OHS 621 FINAL EXAM | 220 QUESTIONS AND
ANSWERS | 2025/2026 UPDATE | 100% CORRECT
What is the definition of occupational hygiene? Answer - The science and art
devoted to the anticipation, recognition, evaluation and control of those
environmental factors or stresses arising in or from the workplace which may
cause sickness, impaired health and well-being, or significant discomfort
among workers or among citizens of the community
What are 5 reasons for hygiene management? Answer - One or a combination
of the following:
1. To carry out qualitative and quantitative assessment of workplace health
hazards
2. To determine whether exposure to a particular hazard is in compliance with
exposure limits
3. To relate health effects with exposure to specific hazards
4. To evaluate the effectiveness of exposure controls
5. To obtain exposure information for health research or epidemiological
studies
What are the 2 types of air contaminants? Answer - Generally, two types of
airborne contaminants:
A. Particulates
B. Gases and vapours
,What are particulates? Answer - A complex mixture of solid and/or liquid
particles suspended in air
Aerosol: liquid droplets or solid particles dispersed in
air.
Dust: solid particles generated by mechanical action
(crushing, grinding, sanding) Size 0.01 μm to 30 μm.
Fume: airborne solid particles formed by condensation
of vapour (metals, polymers) Size 0.01 μm to 10 μm.
Mist: suspended liquid droplets generated by
condensation or atomization (fog is formed by
condensation) Size 0.01 μm to 10 μm.
Smoke: aerosol of fine particulate matter orginating
from combustion containing both droplets & dry
particles Size 0.01 μm to 1.0 μm
What are gases and vapours? Answer - Gases: substances that completely
occupy a space and can be converted to liquid or solid by increasing pressure
or decreasing temperature.
Vapours: gaseous form of a substance that is normally a solid or liquid at room
temperature.
,What are the 3 categories occupational exposure limits (OELS)? Answer - Three
categories:
1. "TWA" or "Time-Weighted Average Limit" means
the time-weighted average airborne concentration of a
biological or chemical agent to which a worker may be
exposed in a work day or work week. The calculation is
based on the cumulative daily or weekly exposure
divided by 8-hour or 40-hour respectively
2. "STEL" or "Short-Term Exposure Limit" means the
maximum airborne concentration of a biological or
chemical agent to which a worker may be exposed in
any 15-minute period
3. "C" or "Ceiling Limit" means the maximum airborne
concentration of a biological or chemical agent to which
a worker may be exposed at any time
What is an action level? Answer - Defined as 50% of the 8-hr exposure limit
- At this level, further "action" is required - includes
additional monitoring and/or improvements to
exposure control measures
Derived from statistics
- Because exposure monitoring is generally performed
in one day and conclusions are based on these results
- However, there are variations in exposure levels daily
, - Therefore, you want to have confidence that high
percentage of actual daily exposures are below the
standard
Not legally required but serves as a guide
Estimating TWA exposure, what are the 4 types of samples? Answer - 1. Full
period single sample (covers all)
- A single sample collected for the full period required for comparing to OEL-
TWA i.e. 8 hrs/day or 40 hrs/week
- Gives a true picture of the worker's TWA exposure
- Be careful not to over saturate sampling media
2. Full period consecutive samples (covers all)
- A series of samples collected for the full period required for comparing to
OEL-TWA i.e. 8 hrs/day or 40 hrs/week
- Considered best for exposure estimate
- Can also measure for specific work activities
3. Partial period consecutive samples (does not cover all)
- Most common measurement type; however, only covers a portion of the
worker's workshift
- Need to interpret exposures for the unsampled period in order to compare to
OEL-TWA
4. Grab samples (covers minimal amount)
- Least desirable measurement method to estimate 8-hr OEL-TWA
- Collected for short periods of time (seconds or minutes)
ANSWERS | 2025/2026 UPDATE | 100% CORRECT
What is the definition of occupational hygiene? Answer - The science and art
devoted to the anticipation, recognition, evaluation and control of those
environmental factors or stresses arising in or from the workplace which may
cause sickness, impaired health and well-being, or significant discomfort
among workers or among citizens of the community
What are 5 reasons for hygiene management? Answer - One or a combination
of the following:
1. To carry out qualitative and quantitative assessment of workplace health
hazards
2. To determine whether exposure to a particular hazard is in compliance with
exposure limits
3. To relate health effects with exposure to specific hazards
4. To evaluate the effectiveness of exposure controls
5. To obtain exposure information for health research or epidemiological
studies
What are the 2 types of air contaminants? Answer - Generally, two types of
airborne contaminants:
A. Particulates
B. Gases and vapours
,What are particulates? Answer - A complex mixture of solid and/or liquid
particles suspended in air
Aerosol: liquid droplets or solid particles dispersed in
air.
Dust: solid particles generated by mechanical action
(crushing, grinding, sanding) Size 0.01 μm to 30 μm.
Fume: airborne solid particles formed by condensation
of vapour (metals, polymers) Size 0.01 μm to 10 μm.
Mist: suspended liquid droplets generated by
condensation or atomization (fog is formed by
condensation) Size 0.01 μm to 10 μm.
Smoke: aerosol of fine particulate matter orginating
from combustion containing both droplets & dry
particles Size 0.01 μm to 1.0 μm
What are gases and vapours? Answer - Gases: substances that completely
occupy a space and can be converted to liquid or solid by increasing pressure
or decreasing temperature.
Vapours: gaseous form of a substance that is normally a solid or liquid at room
temperature.
,What are the 3 categories occupational exposure limits (OELS)? Answer - Three
categories:
1. "TWA" or "Time-Weighted Average Limit" means
the time-weighted average airborne concentration of a
biological or chemical agent to which a worker may be
exposed in a work day or work week. The calculation is
based on the cumulative daily or weekly exposure
divided by 8-hour or 40-hour respectively
2. "STEL" or "Short-Term Exposure Limit" means the
maximum airborne concentration of a biological or
chemical agent to which a worker may be exposed in
any 15-minute period
3. "C" or "Ceiling Limit" means the maximum airborne
concentration of a biological or chemical agent to which
a worker may be exposed at any time
What is an action level? Answer - Defined as 50% of the 8-hr exposure limit
- At this level, further "action" is required - includes
additional monitoring and/or improvements to
exposure control measures
Derived from statistics
- Because exposure monitoring is generally performed
in one day and conclusions are based on these results
- However, there are variations in exposure levels daily
, - Therefore, you want to have confidence that high
percentage of actual daily exposures are below the
standard
Not legally required but serves as a guide
Estimating TWA exposure, what are the 4 types of samples? Answer - 1. Full
period single sample (covers all)
- A single sample collected for the full period required for comparing to OEL-
TWA i.e. 8 hrs/day or 40 hrs/week
- Gives a true picture of the worker's TWA exposure
- Be careful not to over saturate sampling media
2. Full period consecutive samples (covers all)
- A series of samples collected for the full period required for comparing to
OEL-TWA i.e. 8 hrs/day or 40 hrs/week
- Considered best for exposure estimate
- Can also measure for specific work activities
3. Partial period consecutive samples (does not cover all)
- Most common measurement type; however, only covers a portion of the
worker's workshift
- Need to interpret exposures for the unsampled period in order to compare to
OEL-TWA
4. Grab samples (covers minimal amount)
- Least desirable measurement method to estimate 8-hr OEL-TWA
- Collected for short periods of time (seconds or minutes)
