The asbestos clearance level used across Canada is 0.01 fibres per cubic centimetre (f/cc) of air or less, measured inside the enclosure after the work area has been cleaned and has dried. In Ontario, where Ottawa homeowners work, that figure appears in O. Reg. 278/05, and the barriers cannot come down until every required sample passes. We handle abatement, air testing and the paperwork in Ottawa, so here is what the number means and how to read the result you are handed.
TL;DR
- The clearance level is 0.01 f/cc or less of airborne asbestos fibres inside the enclosure, tested after cleaning and drying.
- Clearance has two parts: a visual inspection for dust and debris, then air sampling. Both must pass before the enclosure is dismantled.
- Air clearance is different from the 0.1 f/cc occupational exposure limit for workers. It is a much lower, re-entry standard.
- A failed test means re-cleaning, re-inspecting, drying and retesting. The containment stays up until the area passes.
- Keep the written results. They are the record that the space was safe to reoccupy.
Table of Contents
- What a clearance level actually measures
- Clearance level vs exposure limit: two different numbers
- The two parts of clearance: visual first, then air
- PCM and TEM: how the lab counts fibres
- How many samples, and who takes them
- The “3-5-7 rule” is about something else
- When clearance testing applies to your project
- What happens if the area fails
- Reading your clearance results and paperwork
- Our view on clearance
- Planning clearance into an Ottawa project
- FAQ
- Sources
What a clearance level actually measures
A clearance level is the pass mark for the air inside a sealed work area once asbestos removal is finished. The federal guideline describes clearance air sampling as sampling to decide whether the concentration of airborne asbestos fibres inside an enclosure is below the limit set in the regulations, so that the enclosure can come down.
The same guideline treats 0.01 fibres/cm³ or less as a successful clearance. Fibres per cubic centimetre is simply a count of fibres in a defined volume of air. A lower number means cleaner air.
Two points help homeowners:
- The number applies to the inside of the enclosure, not to your whole house. The enclosure is the plastic-sheeted, sealed area the abatement crew builds around the work.
- The sample is taken under deliberately harsh conditions. The regulation requires forced air, such as fans or blowers, to stir up and keep any settled fibres airborne during sampling. A pass is therefore a tougher test than ordinary room air.
Clearance level vs exposure limit: two different numbers
People often mix up the 0.01 f/cc clearance level and the occupational exposure limit. They answer different questions.
The occupational exposure limit is the airborne concentration a worker may be exposed to during work. Under federal rules, the limit for chrysotile asbestos is 0.1 f/cc, reduced from 1 f/cc. It governs daily monitoring while work is under way, and the guideline allows 50% of the limit to serve as an action level that triggers extra controls.
The clearance level is ten times lower. It decides whether the space is clean enough to be opened up and reoccupied. During work, workers wear respirators and the area is sealed. At clearance, the barriers come down and people, including you, walk in without protection.
| Exposure limit | Clearance level | |
|---|---|---|
| What it answers | Is the work air within the worker limit? | Is the finished area clean enough to open? |
| Figure (federal rules) | 0.1 f/cc | 0.01 f/cc or less |
| When it applies | During the work | After cleaning and drying, before dismantling |
| Who is protected | Workers | Occupants and anyone entering afterward |
The two parts of clearance: visual first, then air
Ontario’s regulation sets out clearance as a sequence. According to O. Reg. 278/05, after the work is complete:
- Negative air pressure is maintained in the enclosure, so air flows in rather than leaking out.
- The enclosure and work area are cleaned by thorough washing or HEPA vacuuming. A HEPA vacuum is one with a filter built to trap very fine particles.
- Equipment is cleaned.
- A competent worker carries out a visual inspection.
- The area is allowed to dry.
- Clearance air testing is done.
The barriers and the decontamination facility cannot be removed until cleaning is done and the air test is passed. The regulation makes an exception for buildings to be demolished that no one will enter.
What visual clearance involves
Visual clearance is an inspection by a competent worker to confirm the enclosure and work area are free of visible dust, debris or residue that may contain asbestos. The Construction Safety Association of Ontario’s DS037 guide adds that it follows ASTM E1368 procedures, and any residue found is cleaned by wet wiping or HEPA vacuuming before lockdown and air sampling.
A visual check confirms that bulk material is gone. It cannot tell you about fibres too small to see, which is why it is never the whole story.
