2013-01-17 10:29:32
In February 2009, the Agency published a collective expert report and issued an opinion relating to short fibers (fiber length < 5µm, diameter < 3µm and L/D ratio ≥ 3) and fine fibers (FFA: fiber of length ≥ 5µm, diameter < 0.2 µm and L/D ratio ≥ 3) of asbestos.
Concerning the professional environment, the recommendations of this report mainly indicate the need to take into account fine asbestos fibers whose carcinogenicity has been confirmed in the expertise and for this to replace the method of counting fibers by optical contrast microscopy phase by analytical transmission electron microscopy (META).
The Agency, in its opinion, also recommended a reassessment of collective and individual protective equipment in order to assess their effectiveness with respect to these two types of fibers.
Following this work, the Agency was contacted by the Ministry of Labor in March 2009 to assess the effectiveness of collective protection means and individual protective equipment with respect to worker exposure. short fibers and fine asbestos fibers. This involved carrying out three different types of work:
- and inventory of existing means of collective protection and individual protective equipment in the workplace to protect yourself from asbestos;
- a evaluation of their effectiveness with regard to the different asbestos fibers (FFA, FCA) by indicating their possible limits;
- a definition of suitable types of personal protective equipment in function :
- the duration of the activities and the wearing of this equipment;
- dust levels encountered;
- techniques used;
- the nature of the operations;
- new exposure limit values to be respected;
- protective factors of PPE.
To the extent that the standardized tests making it possible to evaluate the performance of personal protective equipment on the market are carried out with sodium chloride aerosols whose size is representative of the size of the most penetrating particles (known in English as MPPS: most penetrating particle size), it was considered essential, prior to any evaluation work, to determine whether the asbestos fibers (all fibers combined: FFA, FCA and OMS- fiber of length ≥ 5µm, diameter between 0, 2 and 3 µm and L/D ratio ≥ 3 (Afsset, 2009)) could be compared to these sodium chloride aerosols, with regard to their filtration behavior.
On the other hand, the problem of the effectiveness of PPE with regard to asbestos had to be better understood by identifying the different factors that could influence their effectiveness.
Method of working
It was therefore proposed to carry out a technical inventory of the knowledge and obligations relating to collective and individual protective equipment. This work includes:
- the inventory of regulatory requirements in terms of collective and individual protection with regard to asbestos;
- the census of requirements standards relating to this protective equipment against asbestos;
- and inventory of collective protective equipment and usable personal protective equipment in the workplace in the asbestos field;
- a bibliographic summary on the effectiveness of protective equipment (collective and individual) regarding asbestos in order to identify:
- the parameters having a preponderant role in the effectiveness of personal protective equipment (inward leak, filter penetration, etc.);
- the different factors that can influence the effectiveness of collective protective equipment (CPE) and personal protective equipment (PPE);
- studies carried out to specifically evaluate the effectiveness of PPE against asbestos (normative tests and field tests); publications dealing with the relevance of the assimilation of asbestos fibers to MPPS particles, that is to say dealing with the comparison of the levels of protective effectiveness determined with asbestos fibers in relation to the levels of protection obtained with an aerosol of MPPS particles.
Results
This report, which lists the regulatory requirements relating to asbestos in terms of collective protection means and personal protective equipment in the workplace as well as the standards of requirements relating to all of these protective devices, allowed us to highlight the following points:
- there is currently a distinction between regulations regarding the removal of friable asbestos-containing materials and the removal of non-friable asbestos-containing materials, particularly with regard to the measures to be implemented (in terms of containment and means of protection). The question of the relevance of this distinction deserves to be asked at the end of this report but requires, in order to be able to answer it, to have exposure levels during work involving exposure to these two types of asbestos;
- there are differences in the methods used in tests to assess filter penetration : on the one hand for very high efficiency particle filters used in ventilation systems and on the other hand for the filters of respiratory protection devices. The question of the application of the approach, which consists of first finding the particle size for which penetration is maximum before carrying out the penetration evaluation tests, deserves to be examined in the context of the penetration tests. certification of respiratory protection devices;
- the normative certification tests for the marketing of respiratory protection devices use a sodium chloride aerosol and use flame photometry as an analytical measurement technique. This technique, which consists of measuring the weight concentration of particles, therefore underestimates the contribution of the finest particles when evaluating the penetration of filters used on respiratory protection devices. So for asbestos fiberswhose pathogenicity is linked to the number of fibers rather than the mass of inhaled fibers, it might be more appropriate to adopt an approach to determining the number of particles rather than the mass.
Concerning the relevance of deducing the protective effectiveness in real conditions of use from those established by the normative tests, it follows that even if the normative tests take into consideration the preponderant factors in the protective effectiveness collective protective equipment and respiratory protection devices, some authors recommend that filter penetration tests be carried out at higher ventilatory flow rates, making it possible to better simulate the respiratory flow rate during an intense workload.
It should also be remembered that the penetration of the filter is one component among the possible sources of leakage towards the interior of respiratory protection devices and that it contributes very little to the total leakage towards the interior (the main leak being the leak to the face). Thus, even if the performance of the filters improves, the fact remains that the problem of sealing the face remains and that this phenomenon is still little studied in real situations (several authors endeavor to study induced leaks (piercing of the face piece, defective valve, etc.) but do not focus on studying the characteristics of the leak to the face. The level of protection offered by a respiratory protective device requiring adjustment to the face (mask , ½ mask, etc.) could be improved by verifying this adjustment by measuring the adjustment factor. Numerous studies highlight the improvement brought about by this prior verification and by the implementation of a respiratory protection program such as as described by standard NF EN 529.
Thus, all studies aimed at determining the effectiveness of protection in real use situations (exposure to asbestos or other particles) highlight the fact that the level of protection offered by the respiratory protection device is lower than the level determined by normative tests. The nominal protection factors, deduced from normative tests, are therefore not representative of the level of protection offered by the respiratory protection device in a real situation.
Regarding the verification of the effectiveness of collective protective equipment and individual protective equipment with respect to fine and short asbestos fibers, it seems that the protective effectiveness of respiratory protection devices depends of the particle size of the aerosol, rather than the fibrous form of the aerosol. It is therefore a question of assessing the relevance of reassessing the protection factors of respiratory protection devices against an aerosol of particles with a particle size similar to that of fine and short asbestos fibers.
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