A Semi-Quantitative Method

to

Assess Occupational Exposure

to

Harmful Chemicals
Ministry of Manpower
Occupational Safety and Health Division
18 Havelock Road
#03-02
Singapore 059764

Email: mom_oshd@mom.gov.sg

All rights reserved. No part of this

publication may be reproduced or
transmitted in any form or by any
means, without the prior permission
of the copyright holder.
 A Semi-Quantitative Method to Assess Occupational Exposure to Harmful Chemicals

Introduction

Risk may be defined as the likelihood

of occurrence of an event resulting in
certain consequences. Different
chemicals have different properties
and toxicity. Exposure to toxic
chemicals can result in different effects
depending on the routes and levels of
exposure.

A risk assessment of toxic or harmful

chemicals determines the risk levels
they present to the users. It also
enables decisions to be made on
whether measures need to be taken to
safeguard or protect persons against
the chemicals. Under the Factories
Act, factory occupiers or employers
must take measures to ensure the safe
use of chemicals. To discharge this
duty, an assessment of all chemicals
used in the workplace must be carried
out in order to identify, evaluate and
control any health risk associated with Objectives
work activities involving the use of the
chemicals.
The purposes of conducting a risk
assessment of harmful chemicals are
The purpose of these guidelines is to
to
provide guidance to factory occupiers,
employers, health and safety
personnel, as well as users of • identify the hazards posed by each
chemicals on the methods and chemical used or handled
procedures of assessing health risks • evaluate the degree of exposure to
arising from the use of toxic or harmful the toxic or harmful chemicals
chemicals. These guidelines are not • determine the likelihood of the
mandatory and may be used to adverse effects from exposure to
complement other risk assessment the chemicals
methods. The guidelines do not
address flammable and other The main outcome of the risk
hazardous chemicals, which may pose assessment is to assign a risk rating to
fire or explosion and other hazards. different work tasks involving exposure
hazards. The hazard scenarios are
then ranked and the ranking is used
These should be separately assessed for prioritizing actions to address the
by appropriate methods. hazards and to reduce the risk.
 A Semi-Quantitative Method to Assess Occupational Exposure to Harmful Chemicals

Without a system that ranks hazards machine, equipment and control

according to their potential risk, time system that may eventually lead to
and resources could be diverted to an accident or incident.
addressing low-risk hazards while • They also do not address the risks
more significant ones could be to those in the immediate
neglected. neighbourhood, to the public or to
the environment.
• The assessment does not take into
account persons with
Scope hypersensitivity.
• The assessment does not take into
account dermal exposure and
• In these guidelines, the ingestion. However, sample
assessments are concerned only calculations of dermal exposure is
with the health risks to people in included in Annex 1.
the workplace.
• These guidelines are applicable to
plants handling toxic or harmful
chemicals including raw materials,
products, ingredients and by
products.
• These guidelines provide guidance
on the steps of deciding who
should do the assessments, and
determining what work should be
assessed.
• These guidelines outline a general
process for the assessment of risk
in work releasing or generating
toxic or harmful chemicals.
• These guidelines also describe the
actions that should be taken
following an assessment and the
requirements for recording and
reviewing assessments.
• These guidelines may be used by
health and safety practitioners and
others who might be involved with
risk assessment.
• The assessment can provide an
indication of relative risk if the
parameters used for assessment
are known. However, the results
can be questionable if meaningful
information and data are not
available or if human errors are
made in the process of
assessment.
• These guidelines do not address
the risk related to failure of any
 A Semi-Quantitative Method to Assess Occupational Exposure to Harmful Chemicals

Definitions
Commitment of Management:
Hazard is the general term for 1 Formation of a workgroup
anything that has the ability or
potential to cause injury. The hazard
associated with a potentially toxic Hazards/Identification and Rating:
chemical is a function of its toxicity.
2 Breakdown of work process
Risk is the term applied to the 3 Identification of chemicals
predicted or actual frequency or 4 Determination of hazard rating
likelihood of occurrence of an adverse 5 Conducting work inspection and
effect of a chemical or other hazard. interviews
Risk assessment is the identification Exposure Evaluation:
and quantification of the risk resulting
from a specific use of a chemical, 6 Obtaining information on
taking into account the possible frequency and duration of
harmful effects on people using the exposure
chemical in the amount and manner 7 Determination of exposure
proposed and all the possible routes of rating
exposure.
Assessing Risk:
Toxic is the adjective applied to any
chemical or substance able to cause 8 Evaluation of risk
injury to living organisms. 9 Taking corrective actions
10 Record of assessment
Toxicity of a chemical is its ability to 11 Review of assessment
cause injury to a living organism.

There are three methods to conduct

exposure evaluation. The assessor
can use the actual exposure levels to
Semi-Quantitative determine the exposure rating and risk
Risk Assessment level. If exposure levels are not
available, exposure factors or
This method systematically identifies parameters can be used to determine
the chemical hazards, evaluates the the exposure index and rating. For
exposure or likelihood of exposure, risk assessment of exposure hazard at
determines the risk level, and plant or process design stage, the
prioritises actions to address the risks. exposure may be estimated using
empirical or theoretical formulas.

There are eleven steps involved in a

semi-quantitative risk assessment
 A Semi-Quantitative Method to Assess Occupational Exposure to Harmful Chemicals

Process Flow Chart of Semi-Quantitative Method

Formation of a workgroup to
conduct assessment

Breakdown of
work process (Form 1)

Identification of (Form 1)
chemicals for each task

Determination of hazard
rating

Conducting work
inspection and interviews

Computing exposure index Obtaining exposure Calculating exposure

using exposure factors concentrations from air concentrations using
(without air monitoring) monitoring empirical and
theoretical equations
(Form 2a)
(Form 2b) (Form 2a)

Determination of
exposure rating

(Form 3)
Evaluation
of risk

Taking corrective actions

Review of
assessment

Record of
assessment
Any changes in
production rate and
modification of the plant
STEP 1 Formation of a
workgroup
The competent person could be an
employee or any person who has
A workgroup or team consisting of adequate training and experience
representatives of both the in management of hazardous
management and the employees substances and in risk assessment
as well as a competent person and risk management.
could be set up to conduct the risk
assessment. Alternatively, a safety

consultant or an industrial hygienist

could be engaged to carry out the
assessment. STEP 2 Breakdown of
work process
There should be consultations
between the management and the
employees. The employees who It is useful to group employees by
actually carry out the work should job tasks in the following sequence:
be of great help. The participation
of both the employees and their
representatives in the committee • List the different departments in
can help in obtaining information the company
about the way the task is carried • List the different processes in
out, the substances used and the each department
different routes of exposure to the • Divide the processes into
substances. The management different tasks
should be committed to conduct the • Group the employees who
risk assessment and to implement perform the same task in the
any control measures or corrective same area.
actions to manage the risk.
• For those whose jobs require
movement around the plant, STEP 3 Identification of
consider their jobs individually. chemicals
Tasks like maintenance should
also be included although these
may not be done daily or Identify all the chemicals that are
frequently. used or produced, e.g. raw
• Ensure that all persons who are materials, intermediates, main
or may be exposed to the products and secondary products.
substances are included. A chemical might be in the form of
These include employees a solid, liquid, gas, vapour, dust,
involved in production, repairs, mist or fume. All chemicals must
maintenance, research or be included regardless of any
development, cleaning and any control that may be in place.
on-site contractors.

