Chemicals

1. Measurement and Analysis

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

6. Initial Appraisal:

Simple qualitative tests can be carried out:

 Dust lamps
 Smoke tubes
 Stain tubes

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