The four-stage clearance procedure is a mandatory process that must be completed at the end of every licensed asbestos removal project before the area can be reoccupied or handed back for other use. It cannot be carried out by the removing contractor — it must be conducted by an independent UKAS-accredited analyst. It is a fundamental safeguard for building occupants, employers and the wider public.
Why Is Four-Stage Clearance Required?
During licensed removal of high-risk materials such as AIB and pipe lagging, asbestos fibres become airborne within the enclosure. Even after removal is complete and thorough cleaning is done, residual fibres may be present at levels that pose a health risk. Four-stage clearance provides an independent, objective verification that the area is safe for reoccupation. The procedure is set out in the HSE guidance document HSG248 — Asbestos: The Analysts' Guide and is a mandatory requirement of CAR 2012 for all licensed removal works.
Stage 1: Thorough Visual Inspection
An independent UKAS-accredited analyst conducts a detailed visual inspection of the entire enclosure, checking that all visible asbestos has been removed, all surfaces are clean and free from visible dust and debris, enclosure sheeting and airlocks are intact, and NPUs are operating correctly. If Stage 1 fails, the area must be re-cleaned before proceeding.
Stage 2: Background Air Monitoring
Before the enclosure is disturbed, background airborne fibre levels are measured just outside. This establishes a baseline reference level for the final clearance samples.
Stage 3: Enclosure Dismantlement and Final Clean
The enclosure is carefully dismantled by the removal contractor. A final visual check and Type H vacuum clean of all surfaces is completed. All enclosure sheeting, waste bags and contaminated materials are sealed, labelled and removed from site.
Stage 4: Reassurance Air Monitoring
The analyst takes a series of air samples from within the cleared area. These are sent to a UKAS-accredited laboratory and analysed using phase contrast microscopy (PCM). Results are compared to the clearance indicator — typically 0.01 fibres per millilitre (f/ml) for licensed work. If results fall below this threshold, a Certificate of Reoccupation is issued. If not, the area must be re-enclosed, re-cleaned, and the full procedure repeated.
AIB Solutions coordinates independent clearance analysts on all licensed projects. For more detail see our asbestos removal page and our testing and monitoring page. For commercial clients see our commercial removal page.