International Module W501
Measurement of Hazardous Substances
(including Risk Assessment)
Day 1
Insert site Emergency procedures
•Insert Lecturer(s) Background
Your Background?
Two (2) minute overview of your background
Course Aims
• To provide participants with a sound understanding
of the techniques for assessing exposure to
hazardous substances in the workplace
• To understand how exposure information can be
used to assess risk
Course Learning Outcomes
• Participants will be able to:
– Describe the general approach to occupational health risk
assessment including role of atmospheric monitoring
– Select the appropriate equipment to measure specific
airborne contaminants & devise a suitable sampling
strategy
– Present the results in a useful form
What is Required to Complete this Course
• Ask questions as we go through the notes
• Participate in the case study discussions
• Participate in the practical exercises
• Attempt the questions each night
What is Occupational Hygiene ?
'Occupational Hygiene is the discipline of
anticipating, recognising, evaluating and
controlling health hazards in the working
environment with the objective of protecting
worker health and well-being and safeguarding
the community at large.'
(Source IOHA)
Topics to be Discussed
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Basic physiology & toxicology
Risk assessment
Hygiene standards
Air sampling theory & practice
Biological monitoring
Sample analysis
Dusts, fumes & fibres
Vapours & gases
Presentation of results
Today’s Learning Outcomes
• Physiology & toxicology
– Understand and be aware of the features of the
interacting systems of the human body
– Understand the routes of contaminant entry into
the human body and their target organs and
systems
– Understand the concept of dose response
Today’s Learning Outcomes (cont)
• Risk Assessment
– Understand principles & processes of risk
assessment
– Be able to apply these principles & processes in a
workplace situation
Today’s Learning Outcomes (cont)
• Hygiene standards
– Understand the principles of setting hygiene
standards
– Understand the application and limitations of
hygiene standards
Work Groups
• Each participant will be assigned a work group for
the duration of the course
• The work groups are expected to work as a team
when evaluating cases studies and undertaking
practical sessions
Introduction to Physiology & Toxicology
Discussion Topics
The Human Body
Routes of Entry
Target Organs & Systems
Concept of Dose Response
The Human Body
12 Interacting systems:
Cardiovascular
Muscular
Digestive
Nervous
Endocrine
Reproductive
Immune
Respiratory
Integumentary
Skeletal
Lymphatic
Urinary
Cardiovascular System
• Includes the heart, blood & the blood vessels
(arteries, capillaries & veins)
• Arteries bring oxygenated blood from heart to the
tissues
• Veins bring deoxygenated blood back to the heart
Digestive System
• Takes in food, digests it & extracts energy &
nutrients & expels the waste
• Nutrients can be absorbed into blood & lymph
systems
• Some used for energy, some for building tissues &
cells & some stored for future use
Endocrine System
• Control system of glands which secrete chemical
messengers or hormones
• Endocrine glands release hormones directly into
bloodstream of the body
• Regulate metabolism, growth & sexual development
Immune System
• Protects body from infection by creating &
maintaining barriers to prevent that bacteria &
viruses entering the body
e.g. hepatitis, influenza, cholera, typhoid & malaria
Integumentary System
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Comprises skin (cutaneous
membrane) & hair, nails &
endocrine glands
– epidermis
– dermis
– subcutaneous tissue
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Largest organ of body
– interface with surroundings
– Insulation & temp regulation
Lymphatic System
• Major component of immune system
• Complex system of lymphoid organs, lymph ducts &
lymph vessels that produces & transport lymph fluid
from tissues to circulatory system
– Removal of excess fluids from body tissues
– Absorption of fatty acids & transport of fat to
circulatory system
– Production of immune cells e.g. lymphocytes,
monocytes & antibody producing plasma cells
Muscular System
• Muscle attached to bone by tendons & other tissues
• Exerts force by converting chemical energy into force
• Nerves link muscle to CNS
• Function
– Produce movement
– Maintain posture
– Stabilise joints
Nervous System
• Electrical impulses carried along nerve cells
• CNS – body’s control centre
• PNS – all other nerves & neurons
– Somatic :
• body’s movement & conscious control
– Autonomic:
• Sympathetic – responds to impending danger or stress
• Parasympathetic – evident when resting relaxed
Reproductive System
Produces offspring by fertilisation or fusion of a
sperm and one ovum and the subsequent
development of the offspring
Respiratory System
• Responsible for carrying oxygen from inhaled air to
