New leak testing guidance for asbestos enclosures: what changes, and how to show clients you follow it.
Industry guidance on when to leak test asbestos enclosures has been approved for publication. It tightens one rule absolutely, makes everything else a recorded, risk-based decision, and gives clients a new question to ask you. Here is what it says, what it means on site and how to make your approach visible before the tender.
- The Asbestos Network Technical Working Group approved the leak testing appendix on 3 August 2026. It is being published as a free PDF on the Asbestos Network section of the CONIAC website.
- One requirement is absolute: where a negative pressure unit vents inside the building, leak testing should always be carried out at the discharge point.
- Everything else is a risk-based decision covering occupied areas, the vicinity of the enclosure, sensitive areas and anticipated fibre levels.
- A decision not to leak test must be recorded specifically in the plan of work. Generic wording that appears on every plan will not do.
- Clients in schools, hospitals and care homes will start asking how you decide. A clear page on your website answers them before they ask.
What has been approved
The Asbestos Network Technical Working Group signed off the final wording of a new appendix on leak testing at its meeting on 3 August 2026, according to the autumn issue of ARCA News. It is aimed mainly at licensed asbestos removal contractors and sets out how to decide whether leak testing is needed on a given job, where to concentrate it and how often to do it. ARCA was represented on the drafting group by its chief executive.
The appendix does not create new law. It applies the duties already in the Control of Asbestos Regulations 2012: regulation 16, to prevent or reduce the spread of asbestos, and regulation 11, to protect anyone who may be affected by the work, not only your own operatives. Paragraph 79 of the Approved Code of Practice, L143, spells out who that includes: other contractors, occupants, visitors and members of the public. Paragraph 416 says where to check: the enclosure perimeter, airlock and baglock positions, plus the discharge of extraction equipment sited internally.
The one rule that is not a judgement call
Where a negative pressure unit does not vent to atmosphere outside the building, leak testing should always be carried out at the discharge location. There is no balancing exercise. The annex explains why smoke tests, airflow readings and flap deflection are not enough on their own: a pinhole in an NPU's HEPA filter can leak fibres without any noticeable change in pressure across the filter.
Everything else is a recorded, risk-based decision
The appendix sets out four considerations.
- Occupied areas. If anyone other than removal operatives, analysts, auditors or HSE inspectors occupies areas near the enclosure, leak testing should be carried out. Deliveries, cleaning, maintenance and security access count where they are reasonably foreseeable.
- The vicinity of the enclosure. Deliberately not defined by distance. The question is whether fibres could migrate into a space and affect someone if the enclosure failed: waste routes, shared ventilation, corridors, stairwells, lift shafts, voids, ducts and pipe penetrations all count.
- Sensitive areas. Places where a leak would shut down vital services or force an evacuation: schools, care homes, hospital wards and 24-hour control rooms are the examples given.
- Anticipated fibre levels. Spray coating removal, lagging removal and AIB removal with significant breakage sit at the higher end; small amounts of AIB debris and intact AIB removed without breakage sit lower.
The guidance also puts planning first. Where reasonably practicable, licensed work should be scheduled when occupied premises are empty, using weekends, holidays and planned closures, because removing people from the building reduces the consequences of a failure rather than just detecting it.
Recording the decision
This is the change most firms will feel. If you decide not to leak test, that decision must be recorded specifically in the plan of work for that job. A standard sentence pasted into every plan will not meet the requirement. Where testing goes ahead, the appendix refers to HSG248: daily short-term sampling soon after removal starts, with replicate samples pooled to at least 480 litres, then extended sampling each day. Any single result above 0.010 f/ml should stop work and trigger an investigation. It should be read alongside L143, HSG247 and HSG248.
Most contractor websites say nothing about how containment is checked.
A short, plain page explaining how you plan around occupancy, when you leak test and how the decision is recorded answers a facilities manager before they ask. Every Envirorank website includes method and sector pages written in exactly that way.
Why this matters to your website, not just your plan of work
Schools, NHS trusts, care home operators and housing providers are the buyers this guidance names. Their estates and procurement teams read industry guidance, and the better ones will start asking how a contractor decides on leak testing in occupied buildings. Most contractor websites cannot answer that, because they describe licensed removal in one paragraph.
A contractor whose site explains, in plain English, how it plans work around occupancy, when it always leak tests and how it records the decision is easier to shortlist. It is also exactly the kind of specific, verifiable content AI assistants quote when someone asks how to choose a contractor for work in a school. We explain why in how AI search chooses asbestos companies, and what buyers check first in what buyers check before shortlisting.
What to add, in practice
- A section on your licensed removal page headed "How we protect occupied buildings", covering scheduling around occupancy, enclosure checks and leak testing.
- Sector pages for schools, healthcare and care settings that reference the guidance and your approach. See winning frameworks for why sector pages matter.
- One case study from an occupied building, describing the containment approach and the clearance outcome.
- Your licence and memberships in text, linked to the registers, as set out in how to show your credentials online.
New guidance raises the bar your website has to clear.
Every time the industry tightens how licensed work is planned and recorded, the gap widens between contractors who can explain their approach and those who cannot. Estates teams in schools, hospitals and care homes now have a specific question to ask about containment in occupied buildings, and many of them will put it to ChatGPT or Google AI before they put it to you.
Those tools answer from what is written on contractor websites. A site with a clear page on how you protect occupied buildings, sector case studies and credentials in text gets quoted. A five-page brochure site with a logo in the footer does not. That is why a new website built around how asbestos work is bought, and monthly AI visibility work to keep it current, matter more now than they did a year ago. We explain the mechanism in how AI search chooses asbestos companies.
Sources: ARCA News, Issue 133, Autumn 2026; Control of Asbestos Regulations 2012; L143; HSG247; HSG248. Read the appendix itself when it is published on the CONIAC website.
Questions this raises
When should an asbestos enclosure be leak tested?
Always at the discharge point where a negative pressure unit vents inside the building. Otherwise it is a risk-based decision covering occupied areas, the vicinity of the enclosure, sensitive areas such as schools and hospitals, and the fibre levels the work is likely to produce.
Do I have to record a decision not to leak test?
Yes. The new appendix requires the decision to be recorded specifically in the plan of work for that job. Generic wording repeated on every plan is not sufficient.
What result should stop work during leak testing?
Following HSG248, any single result above 0.010 f/ml should stop work and trigger an investigation.
Show schools and hospitals exactly how you protect their buildings.
Run the free check. It shows whether your website gives buyers the method, sector and credential detail they look for, and our team reviews it within one working day.
