Excavation Safety
Basic
This course introduces the student to the safety hazards, precautions, and
requirements within OSHA 1926, Subpart P, Excavations. This course
provides general information about the hazards, protective systems, and
safe work practices related to working in excavations and trenches.
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OSHAcademy Course 157 Study Guide
Excavation Safety: Basic
Copyright © 2018 Geigle Safety Group, Inc.
No portion of this text may be reprinted for other than personal use. Any commercial use of
this document is strictly forbidden.
Contact OSHAcademy to arrange for use as a training document.
This study guide is designed to be reviewed off-line as a tool for preparation to successfully
complete OSHAcademy Course 157.
Read each module, answer the quiz questions, and submit the quiz questions online through
the course webpage. You can print the post-quiz response screen which will contain the correct
answers to the questions.
The final exam will consist of questions developed from the course content and module quizzes.
We hope you enjoy the course and if you have any questions, feel free to email or call:
OSHAcademy
15220 NW Greenbrier Parkway, Suite 230
Beaverton, Oregon 97006
www.oshatrain.org
instructor@oshatrain.org
+1 (888) 668-9079
Disclaimer
This document does not constitute legal advice. Consult with your own company counsel for advice on compliance with all applicable state and
federal regulations. Neither Geigle Safety Group, Inc., nor any of its employees, subcontractors, consultants, committees, or other assignees
make any warranty or representation, either express or implied, with respect to the accuracy, completeness, or usefulness of the information
contained herein, or assume any liability or responsibility for any use, or the results of such use, of any information or process disclosed in this
publication. GEIGLE SAFETY GROUP, INC., DISCLAIMS ALL OTHER WARRANTIES EXPRESS OR IMPLIED INCLUDING, WITHOUT LIMITATION, ANY
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Taking actions suggested in this document does not guarantee
that an employer, employee, operator or contractor will be in compliance with applicable regulations. Ultimately every company is responsible
for determining the applicability of the information in this document to its own operations. Each employer’s safety management system will be
different. Mapping safety and environmental management policies, procedures, or operations using this document does not guarantee
compliance regulatory requirements.
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Course 157
Contents
Modules and Learning Objectives .................................................................................................. 1
Course Introduction ........................................................................................................................ 3
Module 1: The Hazards ................................................................................................................... 4
Excavation vs. Trench.................................................................................................................. 4
How Cave-ins Occur .................................................................................................................... 5
Common Soil Problems ............................................................................................................... 5
Soil Mechanics ............................................................................................................................ 5
Tension Cracks ........................................................................................................................ 6
Sliding or Sluffing .................................................................................................................... 6
Heaving or Squeezing.............................................................................................................. 7
Boiling ..................................................................................................................................... 7
Unit Weight of Soils .................................................................................................................... 7
Sliding Problems.......................................................................................................................... 8
Soil Testing .................................................................................................................................. 9
Soil and Stability .......................................................................................................................... 9
Visual Tests................................................................................................................................ 10
Manual Tests ............................................................................................................................. 10
Manual Test Examples .......................................................................................................... 11
Competent Person .................................................................................................................... 11
Module 2: Protection Systems ...................................................................................................... 13
Pre-Job Planning ....................................................................................................................... 13
Protective Systems .................................................................................................................... 13
Other Safety Precautions ...................................................................................................... 14
Course 157
Installation and Removal of Protective Systems ...................................................................... 15
Appropriate Protective System Designs ................................................................................... 16
Method 1: Sloping ..................................................................................................................... 16
Method 2: Design Using Data ................................................................................................... 17
Method 3: Trench Box or Shield ............................................................................................... 17
Benching.................................................................................................................................... 18
Shoring Types ............................................................................................................................ 18
Hydraulic Shoring .................................................................................................................. 19
Pneumatic Shoring ................................................................................................................ 19
Other Protective Systems ......................................................................................................... 20
Ingress and Egress ..................................................................................................................... 20
Additional Hazards and Protections ......................................................................................... 20
Additional Resources .................................................................................................................... 22
Course 157
Modules and Learning Objectives
Module 1 – The Hazards
Learning objectives in this module include:
•
Describe the difference between an excavation and a trench.
•
Describe some common soil problems that create hazards in excavations.
•
Describe soil mechanics causing tension cracks, slide or sluffing, and heaving or
squeezing.