the bloodstream & expelling the waste product of
carbon dioxide
Skeletal System
• 206 bones joined by ligaments & tendons
• Protective & supportive framework for attached
muscles & soft underlying tissues
• Produces red & white blood cells in bone marrow
• Bones store minerals eg calcium & can be
transported elsewhere
Urinary System
• The body’s filtering system via the kidneys which
reabsorb approx 99% of the fluid into the blood
• Waste or urine passed to the bladder for excretion
Routes of Entry
• Inhalation
– By far most common route of entry
• Skin absorption
– Via direct contact major source of entry of
organics eg solvents and pesticides
Routes of Entry (cont)
• Ingestion
– Relatively minor route of accidental
ingestion or poor personal hygiene
• Eye
– Direct entry point for some solvents and also at
risk by direct contact
Target Organs & Systems
Upon entry to the body contaminants can have an
adverse effect on one or more organs (target organs)
• Respiratory
– Irritant & toxic gases eg Carbon monoxide &
sulphur dioxide
– Dusts & fibres eg silica & asbestos
• Blood
– Lead and mercury
Target Organs & Systems (cont)
• Central Nervous System
– Solvents eg toluene, xylene, MEK
– Polycyclic and polyaromatic hydrocarbons
• Liver
– Alcohols & solvents
• Kidneys
– Selenium, alcohol & sodium compounds
Target Organs & Systems (cont)
• Brain
– Mercury - “as mad as a hatter”
• Urinary
– Biological agents
– Some metals
• Reproductive
– Lead, organic mercury
Target Organs & Systems (cont)
• Fatty tissues
– Solvents
• Skin
– Acids, alkali
– Epoxy resins
• Skeletal
– Lead
– Benzene
Target Organs & Systems (cont)
• Endocrine
– Lead, cadmium
– Carbon disulphide
Concept of Dose Response
“No substance is a poison by itself, it is the dose
that makes a substance a poison”
Paracelsus 1540
Dose Effect Relationship
• For each chemical there is a dose-effect relationship
– Acute (immediate) effects (Irritants, CO)
– Chronic (long-term) effects (Benzene, Asbestos)
– Local effects occur at point of contact
– Systemic effects occur at distant target organs
Dose Effect relationship (cont)
• Factors effecting this relationship include
– Physical state of the material
– Concentration
– Possible routes of entry to the body
– Target organs
Dose Effect Relationship (cont)
– Retention rate in the body
– Human pre-disposition (pre-existing medical
condition)
– Individual sensitivity
– Frequency & duration of exposure
– Potency of compound
– Synergistic effects with other compounds
(e.g. asbestos & smoking)
Key Factors
• Dose
• Effect
• Critical organ concentration
Dose
The concentration of a substance at the site of effect
(regard being made for the time which substance
concentration is maintained)
Dose = concentration x duration of exposure
Effect
Any observable biological change associated with the
contaminant concerned:
– Should be quantifiable
– Does not need to be an adverse observable effect
– Certain effects can be beneficial and only become
adverse if the dose is excessive or remains for a
critical period of time
Critical Organ Concentration
That concentration beyond which organs exhibit
some effect
– May not be organ of concentration (eg bone
accumulates lead but critical organ is bone
marrow)
Target Organs
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Respiratory system
Skin
Eyes
Blood
Liver
Kidneys
Bladder
Nervous system
Dose Effect v Dose Response
• Dose effect: Correlation between dose and the
magnitude of effect
• Dose response: Correlation between response of an
organ with estimates of dose
Threshold
• The dividing line between no-effect and effect levels
of exposure
• For each substance there is a threshold of
intoxication which is usually different for individual
substances
Dose Response Curve
Source: Tranter 1999 –Reproduced with permission
Dose Response Curve
Threshold of Intoxication
• For each substance, no matter how toxic, there exists
a dose level called the threshold of intoxication,
which the human body is capable of accepting and
detoxifying without injury to itself
Individual Susceptibility
Source: AIOH 2007-Reproduced with permission
Risk Assessment
Definitions
– Hazard: potential for a substance to cause harm,
injury etc
– Exposure: the ability (or potential) for someone to
come into contact with a substance by breathing it
in (inhalation), getting it onto the skin or into the
eyes (absorption) or swallowing it (ingestion)
Definitions (cont)
– Risk: likelihood that the substance will cause
injury or illness in the conditions of its use
Note: the terms “risk” & “hazard” are treated solely
in relation to chemical (substance) safety and not
any broader concept
The Risk Assessment Process
• Risk management is used in all sectors of the
political, business & community environment
• Part of our everyday activities (e.g. driving to work)
• Central to OH&S legislation in many countries
• Extends to occupational hygiene hazards (e.g.
