Personal sampling for compliance under CAWR
The filter holder should point downwards and be fixed to the upper lapel or shoulder of the worker’s clothing, as close to the mouth and nose as practicable, and preferably within 200 mm. Due regard must be given to localised concentrations: in such cases, the sampling head should be positioned on the side expected to give the higher result. If a respirator is worn, the sampling head should be positioned away from the clean air exhaust.

Background and reassurance sampling
The sampling strategy to be employed in these situations usually will be the same as in clearance indicator sampling. To achieve the limit of detection (0.01 f/ml), each measurement must result from a total of at least 480 litres in volume. Fewer measurements may be generated during background and reassurance sampling than for clearance sampling, but the distribution of samples should cover likely sources of fibre and likely areas of frequent human occupation.

Leak testing
This is testing to support the frequent thorough visual inspections of the enclosure as described in EH51. 11A number of sample positions should be considered: for example, near an air lock, near a gag-lock, and near the exhausts of negative pressure units. For this type of testing it may be possible only to sample for a few minutes, in which case a high flowrate should be used and the cause of any fibres above background should be investigated. If fewer than 20 fibres are counted, or less than 480 litres of air is sampled, then a calculated result greater than 0.01 f/ml will have a large imprecision and account must be taken of this by proportionally increasing the limit of detection.

Personal sampling to assess respiratory protection
This can be achieved by personal sampling with the pump attached to the respirator belt and the filter holder attached to the hood of the wearer’s overall. Airborne fibre concentrations may vary from the detection limit of 0.01f/ml up to a level in excess of 650 f/ml (if dust control is poor)

Clearance indicator sampling (clearance testing)
Clearance indicator sampling should take place only when the enclosure is dry and a visual inspection confirms that it is free from dust. 6 Practical advice on the preparation of the enclosure, and application of clearance tests, is given in Guidance Notes. 11,22 The filter holders should point downwards, be fixed 1-2 m from the floor and be distributed throughout the enclosure. In tall enclosures (for example, vertical pipework or lift shafts), samplers should be placed at representative exposure heights, especially in areas where residual dust may be difficult to detect. There should always be at least two measurements (unless the volume of the enclosure is less than 10 m 3, in which case one measurement is adequate). With that overriding condition, the number of samples should be at least the integer (whole number) next below (A 1/3 –1) where A is determined as follows.

a) if the enclosure is less than or equal to 3 m in height, or in enclosures which are higher than 3 m but where exposure is likely to be at ground level only, A is the area of the enclosure in square metres;

b) in other cases, A is one-third of the enclosure volume in cubic metres; if there are large items of plant (such as boilers) in the enclosure, their volumes may be subtracted from the gross volumes before calculating A.