Air monitoring measures fibres in the air rather than asbestos in a material, and it answers a different question from a survey. It is done by an analyst working to HSG248, normally from an organisation accredited by UKAS for the activity, and its most important use is the four stage clearance that decides whether people can go back into an area after licensed removal.
The four kinds of test
Background monitoring, taken before work starts so there is something to compare against. Leak monitoring, taken outside an enclosure while work goes on. Reassurance monitoring, taken after non-licensed work or after a disturbance to show an area is fit to use. And clearance air monitoring, the fourth stage of the certificate procedure after licensed removal. They differ in when they are taken and in what a result means.
The four stage clearance
After licensed removal the analyst carries out a preliminary check of the site and job paperwork, a thorough visual inspection inside the enclosure, the clearance air test itself, and a final assessment after the enclosure comes down. Passing all four produces the certificate of reoccupation. Air monitoring alone is not a clearance, and a certificate issued without the visual inspection is not worth the paper.
Independence
The analyst who clears the site should be independent of the contractor who did the removal. A firm certifying its own work has an obvious interest in the answer, and separating the two is one of the cheapest protections available to a client. Ask who the analyst is and who is paying them before the job starts, not afterwards.
What the numbers mean
Results are reported as fibres per millilitre of air against a stated clearance indicator, with the sampling method and duration recorded. A pass says the air met that indicator at that time in that place; it is not a statement that the building is now free of asbestos, and the register still governs what remains.
Questions people ask about asbestos air monitoring
Who can carry out clearance air testing?
An analyst working to HSG248, from an organisation accredited for the activity. Accreditation and independence are the two things worth checking before the job rather than after.
Is a reassurance test the same as a clearance?
No. Reassurance monitoring shows an area is fit to reoccupy after non-licensed work or a disturbance; clearance is the formal four stage procedure that follows licensed removal.
What is an asbestos removal certificate?
In everyday use it means the certificate of reoccupation issued at the end of the four stage clearance. Ask for it in writing and keep it with the register.