conduct of RA for hazardous substances)
Key Steps to a Successful Risk Assessment
Identify substances in the workplace
Establish which are hazardous & obtain information
on their properties
Assess the exposure of workers
Key Steps to a Successful Risk Assessment
Evaluate the risks
Identify actions
Document & communicate outcomes to stakeholders
Information
• Primary sources of information:
– Suppliers MSDS
– Label fixed to product
What Does an MSDS Tell You?
• Product Name
• Codes, Listings
• Major Uses
• Ingredients
• Physical Characteristics
• Precautions for Use
• Safe Handling and Storage Information
• First Aid/Emergency
To Be Useful, MSDS’s, Must Have…
• Issue Date
• Company Details (Not O/Seas)
• Substance Name
• Health Effects/First Aid
• Engineering Controls
• Flammable/Fire & Explosion Hazards
• Storage & Handling
• Spills & Disposal
What Information Can You Obtain From a MSDS?
– Toxic effects
– Safe handling procedures
– Exposure standards
– Control technologies
• Engineering
• PPE
– Reference to other analogous compounds
What Information Can You Obtain From a Label
• Much less detail than a MSDS but usually
– Name of compound
– Safety phrases
– Risk phrases
– Pictograms
– Suppliers details & emergency number
Examples of Risk Phrases
– R26
Very toxic by inhalation
– R27
Very toxic in contact with skin
– R34
Causes burns
– R37
Irritating to respiratory system
– R42
May cause sensitisation by inhalation
– R45
May cause cancer
Examples of Safety Phrases
– S3
Keep in a cool place
– S8
Keep container dry
– S15
Keep away from heat
– S22
Do not breathe dust
– S23
Do not breathe vapour
– S24
Avoid contact with skin
United Nations - GHS
GHS - Globally harmonised system of classification and
labelling chemicals
– Single international system
– Currently being implemented by many countries as
part of national chemical regulations systems
– Risk & safety phrases will be replaced by hazard
statements
Projected GHS Benefits
– Enhancement of the protection of human health
and the environment by providing an
internationally comprehensible system for hazard
communication
– Will provide a recognised framework for those
countries without an existing system
Projected GHS Benefits (cont)
– Will reduce the need for testing and evaluation of
chemicals, and
– Will facilitate international trade in chemicals
whose hazards have been properly assessed and
identified on an international basis
GHS Pictograms
Source: ASCC information sheet
Other Sources of Information
Collection Method
Interviews of workers,
managers and engineers
Type of Information
Tasks
Work practices
Health issues
Processes
Exposure controls
Maintenance
Environmental agents
Other Sources of Information (cont)
Collection Method
Interviews of medical
and safety staff
Type of Information
Health problems
Patterns of problems
Work practices
Exposure history
Environmental agents
Other Sources of Information (cont)
Records:
Process standards
Standard operating
procedures
Production
Personnel
Medical
Engineering
Environmental reports
Process flow diagrams
Historic conditions
Chemical inventories
Usage amounts
Tasks
Work histories
Performance of
engineering controls
Past environmental
monitoring results
Past biological monitoring
results
Other Sources of Information (cont)
Governmental and nongovernmental standards
Current exposure limits
Proposed exposure limits
Literature
Epidemiological studies
Toxicological studies
Emerging issues
Walkthrough Survey
• Can provide information that may not be otherwise
evident
• Involves commencing at the starting point of a
process and following the various components until
the end product is reached
• To be useful must involve someone familiar with each
step of the process
Basic Information From a Walkthrough Survey
•
An understanding of the process
• The number of workers involved
• The materials (including quantities) used or
handled
• Evidence of reactions and any material
transformations
• Engineering controls in place and their
effectiveness
Basic Information from a Walkthrough Survey (cont)
• Housekeeping standards
• Visible conditions at the site (any dusts,
mists, etc)
• Possible routes of entry to the body
•
Personal protective equipment and its use
Generation of Hazardous Substances
• May be generated as a result of the process and not
by any individual chemical
• Process itself may change the form of a substance
making it harmful
– Fine dusts from solids
– Fumes from heating chemicals (ammonia
compounds)
Assessing the Risk
• Factors influencing the level of risk
– How much a worker is exposed to a hazardous
substance (exposure)
– Route of entry to the body (inhalation, skin etc)
– Severity of adverse health effects under conditions
of exposure (hazard)
– Duration and frequency of exposure
Level of Risk
As a result of using a hazardous substance without
controls the level of risk depends upon the
combination of the:
• hazard of that substance under its condition of use
