaluator observes performance. The tasks that are given to the user should be
representative of the tasks associated with use of the product, as intended by the
manufacturer, and the set of tasks should be comprehensive. A list of tasks may be
generated by a task analysis, which may involve observing several users as they interact
with the product. By observing several users, rather than just one, the observer is more
likely to capture all tasks associated with the product.
Direct Measurement. The direct measurement approach allows the collection of
detailed data about the ability of a single individual to interact with a given product,
although the findings may not generalize to a larger population. More robust direct
measurement studies adopt effective population sampling strategies. By testing a diverse
and representative group of users, the evaluator can generalize findings to a larger
population segment with much better accuracy. Effective sampling for ease of use
evaluations for people with arthritis can be very challenging. The variety of functional
abilities and limitations within the population of individuals with arthritis must be
considered. For example, some users may have limited strength, but normal dexterity.
Others may have normal strength, but may experience considerable pain when exerting
force. Still others may have limited reaching and grasping capabilities. A user’s level of
13
experience with the type of product being evaluated may also have a significant impact
on the outcome of the evaluation. For example, experience with difficult inner safety
seals may lead a user to puncture the seal with a fingernail, rather than attempt to grasp
the edge of the seal and peel it off. Therefore, it is necessary to obtain a reasonably large
and diverse sample of the population to which the evaluator wishes to generalize.
Derived Assessment. Derived assessment methods, such as functional assessments,
checklist evaluations, or expert inspections, do not seek to measure human performance
directly. Instead, such techniques are used to determine the extent to which a product
meets formal or informal guidelines that have been associated with desired usability
objectives. A checklist evaluation, also known as a heuristic evaluation, is employed
where a considerable body of knowledge exists about a specific domain of human
performance relative to the product of interest [21]. For example, a significant amount of
data has been collected on the grip and torque strengths of individuals with arthritis.
These data can be used to determine whether a product’s force requirements are likely to
exceed the capabilities of the population of interest. However, given the number of
factors that affect the usability of a container (e.g., size and texture) and the wide
variations of each factor, it may not be feasible to assess a product solely by its adherence
to guidelines. Therefore, it is advisable to combine direct measurements with derived
assessments.
Given the challenges of sampling from a diverse population and the somewhat limited
knowledge of designing for people with arthritis, it is necessary to combine data from
both direct measurement and derived assessment evaluation techniques to obtain the
desired degree of confidence in the evaluation results. Gaps in the knowledge regarding
designing for people with arthritis can be addressed by performing user testing.
Similarly, the sampling issues associated with human performance testing for
accessibility can be addressed by using the derived assessment results to eliminate the
need to test some populations and focus the assessment on others.
A variety of evaluation techniques and methodologies are available to the evaluator
interested in measuring ease of use for individuals with arthritis. For best results, a
combination of objective and subjective measures should be used.
The first stage of the evaluation may be accomplished without user participation. The
evaluator first performs a task analysis in order to identify the actions that are involved in
using the product. Next, the evaluator measures the force required for each of the
physical actions identified in the task analysis. For example, the evaluator may measure
the torque required to break the factory-tightened cap, and the linear force required to
puncture a safety seal. Finally, the evaluator determines whether the product meets a prespecified set of design guidelines that are based on prior research.
The second stage of the evaluation involves user participation. The evaluator should
obtain measurements of the relevant functional capabilities of each user, such as grip and
pinch strengths (see Figure 11).
14
Figure 11: A user's grip strength (left) and pinch strength (right) are measured.
The evaluator may then objectively measure the forces that each user is able to generate
upon the container. This requires instrumentation of the container by, for example,
affixing a torque meter to the base of the container and a connecting rod to the cap.
Objective force measurements for each user may be compared against the forces that are
required to use the product, as measured during the first stage of the evaluation. If a
number of participants are unable to generate the required forces upon the instrumented
container, then a significant portion of the population with arthritis may experience
difficulty with the product.
Next, the user is given an unopened, unmodified product, and is asked to perform the set
of tasks identified in the task analysis. During each task, the evaluator observes
performance and records any difficulty or problems that arise. After each task, the user
may provide subjective feedback about the experience in a free response format, and in
the form of an ease-of-use rating scale. Users may also be asked to report any pain
experienced and rate the severity of their pain, using an instrument such as the WongBaker FACES Pain Rating Scale (see Figure 12). The evaluator should record all such
data, allowing the users to focus their attention on the product. After all tasks are
completed, the users may be asked to rate their agreement with a series of statements
about the product (e.g., “I can use this product without overexerting myself.”). Finally,
the results of the evaluation should be documented in order to affirm or deny the
product’s ease of use, and to provide recommendations to the manufacturer.
Figure 12: The Wong-Baker FACES Pain Rating Scale.
15
Ease of Use Issues and Potential Solutions
Containers have a number of ease of use issues related to the following components:
 Container body
 Twist-off cap
 Pop-open cap
 Outer safety seal
 Inner seal
 Instructions and labeling
The following sections contain detailed information about common ease of use issues for
each of these components. Potential solutions to each issue are proposed, and relevant
design guidelines are presented.
16
What are the common issues associated with the body of the
container?
The body of a container is grasped and lifted during regular use of a container. The
following tasks entail grasping and often lifting the body of a container:
 Transporting the product
 Removing the outer safety seal
 Opening and closing the cap
 Opening or removing the inner seal
 Reading instructions and labels
 Dispensing contents
A number of factors influence the ease with which an individual with arthritis can grasp
and lift a container. These are discussed in the sections below.
The container may be too large to be gripped comfortably with
adequate force.
Detailed Description: Gripping a large container requires a wide grip. Because
individuals with arthritis often experience limited range of motion in affected
joints, they may be simply unable to open their hands wide enough to grasp a
large container. Furthermore, strength declines as grip widens past moderate
flexion. This means that even if a user is able to stretch his or her hand to fit the
container, he or she may be unable to grasp the container tightly enough to
perform other operations.
The hand is most powerful when it is flexed moderately [25]. When the hand
grips a smaller object, grip force is decreased due to inadequate contact with the
object and due to shortening of the muscles. When the hand grips a larger object,
the change in geometry results in a decrease in the amount of grip force that can
be applied. Also, a larger grip places the thumb and fingers in opposition to each
other, rather than in opposition to the palm.
Potential Solutions: Provide grasp points that are narrower than the main body
of the container. If the body of the container is too large to be comfortably
grasped with adequate force, an indention can provide a more narrow grasping
point (see Figure 13). It may not be practical to provide an indentation wide
enough to accommodate the entire hand, but at least the thumb and two fingers
should fit into the indention.
17
Figure 13: Indentions in a container allow a smaller grip diameter.
On very large containers, it may not be feasible to incorporate an indention that
encircles the entire container. In such cases, it may be sufficient to place a pair of
cutouts on one side of the container (see Figure 14).
Figure 14: Indentions in the side of a large container provide good grasping points.
Laboratory testing at GTRI has indicated that the separation between indentations
such as those shown in Figure 14 should not exceed 3 inches (75 mm).
Individuals with arthritis found that a container with a 3.35 inch (85 mm) grip
span was considerably more difficult to hold and lift than a product with a 3 inch
(75 mm) grip span. Steinfeld and Mullick (1990) recommend that a grip span of
no more than 2.8 inches (71 mm) be required [26].
Reduce the diameter of the container. Another solution is to simply decrease the
diameter of the container, or to offer containers of several different sizes from
which users can choose. Individuals with arthritis who struggle with wide grips
can choose to purchase the smaller version of the product. Alternatively,
container volume could be held constant by reducing its diameter and increasing
its height.
18
For maximum grip power, what is the optimal container diameter? The answer
depends in part on the user’s hand size and maximum grip diameter, because
wider grips are associated with decreased strength. Maximum grip diameter is
defined as the maximum diameter of a cylinder that a person can grasp while
maintaining contact between the thumb and middle finger. For non-disabled
adults, maximum grip power can be exerted on cylinders with diameters
approximately 10 mm (0.4 inches) smaller than the maximum grip diameter.
Specifically, the average non-disabled adult can exert maximum grip power on a
cylinder with a diameter of 40 mm (1.6 inches) [25], which is approximately 10
mm less than their median maximum grip diameter ([10]; see Table 4). This
diameter allows the thumb and middle finger to slightly overlap and directly
oppose the palm.
Table 4: Maximum grip diameters of individuals with and without dexterity disabilities (Source:
[10]).
Gender 5th percentile (mm) 50th percentile (mm) 95th percentile (mm)
Non-disabled
Dexterity-disabled
Male
45
52
59
Female
43
48
53
Male
34
40
47
Female
34
40
48
Note that the relationship between maximum grip diameter and optimal diameter
for grip force is somewhat speculative, because the data on these two parameters
were derived from two separate studies [10, 25]. A single, systematic study is
needed to confirm this relationship. Assuming that such a relation exists,
however, we can infer the diameter of a container that should yield maximum grip
power for dexterity-disabled adults, including those with arthritis. The median
maximum grip diameter of dexterity-disabled adults is 40 mm (1.6 inches) (see
Table 4). Therefore, they might be expected to exert maximum gripping force on
30 mm (1.2 inches) cylinders, in comparison to 40 mm cylinders for non-disabled
adults (see Table 5). Although it might not be feasible to design containers with
diameters of only 30 mm, these data highlight the importance of maintaining a
small diameter at the location intended for grasping.
Table 5: Relationships between maximum grip diameter and cylinder diameter for maximum grip
force.
Median Maximum Grip
Diameter for Maximum
Diameter (male & female)
Grip Force (mm)
(mm)
Non-disabled
50 A
40 B
Dexterity-disabled
40 A
30 C
A: Source [10]; B: Source [25]; C: Inferred.
19
Applicable Guidelines:
 Guideline: Ensure that the product is easy to grip and control. The shape
of the product should be easy to hold, so that it fits the hand. There should
also be a texture to the surface so that it can be gripped and held onto.
Sources: Cushman and Rosenberg, 1991 [7]; Haigh, 1993 [16]