•
Discuss how soil is weighed and how soil weight is a major hazard for excavation
workers.
•
Describe the differences among Type A, B, and C soils in terms of stability.
•
Describe the various visual and manual soil testing methods.
•
Discuss the role of and requirements for the excavation competent person.
Module 2 – Protection Systems
Learning objectives in this module include:
•
Describe the importance of completing pre-job planning activities.
•
Describe the three primary protection methods: sloping, shoring, and shielding, and give
examples.
•
Briefly describe the steps in installing and removal of protective systems.
•
Discuss the design requirements for sloping and shoring, the use of data, and trench
boxes.
•
Discuss the design requirements for benching.
•
Describe the use of hydraulic and pneumatic shoring systems.
•
Discuss the requirements for safe ingress into and egress from excavations.
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•
Discuss various additional safety precautions for workers while working in the
excavation.
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Course Introduction
Excavation and trenching are among the most hazardous construction operations. OSHA's
standard, 1926, Subpart P, Excavations, contains requirements for excavation and trenching
operations.
Proper trenching operations are necessary to protect the workers from soil collapse. The basic
trenching operations that help make a trench safe for workers are described and illustrated in
this course. The methods of shoring installation are also discussed briefly. This course is not
intended to be used as a step-by-step guideline in the excavation process.
This course highlights methods for protecting employees against cave-ins, and describes safe
work practices for employees. A necessary first step in planning the approach to any trenching
or other excavation project is to understand what could go wrong. This understanding can help
avoid many of the problems associated with excavation.
This course is also not intended to be a guideline for compliance with all pertinent OSHA
regulations, but rather an overview of safe practices in trenching operations. Though the course
is not intended to be inconsistent with OSHA standards, if an area is considered by the reader
to be inconsistent, the OSHA standard should be followed.
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Module 1: The Hazards
Trenching and excavation work presents serious hazards to all workers involved. Cave-ins pose
the greatest risk and are more likely than some other excavation-related incidents to result in
worker fatalities. One cubic yard of soil can weigh as much as a car. Employers must ensure that
workers enter trenches only after adequate protections are in place to address cave-in hazards.
Other potential hazards associated with trenching work include falling loads, hazardous
atmospheres, and hazards from mobile equipment.
Excavation vs. Trench
Dig a hole in the ground and you've made an excavation. Excavations can be any size: wide,
narrow, deep, or shallow.
A trench is a narrow excavation, not more than 15 feet wide at the bottom. If you install forms
or other structures in an excavation that reduce its width to less than 15 feet, measured at the
bottom, the excavation is also considered a trench.
•
If you work in an excavation that's five feet deep (or deeper) you must be protected
from a cave-in.
•
If a competent person, who has training in soil analysis, determines that there's a
potential for an excavation to cave-in, you must be protected regardless of its depth.
Quiz Instructions
After each section, there is a quiz question. Make sure to read the material in each section to
discover the correct answer to these questions. Circle the correct answer. When you are
finished go online to take the final exam. This exam is open book, so you can use this study
guide.
1. A _____ is not more than 15 feet wide at the bottom.
a.
b.
c.
d.
channel
ditch
excavation
trench
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How Cave-ins Occur
Undisturbed soil stays in place because opposing horizontal and vertical forces are evenly
balanced. When you create an excavation, you remove the soil that provides horizontal
support. Soil will eventually move downward into the excavation. The longer the face (a side of
the excavation) remains unsupported, the more likely it is to cave in.
Common Soil Problems
The terms soil and earth are commonly referred to in the excavation process to describe the
naturally occurring materials uncovered on a project. Soil conditions vary from one site to the
next. Soil may be loose or partially cemented, organic or inorganic. However, most soils can be
referred to as a mixture or an accumulation of mineral grains that are not cemented together.
An exception is hard rock, which remains firm after exposure to the elements.
Soil failure is defined as the collapse of part or all of an excavation wall. The most common soil
failure is typically described as an unexpected settlement, or cave-in, of an excavation. Soil
sliding is the most common factor leading to soil failure.
Proper planning and supervision can avoid the unsafe working conditions caused by soil sliding.
Unless such safety precautions have been implemented, sliding soil failure can occur in all types
of excavations (including sloped trenches and excavations with braced trench boxes).
