2. To identify and quantify chemical health
hazards
Health effects can be acute or chronic, so there
are different types of measurement to account
for this:
Long-term measurements to assess average
exposure over a given time period
Continuous measurements that can detect short-
term acute exposure to high concentrations of
contaminants
Spot readings to measure acute exposure if the exact
point in time exposure is known
3. 2 types of sampling:
Static sampling
Primary aim is to assess effectiveness of engineering
controls or measure plant emissions into work
environment
Levels should be set well below personal exposure
limits
Personal sampling
Assess individual exposure
4. Factors influencing airborne concentrations:
No. of sources of contaminant
Rates of release from each source
Type and position of each source
Dispersion or mixing of contaminants
Ambient conditions e.g. wind speed, air temp.
5. Before devising sampling strategy, carry out
initial appraisal. Info. required:
Substances which occur in workplace
Airborne nature of substances
Hazardous properties of substances
Synergistic effects
Possible exposure by inhalation, ingestion, skin
contact?
During which processes/tasks will exposure occur?
Groups/individuals at risk
Likely pattern and duration of exposure
7. Strategies:
First level for basic surveys
Second level for more detailed surveys
Third Level for surveys needing high degree of
sophistication
8. First level strategies:
Used where crude quantitative information is
required so that decisions can be taken as to whether
problem actually exists, prior to conducting detailed
survey
Divide population into groups in relation to work or
degree of exposure
High risk groups can be studied in detail
Personal sampling, especially at peak periods
9. Second level strategies:
Appropriate for most detailed surveys and for
routine monitoring
Emphasis on accurate measurement of average
exposures and relating them to OEL’s
Entire period of exposure should be covered
10. Third level strategies:
Occasionally high degree of sophistication required
E.g. if all reasonably practicable steps have been
taken and exposure is still close to OEL; or
Where OEL is very low so small changes in exposure
are significant
11. Consideration of results should always lead to
answers to 5 questions:
Is immediate action necessary to eliminate or reduce
exposure?
Is immediate action necessary to re-establish
adequate control?
Is a programme of planned improvements
necessary?
Is a more detailed survey required?
Should routine monitoring be implemented or
continued?
12. Series of detailed descriptions of analytical
methods approved by HSE
Provide reliable and consistent methods
Covers sampling AND analysis
13. 2 Fractions:
Inhalable fraction:
Total particles inhaled through nose and mouth
Respirable fraction
Less than 10 microns
Able to penetrate the respiratory system as far as the
alveolar region
Fibrous particles:
Shape is as important as size
Long thin fibres more dangerous
14. Components:
Sampling head
Size selection
Cyclones to separate respirable fraction
Filters
Used to collect sample before assessment
Wide range depending on contaminant
Pumps
Must be able to be worn on body if personal sampling
required
Flow meter required
15. Static sampling:
Complete assembly includes filter, pump and flow
meter
Left unattended in workplace
Use cyclones to remove larger particles
Personal sampling:
Preferred technique - more realistic measurement of
exposure
Cyclones used to remove larger particles
16. Direct Reading Instruments:
Gives instantaneous result
Can be:
Light scattering
Beta particle attenuation
Oscillating micro-balance (quartz crystal oscillation
changes with build up of dust)
17. Measured volume of air drawn through filter
Mass of dust collected is determined by weighing filter
before and after sampling
Size selection devices can be used to measure respirable
dust
Volume of air passing through filter is calculated by
multiplying flow rate (cubic m per minute) by
sampling time (minutes)
Weight gain of filter (mg), divided by the volume
sampled, gives average dust concentration in mg per
cubic meter of air (mg/m3)
18. Similar to dust, except:
Open faced filter holder
Membrane filters which can be rendered transparent
to allow fibre counting by phase contrast microscopy
Flow rate is specified and measurement must be over
4 hour period
Fibres are counted on membrane filter
Concentration is calculated by dividing total no. of
fibres collected on filter by total volume of air to give
fibres per millilitre (f/ml)
19. Grab Sampling:
Sample taken in flask, bottle bag etc.
Useful for peak concentration or when
concentrations are constant
Continuous or Long-Term Sampling:
Sample removed from air over measured time
period and concentrated by passage through solid or
liquid sorbent
Useful if:
Concentration varies time with time
Concentration is low
TWA exposure is required
20. Evacuated flasks
Atmosphere drawn in
Gas/Liquid displacement container
Flask connected to a pump
Flexible plastic containers
Plastic bags
Hypodermic syringes
21. Liquid sorbents
Cold traps
Plastic sampling bags
Solid sorbents
Charcoal or Silica gel
22. Sampling equipment:
Pump
Adjustable flow rate
Able to be worn if personal sampling required
Flow measurement
Important to know flow rate to calculate exposure
23. Diffusive samplers
Badge or tube type
Factors affecting performance:
Temperature and pressure
Humidity
Concentration variations
Sorbent efficiency
Face velocity
24. Sample positioning:
General working atmosphere (grab sample)
Operator’s breathing zone (TWA sample)
Close to contaminant generation (continuous
monitored sample)
Sampling frequency:
Statutory in some cases (asbestos every 4 hours)
Depends on level of risk
25. Most involved subjecting substance to burst of energy and
examining way substance responds
Response is characteristic of substance and can be used as
“fingerprint”
Magnitude of response can be used to estimate how much of
agent is present
Techniques:
Gas Chromatography
Atomic Absorption Spectroscopy
Infra Red Spectroscopy
X-Ray Diffraction
Optical Microscopy
26. Chemical is carried down an absorbent column
by a carrier gas
The length of time the sample takes to travel
down the column is unique to the substance
Size of spectrum peak indicates quantity of
substance
Mixed substance can be separated
27. Used for metallic substances
If certain metals are heated to high temperatures
in a flame, electronic changes in the metal atom
cause a change in colour to the flame
Sample is injected into an air-acetylene flame
and resultant spectrum is analysed by an atomic
absorption spectrometer
Both identity and quantity of substance can be
determined
28. Based on principle that chemical bonds that
connect atoms into molecules are continuously
vibrating and the energy of this vibration falls
within the infra-red wavelength range
Infra-red radiation is passed through the
sample and the absorption spectrum gives a
characteristic fingerprint of the substance
Identifies and quantifies substance
29. Used for solid analysis
X-rays passed through a sample are diffracted
in a characteristic fashion, which depends on
the crystal structure and spacing between
atoms
Gives characteristic fingerprint of substance
30. Mostly widely used for fibrous dust
Dust is collected on membrane filter, then
counted under optical microscope
As sampling time and flow rate are know,
fibres per unit volume can be calculated
Where it is necessary to determine type of
asbestos, polarised light microscopy is used
Different types of fibre show different colours
under polarised light