Guideline: Allow for alternatives to a standard grip. Size the gripping
area and clearances to allow alternatives to the standard grip, including
knuckles, the side, back and heels of the hand, and two-handed “pinch”
grips.
Source: Steinfeld and Mullick, 1990 [26]

Guideline: Require a grip span of no more than 2.8 inches (71 mm) for
products that are intended to be grasped with one hand. If the size of the
container exceeds the maximum grip span recommendations, then add
design features such as handles or cutouts to facilitate a reduced grip span
requirement.
Source: Steinfeld and Mullick, 1990 [26]
20
The container may slip in the user’s hand.
Detailed Description: Individuals with arthritis typically have weaker grips than
those without arthritis. A weakened grip may allow a container to slip in the hand
as the user attempts to lift or manipulate the container. Slippage can prevent the
user from performing such actions as lifting the container, removing its cap, or
removing its seal. The size of a container partially determines how tightly an
individual can grasp it. For further discussion of container size, refer to the
section entitled “The container may be too large to be gripped comfortably with
adequate force.” In addition to container size, other important factors include
container shape, surface texture, and material composition. Traditional smooth,
cylindrical containers may be unsuitable for many users with arthritis because
they provide little friction, no leverage, and are not contoured to the user’s hand.
Potential Solutions: Maximize friction between the container and the hand.
Friction can be increased by making the surface of the container rough or by using
a “sticky” material such as rubber. Certain plastic and paper wrappings may
provide more friction than others.
Use a non-cylindrical shape for the container. Container slippage can be reduced
by using a non-cylindrical container shape. The uniform contour of a cylinder
allows it to slide easily in a weak grip. In contrast, elliptical and rectangular
containers provide leverage points (see Figure 15). These surfaces can act as
lever arms, and can reduce grip strength requirements during cap opening.
Figure 15: A non-cylindrical container is easier for users to grasp.
Applicable Guidelines:
 Guideline: Ensure that the product is easy to grip and control. The shape
of the product should be easy to hold, so that it fits the hand. There should
also be a texture to the surface so that it can be gripped and held onto.
Sources: Cushman and Rosenberg, 1991 [7]; Haigh, 1993 [16]

Guideline: Allow for alternatives to a standard grip. Size the gripping
area and clearances to allow alternatives to the standard grip, including
21
knuckles, the side, back and heels of the hand, and two-handed “pinch”
grips.
Source: Steinfeld and Mullick, 1990 [26]

Guideline: Require a grip span of no more than 2.8 inches (71 mm) for
products that are intended to be grasped with one hand. If the size of the
container exceeds the maximum grip span recommendations, then add
design features such as handles or cutouts to facilitate a reduced grip span
requirement.
Source: Steinfeld and Mullick, 1990 [26]