It is necessary to visit the

workplace, and to follow the floor
plans to ensure that all work areas
are covered. The task is usually
separated by physical or
geographical sections. Process
flow diagrams and process
instrumentation diagrams may be
used to identify the tasks for risk
assessment.

For example, a company may have

a premix department, an
adjustment department, and a
packaging department. In the
premix department, there are
processes like mixing, pretreatment
and colour matching. The process
of mixing involves tasks like
collecting raw materials, weighing,
pouring raw materials into tanks,
auto/manual stirring, checking and
sampling.

Form 1 should be used to

document the breakdown of the
work process.
The presence of chemicals may be STEP 4 Determination of
identified by: hazard rating
• looking at the stock lists,
inventories, registers, material
safety data sheets (MSDS) and Having identified the chemicals
container labels used or present, the next step is to
• inspecting all locations where determine if they are toxic or
chemicals are stored or used harmful to health. The hazard of a
chemical depends on its toxicity,
• considering the substances that
routes of exposure and other
may be produced during any
factors. The hazard rating can be
work process as intermediates,
determined from the toxic or
• by-products, finished products
harmful effects of the chemical
or given off as wastes, residues
(Table 1). Alternatively, the rating
or fugitive emissions
can be determined from the acute
• considering all substances that toxicity of the chemical in terms of
are used, or may arise from lethal dose (LD50) and lethal
work such as maintenance and concentration (LC50) – Table 1A.
repair, cleaning or testing. Information on the toxic effects of a
chemical, its LD50 and LC50 can be
For example, formaldehyde might obtained from the MSDS.
be emitted during injection
moulding and ethyl acetate is used
to remove grease on the injection
moulding machine. Therefore
these chemicals should be included
for risk assessment.

For each work process or task

identified, list the chemical(s)
involved using Form 1.
Table 1 : Hazard Rating

Hazard Description of Effects/Hazard Category Example of

Rating chemicals
1 − No known adverse health effects sodium chloride,
− ACGIH* A5 carcinogens butane, butyl
− Not classified as toxic or harmful acetate, calcium
carbonate
2 − Reversible effects to the skin, eyes or acetone, butane,
mucous membranes, not severe enough to acetic acid (10%
cause serious health impairment concentration),
− ACGIH A4 carcinogens barium salts,
− Skin sensitisers and skin irritants aluminium dust

3 − Possible human or animal carcinogens or toluene, xylene,

mutagens, but for which data is inadequate ammonia,
− ACGIH A3 carcinogens butanol,
− IARC* Group 2B acetaldehyde,
− Corrosive (pH 3 to 5 or 9 to 11) , respiratory acetic anhydride,
sensitizers, harmful chemicals aniline, antimony

4 − Probable human carcinogens, mutagens or formaldehyde,

teratogens based on animal studies cadmium,
− ACGIH A2 carcinogens methylene
− NTP* Group B chloride, ethylene
− IARC Group 2A oxide,
− Very corrosive (pH 0 to 2 or 11.5 to 14) acrylonitrile, 1, 3-
− Toxic chemicals, butadiene

5 − Known human carcinogens, mutagens or benzene,

teratogens benzidine, lead,
− ACGIH A1 carcinogens arsenic, beryllium,
− NTP Group A bromine, vinyl
− IARC Group 1 chloride, mercury,
− Very toxic chemicals crystalline silica

*Please refer to Annex 2 for the classification of carcinogens.

Table 1A – Hazard Rating by Acute Toxicity

Hazard LD50 absorbed LD50 dermal LC50 absorbed LC50 absorbed by

Rating orally in rat absorption in rat
by inhalation inhalation
mg/kg body or rabbit mg/kg in rat, mg/litre In rat, mg/litre per 4
weight body weight per 4 h h
Gases and Aerosols and
Vapors particulates
2 > 2000 > 2000 > 20 >5
3 > 200 to ≤ 2000 > 400 to ≤ 2000 > 2.0 to ≤ 20 > 1 to ≤ 5
4 > 25 to ≤ 200 > 50 to ≤ 400 > 0.5 to ≤ 2.0 > 0.25 to ≤ 1
5 ≤ 25 ≤ 50 ≤ 0.5 ≤ 0.25

Determine the hazard rating (HR) of each chemical identified and record it in
Form 1.
STEP 5 Conducting work
inspection and interviews could affect the work involving toxic
or harmful chemicals.

If a new job, process or work unit is

Conduct a ‘walk-through’ inspection being planned but not yet in
according to the work tasks listed in operation, evaluation of the
Form 1 and interview the relevant work process, plan or
employees. design is required, and it should be
included in Form 1.

A checklist for inspection is

attached in Annex 3. The
inspection checklist addresses
these four areas:-
1) Work unit where toxic or
harmful chemicals are used or
generated
2) Work practices
3) Emission of contaminants
4) Areas of concern

STEP 6 Obtaining
information on frequency and
duration of exposure

For employees who are or might be

exposed to toxic or harmful
The aim of the interview is to find chemicals, estimate the degree of
out if all the tasks are listed in Form exposure, taking into account the
1 and whether all the worker level, frequency and duration of
groups are accounted for. In order exposure, as well as the different
to assess whether the workers are routes of exposure.
exposed to toxic or harmful
chemicals, it is important to talk to If air monitoring results are
the employees regarding their work available for certain tasks, Form 2a
practices and procedures. For should be used. Where air
example, they could describe what monitoring results are not available,
happens during a breakdown, exposure factors could be used for
maintenance, manpower shortage, hazard rating and Form 2b should
changes in personnel or volume of be used instead.
production, or other changes that
Form 2a (monitoring results are Form 2b (monitoring results are
available) not available)
In Form 2a, the duration of the In Form 2b, there are five factors
specific task must be known. If the that determine the exposure rating.
duration of the task is less than 8 These are vapour pressure,
hours, the frequency must be detectable odour/permissible
specified. For example, weighing exposure level, hazard control
of raw material takes about 2 hours measure, amount of chemical used
(D = 2), but its frequency is twice a and duration of work per week.
day or 10 times a week (F = 10 per However, not all the factors will be
week). Injection moulding takes full utilized in a risk assessment,
shift, that is 8 hours (D =8) and its depending on whether the
frequency is once a day or 5 times parameters are available.
a week ( F = 5).

If there is exposure to two or more

chemicals having similar health
effects, fill in the row that indicates
‘Chemicals with similar effects’ with
‘Y’. Information on health effects of
chemicals can be obtained from
MSDS.
Step 7 Determination of exposure rating

Exposure rating can be determined using actual exposure level or exposure

index.

