4.2 Strategies, methods and equipment for the sampling and measurement of airborne contaminants

Question 1

Monitoring of hazardous substances is necessary: 4

Answer 1

 when failure of control measures could result in a serious health effect
 to demonstrate that a WEL is not being exceeded
 as an additional check on the effectiveness of control measures
 when changes in work occur that could affect employees’ exposure, for example:
increase in quantity of a substance used; new systems of work or new plant.

Question 2

There are different types of monitoring and equipment that may be required. These
relate to the following terms. 3

Answer 2

 Type of sampling: personal or static (environmental).
 Timescales: short or long term.
 Types of equipment: direct reading or indirect reading; active or passive air
sampling.

Question 3

Active air sampling

Answer 3

Uses a calibrated air pump to draw a known
volume of air over the reagent, over a known
period of time.

Question 4

Passive air sampling

Answer 4

Allows air to diffuse over the sampling head
which may be a badge, impinger / bubbler or
dosimeter tube (no pump).

Question 5

stages of the monitoring strategy

Answer 5

Initial appraisal 
Basic survey 
Detailed survey 
Reappraisal 
Routine monitoring

Question 6

The initial appraisal is

Answer 6

Qualitative sampling methods may be used to carry out the initial appraisal, for
example:
 Smoke tubes can illustrate the movement of air under the influence of draughts, general and local exhaust ventilation systems, and show what the effects are.
 A dust lamp helps to identify emission sources and watch the movement of airborne dust.
 Smell can also be used as an indicator of contamination, however, this is an
unreliable method.

If the initial appraisal were to indicate that there would be significant exposure, a
basic survey would be necessary.

Question 7

A basic survey is

Answer 7

The basic survey estimates employees’ personal exposure and provides an indication of the efficiency of process and engineering controls.

It usually surveys the worst-case situations, for example: the ‘dirtiest’, or where employees have made complaints.

Qualitative and semi-quantitative sampling methods can be used to estimate personal exposure. These provide a rough numerical estimate of exposure.

Some semi-quantitative methods are comparatively inexpensive and easy to use, for example: chemical indicator tubes or dust lamps.

Question 8

Some semi-quantitative methods are comparatively inexpensive and easy to use,
for example:

Answer 8

chemical indicator tubes or dust lamps.

Question 9

The basic survey may highlight defects and deficiencies in control strategies. If the
conclusion is not certain, there will be two choices:

Answer 9

(1) To carry out a more detailed survey and take remedial action as necessary.
(2) Take direct action to control exposure.

Question 10

A detailed survey may be required when:

Answer 10

 The extent and pattern of exposure cannot be confidently assessed by a basic
survey.
 Exposure is highly variable between employees doing similar tasks.
 Carcinogenic substances, respiratory sensitisers or mutagens are involved.
 Undertaking major maintenance and one-off jobs, such as plant decommissioning
 The initial appraisal and basic survey suggest that:
- the time-weighted personal exposure may be very close to the WEL
- the cost of additional control measures cannot be justified without evidence
of the extent of exposure variability.

Question 11

A detailed survey would have a greater emphasis on personal sampling over longer
periods of time, and the taking of a greater number of samples over a wider range of
conditions. More sophisticated quantitative sampling methods and equipment
would be used, for example:

Answer 11

those reliant on laboratory analysis and biological

monitoring

Question 12

A detailed survey will require an in-depth investigation of the process, and its
environment, including: 11

Answer 12

 Existing CoSHH assessments.
 Procedures and work methods.
 Maintenance procedures.
 Existing control measures and their suitability, For example: the results of the
annual examination and testing of the local exhaust ventilation could be
compared with its commissioning data.
 Existing PPE provided and its suitability. For example: the
 comparison of the
chemical resistance of gloves against information contained in material safety
data sheets (MSDS).
 Workplace exposure limits, with a comparison between actual exposures from
personal sampling to the relevant WELs
 Results of biological monitoring and those of biological monitoring guidance
values (BMGV).
 Previous environmental monitoring results.
 Results of health surveillance programmes.
 Information and instruction provided to the employees for carrying out the tasks
involved.
 Training provided to employees.

Question 13

A reappraisal is

Answer 13

an assessment to determine whether changes to control measures
have had a positive effect.

Question 14

Schedule 5 of the CoSHH Regulations requires continuous monitoring for the
following chemical exposures:

Answer 14

 Vinyl chloride monomer.
 Hexavalent chromium: every 14 days for sprays given off from vessels during
electroplating processes.

Question 15

Factors which influence the release and airborne

concentration of substances include: 7

Answer 15

 Physical and chemical properties of the substance, for example: vapour pressure,
boiling point and particle size.
 The number of sources from which the substance is released.
 Rate, duration and speed of release from each source.
 Arrangement of the process, temperature and design of the control measures.
 Variations in the process, job and tasks being carried out, for example: hour, day
or even week.
 Dispersion or mixing of the substance in the workplace air due to general or local
ventilation.
 Ambient conditions (temperature, pressure and humidity).