2. In an excavation, what is the most common factor leading to soil failure?
a.
b.
c.
d.
Tension cracks
Soil sliding
Boiling
Prior disturbance
Soil Mechanics
A number of stresses and deformations can occur in an open cut or trench. For example,
increases or decreases in moisture content can adversely affect the stability of a trench or
excavation. The following diagrams show some of the more frequently identified causes of
trench failure.
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Tension Cracks
Tension cracks usually form at a horizontal distance of one-half to three-quarters times the
depth of the trench, measured from the top of the vertical face of the trench.
Sliding or Sluffing
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This may occur as a result of tension cracks.
3. Tension cracks usually form at a horizontal distance of _____.
a.
b.
c.
d.
twice the depth of the trench
one-half to three-quarters times the depth of the trench
within one foot of the vertical face of the trench
about twice the width or one-half the height of the trench
Heaving or Squeezing
Bottom heaving or squeezing is caused by the downward pressure created by the weight of
adjoining soil. This pressure causes a bulge in the bottom of the cut, as illustrated below.
Heaving and squeezing can occur even when shoring or shielding has been properly installed.
Boiling
Boiling is evidenced by an upward water flow into the bottom of the cut. A high-water table is
one of the causes of boiling. Boiling produces a “quick” condition in the bottom of the cut and
can occur even when shoring or trench boxes are used.
4. What causes bottom heaving or squeezing in a trench?
a.
b.
c.
d.
Downward pressure created by the weight of adjoining soil
Upward movement of the soil due to loss of downward pressure
A high-water table causes upward movement of trench base
A lack of downward pressure from directly above
Unit Weight of Soils
This refers to the weight of one unit of a particular soil. The weight of soil varies with type and
moisture content. One cubic foot of soil can weigh from 110 pounds to 140 pounds or more,
and one cubic meter (35.3 cubic feet) of soil can weigh more than 3,000 pounds.
A safe slope can be defined as the maximum angle of the edge wall or bank of an excavation at
which sliding will not occur. The unique mixtures of the different types of soil (sand, clay, silt
and rock) necessitate different safe slopes from one excavation site to the next.
There are other complicating factors that can result in sliding soil failures. During an excavation,
visibly different layers of soil may be uncovered. Each of those layers may call for different safe
slopes. It is essential to plan your excavation around the most gradual (rather than steepest)
safe slope for all of the different soil types and layers encountered during the excavation.
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Another complicating factor is that soil composition mixtures may vary significantly from one
area of the project to another. During an excavation, as the soil composition changes, the safe
slope for trench wall excavation also changes. Thus, across an excavation site, the slope of the
bank may need to be different to provide a safe working environment.
5. One cubic foot of soil can weigh _____, and one cubic meter of soil can weigh _____.
a.
b.
c.
d.
up to 100 pounds, as much as 500 pounds
100 pounds, up to 1,500 pounds
140 pounds or more, more than 3,000 pounds
280 pounds, around 2,000 pounds
Sliding Problems
Sliding and other modes of failure can also occur in soils that are not densely compacted. For
example, a trench that is made close to a previously dug trench is very unstable. If noncompacted soil is discovered, the normal safe slope for dense soil will not be enough to prevent
sliding. Bracing or further sloping may be necessary.
If cracks are observed in rocky types of soil, sliding has already occurred. These cracks should
signal that a more gradual slope for excavation is needed because the rocky soil is very
susceptible to slides and other types of failure.
Excavations that have been stable for long periods are also subject to sliding types of failure.
After prolonged exposure to the elements, the moisture content in the soil may increase. This
increase in moisture may be due to various causes, such as rainfall or a broken water line. The
extra soil moisture tends to speed up sliding soil failures.
Determining the correct safe slope can be quite difficult for certain types of soil. The OSHA
standard has developed a simple method of determining safe excavation bank slopes for
different soil types. This method will be discussed in more detail in a later section of this
document.
Soil failure can occur for any number of reasons. Factors that increase the chances of soil failure
are:
1. excessive vibration - heavy equipment movement, earthquakes
2. surface encumbrances - obstructions, broken water lines
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3. weather conditions - prolonged periods of rain
6. Each of the following is a factor that increases the chance of soil failure, EXCEPT _____.
a.
b.
c.
d.
excessive vibration
compaction
surface encumbrances
weather conditions
Soil Testing
A competent person must conduct visual and manual soil tests before anyone enters an
excavation. Visual and manual tests are a critical part of determining the type of protective
system that will be used.
