Dust to Dust

Asbestos today, more than ever, raises concerns in the general population. Many public and residential buildings, especially those built before 1980, are often made out of construction materials containing asbestos. Over the years, these materials deteriorate or may be disturbed during ad hoc maintenance or renovation work. In these occasions, asbestos fibres become airborne and occupants can be exposed to asbestos dust.

In Quebec, a material or product is considered to contain asbestos when the level of asbestos it contains exceeds 0.1 fibres per cubic centimetre (0.1%). In such case, any work requiring that the asbestos containing material be disturbed or removed must be carried out in compliance with the Canada Centre for Occupational Health and Safety (CCOHS). Quebec has much the same threshold limit value for asbestos, which must be removed under the Regulation Respecting Occupational Health and Safety (RROHS) and section 3.23 of the Safety Code for the construction industry (Code).

The RROHS and the Code offer a good framework for asbestos containing material management. Procedures and guidelines are well known by specialized contractors and consultants. Standards were developed to assess air quality after asbestos removal work, and exposure values exist for workers likely to be exposed to asbestos dust during their work shift.

However, there are still today no acceptable exposure values for asbestos in ambient air of public or residential buildings. This situation creates a grey area that generates differences of opinion among specialized consultants when assessing asbestos-related risk is required.

Although it is generally accepted that corrective action must be carried out when asbestos fibre levels in ambient air exceed 0.01f/ml, asbestos-related risk assessment should also include a verification of asbestos-containing material condition and accessibility, sensitivity of individuals, incidence on the risk of cancer and the presence of asbestos in settled dust.

Addressing Asbestos containing settled dust

Asbestos is present in many construction materials used before 1980. Consequently, it’s not abnormal to find asbestos fibres in settled dust of buildings constructed prior to this time, especially if the building contains friable asbestos in bad condition.

Other sources can explain the presence of asbestos in ambient air and settled dust of a building. For example, even today, imported break pads of certain vehicles may contain asbestos, and mining activities in some regions can also account for residual levels of asbestos in ambient air and settled dust.

Some fibres are very thin and can be carried on long distances while airborne. It is then not surprising to occasionally detect asbestos fibres in ambient air or settled dust, even in buildings considered exempt of asbestos-containing materials.

When settled dust is disturbed, the asbestos fibres it contains will become airborne and represent a risk for the health of the building’s occupants.

In Quebec, the majority of consultants use the same method of detection for asbestos in settled dust and asbestos in bulk materials. A sample of dust is collected the same way a sample of a given construction material would.

The sample collected is then analyzed using Polarized Light Microscopy (PLM). If it contains more than 0.1% of asbestos, the consultant will likely recommend that settled dust be removed using procedures established by the Code.

If level of asbestos in the settled dust is detectable but lower than 0.1%, the consultant may recommend minimal risk procedures as a precautionary measure. If no asbestos is found, no specific recommendation is needed.

The Environmental Protection Agency (EPA) in the U.S. does not promote this approach for settled dust. The EPA believes that PLM does not have a sufficient resolution to detect very fine asbestos fibres likely to be present in settled dust.

The American approach rather rests on Transmission Electron Microscopy (TEM). The TEM has a much greater resolution, which allows the detection of very fine fibres not visible using PLM. The new edition of the analytical method for detection of asbestos fibres in settled dust and bulk material from the Institut de recherche Robert-Sauvé en santé et en sécurité du travail au Québec (IRSST) recognizes the use of TEM microscopy for the detection of fine fibres. However, it is mainly used to detect fine fibres in floor tiles and not usually in settled dust.

Analyzing settled dust samples from buildings in which there is asbestos-containing material, using TEM, will often reveal asbestos fibres. Overtime, the building’s asbestos containing materials may have been the object of renovation or maintenance work, generating dust. Analysis will likely detect the asbestos content of the dust, even at very low levels.

If we believe that even an infinitesimal quantity of asbestos poses health and safety risks, remediation procedures would be required in the majority of public and residential buildings in which there is asbestos-containing materials.

This is why the TEM analysis results are usually coupled with a predicted excess cancer risk evaluation. This reduces uncertainties related to asbestos in settled dust and allows regulatory agencies to take informed decisions regarding the actual risk.

Appropriate triggers?

If asbestos is detected in a material or a product in any given concentration, but the product or material is in good condition and not likely to emit airborne asbestos, it is not required to remove it.

However, when one plans on disturbing or removing a material or a product containing at least 0.1% of asbestos, or that such product or material is in bad condition and likely to release airborne asbestos, it is mandatory to repair it or manage it in compliance with the RROSH and the Code.

The ambiguity arises when asbestos is detected in a product or material in concentrations below 0.1% and that this product or material is likely to release airborne fibres as is often the case with settled dust. Is the risk acceptable when the asbestos level is lower than the 0.1% standard?

We believe it is not up to the consultant to decide whether the risk is acceptable or not. Their role is to document the risk and set the context.

However, given the absence of clear guidelines and specific standards, some consultants will not hesitate to consider that even the smallest quantity of asbestos in settled dust causes an unacceptable risk and will recommend the removal of all dust using extensive asbestos abatement procedures, no matter how small the quantities.

This usually translates in significant costs for precautionary measures, when a more moderate approach could have mitigated the risk and reduced the cost of the intervention.

At CEP Forensic Engineering, we believe that settled dust sampling is a good indicator of the building condition as to which regards asbestos related risk. However, we recommend that sampling method and interpretation of results be made with precaution and by appropriate professionals.

Michel Millmore, P.T. CEA, is a Professional Technologist in Quebec and has been practicing in Environmental Assessment and Remediation since 1993. He is listed on the List of Experts of the Ministry of Sustainable Development, Environment, Wildlife and Parks (MSDEWP) and is a member of CEP Forensic Engineering team since 2012. He can be reached at millmore@expcep.com.