Guideline: Provide a high friction grip surface on cylindrical containers.
Tight grasping of the container is required to provide a counter-rotational
force when removing a twist off cap. Provide a high friction surface on a
cylindrical container to facilitate tight grasping.
Source: GTRI


Guideline: Provide a non-cylindrical grip feature, such as grip indentions,
or use a non-cylindrical container.
Source: GTRI
22
What are the common issues associated with removing a twistoff cap?
The act of removing a twist-off cap entails gripping the container in one hand while
tightly gripping and applying rotational force to the cap with the other hand. For a
discussion of issues related to grasping the container, refer to the section entitled “What
are the common issues associated with grasping and lifting a container?” The
simultaneous actions of grasping the cap and twisting may be especially difficult for
some individuals with arthritis. In the sections below, issues related to the cap are
discussed. Child safety mechanisms have not been addressed, and are reserved for future
consideration.
Removing a factory sealed cap may require too much force.
Detailed Description: Many individuals with arthritis experience difficulty when
exerting the force that is required to open some containers. The factory sealed
caps that have been tested at the Accessibility Evaluation Facility at GTRI have
required between just a few pound-inches (~0.2-0.3 N m) of torque to over 20
pound-inches (2.3 N m) to open. In laboratory tests at GTRI with various caps,
users with arthritis have typically been able to exert approximately 5 to 30 poundinches (0.6-3.4 N m) of rotational force on the caps before experiencing pain.
This wide range is the result of differences among individuals and among cap
designs.
When high torque is required, high grip force is also required. In order to prevent
a cap from slipping in the hand, the user must apply sufficient grip force. Thus,
users with arthritis may experience pain in the wrist as they apply rotational force
and in the hand and fingers as they apply grip force.
Potential Solution: Limit the amount of rotational force that is required to
remove a factory sealed cap to 10 pound-inches (1.1 N m) or less. The key to
reducing user difficulty is to reduce the amount of force that is required, although
product safety and integrity must also be considered. To accommodate
approximately 90% of users with arthritis, rotational force requirements should
not exceed 10 pound-inches (1.1 N m). Reducing the amount of force required
for rotation also reduces the amount of grip force that is required to prevent the
cap from slipping in the hand.
Applicable Guidelines:
 Guideline: Minimize rotational force required to remove the cap from the
factory sealed position.
Sources: Berns, 1981 [3]; Langley, Janson, Wearn, and Yoxall, 2005 [19];
Voorbij and Steenbekkers, 2002 [29]
23

Guideline: Provide at least one mode of operation that does not require
fine motor control or simultaneous actions, and that is operable with
limited reach and strength.
Source: Section 508 1194.31(f) [13]
24
Removing a cap may be difficult after it has been tightened by a user.
Detailed Description: After the initial opening, caps can be retightened with a
variable amount of rotational force, and this may affect the ease of future
openings. Hence, even if a factory sealed bottle is easy to open for a user with
arthritis, it may be difficult on subsequent uses. A friend or family member might
tighten the cap too much, or an individual with arthritis might tighten it too much
on a day when he or she is not experiencing severe symptoms (symptoms can
vary dramatically between days).
Potential Solution: Use steep threading rather than shallow threading. The
tendency for users to over tighten a cap might be reduced by using steep threading
(causing the cap to rise more rapidly as it is unscrewed). Preliminary testing at
GTRI with 6 different bottles suggests that caps with steep threading cannot be
tightened onto the bottle as tightly as those with more shallow threads (see Figure
16). After tightening caps with 15 pound-inches (1.7 N m) of torque, those with
steep threading (average incline 4.5°) required approximately 33% less force to
open than those with shallow threading (average incline 1.8°).
Figure 16: Containers with shallow threading (left) and steep threading (right).
Applicable Guideline:
 Guideline: Provide at least one mode of operation is that does not require
fine motor control or simultaneous actions, and that is operable with
limited reach and strength.
Source: Section 508 1194.31(f) [13]
25
The cap may slip in the user’s hand as he or she attempts to twist it.
Detailed Description: If a cap is tightly secured to a container, users’ hands may
slip on the cap as they attempt to twist it. To prevent slippage, users may need to
exert considerable grip force.
Potential Solutions: Reduce the required grip force by increasing the friction
between the cap and the hand. A common method of increasing friction is to
incorporate ridges or serrations into the cap’s surface. These should be large
(deep and wide) enough to provide friction, but not so wide as to produce
discomfort on the skin. Surface friction can also be introduced by using different
types of materials other than plastic. For example, a rubber surface coating can
provide excellent grip.
Figure 17: A rubber coating on the cap increases surface friction and decreases required grip force.
Reduce the required grip force by providing grip features on the cap. Knurled,
square, and elliptical caps provide grip features that may reduce grip strength
requirements. Individuals with and without arthritis are able to generate more
torque on knurled objects than smooth objects ([9]; see Figure 18 and Figure 19).
Figure 18: A smooth knob (left) and knurled knob (right) (Source: [9]).
26
Figure 19: Average torque generated on round and knurled caps by individuals with arthritis.
Knurl contours should be smooth and gradual, because small or sharp points of
contact can create uncomfortable pressure points. The knurls shown above in
Figure 18 might produce pressure points. Rounder knurls, such as those shown in
Figure 20, might be more suitable.
Figure 20: Smoothly contoured knurls.
In one case of laboratory testing at GTRI, some users preferred a traditional round
cap over a knurled cap, because the later caused painful pressure points. The
discomfort that some users experienced was most likely due to the abrupt edges in
the knurling pattern, somewhat like those shown in Figure 18. To prevent painful
pressure points, knurls should be rounded. Perhaps the best strategy is to use
widely spaced, rounded knurls, such as those shown in Figure 21. The “valleys”
in this knurling pattern can accommodate a large portion of the user’s fingers, and
might therefore reduce pressure points. However, further laboratory testing is
needed to determine the optimal knurling style.
27
Figure 21: Widely spaced, smooth knurls.
An alternative to knurls is to use two smooth, rounded protrusions separated by
180°. Such a design would be similar in shape and functionality to an elliptical
cap. Another alternative is to use a square cap (with a rounded interior, of
course). Although no such designs have been directly evaluated by users with
arthritis at GTRI, the principles derived from other designs suggest that these
might be successful.
Applicable Guidelines:
 Guideline: Ensure that the product is easy to grip and control. The shape
of the product should be easy to hold, so that it fits the hand. There should
also be a texture to the surface so that it can be gripped and held onto.
Sources: Cushman and Rosenberg, 1991 [7]; Haigh, 1993 [16]