Soil and Stability
Some soils are more stable than others. The type of soil is one of the factors that determine the
chance that an excavation will cave in. There are three basic soil types that you may encounter:
•
Type A – very stable. Clay is an example.
•
Type B – less stable than type A soil. The soil will crack or fissure. Crushed rock, silt, and
soils that contain an equal mixture of sand and silt are examples.
•
Type C – the least stable soil. Particles do not stick together. Gravel and sand are
examples.
Soil has other qualities that affect its stability. These include granularity, saturation,
cohesiveness, and unconfined compressive strength.
•
Granularity refers to the size of the soil grains; the larger the grains, the less stable the
soil.
•
Saturation means how much water soil will absorb.
•
Cohesiveness means how well soil holds together; clay is a cohesive soil.
•
Unconfined compressive strength is determined by a test that shows how much
pressure it takes to collapse a soil sample. For example, type A soil must have an
unconfined compressive strength of at least 1.5 tons per square foot.
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7. Which of the following soil types is least stable?
a.
b.
c.
d.
Class A
Class B
Class C
Class D
Visual Tests
Visual testing involves looking at the soil and the area around the excavation site for signs of
instability. The competent person might do visual tests such as the following:
•
Observe the soil as it is excavated. Soil that remains in large clumps when excavated
may be cohesive. Soil that breaks up easily is granular.
•
Examine the particle sizes of excavated soil to determine how they hold together.
•
Look for cracks or fissures in the faces of the excavation.
•
Look for layers of different soil types and the angle of the layers in the face of the
excavation that may indicate instability.
•
Look for water seeping from the sides of the excavation.
•
Look for signs of previously disturbed soil from other construction or excavation work.
•
Consider vibration from construction activity or highway traffic that may affect the
stability of the excavation.
8. Which of the following visual tests indicate stability?
a.
b.
c.
d.
Signs of previously disturbed soil
Soil that forms large clumps
Cracks or fissures
Layers of different soil
Manual Tests
Manual testing involves evaluating a sample of soil from the excavation to determine qualities
such as cohesiveness, granularity, and unconfined compressive strength. Soil can be tested
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either on site or off site but should be tested as soon as possible to preserve its natural
moisture.
Manual Test Examples
Plasticity test: This is sometimes called the "pencil test." Shape a sample of moist soil into a ball
and try to roll it into threads about 1/8-inch in diameter. Cohesive soil will roll into 1/8-inch
threads without crumbling.
Dry strength test: Hold a dry soil sample in your hand. If the soil is dry and crumbles on its own
or with moderate pressure into individual grains or fine powder, it’s granular. If the soil breaks
into clumps that are hard to break into smaller clumps, it may be clay combined with gravel,
sand, or silt.
Thumb penetration test: This test roughly estimates the unconfined compressive strength of a
sample. Press your thumb into the soil sample. If the sample resists hard pressure it may be
type A soil. If it’s easy to penetrate, the sample may be type C.
Pocket penetrometers: offer more accurate estimates of unconfined compressive strength.
These instruments estimate the unconfined compressive strength of saturated cohesive soils.
When pushed into the sample, an indicator sleeve displays an estimate in tons per square foot
or kilograms per square centimeter.
9. Which of the following manual test results indicates Class C soil?
a.
b.
c.
d.
The soil sample is hard to break into smaller clumps
The soil sample does not crumble using the plasticity test
The thumb easily penetrates the soil sample
The pocket penetrometer over 1.5 tons per square foot
Competent Person
A designated competent person who has training in soil analysis, protective systems, and
OSHA's excavation requirements must be on site to classify the soil, select a protective system,
oversee installation, and inspect the system after installation.
•
If there are no existing hazards the competent person can leave the excavation site for a
short time, but must be present when a protective system is moved. Soil conditions
could change or new hazards may arise that require the competent person’s judgment.
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•
The competent person must be knowledgeable about the type of soil excavated and the
protective system used and must inspect them daily for signs of instability, damage, or
other hazards;
•
The competent person must approve any changes. Inspections are also necessary after
heavy rain or activities such as blasting that may increase the risk of cave-in.