• duration & frequency of exposure
i.e. Risk = combination of hazard and exposure
Types of Risk Analysis
• Qualitative analysis
– Uses words to describe magnitude of potential
consequences and likelihood that those
consequences will occur
– Used as a screening activity, where basic analysis
is appropriate for decisions or where numerical
data or resources are inadequate for a quantitative
analysis
Types of Risk Analysis
• Quantitative analysis
– Uses numerical values for both consequences &
likelihood
– Quality of analysis depends on accuracy &
completeness of numerical values and validity of
models used
– Consequences may be determined by modelling
the outcomes of events or extrapolation from past
studies or data
Process of Risk Analysis
• Assessing the risk requires a judgment on the
likelihood that a hazardous substance will effect
someone’s health
• Ask yourself these questions
– How much of the substance is used or produced &
how could workers be exposed ?
– Who could be exposed & how often ?
– What are the routes of entry to the body ?
– What are the consequences of exposure ?
Process of Risk Analysis (cont)
• Gathering information to answer previous questions
• Monitor workplace (for quantitative analysis)
• Determine level of risk
Non Monitoring Approaches
• HSE (UK) COSHH Essentials
• ILO Chemical Control Tool kit
HSE (UK) COSHH Essentials
• Control banding tool for small to medium size
enterprises to do risk assessments for chemicals &
mixtures of chemicals
• Required information
– Type of task – shoveling, drilling
– Hazard classification (using risk & safety phrases
from MSDS )
– Volatility or dustiness (from guidance material)
– Amount used- kg,mg,litres,milliliters
HSE (UK) COSHH Essentials (cont)
• System identifies
– Control band (control approach)
– Produces advice on controlling risk from the
chemical being used in the task
– Provides written guidance & documentation
ILO Chemical Control Tool kit
• Very similar to COSHH Essentials
• Does not apply to process dusts or fumes due to the
fact that these are not classified by the supplier of
individual chemicals
• Has general application to many situations in
developing countries but susceptible groups (child
workers & pregnant women) need to be considered
Stages of the ILO Chemical Control Toolkit
Stage 1 – Hazard Classification
Stage 1 – Hazard Classification (cont)
Stage 2 – How Much is Used
Stage 3 - Dustiness
Stage 3 – Volatility
Source: ILO toolkit
Stage 4 – Control Approach
Source: ILO toolkit
Stage 5 – Task Specific Control Guidance Sheet
Source: ILO toolkit
Stage 5 – Task Specific Control Guidance Sheet
Source: ILO toolkit
Stage 5 – Task Specific Control Guidance Sheet
Source: ILO toolkit
Outcomes of a Risk Assessment
• Significant risk
– Exposure is high or the substance used is highly
toxic
– A dangerous reaction with other substances
possible
– Reasonably foreseeable that leaks or spills of a
hazardous substance may occur
• Not significant risk
Actions
• Process of risk evaluation provides a list of risks
requiring control, often with priorities
• Need to identify a range of possible control options,
evaluating them, selecting appropriate control
options and implementing them in the workplace
• Control options should be considered as part of
overall site or process risk management strategy
Actions (cont)
• Possible control measures (Hierarchy of Control)
– Elimination of the substance
– Substitution of the substance
– Segregation of the substance from workers
– Engineering methods
– Administrative controls
– Personnel protective equipment
Elimination
• Difficult to achieve in practice
– production
– quality
– cost
• Some examples
– preformed components (eliminating dust)
– components that can be clipped, screwed or bolted
together (eliminating adhesives)
Substitution
• Use a safer form of the same substance ( e.g. using a
substance in pellet rather than powder form)
• Use a safer (less hazardous / less volatile) substance /
product (e.g. use water based paint rather than oil based
paint)
• Process modification (e.g. applying a substance with a brush
instead of spraying the substance)
Segregation (Isolation)
Can be achieved by separating people from a harmful
agent / process by:
• distance
• time
• barriers
Engineering Controls
• The use of equipment or processes, to prevent or
minimise the release of hazardous chemical agents
• Options include:
• automation / robots
• total enclosure / containment
• partial enclosure
• partial enclosure plus local exhaust ventilation
• local exhaust ventilation
• general (dilution) ventilation
Total Enclosure / Containment
• The operator controls the process from outside the
enclosure, and the hazard is contained. It is used
when working with;
– carcinogens
– sensitisers
– materials under high temperature or pressure
• Examples include:
– Pharmaceuticals, chemical plants and refineries
– Closed loop sampling systems