Using exposure level

Where air monitoring results are available, the weekly time weighted average
exposure may be estimated using the following equation.

FxDxM
E = (1)
W

where
E = weekly exposure (ppm or mg/m3)
F = frequency of exposure per week (no. per week)
M = magnitude of exposure (ppm or mg/m3)
W = average working hours per week (40 hours)
D = average duration of each exposure (hours)

Equation (1) assumes that there is no exposure when the task is not carried out.
The assumption must be tested in each case to confirm that it is true.

Exposure Rating (ER)

The exposure (E) is then compared to the PEL (Long Term) and the exposure
rating can then be determined using the following Table.

Table 2 : Exposure Rating

E / PEL Exposure Rating

(ER)
< 0.1 1
0.1 to < 0.5 2
0.5 to < 1.0 3
1.0 to < 2.0 4
≥ 2.0 5

Combined Exposure

For exposure to two or more chemicals having similar effects, the combined
exposure (Ecombined) has to be considered i.e. for those chemicals in Form 2a
where there are indications of ‘Y’ (yes to additive effect), the following equation
should be used to determine the degree of exposure.
 E1 E2 En
E combined = + + ..... + (2)
PEL1 PEL2 PELn

where
E is the exposure and PEL is the corresponding permissible exposure
level.

Exposure Exceeding 40 hrs/week

The PEL (Long Term) value has to be reduced for exposure of more than 40
hours per week. A weekly reduction factor (f) must be multiplied to the PEL(Long
Term) value and it is obtained using the following equation:

40 (168 - H)
f = x (3)
H 128

where
H = number of hours worked per week

The above equation uses a conservative approach and results in the most
reduction. There are other techniques available such as the OSHA model and
Pharmacokinetic models. When adjustments are necessary, it is recommended
that a competent person be consulted to ensure that the adjustment is
appropriate and applicable as the models are theoretical and involve
assumptions that may not apply to every chemical. An understanding of the
chemical is needed and care must be taken where toxicity data is limited.
However, the benefits of adjusting exposure limits outweigh the uncertainty of the
models. Where unusual work schedules are common, the need to adjust
exposure limits should be explored and the most appropriate model selected.

For short term exposure of up to15 minutes during any time of the day, the
magnitude of exposure should be compared with the PEL (Short Term) value.
Record the exposure rating in Form 3.

Using exposure index

Where air monitoring results are not available, the exposure rating can be
determined from the exposure index (EI) using the following equation:

1
ER = [EI1x EI2 x ......xEIn ] n (4)

where
n is the number of factors used.
The exposure indexes are rated on a five-scale rating from 1 to 5 in an increasing
order of magnitude i.e. 1 means very low, 5 means very high and 3 is medium.

Table 3: Exposure Factors and Index

Exposure 1 2 3 4 5
Index

Exposure
Factor
Vapour < 0.1 0.1 to 1 >1 to 10 > 10 to 100 >100
pressure or mmHg mmHg mmHg mmHg mmHg
particle size
(aerodynamic Coarse, coarse and dry and dry and fine dry and
diameter) bulk or dry small particle material fine
wet material size 10 to 100 powdered
material > 100 µm µm material
< 10 µm
Ratio of <0.1 0.1 to 0.5 > 0.5 to 1 >1 to 2 ≥2
*OT/PEL

Hazard Adequate Adequate Adequate Inadequate No control

control control control with control control; at all; very
measure with irregular without dusty dusty
regular maintenan maintenance
maintena ce ; moderately
nce dusty
Amount used Almost Little Medium Large Large
per week negligible amount amount amount amount
amount used (1 to used, used, used,
used (< 1 <10 kg or l) workers are workers are workers
kg or l) trained on trained on are not
handling the handling the trained on
chemical (10 chemical handling
to < 100 kg (100 to the
or l) 1000 kg or chemical
l) (> 1000 kg
or l)
Duration of <8 hrs 8 to 16 hrs 16 to 24 hrs 24 to 32 hrs 32 to 40
work per hrs
week
* Odour threshold (OT) divided by the permissible exposure level (PEL)
In the first row of the above Table, when the chemical is a liquid at room
temperature, its exposure hazard depends on its vapour pressure which can be
obtained from the MSDS. Vapour pressure depends on temperature. When the
liquid is at a different temperature from the one stated in the MSDS, its vapour
pressure can be determined using the Antoine equation. When the chemical is a
solid, its inhalation hazard depends on the size of the solid particles. This might
require an on site judgement. The particle size refers to its aerodynamic
diameter, and is given by this formula:

Da = Dp s.g (5)

where
Da = aerodynamic diameter
Dp = diameter of the particle
s.g = specific gravity of the bulk chemical

The exposure rating depends on the permissible exposure level and the
detectable odour threshold (second row) of the specific chemical. They can be
found in Annex 4 and Annex 5 respectively.

The likelihood of exposure to a chemical is largely determined by the presence of

engineering control measures and their effectiveness. A properly designed and
well-constructed local exhaust system will greatly reduce the exposure risk,
whereas an open process or poorly designed and maintained system can result
in high exposures. The differences are reflected in the hazard control measure
ratings (third row of Table 3). Examples of adequate control measures are
process containment or enclosure with no direct contact, no visible contaminant
release or emission, adequate capture velocity. The provision of personal
protective equipment is not a form of control.

The degree of exposure to a chemical also depends on the amount of chemical

used and the duration of work or exposure. These are shown in the fourth and
fifth rows of Table 3 respectively. A weekly work shift (usually 40 hours) is used
as the basis for assigning exposure rating as the PEL values are based on 40-
hour exposures.

Example, fine powdered silica dust (EI = 5) is generated during weighing and this
task takes 1 hour per day or 7 hours per week (EI = 1). There is moderate dust
by visual inspection (EI = 3). The amount used is little (EI = 2).

ER = (5 x 3 x 2 x 1)1/4
= 2.3
 Step 8 Evaluation of risk

The risk can be expressed in the following form:

Risk = (HR x ER) ( 6)

where
HR = hazard rating on the scale of 1 to 5 (see Table 1)
ER = exposure rating on the scale of 1 to 5

The square root is to limit the risk value within the scale of 1 to 5. When the risk
rating is not a whole number, it should be rounded up to the nearest whole
number.

Example.
HR = 4, ER = 3, Risk = 4x3 = 3.5 round up to 4.

Significance of Risk
Determine the risk of each task and rank it in accordance with the following
Table:

Table 4 : Risk Rating

Risk Rating Ranking

1 Negligible
2 Low
3 Medium
4 High
5 Very High

Alternatively, the matrix below can be used to determine the risk level.
 Risk Rating Matrix
Legend
HR 1 2 3 4 5
ER = negligible
1 1 1. 1. 2 2. = low
7 2 = medium
4
= high
2 = very high
1. 2 2. 2. 3.
4 4 8 2
3 1. 2. 3 3. 3.
7 4 5 9
4 2 2. 3. 4 4.
8 5 5

5 2. 3. 3. 4. 5
2 2 9 5

The risk rating scaling of 1 to 5 is in increasing order of magnitude. Rating of 1

implies negligible risk and a rating of 5 implies very high risk. Record the risk
rating and rank it in Form 3. This ranking will enable a prioritization of action
plans to reduce the risk of exposure.