Question 16

From the exposure monitoring results the following conclusions may be made: 4

Answer 16

 The data is, or is not, adequate and/or representative of all those exposed.
 Compliance with WELs, etc. has, or has not, been achieved.
 Further actions are, or are not, necessary to prevent or reduce exposure.
 More monitoring is, or is not, needed.

Question 17

Qualitative methods are

Answer 17

simple observational techniques that do not involve any
quantified measurement. They rely on judgment, knowledge and experience. The
threshold of smell and the Tyndall light beam are examples of qualitative sampling
methods.

Question 18

The strengths of using stain detector tubes

Answer 18

Relatively cheap. 
Simple  to  use  –  no  major  costs  for 
training or expertise. 
Direct reading – immediate result. 
Provides an indication of the need for 
more sophisticated measurement.

Question 19

The weaknesses of using stain detector tubes

Answer 19

Substance specific – the correct tube 
must be specified for the suspected 
contaminant. 
Only  suitable  for  chemical  contaminants 
(gases and fume). 
Not very accurate – variables include: 
  bellows efficiency 
  wrong number of pumps 
  cross sensitivity and date sensitivity of 
tubes 
  sampling  point  –  proximity  to 
contaminant. 
A grab sample may miss the presence of 
the contaminant.

Question 20

Qualitative sampling methods (examples)

Answer 20

Threshold of smell

Tyndall light beam

Question 21

Semi-qualitative sampling methods (examples)

Answer 21

stain detector tube

Question 22

Personal monitoring sampling apparatus consists of:

Answer 22

a sampling head,
positioned in the wearers breathing zone (clipped to collar, for example), connected
with tubing to a calibrated portable medium flow pump (powered by rechargeable
battery) and clipped to a belt or carried in a holster

Question 23

There are four types of sampling head recommended for particulate sampling:

Answer 23

IOM
sampling head, multi-orifice total inhalable sampler, conical inhalable sampler and
respirable dust cyclone sampler.

Question 24

The process for taking a personal sample is as follows: 11

Answer 24

(1) A filter is dried out in a clean area and weighed.
(2) The sampling head is cleaned before use.
(3) The pre-weighed filter is placed in a sampling head in a clean, dust-free
environment.
(4) Each sampler is labelled so that it can be uniquely identified and sealed with
its protective cover, or plug, to prevent contamination.
(5) The volumetric flow rate is set, for example: two litres per minute (±0.1
litre/min).
(6) Each loaded sampler is connected to a sampling pump, ensuring that no leaks
can occur.
(7) The protective cover from the sampler is removed.
(8) The sampling pump is then switched on, and attached to a calibrated flow
meter so that it measures the flow through the sampler’s inlet orifice(s).
(9) Air is drawn through the filter over a known period of time, for example: 4
hours.
(10) The filter is then sent to an approved laboratory to be dried out again for
gravimetric analysis.
(11) The filter is re-weighed.

Question 25

The volume of air passing through the sampler is calculated by

Answer 25

multiplying the
mean volumetric flow rate in cubic metres per minute by the sampling time in
minutes

Question 26

Average dust concentration (mg/m3) =

Answer 26

The net weight gain (mg) of the sample substrate is divided by the volume of air
sampled (m3)

Question 27

The strengths of personal dust sampling are

Answer 27

Accurate

Indicates the workers actual exposure
during real work activity

Allows  direct  comparison  to  workplace 
exposure limits (WEL) 

Can be used to identify a chemical

Question 28

The weaknesses of personal dust sampling are

Answer 28

Expensive

Requires expertise to set up

Time  consuming  (sample  to  lab  for 
analysis) 

May be tampered with by wearer

Question 29

Spectrometry, spectroscopy and chromatography are

Answer 29

analysis techniques that

can identify both the chemical and its concentration

Question 30

Spectrometry

Answer 30

measures the intensity of light in a part of the spectrum specially
transmitted or emitted by particular substances. This is measured using a
spectrophotometer.

Question 31

Spectroscopy

Answer 31

Spectroscopy is concerned with the 
investigation and measurement 
spectra produced when matter 
interacts with or emits 
electromagnetic radiation. It relates 
to the dispersion of an object's light 
into its component colors (i.e. 
energies). By performing this 
dissection and analysis of an 
object's light, analysts can infer the 
physical properties of that object, 
for example: temperature, mass, 
luminosity and composition.

Question 32

Chromatography

Answer 32

Chromatography is the separation of a mixture by passing it in solution or
suspension, or as a vapour (as in gas chromatography), through a medium in which
the components move at different rates.

The mixture is dissolved in a fluid called the
‘mobile phase’, which carries it through a
structure holding another material called the
‘stationary phase’. The various constituents of
the mixture travel at different speeds, causing
them to separate.

Chromatography can separate complex mixtures with great precision. Even very
similar components, such as proteins that may only vary by a single amino acid, can
be separated with chromatography.