W201 Day 2 – Overnight Questions with Answers
MEASUREMENT OF AIRBORNE CONTAMINANTS
1. For each of the terms below indicate what is the state of matter (Gas,
Liquid or Solid) and define the term.
Term
State of matter
Definition
Vapour
Gas
The gaseous state of a substance which is liquid at
25°C and 760 mm Hg (STP).
Mist
Liquid
Liquid particles, large size generally produced by
bubbling, splashing or boiling of a liquid.
Fume
Solid
Solid particles produced by condensation from a liquid
or a reaction between two gases. The particle size of a
fume <1 micron (µm) diameter anything larger is
considered a dust particle.
Dust
Solid
Particles of solid material in the broad size range of 1
micron to 1 millimetre diameter. Anything of a larger
particle size is considered to be grit and will be too
heavy to remain airborne
Aerosol
Solid or Liquid
General term for the dispersions of solid or liquid
particles of microscopic size in a gaseous medium e.g.
fog, smoke etc. although commonly used to term fine
liquid spray (e.g. ‘aerosol can’).
Fibre
Solid
Solid particulate which is long and thin i.e. has a high
aspect ratio of length to breadth.
2. In each of the following pairs indicate which generally involves the larger
particles.
1
2
3
4
5
Fume or dust
Vehicle exhaust or cement dust
Respirable particles or inhalable
particles
Mist or spray
Viruses or bacteria
Dust
Cement dust
Inhalable particles
Spray
Bacteria
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W201 Day 2 – Overnight Questions with Answers
3. For each of the following, name the equipment and indicate what
substances and what type of sampling it might be used for.
IOM sampling head
Inhalable dust monitoring
Long term sampling
Cyclone sampling head
Respirable dust
Long term sampling
Colorimetric tubes
Gases and vapours
Grab samples
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W201 Day 2 – Overnight Questions with Answers
Passive/diffusion sampler
Gases and vapours
Long term sampling
Charcoal tubes
Gases and vapours
Long term sampling
Direct reading photoionization detector
Organic compounds (gases/vapours)
Grab samples or continuous
monitoring
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W201 Day 2 – Overnight Questions with Answers
4. The data below represents the information collected during an air
monitoring exercise for Total inhalable dust. For each sample calculate the
measured concentration of dust in mg.m-3.
Sample
No:
Start
(hh:mm)
Stop
(hh:mm)
Flow Rate
(l.min-1)
Filter Pre
weight (mg)
Filter post
weight (mg)
1
09:00
17:00
2.0
25.34
25.59
2
09:15
12:30
2.0
24.99
27.49
3
13:30
16:58
2.0
26.01
28.09
4
08:00
16:30
2.0
25.45
26.21
5
09:17
15:16
2.0
25.11
26.37
Sampling
Time
(mins)
Weight
Change of
Filter (mg)
Volume of air
sampled
Concentration
(mg.m-3)
480
0.25
960
0.3
195
2.50
390
6.4
208
2.08
416
5.0
510
0.76
1020
0.7
359
1.26
718
1.8
(litres)
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W201 Day 2 – Overnight Questions with Answers
HYGIENE STANDARDS AND OCCUPATIONAL EXPOSURE LIMITS
5. For each of the following measured exposures calculate the appropriate 8hour time weighted average
a. The operator works for eight hours on a process in which he is exposed to a
substance hazardous to health. The average exposure during that period is
measured as 0.15 mg.m-3.
The 8-hour TWA =
(0.15 x 8) / 8
= 0.15 mg.m-3
b. Working periods may be split into several sessions for the purpose of
sampling to take account of rest and meal breaks etc. This is illustrated by the
following example:
Working period Exposure (mg.m-3) Duration of sampling (h)
0800-1030
0.32
2.5
1045-1245
0.07
2
1330-1530
0.2
2
1545-1715
0.1
1.5
Exposure is assumed to be zero during the periods 1030 to 1045, 1245 to
1330 and 1530 to 1545.
The 8-hour TWA =
(0.32 x 2.5) + (0.07 x 2) + (0.20 x 2) + (0.10 x 1.5) + (0 x 1.25)
8
0.80 + 0.14 + 0.40 + 0.15 + 0
8
= 0.19 mg.m-3
c. An operator works for eight hours during the night shift on a process in which
he is intermittently exposed to a substance hazardous to health. The
operator’s work pattern during the working period should be known and the
best available data relating to each period of exposure should be applied in
calculating the 8-hour TWA. These should be based on direct measurement,
estimates based on data already available or reasonable assumptions.
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W201 Day 2 – Overnight Questions with Answers
Working
period
Task
Exposure (mg.m-3)
2200 to 2400
Helping in workshop
0.1 (known to be exposure of full-time
group in workshop)
2400 to 0100
Cleaning elsewhere in
factory
0 (assumed)
0100 to 0400
Working in canteen
0 (assumed)
0400 to 0600
Cleaning-up after breakdown 0.21 measured
in workshop
The 8-hour TWA =
(0.10 x 2) + (0.21 x 2) + (0 x 4)
8
= 0.078 mg.m-3
d. The operator works a 12-hour shift each day for five days, and then has seven
days’ rest. The exposure limits are based on an 8-hour reference period in
each 24 hours in which an exposure occurs; the seven days’ rest makes no
difference. While at work, the operator is exposed to 4 mg.m-3.
The 8-hour TWA =
(4 x 12)
8
= 6 mg.m-3
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W201 Day 2 – Overnight Questions with Answers
BIOLOGICAL MONITORING AND HEALTH SURVEILLANCE
6. What are the three main reasons for undertaking Health Surveillance?



to ensure adverse health effects related to the work are identified at an early
stage; in some countries there may be statutory requirements.
to ensure continued medical fitness for specific tasks like diving or fire fighting
to promote general health.
7. What kind of information can biological monitoring provide?




the content of a toxic material or its metabolite in blood, urine and breath
Its effects on enzyme systems or metabolic pathways
Early reversible tissue change
Physiological changes Immunological changes.
CONTROL
8. Name the elements of the Hierachy of Control and list them in order of
performance.
Elimination
Isolation
Segragation
Engineering Controls Including LEV
Increasing preference
Substitution
Administrative Controls
Personal Protective Equipment
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W201 Day 2 – Overnight Questions with Answers
VENTILATION
9. Name the general components of a Local Exhaust Ventilation system
10. What elements need to be considered when trying to control an airborne
contaminant using Local Exhaust Ventilation?
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W201 Day 2 – Overnight Questions with Answers
11. Give names to each of the hoods shown and describe how they control
airborne contaminants.
Enclosing hood –
surrounds the
contaminants and
minimises escape
by drawing air
through open
faces.
Receptor Hood –
receives materials
in the direction
they are ejected.
Capture hood –
provides suction
beyond the face of
the hood to
capture
contaminants and
draw them into the
hood.
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