Recommendation from the Scientific Committee on Occupational Exposure Limits: Risk assessment for Wood Dust

Woods are customarily divided into two types: hardwood and softwood. Softwoods are generally conifers (pine, fir, spruce, cedar, etc.) and hardwoods come from deciduous trees (oak, beech, ash, silver birch, etc.) and from certain tropical species (mahogany, teak, etc.). This distinction is purely botanical, softwoods corresponding to the gymnosperms and hardwoods to the angiosperms, and certain characteristics such as the density and hardness of the two types are largely superimposed (Fengel et al., 1989). Wood consists essentially of cellulose, hemicellulose and lignin. The compounds that can be extracted with solvents represent less than 1% of the wood’s mass and are mainly aliphatic substances (fatty acids and glycerides), terpenes and phenolic compounds. The biological and physical properties of softwood and hardwood dusts are largely the same (Fengel et al., 1989). Several studies have shown that most of wood dust’s mass consists of particles with aerodynamic diameters equal or greater than 10 μm (Chung et al., 2000, IARC., 1995, Pisaniello et al., 1991, Whitehead et al., 1981 b). The size of the particles constituting the wood dust depends on the type of operation carried out on the wood; sawing produces particles with larger volume than does sanding. On the other hand, the particle size does not seem to depend systematically on the type of wood. For a given process, several studies report very similar particle size distributions between pine and oak; others report that dust from hardwood is finer than dust from softwood (IARC, 1995). Depending on the treatments to which the wood has been subjected before machining, the dust can contain additives, preservatives or adhesives.