What air clearance involves
Air clearance measures the fibres themselves. It happens only after surfaces are completely dry, and forced air is used immediately before and during sampling. Each sample draws air through a filter that a lab then analyses. The two main analysis methods are covered below.
The short answer to the “visual vs air” question: visual clearance checks for what you can see, air clearance checks for what you cannot, and a Type 3 job needs both.
PCM and TEM: how the lab counts fibres
The 0.01 f/cc figure can be reached by two analysis methods, and the difference matters if you are reading a lab report.
PCM (phase contrast microscopy) is the standard method. Ontario’s regulation requires that PCM clearance follow NIOSH Method 7400, with at least 2,400 litres of air drawn per filter. The area passes only if every sample is at or below 0.01 f/cc. A PCM count has a limitation, explained in an OSSTF hazard alert: it counts fibres longer than 5 microns and cannot tell asbestos from other fibres, such as those from insulation or clothing.
TEM (transmission electron microscopy) looks at much higher magnification. The same bulletin explains that TEM can see thinner fibres and identify asbestos chemically, which suits building interiors where asbestos is often only a small share of the fibres in the air.
Ontario sets two linked rules:
- If a PCM sample fails, the cleaning and inspection steps are repeated and the area dries before retesting. Alternatively, the samples may be re-analysed by TEM, which must also show 0.01 f/cc or less of asbestos fibres.
- A full TEM clearance procedure under the regulation takes at least five samples inside the enclosure and five outside it but inside the building, taken at the same time. The area passes if the inside average is statistically less than, or not statistically different from, the outside average.
For a deeper look at how fibre-counting methods compare, a guide on indoor mold testing and mitigation shows how air sampling and lab analysis work in a related setting. For asbestos, the lab method is stated in your report. It should name NIOSH 7400 for PCM or 7402 for TEM.
How many samples, and who takes them
Sample counts depend on the rule that applies to your building. The federal Canada Occupational Health and Safety Regulations require a qualified person to take samples. For enclosures of 10 m² or less, the federal guideline calls for 2 samples; for 10 to 500 m², 3; and for more than 500 m², 5. Results must be posted within 24 hours. Public Services and Procurement Canada’s Standard on Asbestos Management, effective April 1, 2024, uses the same 2, 3 and 5 pattern and the same final criterion of less than 0.01 fibres/cm³. Those rules cover federal workplaces and properties.
For a private home or commercial building in Ottawa, provincial rules under O. Reg. 278/05 apply: the 0.01 f/cc limit, the PCM or TEM procedures above, and posting of results. Ottawa owners should not borrow numbers from another province. For comparison:
- New Brunswick’s Code of Practice uses 0.01 fibre/cm³ and at least two clearance samples in work areas up to 115 m².
- The Northwest Territories makes clearance sampling compulsory for Class 3 projects where the site will be reoccupied, also at 0.01 fibre/cm³.
The pattern is consistent across jurisdictions: 0.01 is the number. What varies is the sample count, the method and the exceptions.
The “3-5-7 rule” is about something else
The “3-5-7” question usually refers to bulk sampling, not clearance. Bulk sampling means taking pieces of suspect material to find out whether it contains asbestos before work starts. New Brunswick’s code, for example, sets graduated minimums: at least 1 sample for areas up to 100 sq ft, 3 for 101 to 1,000 sq ft, 5 for 1,001 to 5,000 sq ft, and 7 above that. It has nothing to do with the air pass mark at the end of a job. If you are still at the stage of finding out what is in your walls, see our guide on testing before you tear out.
When clearance testing applies to your project
Ontario classifies asbestos work as Type 1, Type 2 or Type 3, with Type 3 being the highest-risk category. Clearance air testing is the requirement for Type 3 work. The CSAO guide notes exceptions: non-friable material removed without power tools, outdoor work and buildings being demolished.
For a homeowner this means:
- Small Type 1 or 2 jobs: generally lower-disturbance work. Ask what documentation you will receive at the end.
- Vermiculite attic removal and whole-home or Type 3 work: expect enclosure, negative air, and full visual and air clearance before the space is reopened.
- Renovation or demolition behind the abatement: carpenters and demolition crews should not enter until the clearance passes.
The reason for the order is practical. Re-occupancy is the moment when a clean-looking but uncleared space could expose people who were never protected. A RenoHouse guide makes the same argument for Ontario Type 3 work.
If you think material has already been disturbed in your home, read our first-hour steps for disturbed asbestos before anything else.