Guideline: Avoid sharp edges. Knurls on twist-off caps should be
rounded.
Source: GTRI

Guideline: Allow for alternatives to a standard grip. Size the gripping
area and clearances to allow alternatives to the standard grip, including
knuckles, the side, back and heels of the hand, and two-handed “pinch”
grips.
Source: Steinfeld and Mullick, 1990 [26]
28
Caps with a large diameter prevent a strong grasp.
Detailed Description: The size of a cap has a great effect on how tightly a user
can grasp it. Very large diameter caps afford weak grips, because the fingers are
weaker when they are near full extension [25]. Caps with very small diameters
may also afford weak grips, due to muscle shortening.
Potential Solution: Use a moderate diameter for caps. Because the hand is most
powerful when it is flexed moderately [25], it may be best to design moderately
sized caps. Maximum force can be generated by non-disabled individuals on caps
with diameters between 1-3 inches (25-75 mm) [22]. This is a very wide range,
the extremes of which may cause discomfort in the hands of users with arthritis.
More moderate cap diameters (e.g., 1.6-2 inches (41-51 mm)) may be preferable.
Applicable Guideline:
 Guideline: Require a grip span of no more than 2.8 inches (71 mm) for
products that are intended to be grasped with one hand. If the size of the
container exceeds the maximum grip span recommendations, then add
design features such as handles or cutouts to facilitate a reduced grip span
requirement.
Source: Steinfeld and Mullick, 1990 [26]
Discussion: This guideline applies to a standard power grip (like grasping
a cylinder) and may not be directly applicable to the key pinch grip
commonly used to grasp a cap.
29
Short caps prevent a strong grasp.
Detailed Description: The height of the cap may affect the ease and strength with
which it can be grasped. Short caps (e.g., 0.4 inches (10 mm)) may be difficult to
grasp for users with arthritis, due to their decreased dexterity and inability to
adopt certain hand positions. A short cap height limits the variety of hand
positions that can be used to grasp the cap, whereas taller caps allow more
flexibility.
Potential Solution: Increase the height of the cap up to 1 inch (25 mm). In order
to increase the ease of grasping and the surface contact between the fingers and
the cap, caps should be made approximately 1 inch (25 mm) in height [17].
Applicable Guideline:
 Guideline: Allow for alternatives to a standard grip. Size the gripping
area and clearances to allow alternatives to the standard grip, including
knuckles, the side, back and heels of the hand, and two-handed “pinch”
grips.
Source: Steinfeld and Mullick, 1990 [26]
30
The amount of angular rotation required to remove the cap may be
too great.
Detailed Description: Some caps require a large rotation to open (e.g., 270°).
Because many individuals with arthritis have limited ranges of motion in their
hands and wrists, they must make many small movements rather than a few large
movements to unscrew the cap. Each movement may be painful for some users.
Potential Solution: Use a steep and short threading so that the cap can be
removed with a limited amount of rotation. Ideally, the removal of a cap should
require no more than ¼ turn. This may be accomplished by using a steep and
short threading design which allows the cap to rise rapidly from the container as it
is turned.
Applicable Guidelines:
 Guideline: Screw top caps should fit in the hand. Their removal should
require no more than ¼ turn for each angular movement, and no more than
two angular movements should be required.
Source: Haigh, 1993 [16]

Guideline: Minimize user actions.
Source: HFDS 2.6.8 [12]
31
What are the issues associated with opening a pop-open cap?
Caps that pop open, rather than twisting open, can offer an easy-to-use solution for many
users with arthritis. There are two basic styles of caps that pop open. The most common
pop-open caps are attached to the bottle by a ring around the bottle neck. Another style
of design features a portion of the cap that pops open; to fully expose the bottle opening,
the user must unscrew the cap. A variant of this design features a push tab that causes an
adjacent section to pop open. See Figure 22 for illustrations of these cap styles.
Figure 22: Three styles of pop-open caps: the entire cap pops open (left), part of the cap pops open
(center), and a button causes part of the cap to pop open (right).
These pop-open mechanisms alleviate the concerns of gripping and twisting that are
associated with twist-off caps, but they introduce new concerns. Some primary concerns
are discussed in the following sections; a more in-depth discussion is reserved for future
work.
The amount of force required to pop open the cap is too great.
Detailed Description: Users with limited strength may struggle to pop open a cap
if too much force is required. This action is typically accomplished with only one
finger or thumb, which greatly limits the amount of force the user can exert on the
tab.
Potential Solution: Minimize operating forces. If the amount of force necessary
to open the cap is limited, most users with arthritis should be able to use the
product with ease.
Applicable Guidelines:
 Guideline: Require no more than 3.3 pounds (14.7 N) to push in a push
tab.
Source: Berns, 1981 [3]
32