– Laboratory glove boxes
Partial Enclosure Plus LEV
•
Common examples include:
– welding and grinding benches,
– spray paint booths and
– fume cupboards
General Ventilation Compared to LEV
General Ventilation
LEV
• Does not remove
contaminant at source
• Draws contaminant away
from source
• Reduces background
levels by addition of fresh
uncontaminated air
• Reduces level of
contaminant inhaled by
employees
• Very effective if
designed and used
correctly
Administrative Controls
• Safe systems of work rely heavily on:
– good management / supervision
– employee engagement / behaviour
– written rules and procedures
– information, instruction and training
• Simple instruction, ‘allow to cool before opening’
Administrative Controls (cont)
• Formal standard operating procedure (in wriwhich if
adopted ensures a task is undertaken the right way
every time
– task analysis,
– in writing,
– training / competence,
– supervision
• Permit to work
– confined space entry
Administrative Controls (cont)
• Reducing exposure time
– Employee rotation
– Work rest regimes
Personal Protective Equipment (PPE)
Head protection
Body protection
Eye protection
Hand protection
Ear protection
Foot protection
Respiratory protection
Actions
• Induction & training
– Extent will depend on level of risk
– Use the information on the hazards and controls obtained in
the risk assessment to prepare training materials
• Ongoing workplace monitoring
– Required where serious health effects may occur if controls
fail
– Statutory requirement for some substances
– Useful to check effectiveness of control measures
Actions (cont)
• Health surveillance
– May be required when there is an identifiable work related
disease
– Likely that disease or condition might occur under
conditions of work
– Valid techniques for early detection are available
• Emergency procedures & first aid
– Need to match level risk and address potential
consequences of an uncontrolled release etc
Records
• Documentation of risk assessments is a fundamental
step in the process
• Needs to be given attention but in some cases is
overlooked once the risk level is established
• Most organisations use the same format to document
risks no matter their origins - brings familiarity to the
process ensuring the level of detail required for
ongoing review is provided in the documentation
Reasons for Documentation (cont)
• Communication with stakeholders
• Evidence of a systematic approach to risk
identification & analysis
• For later review
• Record of risk & develop the organisations
knowledge database
Reasons for Documentation (cont)
• Documentation for managerial approval &
implementation
• To provide an accountability mechanism & tool
• Audit trail
• Share & communicate information
Management
• The use of prescriptive legislation in many countries
is diminishing
• Most authorities have moved to a risk based
approach where the onus is on the employer to
establish the level of risk and manage accordingly
• Covers a broad range of issues including hazardous
substances
• Statutory authorities produce guidance material
which essentially defines minimum standards
Case Study 1 – Risk Assessment
Super IH Paints
Source: BP International
Case Study 1 – Risk Assessment
• Paint Manufacturer - vessel cleaning
• Case Study video together with background
information
• Comment on what you see and hear. Ask questions
• Determine the information you need to complete a
risk assessment on the task of paint vessel cleaning
Case Study 1 – Student Exercise
• Break up into assigned groups
• Critically review the case study video & gathered
information
• Attempt to document a risk assessment & make
conclusions about risk
• Determine actions to improve control
Case Study 1 – Student Exercise
• Use lecture notes for guidance and/or discuss with
lecturer if you require clarification
• Time allowed is 60 minutes
• Be prepared to present your assessment in the group
discussion period
Hygiene Standards
Hygiene Standards
Hygiene standard:
The level of exposure, via
inhalation, that should not cause ill health to a healthy
adult when exposed to the contaminant
Other (interchangeable) terms include:
• Threshold limit values
• Exposure standards
• Occupational exposure limits
• Workplace exposure limits
Background
• Based on “no observed adverse effect level”
• Seems to be “threshold dose”
• Epidemiological studies & occupational hygiene
measurements assist to identify this threshold
• Threshold of intoxication – accepting & detoxification
without injury
Background (cont)
• Also based on physiological response
– Irritants
– Asphyxiants
– Anesthetics
– Carcinogens
– Unbearable odour
– Toxic effect
ACGIH
“Threshold Limit Values – TLVs® - refer to airborne
concentrations under which it is believed that nearly all
workers may be repeatedly exposed, day after day, over
a working lifetime, without adverse effects. TLVs® are
developed to protect normal, healthy adults.”
