The Propobois approach constitutes a new approach to the assessment of wood dust exposure and proposes a decision matrix classifying processes according to their emissivity. The real-time metrology used for this work is proving to be very interesting for a simple and rapid assessment of exposure levels.
The means of reducing the risk associated with wood dust are still the subject of many questions on the regulatory, technical and economic levels. A new evaluation method, based on real-time metrology, tested and validated within the framework of the Démarche de Progrès pour la réduction de l’exposition aux poussières de bois (Propobois) study, offers promising solutions for companies.
Approximately 370,000 employees affected
Exposure to wood dust concerns approximately 370,000 employees¹ , half of whom work in the construction sector, and is still difficult for the companies concerned to understand.
In addition to collection at source and extraction and suction systems, the implementation of effective collective prevention is also based upstream on a risk assessment, the key issue of which is compliance with the occupational exposure limit value (OEL) for wood dust, set in France at 1 mg/m3 over eight hours.
Compliance with the OEL is checked in accordance with the “metrology” order of 15 December 2009, after determining homogeneous exposure groups (GEH). These GEHs correspond to a group of operators performing the same tasks, on similar machines or under similar conditions, representative of an identical level of exposure. The heterogeneity of exposure situations in woodworking workshops does not facilitate the constitution of these HWGs. This difficulty leads, in the current control system, to a very high cost of measurements to be carried out, which is difficult to afford for small structures.
Following this observation, a series of studies (Tempobois 1 & 2, Mesorem), piloted by the Forest, Cellulose, Wood-Construction, Furniture Technological Institute (FCBA) and financed by the Professional Committee for the Development of the French Furniture and Wood Industries (Codifab), highlighted the difficulties encountered by companies in meeting their obligations. The studies also exposed the limits of the “conventional” measurement based on the gravimetric method (weighing). This method provides a diagnosis of whether or not the VLEP is exceeded over eight hours of activity, without however providing information on the exposing task(s), which would nevertheless make it possible to guide companies in a reasoned approach to reducing exposure.
Propobois: tools for self-assessment of exposure
Faced with these difficulties in implementing specific prevention measures to comply with the regulations, the professional organisations of the secondary wood processing industry have continued their efforts by launching the Propobois initiative. One of the components aims to develop and make available to companies tools for self-assessment of exposure to wood dust.
The Propobois study developed a methodology for characterising the emissivity of machines or workstations. It led to the development of 11 “Process” sheets, such as the one on the single-blade edger or the one on the radial saw. These sheets constitute a qualified professional knowledge base rich in operational data.
This study also made it possible to analyse the operational contexts of the exposure results recorded, and to facilitate the constitution of GEHs by the companies. Twenty-eight processes were identified and classified according to their emissivity; they constitute the “Propobois decision matrix“. Of the eleven processes characterised, nine were confirmed in their classification.
Further measurements will be necessary to characterise additional processes and validate their classification in the matrix. In addition, a practical guide, currently being drafted, will promote the elements of the study in the form of an operational self-diagnosis tool that can be used directly by companies.
Interest of the optical sensor
The study also allowed a better understanding of the operation of the optical sensor (direct reading device), for optimal use, and demonstrated the interest of its implementation for real time metrology.
At present, for metrological reasons, real-time measurement cannot replace the method used to carry out regulatory controls, even if it allows the analysis of exposure situations. Indeed, the optical sensor can give relative results: variation of the dust concentration, according to the place in the workshop and according to time. It is therefore a complementary tool to regulatory measurements, which can be used as a means of self-monitoring for a better understanding and faster identification of emission sources, which will then enable preventive solutions to be found that are adapted to the workstation. Real-time metrology therefore appears to be a suitable tool for the prevention of wood dust risk.
Simplification of the regulatory control system
The OPPBTP is in favour of simplifying the occupational exposure control system, with a view to improving the effectiveness of the regulations in the field.
Indeed, the use by companies of direct-reading devices, provided that they are easily accessible, offers many advantages in terms of cost, education, integration into processes, etc.
This self-monitoring allows companies to take back the prevention of risks linked to emissions and exposure to dust of all kinds. This re-appropriation is not possible when the company buys occasional measurements from an external laboratory, spaced out over time.
The work of the OPPBTP on wood dust, carried out with the FCBA technological institute and all the professional organisations of the secondary processing of wood, shows the technical feasibility of such a system.
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