STEP 9 Taking c) Determine if monitoring is

corrective actions required. Please refer to MOM’s
Guidelines on Sampling Strategy
and Submission of Air Monitoring
If the assessment shows that there is
Report.
a significant risk to health, the
d) Determine if medical
appropriate actions should be taken
examinations are required.
to reduce the risk. These include:
Please refer to the Factories
(Medical Examinations)
a) Select appropriate measures to
Regulations.
eliminate or minimize the risk eg
e) Establish emergency and first-aid
substitution of the toxic
procedures if indicated
chemicals, installation of local
exhaust ventilation or dilution
It is the responsibility of the employer
ventilation, implementing
to ensure that the risk is acceptable.
administrative control and issuing
Here are some possible actions for
of personal protective equipment
the different risk levels.
b) Arrange induction and training of
employees
 • Provide suitable personal
Risk Level 1 – Negligible risk protective equipment
• End assessment • Develop and implement safe and
• Review assessment every five correct work procedures
years • Establish first-aid and emergency
procedures if necessary
Risk Level 2 – Low risk • Reassess the risk (carry out a
• Maintain control detailed risk assessment) after all
• Determine if air monitoring is the above have been done
required
• Review assessment every four
years
STEP 10 Record of
Risk Level 3 – Medium risk assessment
• Implement and maintain control
• Determine if air monitoring is
needed All assessments should be properly
• Determine if employee training is recorded in a permanent form, either
needed in writing or on a computer. The
• Review assessment every three record should be concise. It should
years include:
a) name of assessment team
Risk Level 4 – High risk b) description of work unit
c) personnel involved
• Implement effective engineering
d) work area and time
control
e) a list of hazardous substances
• Conduct air monitoring
used or produced in that work
• Conduct training for employees unit and a notation to indicate
• Adopt Respiratory Protection whether MSDS are available
Programme (please see Annex 6) f) hazard information
• Provide suitable personal g) summary of process
protective equipment e.g. h) risk identification
goggles, apron, gloves etc. i) conclusion about risks
• Develop and implement safe and j) recommendations
correct work procedures k) signature, date and position of
• Establish first-aid and emergency the assessment team
procedures if necessary l) signature, date and position of
• Reassess the risk after all the the employer accepting the
above have been done assessment

Risk Level 5 – Very High risk

• Implement effective engineering
control
• Conduct air monitoring
• Conduct training for employees
• Adopt Respiratory Protection
Programme (please see Annex 6)
STEP 11 Review of
assessment • Work-related ill health is reported
• Accidents of near misses have
occurred which may be due to
A review is required if any of the inadequate control
following situations arises: • Monitoring or health surveillance
• There are significant changes in indicates a loss of control
the volume of production, • There is new evidence about
materials, processes or control hazards of substances, perhaps
measures (management of resulting in a reviewed standard,
change) a change in the value of the PEL,
or any properties of the
chemicals
• New or improved control
technology becomes practicable

Some of the common errors in the

risk assessment are:
1) Errors of facts : e.g procedures,
and location of usage of
substances
2) Inadequate identification of
hazards
3) Claims that consequences will be
of limited range or effect, without
convincing justification.
4) The uncertainties of ‘Black Box’
methodologies, models and
assumptions for calculations.
 Exposure Assessment Estimation

This section is applicable for factories at the design phase when air
monitoring data is not available. Theoretically, the risk assessment techniques
can give precise results, however, the scarcity of meaningful data and
equation parameter coupled with human error and inaccuracy makes the
calculated results questionable.

This assessment involves detailed computations of exposure level in ppm or

mg/m3.

The exposure level can then be compared to the PEL (Long Term) values. To
obtain the exposure rating (ER), if the exposure is less than 8 hours, then the
following equation should be used to convert to the 8-hours time-weighted-
average (CTWA) before comparison.

C1T1 + C 2 T2 + .... + C n Tn
C TWA = (7)
8

where
C = concentration of exposure and T is the corresponding exposure
time

Equation to predict Inhalation Exposure- Transfer OperationA

This equation is suitable for any transfer operations like tank car loading and
drumming.

(1.67 x10 4 )(VP V fr )

C ppm = (8)
QK

where
Cppm = airborne concentration at equilibrium, ppm
VP = vapor pressure, atm

Default input value: Container Types

Drums Tank Trucks Tank Cars
V, volume of container, 0.21 19 76
3
m
f, saturation factor, 0.5B,C, 1.0D,E 0.5B,C,1. 0D,E 0. 5B,C,1.0D,E
dimensionless
r, fill rate, units/hour 20B, 30D 2 1
B D
Q, ventilation rate, 85 , 14 6700vB,F, 6700vB,F, 750vD,F
m3/min 750vD,F
k, mixing factor, 0.5B, 0.1D 0.5 B, 0.1 D 0.5 B, 0.1 D
dimensionless
A
Assumes the temperature of the liquid and the temperature of the air are equivalent,
extinction of the substance is negligible, only one generation source is present, steady state
conditions are reached, and that the ideal gas law is applicable. Spillage during filling
operations is neglected. The value 1.67 x 104 incorporates conversion to more conventional
units (i.e., from cm3 to m3 for V, units/sec to units/hr for r, and cm3/sec to m3/min for Q).
B
Default input value for “what-if”hypothetical estimates is the value that lies in the central
portion of the range for the value.
C
Assumes bottom filling technique is used
D
Default input values for bounding estimates are selected such that the resulting estimates
will be higher than that incurred by the individual in the population with the highest exposure.
E
Assume splash filling technique is used
F
Outdoor ventilation rate in units of m3/min is calculated using this unit’s conversion for the
estimated wind speed, “v” in mph.

Equation to predict Inhalation Exposure- Open surface OperationA

This equation may be used for processes like furniture stripping in a dip or
immersion tank, degreasing and cleaning of metal parts.

(720) V P [1 / MW + 1 / 29]0.25 A
C eq = (9)
MW 0.165 Q k ∆x 0.25

where
Ceq = airborne concentration at equilibrium, ppm
VP = vapor pressure, atm
MW = molecular weight, g/g-mole

Default input values: Operation

Sampling Other Open
Surface
A, area, cm2 40B, 80C D

Q, ventilation rate m3/min 85B, 14C 85B, 14C

k, mixing factor, dimensionless 0.5B, 0.1C 0.1B, 0.5C
∆x, pool length in the direction of air 7B, 10C D

flow, cm

A
Assumes that the temperature of the substance and the ambient temperature of the air
equals 298K, that the overall pressure equals 1 atmosphere, and that the air velocity equals
50.8 cm/sec (100ft/min) and is flowing parallel to the pool of liquid. Assumes steady state
conditions are reached, heat of evaporation is provided by the surroundings, diffusion at the
edge of the pool and in the direction of the air stream is negligible, there is no mixing in the
area above the pool of liquid, no local exhaust or physical barriers are present at the edges of
the pool, and that the ideal gas law is applicable. This equation is applicable for substances
with low to moderate vapour pressures (i.e., less than 0.05atm). The value 720 incorporates
conversion to more conventional units (i.e., from cm3/sec to m3/min for Q)
B
Default input value for “what-if” hypothetical estimates is the value that lies in the central
portion of the range for the value.
c
Default input values for bounding estimates are selected such that the resulting estimates will
be higher than that incurred by the individual in the population with the highest exposure.
d
To be estimated based on the operation
Please refer to the article on Evaluation of the Mass Balance Model used by
the Environmental Protection Agency for Estimating Inhalation Exposure to
New Chemical Substances from the American Industrial Hygiene Association
Journal, 1996, Volume 57, page 526-536.