Documentation
The source publication that provides the critical
evaluation of the pertinent scientific information and
data with reference to literature sources upon which
the TLV® or BEI® is based
“Documentation of Threshold Limit Values for
Chemical Substances and Physical Agents and
Biological Exposure Indices”
Three types of TLVs®
•
TLV - Time Weighted Average (TLV - TWA)
•
TLV – Short Term Exposure Limit (TWA - STEL)
•
TLC – Ceiling (TLC - C)
TLV – TWA
“TLV-TWA The TWA concentration for a conventional
8-hour workday and a 40-hour work week, to which it is
believed that nearly all workers may be repeatedly
exposed, day after day, for a working lifetime without
adverse effect.”
TWA (8-hr) = C1T1 + C2T2 +…..CnTn
8
Calculate 8-hour TWA
Working period
mg/m3
Duration of sampling (h)
0800 - 1030
0.32
2.5
1045 - 1245
0.07
2
1330
0.2
2
1545 – 1715
0.1
1.5
Assume exposure is zero in rest breaks 1030–1045, 1245–1330 & 1530–1545
8-hr TWA = (0.32 x 2.5) + (0.07 x 2) + (0.2 x 2) + (0.1 x 1.5) + (0 x 1.25)
8
= 0.8 + 0.14 + 0.4 + 0.15 + 0
8
= 0.19 mg/m3
TLV – STEL
TLV-STEL is a 15 minute TWA exposure that
should not be exceeded at any time during a
workday, even if the TWA is within TLV- TWA
TLV – STEL (cont)
Can be exposed continuously for a short period without
suffering from:
– Irritation
– Chronic or irreversible toxic effects
– Dose-rate dependent toxic effects or
– Narcosis sufficient to increase likelihood of
accident, impaired self rescue, or reduced work
efficiency
TLV – STEL (cont)
• Exposures above TLV-TWA up to TWA-STEL
< 15 minutes
≤ 4 times a day
60 minutes between successive exposures
TLV - C
TLV-C the concentration that should not be exceeded
during any part of the working exposure
• If instantaneous measurements are not available,
sampling should be conducted for the minimum
period of time to detect exposures at or above ceiling
value
Excursion Limits
Excursions limits are applied to TLV-TWAs that do NOT
have TLV-STELs
• Excursions up to 3 x TLV-TWA - less than 30 min/day
and NO excursions above 5 x TLV-TWA, providing
TLV-TWA not exceeded (3 x WEL in UK)
• A process is not considered to be under reasonable
control if these levels occur
Mixtures
When two or more hazardous substances have a
similar toxicological effect on the same target system,
their combined effect rather than that of either
individually, should be considered
Where
C1/TLV1 + C2/TLV2 +…+ Cn/TLVn < 1
the TLV for the mixture should be considered as being
exceeded
Additive Effect
Agent
Acetone
Sec butyl acetate
Methyl ethyl ketone
Full shift results Short term results
(TLV-TWA)
(TLV-STEL)
160 ppm
490 ppm
(500)
(750)
20 ppm
(200)
90 ppm
(200)
150 ppm
(N/A)
220 ppm
(320)
From the TLV® basics column, the Documentation of the TLVs®
and BEIs® all three substances indicate effects on respiratory
system and would be considered additive
Additive Effect (cont)
Full shift calculation
C1/TLV1 + C2/TLV2 +…+ Cn/TLVn ≤ 1
therefore 160/500 + 20/200 + 90/200
= 0.32 + 0.10 + 0.45
= 0.87
Hence full shift additive limit not exceeded
Additive Effect (cont)
Short term calculation
= 490/750 + 150/(200 x 5)* + 220/300
= 0.65 + 0.15 + 0.73
= 1.53
This is >1 hence short term additive limit
