CWE Services Ltd is UKAS accredited to carry out air monitoring and four stage clearances in accordance with HSE guidance (HSG248).

Although not a legal requirement, it is preferred that the analyst is employed by the building owner or occupier for site clearance certification as this avoids any conflict of interest and also enables an independent party to be involved in resolving any problems that may arise during the clearance process.

The Role of the Analyst

The analyst is responsible for completing site clearance certification and for issuing a certificate of reoccupation following HSE notifiable removal of ACMs. Some clients may request a more in-depth participation by the analyst during asbestos removal works; for example overseeing smoke tests, carrying out reassurance, background and personal air tests during the works etc. Our analysts are trained to a high standard to carry these out.

All of our mobile laboratories are fitted out to a high standard in order to allow analysts to carry out all functions from the mobile laboratory. Slides are counted in the mobile laboratory and the certificate handed to the client/contractor whilst on site.

We offer the following types of air tests :-

  • Four stage clearances and issue of certificate of reoccupation
  • Background air monitoring
  • Reassurance air monitoring
  • Personal air monitoring
  • Leak monitoring
  • Smoke tests


Four stage clearances are carried out within an enclosed area on completion of removal or encapsulation works.

Premises are assessed by the analyst following removal of HSE notifiable ACMs or encapsulation thereof to determine whether they are thoroughly clean and fit for reoccupation. All air measurements are carried out in accordance with ISO 17025. Once all four stages have been completed and found to be satisfactory then a Certificate of Reoccupation is issued to the client and/or the contractor (whichever is relevant).

There are four stages to each four stage clearance procedure. Each stage is to be completed in sequence.

Should any of the four stages not pass its assessment then the contractor is to be advised of the reason for the failure and allowed to rectify the problem(s). The reason for the failure must be fully documented on the clearance paperwork and the contractor is to sign acknowledgement of the failure.

Stage 1 : Preliminary Check of Site Condition and Job Completeness
Stage 2 : Thorough Visual Inspection
Stage 3 : Clearance Indicator Air Sampling for the Certificate of Reoccupation
Stage 4 : Final Assessment Post-Enclosure/Work Area Dismantling

Background Air Monitoring

Background sampling is generally carried out to establish ambient fibre levels prior to any activity which may lead to asbestos contamination.

Reassurance Air Monitoring

Reassurance sampling may be required in certain circumstances, for example when an enclosure is being dismantled or following disturbance of ACMs in order to determine whether the ambient fibre levels are less than 0.01 f/ml.

Personal Air Monitoring

Personal air monitoring is carried out to assess the exposure level of an individual whilst carrying out the works. This is used to ensure the effectiveness of control measures, that the appropriate RPE is selected, that the RPE in use delivers the appropriate level of protection and for medical surveillance records.

Leak Monitoring

Leak monitoring is carried out to ensure that the enclosure is secure and not releasing airborne respirable fibres during removal works.

Call us if you have any questions about air monitoring on a continuous basis.