•
The competent person must have authority to immediately correct the hazards and to
order employees to leave the excavation until the hazards have been corrected.
•
An employee who is trained and can identify excavation hazards but doesn't have the
authority to correct them is not a competent person.
10. An excavation competent person must _____.
a.
b.
c.
d.
first obtain permission to make any changes
have at least five years of excavation experience
be a designated registered engineer
have authority to immediately correct hazards
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Module 2: Protection Systems
Pre-Job Planning
Pre-job planning is very important to prevent accidents when trenching. In other words, safety
cannot be improvised as the work progresses.
The following concerns must be addressed by a competent person:
•
Evaluate soil conditions and select appropriate protective systems.
•
Construct protective systems in accordance with the standard requirements.
•
Contact utilities (gas, electric) to locate underground lines.
•
Plan for traffic control, if necessary.
•
Determine proximity to structures that could affect your choice of protective system.
•
Test for low-oxygen, hazardous fumes and toxic gas, especially when gasoline enginedriven equipment is running, or the dirt has been contaminated by leaking lines or
storage tanks.
•
Provide safe access into and out of the excavation.
•
Inspect the site daily at the start of each shift, following a rainstorm, or after any other
hazard-increasing event.
1. What is always required because safety cannot be improvised as part of the excavation
work process?
a.
b.
c.
d.
Conduct pre-job planning
Removal of all archaeological artifact
Report all accidents to OSHA within 24 hours
Continuous improvement processes
Protective Systems
All excavations are hazardous because they are inherently unstable. If they are restricted
spaces, they present the additional risks of oxygen depletion, toxic fumes, and water
accumulation. If you are not using protective systems or equipment while working in trenches
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or excavations at your site, you are in danger of suffocating, inhaling toxic materials, fire,
drowning, or being crushed by a cave-in.
There are different types of protective systems.
•
Sloping involves cutting back the trench wall at an angle inclined away from the
excavation.
•
Shoring requires installing aluminum hydraulic or other types of supports to prevent soil
movement and cave-ins.
•
Shielding protects workers by using trench boxes or other types of supports to prevent
soil cave-ins.
Designing a protective system can be complex because you must consider many factors: soil
classification, depth of cut, water content of soil, changes due to weather or climate, surcharge
loads (For example, spoil and other materials to be used in the trench) and other operations in
the vicinity.
2. Each of the following is one of the three primary protective systems for excavations,
EXCEPT _____.
a.
b.
c.
d.
sloping
shaking
shoring
shielding
Other Safety Precautions
The OSHA standard requires you to provide support systems such as shoring, bracing, or
underpinning to ensure that adjacent structures such as buildings, walls, sidewalks, or
pavements remain stable. The standard also prohibits excavation below the base or footing of
any foundation or retaining wall unless:
•
You provide a support system such as underpinning,
•
The excavation is in stable rock, or
•
A registered professional engineer determines the structure is far enough away from
the excavation and the excavation will not pose a hazard to employees.
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Excavations under sidewalks and pavements are prohibited unless you provide an appropriately
designed support system or another effective means of support. There must not be any
indications of a possible cave-in (while the trench is open) below the bottom of the support
system. Also, you must coordinate the installation of support systems closely with the
excavation work.
Once the work is finished, you are required to backfill the excavation when you take apart the
protective system. After the excavation is cleared, remove the protective system from the
bottom up. Make sure you are careful! In the next section, you'll learn more about safely
installing and removing protective systems.
3. What does OSHA require to make sure buildings, walls, sidewalks and pavements remain
stable?
a.
b.
c.
d.
Ensure the excavation is no closer than 50 feet to walls
Provide warning notices to all building occupants
Install guardrails around all excavations
Provide shoring, bracing, or underpinning
Installation and Removal of Protective Systems
You must take the necessary steps to protect yourself and your employees when installing and
removing a protective system. The OSHA standard requires you to take the following steps to
protect your employees:
•
Connect members of the support systems securely.
•
Install support systems safely.
•
Avoid overloading members of support systems.
•
Install other structural members to carry loads imposed on the support system when
you need to remove individual members temporarily.
In addition, the standard permits excavation of two feet or less below the members of a
support or shield system of a trench if the system is designed to resist the forces calculated for
the full trench depth.