Guideline: Minimize the forces required to open and close flip-top caps.
The forces required to flip the cap open and closed should not exceed 5.0
pounds (22.2 N).
Source: Section 508 1194.23(k)(2) [13]
Discussion: Section 508 sets a broad guideline for maximum linear force
requirements for all user actions. The guideline may not be directly
applicable to removing opening a flip top cap. Further research will be
needed to determine if the 5.0 pound recommendation should be modified
for this application.
33
The surface of the push tab is too small or too sharp.
Detailed Description: Pop-open caps typically have a tab or indention that
provides the user with a surface against which to push the cap upwards. In some
cases, this surface is very small, and may be painful to push against, especially if
its edge is sharp (see Figure 23). Pressing against a small surface might also
require a degree of dexterity that some users with arthritis do not possess.
Figure 23: A push tab that is too small and has a sharp edge.
Potential Solution: Provide a surface for the user to push against that is
sufficiently large and that has a smooth edge. The force required to flip the cap
open can be more easily applied when the area to which the force is applied is
larger. The area where the force is applied (e.g., an overhanging cap and/or an
indention below the edge of the cap) should be large enough to accommodate a
number of methods for opening the cap (e.g., fingernail, one or more fingertips,
tip or side of thumb, side of hand, etc.) (see Figure 24).
Figure 24: The indentation on this flip cap is large and smooth.
Applicable Guideline:
 Guideline: Provide a sufficient area for applying force to open the cap.
Source: GTRI
Discussion: Additional research is required to quantify what constitutes a
“sufficient” area for applying force.
34
What are the issues associated with removing the outer safety
seal or packaging?
Outer safety seals are intended to protect product integrity and safety by providing
evidence of tampering or damage. They must be removed prior to first usage of the
product. In a broad sense, outer safety seals include the tamper-evident wrapping of the
bottle and the box in which the bottle is packaged. Because outer safety seals and
packaging are intended to protect the product and provide evidence of tampering, they
can sometimes be difficult to remove. Users with arthritis, in particular, may often
experience great difficulty when removing the outer safety seal or when opening the
packaging. Although this action is only performed once for each item, it can represent a
significant barrier to overall ease of use and may discourage users from future purchases.
Removal of some outer safety seals requires the use of a tool.
Detailed Description: Some outer plastic wrappings are not perforated or scored,
and therefore cannot be easily torn by hand. Instead, a user must initiate a tear in
the plastic with a tool, such as a knife or scissors. However, the use of tools can
be problematic for two reasons. First, a tool may not be readily available, so the
user may struggle to accomplish the task by hand before searching for a tool.
Second, users with arthritis may experience pain in their fingers, hands, and wrists
while using the tool. Pain may be caused by the narrow grip required to hold the
tool, or by exerting force with the tool against the product.
Potential Solution: Provide a clearly visible perforation or scoring in the seal to
allow users to remove the seal by hand. Perforations or scoring in the plastic seal
allow users to easily tear the plastic. The perforations or scoring in the plastic
should be clearly evident by virtue of their placement and their visual contrast
with the underlying material (see Figure 25). Note that perforations in clear
plastic may be difficult to see, particularly when covering a light-colored
container. Perforations and scoring can be made evident by using a dark plastic
seal, or by placing markings on the seal. In addition to being clearly visible, the
edge of the seal should be easy to grip.
35
Figure 25: The perforations on this outer seal are clearly visible.
Applicable Guidelines:
 Guideline: Ensure that the product is easy to grip and control. The shape
of the product should be easy to hold, so that it fits the hand. There should
also be a texture to the surface so that it can be gripped and held onto.
Sources: Cushman and Rosenberg, 1991 [7]; Haigh, 1993 [16]

Guideline: Provide at least one mode of operation that does not require
fine motor control or simultaneous actions, and that is operable with
limited reach and strength.
Source: Section 508 1194.31(f) [13]

Guideline: Do not require the use of tools.
Source: GTRI

Guideline: Require a pinch force of no more than 3.0 pounds (13.3 N).
Source: GTRI
Discussion: Preliminary data collected during GTRI assessments of users
with arthritis suggested that pinch force requirements should not exceed
3.0 pounds; however, further research is needed to validate this finding.

Guideline: Ensure that the proper method of removing the outer safety
seal is clearly evident, either because of the design of the safety seal or
because of instructions printed prominently on the packaging. For
example, if the seal is removed by twisting the cap to break the seal,
instructions like “Twist cap to break seal” should be provided. If the seal
is removed by pulling a perforated strip, the strip should be clearly visible.
Source: Vanderheiden, 1997 [28]
Discussion: The steps required to open some containers may be intuitively
obvious to most users and therefore may not require printed instructions.
36

Guideline: If the outer safety seal is intended to be torn open, then
provide a perforated strip or a starter slit.
Source: GTRI

Guideline: If the safety seal is removed in an independent action (e.g., by
pulling a perforated strip), the force required to remove the safety seal
should not exceed 5.0 pounds (22.2 N).
Source: Section 508 1194.23(k)(2) [13]
Discussion: Section 508 sets a broad guideline for maximum linear force
requirements for all user actions. The guideline may not be directly
applicable to removing a safety seal. Further research will be needed to
determine if the 5.0 pound recommendation should be modified for this
application.
37
The outer safety seal is intended to be broken as the product is
initially opened, but the force requirement may be too great.
Detailed Discussion: Some outer safety seals may break away from the cap and
container upon initial opening. For example, a serrated strip may tear as the cap
is twisted. This design has the benefit of reducing the number of user actions, but
can be detrimental if too much force is required to simultaneously break the seal
and open the container. If the perforated section of the seal is beneath the user’s
hand, then the material may not break easily.
Figure 26: The outer seal is broken when the user first twists the cap.
Potential Solutions: Reduce the combined required forces required to break the
safety seal and open the factory sealed cap. If the seal is intended to be broken as
the cap is opened, then the total required operating forces should be minimized.
Operating forces should be minimized to any extent possible, while maintaining
the integrity of the safety seal.
Place two or more perforated strips in the safety seal. At least two perforated
strips can be placed in the outer safety seal, in order to reduce the chance that a
user’s grasp will prevent the seal from breaking.
Applicable Guidelines:
 Guideline: Ensure that the proper method of removing the outer safety
seal is clearly evident, either because of the design of the safety seal or
because of instructions printed prominently on the packaging. For
example, if the seal is removed by twisting the cap to break the seal,
instructions like “Twist cap to break seal” should be provided. If the seal
is removed by pulling a perforated strip, the strip should be clearly visible.
Source: Vanderheiden, 1997 [28]
Discussion: The steps required to open some containers may be intuitively
obvious to most users and therefore may not require printed instructions.
38

Guideline: Minimize safety seal removal force. If the safety seal is
broken by simply opening the package (e.g., by twisting a cap), the total
force required to break the seal and open the package should not exceed
the maximum force specified for opening the package when the safety seal
is not present.
Source: GTRI
Discussion: Additional research is required to determine appropriate
maximum force requirements.
39
The packaging box does not have a flap or tab for the user to pull.
Detailed Description: A box can be difficult to open if its opening flap does not
have a tab for users to grasp. Flaps without sufficient gripping space must be
picked at with a tool or a finger nail. This may be somewhat difficult for some
users with arthritis, because it requires relatively fine movement control. A user
might simply tear open the box by inserting a finger under the flap’s edge, but the
force required to do this might cause pain for users with arthritis.
Potential Solutions: Provide a perforated strip that peels away. A perforated
strip can be peeled away easily, provided that the force required is not excessive
(less than 5 lbs (22.2 N)). The end of the strip should have a sufficiently large tab
for grasping (see Figure 27).
Figure 27: A box with a perforated strip.
Provide a large tab under which the user can insert a finger. If a tab is provided
with no perforated strip, the tab should be large enough to accommodate most of
the tip of the finger (see Figure 28). The force required to pull open the tab
should not exceed 5 lbs (22.2 N).
Figure 28: A box that provides a large tab under which the user can insert a finger.
40
Applicable Guidelines:
 Guideline: If the safety seal is removed in an independent action (e.g., by
pulling a perforated strip), the force required to remove the safety seal
should not exceed 5.0 pounds (22.2 N).
Source: Section 508 1194.23(k)(2) [13]
Discussion: Section 508 sets a broad guideline for maximum linear force
requirements for all user actions. The guideline may not be directly
applicable to removing a safety seal. Further research will be needed to
determine if the 5.0 pound recommendation should be modified for this
application.

