Principles of gravimetric methods of measuring airborne dust containing asbestos at the workplace

• Pages: 64-66

C. Principles of gravimetric methods of measuring airborne dust

containing asbestos at the workplace

1. General

1.1. Airborne dust concentrations should be measured in the vicinity of various items

of equipment.

1.2. Airborne dust concentration measurements must be effected in the breathing zone,

account being taken of the main technical processes which could produce such asbestos-

containing dust. In making such measurements, samples are to be taken at a height of 1.5 m

(5 ft) from the floor or the ground.

1.3. Airborne dust samples are taken by drawing air through an analysis filter. Two

samples are simultaneously taken at each point of measurement. The filters should be placed

vertically or slightly inclined.

1.4. Where a team of workers is employed in an area where airborne dust

concentrations are being monitored, a sufficient number of samples must be taken to enable an

accurate determination of the airborne dust to be made, i.e. at least five samples.

1.5. Measurements of airborne dust concentrations should be accompanied by

measurements of environmental temperature, relative humidity and air flow rate. Five sets of

measurements should be taken in a working day.

1.6. When airborne concentrations of dust at workplaces are monitored periodically,

one sample may be taken at each workplace in order to determine the overall maximum

concentration. In such cases, the sampling period should not exceed 30 minutes.

1.7. Where air fl ow rates are in excess of 3 m/s, as may occur when monitoring

airborne dust concentrations in factories, quarries, etc., special nozzles should be used to ensure

equal air velocities and rates of aspiration. Deviations should not exceed ± 20 per cent.

1.8. Measurements shall be considered to be correct if the difference in airborne dust

concentrations between two samples taken at the same time and the difference between the

average characteristics of any two samples taken during a given working day do not exceed 25

per cent. Should the variation be greater, additional measurements shall be taken in order to

determine the reasons for such variations.

2. Materials and equipment for measuring airborne dust concentration

2.1. In gravimetric monitoring of airborne dust, synthetic or glass fibre filters are used.

Membrane and ash-free paper filters may also be used. Preferably, filters with a moisture

content not in excess of 0.5 per cent should be used. Analysis filters should retain at least 95 per

cent of the dust. The margin of error in measurements of the air volume sampled should not

exceed ± 10 per cent.

2.2. The instruments used for monitoring should enable concentrations of airborne dust

to be determined with a precision of 0.3 of the permitted concentration, sampling time not

being limited.

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