Estimating Worker Exposures to Liquid pool Evaporation or Boiling

Released liquids are assumed to form a pool from which chemicals are
released into the atmosphere. This equation is used to estimate the
vaporization rate of volatile from an open vessel.

MKAPsat
Qm = (10)
R g TL

where
Qm = evaporation rate (kg/s)
M = molecular weight of contaminant (kg/kg-mole)
K = mass transfer coefficient (m/s)
A = area of exposure or liquid pool (m2)
Psat = saturated vapour pressure of the liquid (Pa or N/m2)
Rg = ideal gas constant (8.314 Pa m3/mol K)
TL = temperature of liquid (K)

To find mass transfer coefficient of the contaminants:

1/3
 Mo 
K = Ko   (11)
 M 

where
Ko = mass transfer coefficient of reference substance, water
(0.0083m/s)
M = molecular weight of contaminant (kg/kg-mole)
Mo = molecular weight of water (kg/kg-mole)
Estimating Worker Exposures to Toxic Vapours – Dilution Ventilation

The average concentration Cppm of any volatile liquids or substances in an

enclosure given a source term Qm and ventilation rate Qv . It can be applied to
workers standing near a pool of volatile liquid, an opening to a storage tank or
an open container of volatile liquid. Qm can be obtained from equation 10.

Qm R g T
C ( ppm) = x10 6 (12)
kQv PM

where
Cppm = average concentration of volatile vapour in the enclosure
[ppm]
Qm = evolution rate of volatile material [kg/s]
k = non ideal mixing factor (k = 0.1 to 0.5); for perfect mixing (k =
1)
Rg = ideal gas constant (8.314 Pa m3/mole K)
T = temperature of the source (K)
M = molecular weight of the escaping vapour (kg/kg-mole)
Qv = ventilation rate (m3/s)

Assumptions:

1. The vapour concentration calculated is an average concentration in the

enclosure. However, the localized conditions will result in higher
concentrations; e.g. workers directly above an open container will be
exposed to higher vapour concentrations.

2. Steady state conditions assuming there is no accumulation of vapours.

Example
An open tolulene container in an enclosure is weighed as a function of time
and it is determined that the average evaporation rate is 0.1 gm/min. The
ventilation rate is 100 ft3/min. The temperature is 80°F and the pressure is 1
atm. Estimate the concentration of toluene vapor in the enclosure and
compare to the PEL (Long Term) for toluene of 100 ppm.
Solution
Qm = 0.1 gm/min = 2.20 X 10-4 lbm/min
Rg = 0.7302 ft3 atm/lb-mole °R
T = 80°F = 540°R
Qv = 100 ft3/min
M = 92 lbm/lb-mole
P = 1 atm

(2.20 x10 −4 lbm / min)(0.7302 ft 3 atm / lb − mole o R)(540 o R)

kCppm = 3
x10 6
100 ft / min(1 atm)(92lbm / lb − mole)

kCppm = 9.43 ppm

Since k varies from 0.1 to 0.5, the concentration is expected to vary from 18.9
to 94.3 ppm. Actual vapor sampling is recommended to ensure that the PEL
(Long Term) is not exceeded.

Reference Documents

1. Guidance Note for the Assessment of Health Risks Arising from the
use of Hazardous Substances in the Workplace [NOHSC: 3017 (1994)]
2. Assessment of the Health Risks Arising from the Use of Hazardous
Chemicals in the Workplace [Department of Occupational Safety and
Health, Ministry of Human Resources, Malaysia, 2000]
3. Workplace Risk Assessment Course notes [Liberty]
4. Chemical Process Safety: Fundamentals with Applications by Daniel A.
Crowl/Joseph F. Louvar
 WORK PROCESS BREAKDOWN

FORM 1

Name of assessor/team members:

Date of assessment:
Name of company:

Department:
Process Task Description of task No. of Chemicals Hazard Rating,
workers HR
 DETERMINATION OF EXPOSURE RATING
(This form is used if air monitoring results are available)
FORM 2a

Process:
Task:
Chemical 1 Chemical 2 Chemical 3 Chemical 4
Duration of
exposure, D
Frequency of
exposure, F
Magnitude of
exposure (from
air monitoring
results), M
Chemicals with
similar effects
(Y/N)
Exposure level,
E
Exposure
Rating, ER
 DETERMINATION OF EXPOSURE RATING

(This form is used if air monitoring results are not available)

FORM 2b

Process:
Task:

Chemical 1 Chemical 2 Chemical 3 Chemical 4

Vapour
pressure or
particle size
Ratio of
OT/PEL
Hazard
control
measure
Amount used
per week
Duration of
work per week
Exposure
Index, EI
Exposure
Rating, ER
 RESULTS REPORT OF RISK ASSESSMENT

FORM 3

Process Task Hazard Rating Exposure Risk Action/Follow-up

Rating Level

Signature of assessor/date

Signature of employer representative /date

 Annex 1

Estimation of Dermal Exposure to Liquid

Dermal : Exposure to Liquid

The daily total dose resulting from dermal absorption of liquid exposure, Ddl
can be calculated from: -

WxSxAxExF
Ddl = [mg/kg/day] (13)
BW

where
W = weight fraction of substance in product eg. 0.1 for a
10% solution
S = skin absorption rate (taken as 0.32 mg/cm2/hr from
experiment)
A = skin surface exposed (cm2)
[hr / day ][days / yr ]
E = exposure duration =
365 days / yr
F = skin contact time (as fraction of exposure duration eg
F= 2 for 20% of time for intermittent dermal exposure or
F=0.01 for incidental exposure as skin contact)

BW = average body weight of worker (kg),

The standard skin surface areas (A) for an adult male are:-
Arms 2280 cm2
Upper arms 1430 cm2
Forearms 1140 cm2
Hands 840 cm2
Head 1180 cm2

The dose obtained can then be compared against the lethal dose
(LD50) for skin adsorption of the specific chemical.
Example:

Skin absorption rate, S = 0.32 mg/cm2/hr

Skin contact (assume incident), F = 0.01
Area of skin exposed (hand and forearm), A = 1,000 cm2
Exposure duration, E = 4 hr /day for 30days/yr
Weight fraction 90 % of substance in product, W= 0.9
Average body weight of an adult, BW = 70 kg

For dermal expsoure:

WxSxAxExF
Ddl =
BW
= 0.9 x 0.32 mg/cm2/hr x 1000 cm2 x 4 hr /day x 30 days/yr x 0.01
70 kg x 365 days
= 0.014 mg/kg/day
 Annex 2

Categories of Carcinogenicity

ACGIH: American Conference of Governmental Industrial Hygienists

A1 – Confirmed human carcinogen
A2 – Suspected human carcinogen
A3 – Confirmed animal carcinogen
A4 – Not classifiable as a human carcinogen
A5 – Not suspected as a human carcinogen

IARC: International Agency for Research on Cancer

Group 1: Carcinogenic to humans
Group 2A: Probably carcinogenic to humans
Group 2B: Possibly carcinogenic to humans

NTP: National Toxicology Program, Public Health Service, U.S.