Guideline: If the outer safety seal is intended to be torn open, then
provide a perforated strip or a starter slit.
Source: GTRI

Guideline: Require a pinch force of no more than 3.0 pounds (13.3 N).
Source: GTRI
Discussion: Preliminary data collected during GTRI assessments of users
with arthritis suggested that pinch force requirements should not exceed
3.0 pounds (13.3 N); however, further research is needed to validate this
finding.

Guideline: Offer redundant modes of operation utilizing the next larger
set of motor movements (finger to hand, hand to arm). Offer different
ways to accomplish the same task using increasingly larger motor
movements. For example, a tab on a seal should be large enough to grip
between the thumb and knuckle, rather than between the tips of the finger.
Source: Pirkl, 1995 [23]
Discussion: By allowing redundant modes of operation, users might have
the option to avoid using joints in which swelling and pain are most
severe.

Guideline: Provide at least one mode of operation that does not require
fine motor control or simultaneous actions, and that is operable with
limited reach and strength.
Source: Section 508 1194.31(f) [13]
41
What are the issues associated with removing the inner safety
seal?
Inner safety seals are located directly beneath the cap. They maintain product freshness
and provide additional tamper-evident protection. Like the outer seal, the inner seal is
only removed once for each product, yet can represent a significant barrier to overall ease
of use of the product.
The user cannot peel the seal from the container.
Detailed Description: Inner seals can be difficult to remove if no tab is provided
for grasping, or if too much pull force is required to peel the seal from the
container. Many inner seals provide little or no grasping surface. With such
products, some users search in vain for a tab, and then attempt to pinch the tiny
edge of the seal. This can be painful and frustrating for users with arthritis. If the
seal cannot be peeled from the opening, then a user must puncture it and peel
away the remnants. In this case, the user is forced to perform several physical
actions, rather than a single, simple action of peeling the entire seal at once. Even
if a tab is provided, the force required to pull it may exceed the capabilities of
some users with arthritis. Small tabs may be difficult to grasp.
Potential Solution: Provide a large tab on the edge of the seal, and require no
more than 5 lbs (22.2 N) to peel the seal from the container. If a smooth, nontextured tab is provided, it should be at least 0.47 inches (12 mm) wide by 0.79
inches (20 mm) long so that users can grasp it between the thumb and lateral
aspect of the index finger. Smaller tabs may be difficult to grasp and may slide
from users’ fingers, especially if the tabs are not textured. One potential solution
is to use a large tab that flips up from the center of the seal. However, this places
the pull force on the center rather than the edge of the seal, and may require more
force. The optimal pull tab would be large, located on the edge of the seal (see
Figure 29), with a textured surface that reduces slippage (e.g., a foil tab with
raised bumps). The amount of force required to peel the seal away from the
container should not exceed 5 lbs (22.2 N).
Figure 29: The inner seal is easy to remove because of the large tab on the edge.
42
Applicable Guidelines:
 Guideline: Minimize user actions.
Source: HFDS 2.6.8 [12]

Guideline: Do not require the use of tools.
Source: GTRI

Guideline: On smooth inner seal tabs, provide a sufficiently large
grasping point. A tab that is at least 0.47 inches (12 mm) wide by 0.79
inches (20 mm) long is recommended.
Source: Department of Trade and Industry, UK, 2003 [11]
Discussion: The study was based on a smooth tab. The study only looked
at one tab width and two tab lengths (0.47 and 0.79 inches). The tabs were
rectangular. The test population included people with disabilities, but the
sample was relatively small and included a variety of disabilities.

Guideline: Provide texture on the grasp point that facilitates gripping the
tab. The grasp point should be textured with a series of bumps or raised
strips that are perpendicular to the peel direction.
Source: Department of Trade and Industry, UK, 2003 [11]

Guideline: On inner seals that are intended to be grasped and peeled from
the container, place the grasp point in a location selected for the
application of optimum force. The tab should be located along the edge of
the seal if the seal is designed to be peeled from the edge. A tab located
along the top centerline of the seal can also be used, provided the tab runs
across the diameter of the seal.
Source: GTRI

Guideline: Do not glue the grasp point to the inner seal or other surface.
Source: GTRI

Guideline: Provide at least one mode of operation that does not require
fine motor control or simultaneous actions, and that is operable with
limited reach and strength.
Source: Section 508 1194.31(f) [13]

Guideline: Offer redundant modes of operation utilizing the next larger
set of motor movements (finger to hand, hand to arm). Offer different
ways to accomplish the same task using increasingly larger motor
movements. For example, a tab on a seal should be large enough to grip
between the thumb and knuckle, rather than between the tips of the finger.
Source: Pirkl, 1995 [23]
Discussion: By allowing redundant modes of operation, users might have
the option to avoid using joints in which swelling and pain are most
severe.
43
The user cannot puncture the seal with a finger.
Detailed Description: If no tab is provided on the seal, then users must puncture
and tear it. In general, manufacturers should provide a tab, because users may
struggle to puncture the seal with their fingertip. They may have previous
difficult experiences with other products that lacked tabs on the seal, and may
therefore assume that all seals are difficult to puncture. Users may resort to using
a tool, such as a knife or scissors. This can be problematic if a tool is not readily
available, or if use of the tool causes pain in inflamed joints.
Potential Solution: Limit the amount of force required to puncture the seal. The
amount of force that is required to puncture the seal, as measured with a blunt
object that simulates a fingertip, should not exceed 5 lbs (22.2 N) (but see
Guideline Discussion below).
Applicable Guidelines:
 Guideline: Do not require the use of tools.
Source: GTRI

