Just on a point of clarity, and not to do with face fit frequency, an analyst is not entering a ‘live’ enclosure when conducting a 4SC – this was discussed with HSE many years ago when determining suitable RPE during Stage 2. See HSG248 paras 8.3 (page 66):
“8.3 It is generally unlikely that the analyst will be exposed to airborne asbestos fibres at
concentrations above the control limit or the STEL. The exception would be where they enter a ‘live’ asbestos enclosure, ie where removal is taking place. However, entry into live enclosures should be avoided. Analysts supporting licensed contractors by assisting with the management of removal works, inspecting enclosures, witnessing smoke tests and conducting personal monitoring etc should be able to perform most of these activities from outside the enclosure.
8.4 Monitoring of workers to provide an accurate record of their activities should be possible
from outside enclosures by using the viewing panels and CCTV. However, where entry into a live
enclosure cannot be avoided, then time spent should be the minimum necessary to conduct the
checks and inspections. Analysts should not enter live enclosures at the request of the licensed contractor or building client to check on the standard of removal or cleaning. Such inspections by the analyst should only be conducted as part of the 4-stage clearance procedures.”
and 8.11 & 8.12 – that I have not copied here.
A ‘live enclosure’ is where removal work is on-going, and exposure is likely to be above the Control Limit, and an analyst should not, in the normal course of events, be entering the enclosure at this time.
With best regards