Department of Health and Human Services
Group A: Known to be human carcinogens
Group B: Reasonably anticipated to be human carcinogens
 Annex 3

Inspection Checklist

Questions Observations Remarks

Chemicals
a) Are any raw materials, products released or If yes to any of
emitted into the work area? these,
b) Are there other chemicals used for different remember to
products? include the
c) Will the process generate any by-products? chemicals in
Form 1.
Work practices
a) Is there any non-routine activity? If yes, it must
be included in
Form 1.
b) Do current work practices ensure safe If no to any,
handling? other routes of
c) Are appropriate personal protective clothing exposure must
and equipment used? be considered.
d) Are facilities for changing, washing and meal Risk level
areas maintained in good conditions? obtained in
e) Are good housekeeping practices in place? these
guidelines may
not be a
representative
of the actual
situation as it
only addresses
inhalation.
f) Are there any possibility of skin contact? If yes, assess
the extent of
skin absorption
using equation
13
Emission of contaminants
a) Any evidence of contamination (e.g. dust or If yes to any,
fumes visible in the air or on surfaces, this could
substance visible on a person’s skin or mean that
clothing, odour of chemical, visible leaks, control is
spills or residues, chemical splashes)? inadequate(for
Form 2b), or if
b) Are any employees experiencing any
the risk rating
symptoms of exposure?
is low after
c) Any employees’medical reports showing assessment,
abnormal results? consider other
routes of
exposure.

If yes, Form 2a
d) Any air monitoring conducted at the could be used.
workplace? The results are
also an
indication of
whether the
control is
adequate.
Establish areas of concern
a) Are there any workers who are required to If yes to any,
work directly with harmful substances, work remember to
near or pass through areas in which the include tasks
substances are used, produced (including and workers in
discharge of emissions), stored, transported or Form 1.
disposed of?
b) Do workers need to enter a confined space in
which the substance might be present?
c) Do workers clean, perform maintenance or
other work in areas where the substance might
be present?
 Annex 4
Permissible Exposure Levels of Toxic Substances

Toxic Substance Permissible Exposure Level (PEL)

PEL (Long Term) PEL (Short Term)
ppma mg/m3 b ppma mg/m3
b

Acetic acid 10 25 15 37
Acetic anhydride 5 21 - -
Acetone 750 1780 1000 2380
Acrylonitrile (Vinyl cyanide)* 2 4.3 - -
Aluminium dust - 10 - -
Ammonia 25 17 35 24
Aniline* 2 7.6 - -
Antimony and compounds, as Sb - 0.5 - -
Arsenic, elemental and inorganic
compounds, as As - 0.01 - -
Arsine 0.05 0.16 - -
Asphalt (petroleum) fumes - 5 - -
Barium, soluble compounds, as Ba - 0.5 - -
Benzene* 5 16 - -
Beryllium and compounds, as Be - 0.002 - -
Bromine 0.1 0.66 0.2 1.3
1,3-Butadiene 2 4.4 - -
Butane 800 1900 - -
n-Butanol* - - 50 152
sec-Butanol 100 303 - -
n-Butyl acetate 150 713 200 950
Cadmium, elemental and - 0.05 - -
compounds, as Cd
Calcium carbonate (Limestone, - 10 - -
Marble)
Calcium hydroxide - 5 - -
Calcium silicate - 10 - -
Calcium sulfate - 10 - -
Carbon black - 3.5 - -
Carbon dioxide 5000 9000 30,000 54,000
Carbon disulfide* 10 31 - -
Carbon monoxide 25 29 - -
Carbon tetrachloride 5 31 10 63
(Tetrachloromethane)*
Chlorine 0.5 1.5 1 2.9
Chloroform (Trichloromethane) 10 49 - -
Coal tar pitch volatiles (Polycylic
aromatic hydrocarbons),
as benzene solubles - 0.2 - -

Cobalt, elemental and inorganic

compounds, as Co - 0.02 - -
Copper
Fume - 0.2 - -
Dusts & mists, as Cu - 1

Cotton dust, raw - 0.2 - -

Cresol* 5 22 - -
Cyclohexane 300 1030 - -
Cyclohexanol 50 206 - -
Cyclohexanone* 25 100 - -
Cyclohexene 300 1010 - -
Diborane 0.1 0.11 - -
Ethanol (Ethyl alcohol) 1000 1880 - -
Ethyl acetate 400 1440 - -
Ethylene glycol - - 50 127
Ethylene oxide 1 1.8 - -
Ethyl ether (Diethyl ether) 400 1210 500 1520
Ethyl mercaptan (Ethanethiol) 0.5 1.3 - -
Fibrous glass dust - 10 - -
Fluorides, as F - 2.5 - -
Fluorine 1 1.6 2 3.1
Formaldehyde - - 0.3 0.37
Formic acid 5 9.4 10 19
Furfural* 2 7.9 - -
Furfuryl alcohol* 10 40 15 60
Gasoline 300 890 500 1480
Grain dust (oat, wheat, barley) - 4 - -
Graphite, respirable dust - 2 - -
Heptane 400 1640 500 2050
Hexane (n-Hexane)* 50 176 - -
Hydrazine* 0.1 0.13 - -
Hydrogen bromide - - 3 9.9
Hydrogen chloride - - 5 7.5
Hydrogen cyanide* - - 4.7 5
Hydrogen fluoride - - 3 2.6
Hydrogen peroxide 1 1.4 - -
Hydrogen sulfide 10 14 15 21
Iodine - - 0.1 1.0
Iron oxide dust & fume, as Fe - 5 - -
Iron salts, soluble, as Fe - 1 - -
Isobutyl acetate 150 713 - -
Isobutyl alcohol 50 152 - -
Isophorone - - 5 28
Isopropyl acetate 250 1040 310 1290
Isopropyl alcohol 400 983 500 1230
Lead, inorganic dusts and fumes, as
Pb - 0.15 - -
 L.P.G. (Liquified petroleum gas) 1000 1800 - -
Malathion* - 10 - -
Maleic anhydride 0.25 1.0 - -
Manganese, as Mn
Dust and compounds - 5 - -
Fume - 1 - 3
Mercury
Alkyl compounds* - 0.01 - 0.03
Aryl compounds* - 0.1 - -