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4. All of the following steps are required by OSHA when installing or removing a protective
system, EXCEPT _____.
a.
b.
c.
d.
avoid overloading members of support systems
connect members of the support systems securely
limit excavations below shield system to three feet
install structural members to carry sufficient loads
Appropriate Protective System Designs
Designing a protective system can be complex. You must consider many factors, including:
1. soil classification
2. depth of cut
3. water content of soil
4. changes due to weather and climate
5. other operations in the vicinity
Once you have selected an approach, however, the system must meet the required OSHA
performance criteria.
The OSHA standard describes methods and approaches for designing protective equipment.
Let’s discuss the different methods to designing protective equipment.
Method 1: Sloping
Slope the sides to an angle that isn't steeper than 1½:1. (34 degrees measured from the
horizontal) For example, for every foot of depth, the trench must be excavated back 1½ feet. All
simple slope excavations 20 feet or less deep should have a maximum allowable slope of 1½:1.
These slopes must be excavated to form configurations similar to those for Type C soil. A slope
of this gradation or less is safe for any type of soil.
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5. To achieve a slope of 34 degrees, for every one foot in depth, excavate the sides back
_____
a.
b.
c.
d.
1 foot
1½ feet
2 feet
2½ feet
Method 2: Design Using Data
Use tabulated data such as tables and charts approved by a registered professional engineer to
design excavation. This data must be in writing and must include enough explanatory
information, including the criteria for making a selection and the limits on the use of the data,
for the user to make a selection.
At least one copy of the data, including the identity of the registered professional engineer who
approved it, must be kept at the worksite during the construction of the protective system.
After the system is completed, the data can then be stored away from the jobsite. However, a
copy must be provided upon request to the Assistant Secretary of Labor for OSHA.
Method 3: Trench Box or Shield
In this method, you would use a trench box or shield designed or approved by a registered
professional engineer. Timber, aluminum, or other suitable material may also be used in the
construction. OSHA standards permit the use of a trench shield if it provides the same level of
protection as the appropriate shoring system.
Employers can choose the most practical method for the particular circumstance, but that
system must meet the required performance criteria. The standard doesn't require a protective
system when an excavation is made entirely in stable rock or is less than five feet deep.
However, in this case, a competent person must examine the ground and find no indication of a
potential cave-in.
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6. OSHA requires a protective system unless an excavation is _____.
a.
b.
c.
d.
made entirely in stable rock or less than five feet deep
made in Type A soil or under six feet in depth
designed by a registered engineer or made in rocky soil
approved by local utilities or made entirely in stable rock
Benching
There are two basic types of benching: simple and multiple. The type of soil determines the
horizontal to vertical ratio of the benched side.
•
As a general rule, the bottom vertical height of the trench must not exceed 4 feet.
•
Subsequent benches may be up to a maximum of 5 feet vertical in Type A soil and 4 feet
in Type B soil.
•
All subsequent benches must be below the maximum slope allowed for that soil type.
•
Also, in Type B soil, the trench excavation is permitted only in cohesive soil.
•
Type C soil is not stable enough for benching as a protective system: use sloping instead.
7. Benching may be used as a protective system in which two soil types?
a.
b.
c.
d.
Soil types A, B, or C
Soil type A only
Soil type B only
Soils types A and B
Shoring Types
Shoring is the part of a support system for trench faces. It is used to prevent movement of soil,
underground utilities, roadways and foundations. Shoring or shielding is used when the location
or depth of the cut makes sloping back to the maximum allowable slope impractical. Shoring
consists of posts, struts and sheeting. There are two types of shoring: timber and aluminum
hydraulic.
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Hydraulic Shoring
Hydraulic shoring, a pre-fabricated strut and/or wale system made from aluminum or steel.
Hydraulic shoring provides a critical safety advantage over timber shoring because workers do
NOT have to enter the trench to install or remove hydraulic shoring.
Other advantages to most hydraulic systems include:
•
light enough to be installed by one worker
•
gauge-regulated to ensure even distribution of pressure along the trench line
•
can have their trench faces "pre-loaded" to use the soil’s natural cohesion to prevent
movement
•
can be adapted easily to various trench depths and widths
All shoring should be installed from the top down and removed from the bottom up. Hydraulic
shoring should be checked at least once per shift for leaking hoses and/or cylinders, broken
connections, cracked nipples, bent bases, and other damaged or defective parts.