What happens if the area fails
A failed result is not a disaster. It is the system working. Under Ontario’s rules the sequence is:
- Keep the barriers, decontamination facility and negative air units running.
- Repeat cleaning, decontamination, visual inspection and lockdown, as the CSAO guide describes.
- Let the area dry.
- Retest, or have the failed PCM samples re-analysed by TEM.
The usual causes are dust left in corners, ledges and ductwork, or samples taken before surfaces were fully dry. Allowing time for the retest in your schedule is sensible: that is why you should not book flooring, drywall or painting crews for the day after teardown.
Reading your clearance results and paperwork
Ontario requires the owner and employer to post clearance results within 24 hours in a conspicuous place at the workplace. The building owner must keep a copy for at least one year. A residential owner should treat the results as a permanent record, because a buyer, insurer or later contractor may ask for them.
When you get your results, check for:
- The address and the area covered by the enclosure.
- The sampling date and who took the samples.
- The method: NIOSH 7400 for PCM, or TEM.
- Each sample result against the 0.01 f/cc limit, and the number of samples.
- A statement of pass or fail for the area.
We explain the certificate itself in our guide to the asbestos clearance certificate at 0.01 f/cc, and the monitoring side in Canadian air monitoring rules. Commercial owners should see our list of records to demand before abatement and the guide on occupancy after commercial abatement.
Our view on clearance
Most homeowners meet the word clearance for the first time on the last day of a job, when they want their house back. That is the worst moment to learn what it means.
We treat clearance as part of the project from the first estimate, not a formality at the end. Our free estimate lays out the work in a line-by-line quote, so you see what is included before you sign. Our team has more than 25 years of local experience, and abatement, demolition and renovation sit under one roof. That means the crew that opens the walls and the crew that rebuilds them follow the same sequence, and nobody starts finishing work in a space that has not passed.
Our advice is simple. Do not accept a visual look-over as the end of a Type 3 job. Ask for the numbers, the method and the sample count in writing, and keep them with your house records.
Jason
Planning clearance into an Ottawa project
We carry out licensed and insured abatement of asbestos, mould and lead in Ottawa and the surrounding area, including air quality testing, permit management, debris hauling and post-job documentation. The published ranges on our abatement page are:
- Small Type 1 or 2 jobs: 1500-3500 CAD
- Vermiculite attic removal: 5000-15000 CAD
- Testing and lab analysis: 300-600 CAD
- Whole-home or Type 3 work: priced after assessment
If you want a quote with the testing and documentation included, request a free estimate. We aim to respond within 24 hours.
If demolition or a renovation follows the abatement, our renovation services pick up once the area is cleared.
FAQ
What is the clearance level for asbestos in Canada?
The level is 0.01 fibres per cubic centimetre or less, measured inside the enclosure after cleaning and drying. Ontario’s O. Reg. 278/05 uses it, as do the federal standards and several other provinces and territories. In Ontario’s PCM procedure, every sample must be at or below that figure.
Is visual clearance enough?
No, not for work that requires clearance air testing. A visual inspection confirms there is no visible dust, debris or residue, but it cannot detect fine airborne fibres. Under Ontario’s regulation, both the visual inspection and the air test are needed before the enclosure comes down.
How long after abatement can I go back in?
Only after the area has been cleaned, inspected, dried and has passed the air test. There is no fixed number of days, because a failed test means re-cleaning and retesting. Ask your contractor for the written results before moving belongings or starting other trades.
What is the difference between the 0.1 and 0.01 f/cc figures?
The 0.1 f/cc figure is the federal occupational exposure limit for chrysotile asbestos, which governs worker exposure during work. The 0.01 f/cc figure is the clearance level, used to decide whether a finished enclosure can be opened. Clearance is the stricter of the two.
Sources
- Technical guideline to asbestos exposure management, Employment and Social Development Canada
- Standard on Asbestos Management, Public Services and Procurement Canada
- O. Reg. 278/05, Designated Substance: Asbestos on Construction Projects and in Buildings and Repair Operations
- Asbestos Clearance Testing, Type Three Abatement: Hazard Alert, OSSTF
- DS037: Asbestos Controls for Construction, Renovation, and Demolition, CSAO
- A Code of Practice for Working with Materials Containing Asbestos in New Brunswick, WorkSafeNB
- Asbestos Removal and Disposal Guidelines, Government of the Northwest Territories
- Air Monitoring and Clearance Asbestos Toronto: 2026 Guide