Inorganic forms* eg. metalic mercury - 0.025 - -

Methanol (Methyl alcohol)* 200 262 250 328

Methyl acetate 200 606 250 757
Methyl acrylate* 10 35 - -
Methyl n-butyl ketone (2-
Hexanone)* 5 20 - -
Methylene bisphenyl isocyanate
(MDI, Diphenyl methane
diisocyanate) 0.005 0.051 - -
Methylene chloride
(Dichloromethane) 50 174 - -
Methyl ethyl ketone (MEK, 2-
Butanone) 200 590 300 885
Methyl ethyl ketone peroxide - - 0.2 1.5
Methyl isobutyl ketone (Hexone) 50 205 75 307
Methyl mercaptan (Methanethiol) 0.5 0.98 - -
Mineral wool fiber - 10 - -
Molybdenum, as Mo
Soluble compounds - 5 - -
Insoluble compounds - 10 - -
Naphtha 300 1370 - -
Naphthalene* 10 52 15 79
Nickel
Metal - 1 - -
Insoluble compounds,
as Ni - 1 - -
Soluble compounds,
as Ni - 0.1 - -
Nickel carbonyl, as Ni 0.05 0.12 - -
Nickel sulfide, as Ni - 1 - -
Nicotine* - 0.5 - -
Nitric acid 2 5.2 4 10
Nitric oxide 25 31 - -
Nitrogen dioxide 3 5.6 5 9.4
Nitrous oxide 50 90 - -
Nuisance particulates - 10 - -
Octane 300 1400 375 1750
Oil Mist, mineral - 5 - 10
Ozone - - 0.1 0.20
Parathion* - 0.1 - -
Pentane 600 1770 750 2210
Perchloroethylene
(Tetrachloroethylene) 25 170 100 685
Phenol* 5 19 - -
Phosgene 0.1 0.40 - -
Phosphine 0.3 0.42 1 1.4
Phosphoric acid - 1 - 3
Phosphorus 0.02 0.1 - -
Phthalic anhydride 1 6.1 - -
Platinum
Metal - 1 - -
Soluble salts, as Pt - 0.002 - -

Portland cement - 10 - -
Potassium cyanide - - - 5
Potassium hydroxide - - - 2
n-Propyl acetate 200 835 250 1040
n-Propyl alcohol* 200 492 250 614
Propylene oxide (1,2- 20 48 - -
Epoxypropane)
Selenium and compounds, as Se - 0.2 - -
Silica-Amorphous
Diatomaceous earth - 10 - -
(uncalcined)
Precipitated silica - 10 - -
Silica, fume,
respirable dust - 2 - -
Silica, fused,
respirable dust - 0.1 - -
Silica gel - 10 - -

Silica-Crystalline
Cristobalite, respirable
dust - 0.05 - -
Quartz, respirable
dust - 0.1 - -
Tridymite, respirable
dust - 0.05 - -
Tripoli, respirable dust - 0.1 - -

Silicon - 10 - -
Silver
Metal - 0.1 - -
Soluble compounds,
as Ag - 0.01 - -
Sodium cyanide - - - 5
Sodium hydroxide - - - 2
Stoddard solvent 100 525 - -
Styrene, monomer (Phenylethylene,
Vinyl benzene) 50 213 100 426
Sulfur dioxide 2 5.2 5 13
Sulfuric acid - 1 - 3
Talc - 2 - -
Tantalum, metal and oxide, as Ta - 5 - -
Tetraethyl lead, as Pb* - 0.1 - -
Tetrahydrofuran 200 590 250 737
Tetramethyl lead, as Pb* - 0.15 - -
Tin
Metal - 2 - -
Oxide inorganic
compounds, as Sn - 2 - -
Organic compounds,
as Sn* - 0.1 - 0.2

Titanium dioxide - 10 - -
Toluene (Toluol)* 50 188 - -
Toluene-2,4-diisocyanate (TDI) 0.005 0.036 0.02 0.14
1,1,1-Trichloroethane
(Methyl chloroform) 350 1910 450 2460
1,1,2-Trichloroethane* 10 55 - -
Trichloroethylene 50 269 100 537
2,4,6-Trinitrotoluene (TNT)* - 0.5 - -
Tungsten, as W
Insoluble compounds - 5 - 10
Soluble compounds - 1 - 3

Turpentine 100 566 - -

Vegetable oil mists - 10 - -
Vinyl chloride (Chloroethylene) 5 13 - -
Welding fumes - 5 - -
Wood dust
Hard wood - 1 - -
Soft wood - 5 - 10
Xylene 100 434 150 651
Zinc oxide
Fume - 5 - 10
Dust - 10 - -
Zirconium and compounds, as Zr - 5 - 10

Note:
a ppm means parts of the substance per million parts of contaminated air by volume;

b mg/m3 means milligrammes of the substance per cubic metre of contaminated air;
* means the chemicals can contribute to significant exposure through skin adsorption.
The following formula can be used to convert mg/m3 to ppm at standard temperature (25°C) and pressure
(760mmHg) (ppm) = (mg/m3) x 24.5 / molecular weight
 Annex 5