Pneumatic Shoring
Pneumatic shoring works in a manner similar to hydraulic shoring. The primary difference is
pneumatic shoring uses air pressure in place of hydraulic pressure. However, you need to have
an air compressor on site when using pneumatic shoring. Air shoring involves using compressed
air instead of hydraulic fluid to expand the trench jacks into position. Using the air type of
system, pins are put in place to lock the jacks when a desired level of stability is achieved. To
remove this type of trenching system, air is injected into the jacks to extend them. This allows
the pin to be removed. These types of jacks are popular since they are cleaner than hydraulic
jacks and there isn't a danger from the leakage of fluids or other lubrication.
8. Why does hydraulic shoring provide a critical safety advantage over timber shoring?
a.
b.
c.
d.
Hydraulic shoring is less expensive to use
Hydraulic shoring can be loaded with any kind of hydraulic fluid
Workers do not have to enter the trench to install or remove shoring
Timber shoring is heavier and less stable long-term
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Other Protective Systems
As mentioned earlier, when a trench is excavated, employees who work in the area must be
protected from cave-ins. Therefore, the contractor should consider excavating a wider area
than the necessary minimum. When this is done, it provides a more comfortable working
environment for your employees in the trench. This extra working area may provide a way for
workers to escape an unexpected crisis, such as falling objects or debris.
Contractors should also reduce risk by limiting the number of workers in the trench at all times.
The only workers allowed in the trench should be those who are absolutely needed to perform
the task at hand.
As the trench is backfilled, the braces and planks can be removed to be used at another site. If
installed and removed correctly, vertical planks and trench braces may be used several times!
Ingress and Egress
Access to and exit from the trench require the following conditions:
•
Trenches 4 ft. or more in depth should be provided with a fixed means of egress.
•
Spacing between ladders or other means of egress must be such that a worker will not
have to travel more than 25 ft. laterally to the nearest means of egress.
•
Ladders must be secured and extend a minimum of 36 in (0.9 m) above the landing.
•
Metal ladders should be used with caution, particularly when electric utilities are
present.
9. When in a trench, workers should be no farther from a ladder than _____
a.
b.
c.
d.
15 feet
25 feet
30 feet
40 feet
Additional Hazards and Protections
In addition to cave-ins and related hazards, workers involved in excavation work are exposed to
hazards involving falling loads and mobile equipment. To protect workers from these hazards,
OSHA requires employers to take certain precautions. For example, employers must:
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•
Protect workers from excavated or other materials or equipment that could pose a
hazard by falling or rolling inside the excavation by placing and keeping such materials
or equipment at least 2 feet (0.61 meters) from the edge and/or by using a retaining
device to keep the materials or equipment from falling or rolling into the excavation.
•
Provide a warning system (such as barricades, hand or mechanical signals, or stop logs)
when mobile equipment is operated adjacent to an excavation, or when such
equipment must approach the edge of an excavation, and the operator does not have a
clear and direct view of the edge.
•
Protect workers from loose rock or soil that could fall or roll from an excavation face by
scaling to remove loose material, installing protective barricades at appropriate
intervals, or using other equivalent forms of protection.
•
Institute and enforce work rules prohibiting workers from working on faces of sloped or
benched excavations at levels above other workers unless the workers at the lower
levels are adequately protected from the hazards of falling, rolling, or sliding material or
equipment.
•
Institute and enforce work rules prohibiting workers from standing or working under
loads being handled by lifting or digging equipment.
•
Require workers to stand away from vehicles being loaded or unloaded to protect them
from being struck by any spillage or falling materials. (Operators may remain inside the
cab of a vehicle being loaded or unloaded if the vehicle is equipped, in accord with 29
CFR 1926.601(b)(6), to provide adequate protection for the operator.)
10. Which of the following is NOT allowed when working in a trench?
a.
b.
c.
d.
Provide a warning system when equipment is operating by the excavation
Keep materials at least 2 feet from the edge of the excavation
Workers may work under loads only if a spotter is close by
Require workers to stand away from vehicles loading or unloading
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Additional Resources
•
Trenching and Excavation Safety, OSHA
•
Excavations and Trenching, Oregon OSHA
•
OSHA Technical Manual - Excavations, OSHA
•
Safety Manual for Excavation, Ohio BWC
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