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6.6.1 Identification of Airborne Contaminants
The identification of airborne contaminants requires a sampling technique that collects a representative sample. The technique itself is likely to be similar to
those already described, although some alterations may be needed to ensure that sufficient sample is collected for the subsequent analytical technique.
6.6.2 Leakages and Spillages
Leaks and spills require a continuously reading instrument with a rapid response. This type of equipment is normally employed for flammable gases
and potentially oxygen deficient atmospheres, although gases with acute health hazards e.g. hydrogen sulphide, chlorine etc may need to be monitored
in this way. The type of equipment can be portable or fixed position.
6.6.3 Assessment of the Effectiveness of Control Measures
This would normally be performed by employing fixed position sampling devices providing time weighted average concentrations. Sampling can be
repeated periodically and the results compared. Care has to be taken to ensure that the working conditions are the same during each sampling
exercise. Continuous monitoring equipment may be employed to assess any changes that occur during short time periods.
6.7 Methods of Analysis
There are numerous analytical techniques available for the analysis of airborne contaminants. Many are dedicated branches of science in their own
right and require trained and experienced analyststechnicians. Not all techniques are suitable for all contaminants, but most chemical groups can be
analysed by similar methods. The main methods are shown below:
6.7.1 Organic Vapours
These are the most commonly occurring contaminants in a wide variety of industry e.g. used in various paints, coatings and cleaners. They are normally
sampled by collection on to a sorbent tube and then desorbed either by heating and purging directly into a gas chromatograph GC complete with a
73 flame ionisation detection FID, or by desorption in a solvent and subsequent
injection of aliquots of the liquid layer on to a GC. Both techniques are well established and can utilise automatic sampling procedures and computerised
data control systems, so that multiple samples can be analysed and analysis performed 24 hours a day.
6.7.2 Inorganic Gases
Separate techniques are needed for individual gases, whilst some can be analysed by GCthermal conductivity methods, sulphur gases need
photometric and microcoulometry whilst carbon monoxide and dioxide can be detected
by infra-red,
and oxides
of nitrogen
and ozone
by chemiluminescence. In practice it is often easier to measure inorganic gases
using direct reading devices which do not require analysis.
6.7.3 Organic Particulate Matter
Particulate polycyclic aromatic hydrocarbons PCAs are collected on a filter paper medium and solvent extracted and analysed by high pressure liquid
chromatography HPLC. Oil mist is similarly collected and can be analysed gravimetrically or qualitatively by infra-red IR or ultraviolet UV means.
6.7.4 Metals and their Compounds
Metal fumes are collected on a filter paper medium and analysed by Atomic Absorption AA or by Inductively Coupled Plasma Arc Spectroscopy ICP.
6.7.5 Mineral Dusts
Asbestos-in-air is a specialist technique involving collection on a cellulose ester membrane filter and analysis, by counting the number of asbestos type
fibres present on the filter, by phase contrast microscopy. Crystalline silica is similarly collected, and then the filter is analysed quantitatively either by x-ray
diffraction XRD or by infra-red.
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6.7.6 Calibration and Quality Control
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