Guideline: Minimize safety seal removal force. The force required to
remove the safety seal (e.g., by puncturing the seal or by pulling to remove
it) should not exceed 5.0 pounds (22.2 N).
Sources: GTRI; Section 508 1194.23(k)(2) [13]
Discussion: Section 508 sets a broad guideline for maximum linear force
requirements for all user actions. The guideline may not be directly
applicable to puncturing a safety seal. Further research will be needed to
determine if the 5.0 pound recommendation should be modified for this
application.
44
What are the issues associated with instructions and labeling?
Instructions are defined as any textual or graphical information that tells the user how to
operate or consume the product. This includes opening instructions, consumption
instructions, and dosage information. Labels include warnings, product information, and
expiration dates. The ease of use issues associated with instructions and labels are not
unique to users with arthritis, but are common to all users. However, older adults, who
comprise a large portion of the population with arthritis, often experience a decline in
visual acuity. Therefore, the visual design of instructions and labeling are particularly
important for many users with arthritis.
The text or graphics are difficult to see.
Detailed Description: Some users may have difficulty reading text due to its
small size or poor contrast with the background. Textual or graphical instructions
for opening a cap are often engraved into the cap, giving very poor visual
contrast. Additionally, the readability of text may be poor due to small text size
and low contrast. Inability to read instructions and labeling may lead to incorrect
or unsafe usage of the product.
Potential Solution: Enhance readability of all text by increasing font size and
contrast. If instructions are engraved, poor contrast should be compensated for by
increasing the font size. Ideally, all text should be printed with both high contrast
and large font.
Applicable Guideline:
 Guideline: Enhance readability and comprehension of labels, critical
instructions, and expiration dates. Print critical text with large print in a
sans-serif font with high contrast on a solid background.
Source: GTRI
45
The text is difficult to find.
Detailed Description: Instructions and labels may be difficult to find if they are
not preceded by a prominent title, or if they are placed in an unexpected location.
For example, dosage information may be difficult to find if it runs together with
warnings and ingredients.
Potential Solution: Provide clearly visible, prominent titles for each section (e.g.,
Warnings and Active Ingredients), and use white space or lines to separate
sections of text. Visual cues, such as white space, lines, and prominent titles, can
help users as they search for information.
46
The expiration date is difficult to find, read, or interpret.
Detailed Description: Expiration dates may be difficult to find if they are placed
in obscure, atypical locations. For example, if the date is printed on the side of
the bottle, the user must rotate the bottle and search across its entire surface.
Once the date is found, it may be difficult to read if it is printed in small lettering
with poor contrast. Expiration dates are often printed directly on containers that
do not provide enough contrast with the text (Figure 30). Finally, the date may be
misinterpreted or unrecognized if its format is ambiguous. For example, “12 07
11” might mean December 7, 2011 or July 12, 2011, or it might simply be a
product code.
Figure 30: An expiration date that is difficult to read.
Potential Solution: Print expiration dates in a standard location, using an
unambiguous format, large font, and good contrast. The location of the
expiration date should be standardized across products. Users may typically
expect to find them on the bottom of containers. To enhance contrast, the
container should be opaque, or its contents should provide sufficient contrast with
the text (Figure 31). Note that lettering printed on the upper portion of a
transparent container may become difficult to read after some of the contents have
been dispensed.
Figure 31: An expiration date that is easy to read.
47
Applicable Guideline:
 Guideline: Enhance readability and comprehension of labels, critical
instructions, and expiration dates. Print critical text with large print in a
sans-serif font with high contrast on a solid background.
Sources: GTRI
48
Design Guidelines
The design and evaluation of bottles can be informed by guidelines that have been
suggested by researchers. The number of published studies that address human
performance in handling and opening consumer product containers is limited. The
quality of existing research may be questionable if a small subject sample was used or if
the researchers employed flawed experimental designs. Therefore, it is important to
document the sources for the guidance offered in this report. Careful review of the
sources may lead to an understanding of how to allocate future research resources and
make better usage of the guidelines. The container design guidelines used in this report
are shown in Table 6.
Table 6: Ease of use guidelines for container design.
Guideline
Guideline
Source(s)
Discussion
Packages should be designed
to minimize hand and eye
movements, thus maximizing
efficiency.
Applicable
Components
Minimize user actions.
HFDS 2.6.8 [12]
All components
Ensure that the product is easy to
grip and control. The shape of the
product should be easy to hold, so
that it fits the hand. There should
also be a texture to the surface so
that it can be gripped and held onto.
Cushman and
Rosenberg, 1991
[7]; Haigh, 1993
[16]
- Container body
- Cap
- Outer safety seal
- Inner seal
Allow for alternatives to a standard
grip. Size the gripping area and
clearances to allow alternatives to
the standard grip, including
knuckles, the side, back and heels of
the hand, and two-handed “pinch”
grips.
Steinfeld and
Mullick, 1990
[26]
- Container body
- Cap
- Outer safety seal
- Inner seal
Require a grip span of no more than
2.8 inches for products that are
intended to be grasped with one
hand. If the size of the container
exceeds the maximum grip span
recommendations, then add design
features such as handles or cutouts
to facilitate a reduced grip span
requirement.
Steinfeld and
Mullick, 1990
[26]
This includes, but is not
limited to, products that must
be grasped with one hand
while opening the cap with the
other hand. This guideline is
especially important for heavy
containers and for those
whose surface provides little
friction with the hand.
- Container body
Provide a high friction grip surface
on cylindrical containers.
GTRI
Tight grasping of the
container is required to
provide a counter-rotational
force when removing a twist
off cap. Provide a high
friction surface on a
cylindrical container to
facilitate tight grasping.
- Container body
49
Guideline
Guideline
Source(s)
Discussion
Non-cylindrical grip features
can enhance grip while
removing a cap.
Applicable
Components
Provide a non-cylindrical grip
feature, such as grip indentions, or
use a non-cylindrical container.
GTRI
- Container body
Provide at least one mode of
operation that does not require fine
motor control or simultaneous
actions, and that is operable with
limited reach and strength.
Section 508
1194.31(f) [13]
Whenever possible, do not require
simultaneous actions such as pulling
and rotating.
Kanis, 1993 [18]
In some cases, it may not be
possible to avoid simultaneous
actions. For example, users
must simultaneously grip and