exceeded
* where no STEL exists the convention is to
multiply TWA exposure standard x 5 (x 3 in UK)
Units of Measure
• Dusts
– mg/m3
• Gases and vapours
– parts per million (ppm) or % (v/v)
– mg/m3
Conversion of ppm to mg/m3
Conc in mg/m3 = Conc in ppm x molecular weight /24.45
where 24.45 = molar volume of air in litres at NTP
conditions (25°C and 1 atm)
(NB IUPAC use 0°C and 100 kPa, but ACGIH and other
bodies use 25°C and 1 atmosphere)
Conversion of ppm to mg/m3 (cont)
Where STP conditions are required (i.e. 20°C not
25°C) the equation is:
Conc. in mg/m3 = Conc. in ppm x molecular weight
24.06
Definitions & Notations
• Carcinogenicity
A carcinogen is an agent capable of inducing benign
or malignant neoplasms
A1 - Confirmed human carcinogen
A2 - Suspected human carcinogen
A3 - Confirmed animal carcinogen with unknown
relevance to humans
A4 - Not classifiable as a human carcinogen
A5 - Not suspected as a human carcinogen
Definition & Notations (cont)
• Notice of Intended Change (NIC)
– Each year proposed changes are indicated –
comments are sought and suggestions for other
substances to be added are also sought
• Particulate matter / particle size
– For solid and liquid matter, TLVs® are expressed
as “total” particulate matter except where terms
such as inhalable, thoracic or respirable particulate
mass are used
Definition & Notations (cont)
TLV® Basis/Critical Effects
– Is discussed in each documentation.
– The column comments are intended to provide field
reference for symptoms of over exposure and for which
compounds may be considered as acting independently or
additively
• Biological Exposure Indices BEIs®
– Listed when a BEI® is recommended
– Two sub categories added
BEIA = see the BEI® for Acetylcholinesterase inhibiting pesticide
BEIM = see the BEI® for Methemoglobin inducers
Definitions & Notations (cont)
Sen – potential for agent to produce sensitisation.
Does not imply that it is the critical effect
– Respiratory
– Dermal
– Conjunctival
• Skin – where potential significant contribution to the
overall exposure by the cutaneous route by direct
contact with the vapour or direct contact with the skin
Application of Standards
Airborne concentrations are representative of workers
exposure:
• Collected in the breathing zone
• Occupational or personal sampling
Note: If para-occupational or static or area sampling
carried out results should not be compared directly
with exposure standards
Extended Work Shifts
TLVs® developed for conventional 8-hour workday
followed by a 16-hour break from the exposure over a
40-hour week
• Number of models used to adjust TWA for unusual &
extended shifts
• Not necessary to adjust TWA-STEL or TWA-C as
these associated with acute rather than chronic
exposures
Brief & Scala Model
Reduces OEL proportionally for increased
exposure & reduced recovery time
Adjusted OEL = 8 x (24 – h) x TWA
16 x h
where h = hours worked each day
Brief & Scala Model (cont)
Example: Toluene, 12 hour shift, 8 hr TWA is 50 ppm
Adjusted OEL = 8 x (24 – 12) x 50 ppm
16 x 12
= 25 ppm
NB Brief & Scala model developed for petroleum
industry & has not been validated for dust exposures
OSHA Model
Previously, OSHA used reduced PELs.
