When asked to describe the main hazards to health associated with woodworking, most people would discuss machinery. This is logical enough as machines are responsible for a significant number of accidents each year. Such incidents are typically very graphic and there is an obvious cause and effect link between the machine and the resultant damage.

Wood dust is often overlooked in such discussions. This may be because it is viewed as a largely unavoidable natural substance. Also many within the industry have been exposed to wood dust for many years and do not appear to be any worse for it.

Such views are unfortunate. Wood dust can cause a number of significant long term health problems as well as contributing to more immediate incidents. Work by the Health and Safety Executive shows that the majority of woodworking companies are failing to comply with their legal requirements in respect of the substance.

As well as risking prosecution, such companies are vulnerable to the increasing number of compensation claims, both genuine and dubious. The vast majority of companies would not be able to defend themselves in such cases as they could not provide documented evidence that they have assessed and managed the risks as far as practicable. This is often the case in respect of past employees, for example someone employed 15 years ago who claims to have only recently suffered the consequence.

Therefore, all companies involved with timber should be aware of: wood dust hazards; relevant legislation; and appropriate control measures.

Two types of wood dust

Wood dust is often divided into two types; total inhalable and respirable. The former includes all particles which can be inhaled, typically up to 100 microns in diameter which is equivalent to the size of a grain of salt. Respirable dust only includes the finer particles of <10 microns (equivalent to a grain of flour) which can penetrate down the airways. The finer the dust, the further into the lungs it can penetrate and hence the concern with MDF and the fine dust generated from its use.

There are a number of associated health issues:

  • Asthma: around 150,000 people suffer from occupational asthma and wood dust is the fourth largest cause.

  • Carcinogenic effect: hardwood dust is a carcinogen linked to nasal cancer

  • Fire: wood dust is explosive when mobilised in the correct concentration and it will provide fuel to a fire.

  • Slipping hazard: fine dust on smooth floors can lead to a slippery surface.

  • MDF: a hazard assessment document was prepared by HSE. This found that MDF was composed primarily of softwood (85 to 100%) with up to 15% hardwood. Machining leads to an atmosphere containing wood dust, free formaldehyde, resin binder and dust particles onto which formaldehyde is adsorbed. A greater amount of fine dust is given off when working MDF, but the study found no evidence for MDF dust to be treated differently from softwood and hardwood dusts.

COSHH regulations

As a result of these problems, wood dust is classed as a hazardous substance and is controlled under the Control of Substances Hazardous to Health Regulations 2002 (COSHH). These require companies to reduce the level of personal exposure as far as possible. A written risk assessment is required by companies which handle hazardous substances to show that they have identified: the nature of the substance; route of exposure; amount of exposure; the suitability of existing control measures; and remedial actions.

A maximum exposure limit of 5 mg/m3 (MEL) applies to both softwood and hardwood dust. This is the level which cannot be exceeded and which companies must keep as far below as possible.

Work by the HSE shows that many companies fail to meet these requirements. A survey in 1999 produced 386 samples from 47 companies. Of these readings 27.2% were above the MEL, only 34% of sites had a written COSHH risk assessment and only 21% had conducted a local exhaust ventilation test in the past 14 months. In just 34% of companies were all readings below the MEL.

In order to reduce the level of exposure, COSHH promotes a hierarchy of control measures. It is always preferable to eliminate the hazard at source. Therefore, consideration should be given to the potential to remove unnecessary woodworking tasks or to automate them. This is often impractical, so control might be achieved through enclosure, for example machines such as four-cutters can be enclosed to control dust and concentrate the local exhaust ventilation (LEV).

The use of extraction in the form of LEV remains the principal method of ensuring that dust is removed from the working area before it reaches workers. Such systems need regular servicing and maintenance to remain effective, hence the requirement for LEV systems to be tested at least every 14 months.

Additional controls include the use of a safe system of work, for example ensuring that good housekeeping techniques are employed such as regular vacuuming of the working area. HSE is keen to see the removal of brushes and air hoses as these can remove dust from one surface and spread it into the air.

Finally, personal protective equipment (PPE) is a last resort which would be used if the above measures had failed to reduce exposure below 5 mg/m3. However, it only protects the wearer and is never very comfortable so operators will often “forget” to wear it.

It is worth stressing the importance of local exhaust ventilation systems. A capture velocity (speed of air required to pull the dust into the extraction pipe) of 5 to 10 m/s is recommended to ensure the removal of wood dust at its point of production and a transport velocity (speed through the extraction pipe) of at least 15 to 20 m/s. However, the amount of pull from a pipe decreases dramatically just a short distance away. One diameter from the end of a pipe, the airflow will fall to just 7.5% of that within the pipe.

Proper design

Thus, if we have a 20cm wide extraction pipe running to a machine with an airflow of 10 m/s, then 20 cm from the end of this pipe, the pull will have fallen to just 0.75 m/s – well short of the required 5 to 10 m/s. Hence the need for a properly designed capture hood to concentrate the extraction where it is required. For example, an open ended pipe may require a 60% greater airflow to achieve the same pull of contaminants as a well enclosed capture hood.

The requirement for a well designed capture hood is made more necessary by the fact that dust and chips from woodworking machines will invariably have their own momentum resulting from the machine which generated them. This energy should be used to direct the contaminants towards the extraction.

Although the majority of companies struggle to meet the existing UK MEL of 5 mg/m3, a provisional position of the Scientific Committee on Occupational Exposure Limits of the European Union has been published with a suggestion that the limit might need to be tightened to 0.5 mg/m3. At present, there is no formal move by Europe to change wood dust limits but woodworking companies should be aware that if the limits do change, they will only be moving in one direction.