rotate a cap to remove it. In
such cases, the required forces
for each action should be
minimized.
- Cap
- Outer safety seal
- Inner seal
Offer redundant modes of operation
utilizing the next larger set of motor
movements (finger to hand, hand to
arm). Offer different ways to
accomplish the same task using
increasingly larger motor
movements. For example, a tab on
a seal should be large enough to grip
between the thumb and knuckle,
rather than between the tips of the
finger.
Pirkl, 1995 [23]
By allowing redundant modes
of operation, users might have
the option to avoid using
joints in which swelling and
pain are most severe.
- Cap
- Outer safety seal
- Inner seal
Do not require the use of tools.
GTRI
Require no more than 3.3 pounds to
push in a push tab.
Berns, 1981 [3]
The study included people
from the general population as
well as people with a variety
of disability types including
arthritis, multiple sclerosis,
Parkinson’s disease, cerebral
palsy, hemiplegics, and
amputees.
- Cap
- Inner seal
Verify that the requirement for
constant, uninterrupted actions is
minimized by investigating the
required actions for each component
of the container.
Vanderheiden,
1997 [28]
This might apply to hinged
flip-top caps that should
remain open on their own,
rather than being held open by
the user.
- Cap
Verify presence of definitive
feedback cues (e.g., latches should
“snap” into position).
Pirkl, 1995 [23]
- Cap
- Outer safety seal
- Inner seal
- Cap
- Outer safety seal
- Inner seal
- Cap
50
Guideline
Guideline
Source(s)
Discussion
Applicable
Components
Verify that operation of the product
does not violate standard
conventions (clockwise for “close,”
counterclockwise for “open”).
Pirkl, 1995 [23]
- Cap
Screw top caps should fit in the
hand. Their removal should require
no more than ¼ turn for each
angular movement, and no more
than two angular movements should
be required.
Haigh, 1993 [16]
This study did not address
replacing the cap.
- Cap
Avoid sharp edges.
GTRI
The push point of the flip top
cap should be beveled and
devoid of sharp edges. Knurls
and serrations on twist-off
caps should be rounded.
- Cap
Minimize rotational force required
to remove the cap from the factory
sealed position.
Berns, 1981 [3];
Langley, Janson,
Wearn, and
Yoxall, 2005
[19]; Voorbij and
Steenbekkers,
2002 [29]
The research available on this
topic is very limited. The
amount of rotational force that
a user can apply to a twist off
cap is dependent on the
following factors: cap
diameter, cap height, cap
coefficient of friction,
container shape, container
coefficient of friction, skin
moisture, and grasp type.
- Cap
Minimize the forces required to
open and close flip-top caps. The
forces required to flip the cap open
and closed should not exceed 5.0
pounds.
Section 508
1194.23(k)(2)
[13]
Section 508 sets a broad
guideline for maximum linear
force requirements for all user
actions. The guideline may
not be directly applicable to
removing opening a flip top
cap. Further research will be
needed to determine if the 5.0
pound recommendation
should be modified for this
application.
- Cap (flip-top and
pop-off)
51
Guideline
Guideline
Source(s)
Discussion
Applicable
Components
Provide a sufficient area for
applying force to open the cap.
GTRI
The force required to flip the
cap open can be applied more
easily when the area where the
force is applied is larger. The
area where the force is applied
(e.g., an overhanging cap
and/or an indention below the
edge of the cap) should be
large enough to accommodate
a number of methods for
opening the cap (e.g.,
fingernail, one or more
fingertips, tip or side of
thumb, side of hand, etc.).
- Cap (flip-top and
pop-off)
When using knurls to enhance the
grip on a cap, consider that tightly
spaced knurls may not provide
sufficient texture for gripping, and
widely spaced knurls may cause
painful pressure points on the user’s
joints.
GTRI
Additional research is
required to determine
appropriate range of knurl
spacing.
- Cap
Use steep rather than gradual
threading to prevent over tightening
of the cap.
GTRI
Steep threading can also
reduce the extent of rotation
that is necessary to remove the
cap from the container.
- Cap
Require a pinch force of no more
than 3.0 pounds.
GTRI
Preliminary data collected
during GTRI assessments of
users with arthritis suggested
that pinch force requirements
should not exceed 3.0 pounds;
however, further research is
needed to validate this
finding.
- Outer safety seal
- Inner seal
Ensure that the proper method of
removing the outer safety seal is
clearly evident, either because of the
design of the safety seal or because
of instructions printed prominently
on the packaging. For example, if
the seal is removed by twisting the
cap to break the seal, instructions
like “Twist cap to break seal”
should be provided. If the seal is
removed by pulling a perforated
strip, the strip should be clearly
visible.
Vanderheiden,
1997 [28]
The steps required to open
some containers may be
intuitively obvious to most
users and therefore may not
require printed instructions.
- Outer safety seal
If the outer safety seal is intended to
be torn open, then provide a
perforated strip or a starter slit.
GTRI
- Outer safety seal
52
Guideline
Guideline
Source(s)
Discussion
Applicable
Components
Minimize safety seal removal force.
The force required to remove the
safety seal (e.g., by puncturing the
seal or by pulling to remove it)
should not exceed 5.0 pounds (22.2
N).
GTRI; Section
508 1194.23(k)(2)
[13]
Section 508 sets a broad
guideline for maximum linear
force requirements for all user
actions. The guideline may
not be directly applicable to
removing a safety seal.
Further research will be
needed to determine if the 5.0
pound recommendation
should be modified for this
application.
- Outer safety seal
On smooth inner seal tabs, provide a
sufficiently large grasping point. A
tab that is at least 0.47 inches wide
by 0.79 inches long is
recommended.
Department of
Trade and
Industry, UK,
2003 [11]
The study was based on a
smooth tab. The study only
looked at one tab width and
two tab lengths. Only two
pull tab sizes were studied:
0.47 inches and 0.79 inches.
The tabs were rectangular.
- Inner seal
The test population included
people with disabilities but the
sample was relatively small
and included a variety of
disabilities.
Provide texture on the grasp point
that facilitates gripping the tab. The
grasp point should be textured with
a series of bumps or raised strips
perpendicular to the peel direction.
Department of
Trade and
Industry, UK,
2003 [11]
- Inner seal
On inner seals that are intended to
be grasped and peeled from the
container, place the grasp point in a
location selected for the application
of optimum force. The tab should
be located along the edge of the seal
if the seal is designed to be peeled
from the edge. A tab located along
the top centerline of the seal can
also be used, provided the tab runs
across the diameter of the seal.
GTRI
- Inner seal
Do not glue the grasp point to the
inner seal or other surface.
GTRI
- Inner seal
If a pull tab is not provided on the
inner seal, then require no more than
5 pounds of force to puncture the
seal with a blunt object, simulating a
finger tip.
GTRI
- Inner seal
53
Guideline
Enhance readability and
comprehension of labels, critical
instructions, and expiration dates.
Print critical text with large print in
a sans-serif font with high contrast
on a solid background.
Guideline
Source(s)
GTRI
Discussion
Applicable
Components
- Instructions and
labels
54
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