Example: If 10 hour shift being worked,
TWA (10Hr) = TWA (8 hour) x (8/10)
Now, OSHA official must measure the “worst” 8-hour
period and compare result with 8-hour TWA
Only lead has a exposure reduction
Lead PEL = 4000µg/m3 / shift hours
OSHA Model - example
• Toluene, 12 hour shift, 8 hr TWA is 50 ppm
OEL = 50 x 8
12
= 33 ppm
Note difference between Brief & Scala v OSHA models
with same data
Pharmacokinetic Model
Model of Hickey & Reist considers metabolism,
biotransformation and excretion –
Modified TLV
= TLV x 1-e-8k 1-e-120k
1-e-t1k 1-e-t2k
where t1 = hrs worked per day on usual schedule
t2 = 24 x days worked/week on unusual schedule
k = ln2/t1/2
This model beyond scope of this course
WA Department of Minerals & Energy
Source; DOCEP-reproduced with permission
Limitations of Hygiene Standards
• Values do not exist for all substances
• Apply to the workforce – workers healthier than
general public
• Not meant to apply to general population
– Not for environment or boundary emission
standards
– Not for use with a set safety factor eg divide by 100
• Not a fine line between safe and dangerous
concentrations
• For use by trained occupational hygienists
Standards in Other Countries
• Australia – “Exposure Standards”
– Based on ACGIH List with reference to standards from
Germany, Sweden & UK
– www.ascc.gov.au
– Data base exists for 696 current national exposure
standards
– TWA, STEL, peak, carcinogen, Sen, Skin
Standards in Other Countries (cont)
• United Kingdom – Workplace Exposure Limits
– WELs replaced previous Occupational Exposure Limits
(OELs) and Maximum Exposure Limits (MELs)
– HSE EH40/2005 (Workplace Exposure Limits) – list of
assigned substances
– 8-hr TWA & STEL
– Comments Column containing Safety & Risk Phrases plus
the Carcinogenicity, Skin, Sensitivity and Biological
Monitoring Guidance Value notations
Standards in Other Countries (cont)
•
European Limits
Indicative Occupational Exposure Limit Values IOELVs
–
–
–
–
Chemical Agents Directive
Health based
63 substances
8-hr TWA, STEL, skin
Binding Limit Values BLVs
– Carcinogen Directive
– Also reflect socio-economic & tech feasibility factors
– Benzene, hardwood dust, vinyl chloride monomer, lead
Standards in Other Countries (cont)
• USA – OSHA – Permitted Exposure Levels (PELs)
– Based on 1968 TLVs® - approx 400
– Listed updated in 1989
– Number of detailed regulatory requirements
eg asbestos, lead, benzene, methylene chloride, vinyl
chloride etc
– Contained in Title 29 of US Code of Federal Regulations
Standards in Other Countries (cont)
• USA – NIOSH – Recommended Exposure Limits RELs
– NIOSH recommends Standards to OSHA / MSHA (Mine
Safety & Health Administration) & some are lower than
PELs, TLVs® etc
– TWA up to 10-hr day, 40 hour week
– Also STEL, C and Ca, skin
– Available on CD-ROM or website www.cdc.niosh.gov
• Pocket Guide to Chemical Hazards
• NIOSH Recommendations
• Criteria documents etc
Standards in Other Countries (cont)
• USA – AIHA – Workplace Environmental Exposure
Levels (WEELs)
– Intended to provide guidance where NO legal or
authoritative limit exists
– eg benzyl alcohol, butylene oxide
– In current Guide > 100 WEELs
– 8-hr TWA, Ceiling, Short Term TWA plus Skin, Dermal &
Respiratory sensitiser notations
Standards in Other Countries (cont)
• Germany – MAK Commission
– MAK values for volatile chemicals & dusts
– BAT values (biological tolerance values)
– Analytical procedures (air & biological materials)
– Notations for carcinogens, germ cell mutagenic,
sensitizing, percutaneously absorbed & embryonic
effects
– Published & reviewed annually
Review of Today’s Learning Outcomes
• Physiology & toxicology
– Understand and be aware of the features of the
interacting systems of the human body
– Understand the routes of contaminant entry into
the human body and their target organs and
systems
– Understand the concept of dose response
Review of Today’s Learning Outcomes (cont)
• Risk Assessment
– Understand principles & processes of risk
assessment
– Be able to apply these principles & processes in a
workplace situation
Review of Today’s Learning Outcomes (cont)
• Hygiene standards
– Understand the principles of setting hygiene
standards
– Understand the application and limitations of
hygiene standards