The short answer
There are several kinds of asbestos air testing. Some check workers’ exposure, some check that an enclosure isn’t leaking, and some reassure people that an area is clean. After licensed removal, an independent analyst carries out a four-stage clearance and, if the area passes, issues a certificate for reoccupation. The rules are in HSE’s analysts’ guide, HSG248.
Who can do air testing
Air testing must be done to ISO/IEC 17025 standards, and anyone assessing whether premises are fit for reoccupation must be accredited to ISO/IEC 17020 and 17025 (regulation 20). HSE says air monitoring should be done only by an analyst from a UKAS-accredited laboratory, and that HSE recognises only UKAS accreditation for asbestos analysts in Great Britain. Fibre samples are collected by drawing air through a filter, which is then examined under a microscope.
Types of air sampling
| Type | What it’s for |
|---|---|
| Personal sampling | Measures the fibres a worker breathes, to check exposure and that controls and masks are adequate. |
| Background | Sets the normal fibre level before work that might release asbestos. |
| Leak testing | Checks that a removal enclosure stays sealed while work goes on. |
| Reassurance | Confirms fibre levels aren’t raised, for example after removal work or an incident. |
| Clearance | Stage 3 of the four-stage clearance after licensed removal. |
Personal sampling and the employer’s duty
Under regulation 19 employers must monitor their employees’ exposure to asbestos fibres, unless exposure is unlikely to exceed the control limit or they can show compliance another way. Records must be kept. This is the contractor’s responsibility, not the client’s, but it’s fair to ask how they monitor exposure on larger jobs.
The control limit is 0.1 fibres per cm³ averaged over four hours. HSE is clear that it is not a “safe” level. It is a legal ceiling, and exposure must be kept as low as reasonably practicable.
Four-stage clearance
After licensed removal, usually inside a sealed enclosure, the area must be cleared before it is handed back. HSG248 describes four stages:
- Site and paperwork check. The analyst checks the work is complete, including transit and waste routes.
- Thorough visual inspection. No visible debris or dust may remain inside the enclosure.
- Air sampling. Fibre levels inside must fall below the clearance indicator of 0.01 fibres per ml.
- Final assessment. After the enclosure is taken down, the analyst checks the area again.
HSG248 says only UKAS-accredited organisations may carry out four-stage clearance, and HSE strongly recommends the analyst is independent of the removal contractor.
The certificate for reoccupation
When the area passes all four stages, the analyst issues a certificate for reoccupation. It goes to the licensed contractor and to the person responsible for the premises. Keep it with your asbestos records. Read it rather than just filing it: HSE research (RR1218) found certificates were not always clear, unambiguous and accurate.
When each one applies
- Licensed removal (lagging, sprayed coatings, most insulating board): four-stage clearance and a certificate for reoccupation. See licensed asbestos removal.
- Non-licensed work (for example asbestos cement, floor tiles, small areas of textured coating): four-stage clearance isn’t required. Contractors clean up and inspect the area themselves. Reassurance air testing can still be arranged if you want extra confidence.
- After an accidental disturbance: reassurance sampling may help show whether fibres are still present once the area has been cleaned.
Read more in our guide to licensed and non-licensed work, or ask us for a quote for testing or removal.
Quick answers
Do I need an air test after my garage roof is removed?
It isn’t required for non-licensed removal of cement sheets. Some people choose reassurance testing for peace of mind.
Who should do the four-stage clearance?
A UKAS-accredited analyst. HSE strongly recommends one that is independent of the removal contractor.
What does a clearance certificate prove?
That the analyst checked the area through all four stages and found it fit to reoccupy at that time.
This guide is general information, not legal advice. For the law itself, see the Control of Asbestos Regulations 2012 and HSE’s asbestos pages. Not sure what you’re dealing with? Ask us.