Odour Thresholds and Irritation Concentrations of Chemicals

Chemical Low High Description of Irritating

Compound Odour Odour Odour Concentrati
mg/m3 mg/m3 on mg/m3
Acetaldehyde 0.0002 4 Green, sweet, fruity 90
Acetic acid 2.5 250 Sour, vinegar-like 25
Acetic anhydride 0.6 1.5 Sharp odour, sour 20
acid
Acetone 48 1,614 Minty chemical, sweet 475
Acetonitrile 70 70 Ether-like 875
Acrolein 0.05 38 Burnt, sweet 1.3
Acrylic acid 0.3 3 Rancid, sweet -
Acrylonitrile 8 79 Onion-garlic -
pungency
Allyl alcohol 2 5 Pungent, mustard 13
Allyl chloride 1.4 75 Green, garlic, onion 75
Allyl glycidyl ether 44 44 Sweet 1,144
Ammonia 0.03 40 Pungent, irritating 72
Aniline 0.0002 350 Pungent, amine-like -
Arsine 0.8 2 Garlic-like -
Benzene 4.5 270 Sweet, solventy 9,000
Boron trifluoride 4.5 4.5 Pungent, irritating -
Bromine 0.3 25 Bleachy, penetrating 2
1,3-Butadiene 0.4 3 Mild,aromatic
n-Butyl acetate 33 95 Fruity 473
n-Butyl alcohol 0.4 150 Sweet 75
Butyl cellosolve 0.5 288 Sweet, ester -
Butyl cellosolve 0.7 1.3 Sweet, ester -
acetate
Carbon disulfide 0.02 23 Disagreeable, sweet -
Carbon 60 128 Sweet, pungent -
tetrachloride
Cellosolve 2 185 Sweet, pleasant -
Cellosolve acetate 0.3 270 Sweet, musty -
Chlordane 0.008 0.04 Pungent, chlorine-like -
Chlorine 0.03 15 Bleachy, pungent 9
Chlorine dioxide 0.3 0.3 Sharp, pungent 15
Chlorobenzene 1 280 Sweet, almond-like 933
Chloroform 250 1,000 Sweet,pleasant 20,480
Cresol 0.001 22 Sweet, creosote, tar -
Cumene 0.04 6 Sharp, aromatic 23
Cyclohexane 1.4 1.4 Sweet, aromatic 1,050
Cyclohexanol 400 400 Camphor-like 200
Cyclohexanone 0.5 400 Sweet, peppermity 100
Diborane 2 4 Repulsively sweet -
o-Dichlorobenzene 12 300 Pleasant,aromatic 150
p-Dichlorobenzene 90 180 Mothballs 240
Dichloroethane 446 810 Chloroform-like -
Diethylamine 0.06 114 Fishy, ammonical 150
Diisobutyl ketone 0.7 2 Sweet, ester 150
Dimethyl formamide 300 300 Fishy,unpleasant -
1,1- 12 20 Ammonical, amine- -
Dimethylhydrazine like
1,4-Dioxane 0.01 612 Ethyl-like 792
Epichlorohydrin 50 80 Chloroform-like 325
Ethanolamine 5 11 Ammonia 13
Ethyl acetate 0.02 665 Fruity, pleasant 350
Ethyl alcohol 0.3 9,690 Sweet, alcoholic 9,500
Ethyl amine 0.5 396 Sharp, ammonical 180
Ethyl benzene 9 870 aromatic 870
Ethyl ether 1 3 Sweet, ether-like 300
Ethyl mercaptan 3 x 10-5 0.09 Garlic -
Ethylene diamine 2.5 28 Ammonical, musty 250
Ethylene dibromide 77 77 Mild, sweet -
Ethylene dichloride 24 440 sweet -
Ethylene glycol 63 63 sweet -
Ethylene oxide 520 1,400 Sweet, olefinic -
Fluorine 6 6 Pungent, irritating 50
Formaldehyde 1.5 74 Pungent, hay 1.5
Formic acid 0.05 38 Pungent, penetrating 27
Furfural 0.02 20 Almonds 48
Hydrazine 3 4 Ammonical, fishy -
Hydrochloric acid 7 49 Irritating, pungent 49
Hydrofluoric acid 0.03 0.1 Strong, irritating 4
Hydrogen bromide 7 7 Sharp, irritating 10
Hydrogen cyanide 0.9 5 Bitter almond -
Hydrogen sulfide 0.0007 0.01 Rotten eggs 14
Iodine 9 9 Irritating 2
Isophorone 1 50 Sharp, objectionable 50
Isopropyl alcohol 8 490 pleasant 490
Maleic anhydride 1.8 2 Acrid 6
Methyl acetate 610 915 Fragrant, fruity 30,496
Methyl acrylate 70 70 Sharp, sweet, fruity 263
Methyl alcohol 13 26,840 Sweet 22,875
Methyl bromide 80 4,000 Sweetish
Methyl cellosolve 0.3 288 Mild, non-residual 368
Methyl cellosolve 1.6 240 Sweet, ester -
acetate
Methyl chloroform 543 3800 Chloroform-like 5,429
Methyl ethyl ketone 0.7 148 Sweet, acetone-like 590
Methyl isobutyl 0.4 193 Sweet, sharp 410
ketone
Methyl mercaptan 4 x 10-5 0.08 Sulfidy -
Methyl amine 0.03 12 Fishy, pungent -
Methylene chloride 540 2,160 Sweet 8,280
Mineral spirits 157 787 Kerosene-like -
Naphthalene 1.5 125 Mothball, tar-like 75
Nickel carbonyl 0.2 21 Musty -
Nitric acid 0.8 2.5 Acrid, choking 155
Nitric oxide 0.4 1.2 - -
Nitrobenzene 0.02 9.5 Shoe polish, pungent 230
Nitroethane 620 620 Mild, fruity 310
Nitrogen dioxide 2 10 Sweetish, acrid 20
Nitromethane 250 250 Mild, fruity 360
1-Nitropropane 1080 1,080 Mild. fruity 360
2-Nitropropane 18 1,029 Fruity -
Octane 725 1,208 Gasoline-like 1,450
Ozone 0.001 1 Pleasant, clover-like 2
Pentane 7 3,000 Gasoline-like -
Perchloroethylene 31 469 Mildy sweet 1,340
Phenol 0.2 22 Medicinal, sweet 182
Phosgene 2 4 Musty hay, green corn 8
Phosphine 0.03 3.6 Decaying fish 11
n-Propyl alcohol 0.08 150 Sweet, alcohol -
Propyl alcohol 75 500 Sharp, musty 13,750
Propylene 40 116 Aromatic -
Propylene oxide 25 500 Sweet, alcoholic 1,125
Pyridine 0.009 15 Burnt, sickening 90
Stoddard solvent 5 156 Kerosene-like 2,100
Styrene 0.2 860 Solvently, rubbery 430
Sulfur dioxide 1.2 12.5 Pungent, irritating 5
Sulfuric acid 1 1 - 1.1
Tetrachloroethane 21 35 Sickly sweet 1,302
Tetrahydrofuran 7 177 Ether-like -
Toluene 8 150 Rubbery, mothballs 750
Toluene 2,4- 3 17 Sweet, fruity, acrid 4
diisocyanate
Trichloroethylene 1 2,160 Etheral, chloroform 864
like
Turpentine 560 1,120 Pine-like 560
Vinyl acetate 0.4 1.7 Sour, sharp -
Naphtha 4 4 - 435
Xylene 0.4 174 Sweet 435
 Annex 6

Respiratory Protection Programme

These are the key issues which should be included in the respiratory
protection programme:

1. Is there a documented respiratory protection programme?

2. Are the respirators in use suitable?
3. Are workers trained in the use and maintenance of respirators?
4. Is fit-testing carried out once very two years?
5. Are medical fitness test carried out for workers wearing respirators once
very three years?
6. Are there signs displayed designating respiratory protection areas?
7. Are there regular inspection and evaluation of respirators usage?
8. Are respirators maintained in good working condition?
9. Are airline respirators used?
10. Is the air supply tested and of suitable quality?
Acknowledgement

Contributors:
Occupational Safety and Health Division, Ministry of Manpower
Mr Tan Kia Tang Miss Oei Hun Ping
Deputy Director (Hygiene) Industrial Hygiene Engineer

Mr George Na Miss Ng Lee Penn

Senior Officer Industrial Hygiene Engineer

Mr Salim Shaik Mdm Veronica Chow

Industrial Hygiene Engineer Industrial Hygiene Engineer

The Division would like to thank the following for their invaluable
inputs:

• Committee on Management of Chemical Hazards

• Singapore Confederation of Industries

• National Safety Council of Singapore

• Singapore Institute of Safety Officers