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Equipment used for continuous Sampling Equipment
Type Mode of
Operation Advantages
Disadvantages
Flame Ionisation e.g.
organic vapour analyser
OVA or total vapour
analyser TVA Combustion of
organics in an air hydrogen flame
produces ions –
sensed by electrodes and converted into a
voltage signal Portable
Usually intrinsically safe
Limited on range and specificity of
contaminants
Infrared e.g. Miran Analyser
Absorption of IR radiation used to
measure the concentration of
substance Semi-portable,
Limited in the compounds it can
detect Bulky, non-
intrinsically safe
Ultraviolet Absorbance of
ultraviolet Portable
Interferences, calibration, not
intrinsically safe.
6.5.2 Sampling Methods
In deciding what sampling is required, numerous factors have to be considered. Several such as the site of the sampler and duration of sampling
time have briefly been mentioned. However, a thorough knowledge of the processes involved and the likely contaminants to be monitored precedes all
other considerations. Careful work done here can minimize the amount of sampling subsequently undertaken, and optimize the value of the results
obtained. The type of analytical method to be used and criteria against which evaluations are to be made are also important considerations.
Validated methods of sampling and analysis such as those published by the HSE in their Methods for the Determination of Hazardous Substances
MDHS series and the National Institute of Occupational Safety and Health NIOSH should be used where practicable.
71 All instructions included in these methods such as sampling pump flow rates,
calibration schedules and appropriate sample collection medium e.g. adsorbent, filter paper etc, must be strictly adhered to for the sampling
methods to be valid. In addition the following matters should be resolved before sampling
commences:
The Amount of Material Required
The analyst should be provided with enough material to ensure an accurate, representative result.
Always consult the analyst before collecting samples to discuss the type of quantity required, packaging, transport, storage, etc.
Sample Handling
Inappropriate handling and transport of sampled materials may give rise to losses or contamination. Factors include the type of container used as well as
any requirements to store at lower temperatures or away from sunlight. Advice can usually be obtained from the laboratory undertaking the analysis.
6.5.3 Fixed Position Sampling
This can be employed to provide information about contamination from fixed sources and effectiveness of control measures e.g. local exhaust ventilation.
Similar apparatus to that employed above can be used for fixed position sampling as well as larger sampling pumps with sampling flow rates of up to
100 litres per minute. Care has to be exercised in interpreting the results as the particle sizes collected may be different with higher flow rates. In addition,
fixed position samples cannot be used to establish personal exposures or be compared to hygiene standards.
6.6 Sampling Strategies
