Assigned protection factors of respiratory protective devices used on asbestos removal worksites

Outline of reasons and objectives
Following the expert appraisal work published in 2009 by the French Agency for Environmental and Occupational Health & Safety (Agence Francaise de Securite Sanitaire de l’Environnement et du Travail) on asbestos fibre toxicology and metrology, this study, which is part of the INRS “Amiante-META ” project, aimed to re-assess the assigned protection factors of the Respiratory Protective Devices (RPDs) that, in theory, offer the highest performance and that are used during the process of removing asbestos-containing materials, by using Transmission Electron Microscopy (TEM) analysis of the samples.

Approach
The first stage was, working in collaboration with the manufacturers, to develop a modified mask prototype integrating an asbestos fibre sampling system in compliance with Standard XP X 43-269 (2002) inside the RPD. The second stage was to have the modified RPDs certified in compliance with the PPE Directive. In parallel with this work, two modes of operation were developed for taking samples on asbestos removal worksites of levels 2 and 3. The protocols were then applied during nine campaigns conducted on six level-3 worksites and on three level-2 worksites. After analysing the samples collected by analytical TEM, statistical exploitation led to determining the assigned protection factors of the two types of RPD targeted: supplied-air devices, and powered air-purifying devices.

Main results
Firstly, the study monitored operatives wearing positive-pressure supplied-air devices and performing removal or maintenance tasks, during the following processes performed under level-3 conditions: removal of sprayed-on coatings by scraping; removal of ProgypsolR by chipping, very high pressure or tool-holder removal, removal of heat insulation by scraping, removal of InsonasticR by sand-blasting, and removal of CaourepR by chipping. Out of 132 dustiness measurements, 23% exceeded the maximum threshold of 25,000 fibres per litre.
Secondly, operatives equipped with powered air-purifying devices were monitored during processes of removing floor-tile or wall-tile adhesive by chipping or sanding, and during processes of dismantling asbestos-cement pipes. The measurements showed that the threshold value of 6 000 fibres per litre was exceeded very rarely, caused, in part, by poor control of the suction/negative pressure in the zone, and to poor control of the suction/extraction at the source.
The statistical exploitation of the counts gave two protection factor distributions whose 5th percentiles were respectively equal to 250 for the positive-pressure supplied-air RPDs and 100 for the powered air-purifying RPDs.
The data obtained on the INRS samplers in the zone showed that an observer a few metres away from the point of removal was much less exposed than the asbestos-removal operatives.

Discussion
Due to the levels of individual exposure obtained during the study, numerous recommendations for improving task organisation and collective protection have been made and distributed to the companies.
The new assigned protection factor values proposed are strongly related to the specificities of the asbestos removal worksites (other PPE, operative training, adjustment tests, and constraints related to postures, and to confinement). Furthermore, the results obtained for both types of device cannot be compared because they were assessed on types of worksite and under environmental conditions (humidity, general dustiness, etc.) that were very different.