Last reviewed 12 December 2012
Gordon Tranter considers the health effects on employees of dust in the workplace.
Airborne dusts and particles present a considerable risk to the health of employees and others in the workplace. The effects of toxic dusts, such as asbestos, wood dust and crystalline silica have been well publicised. Recent attention however, has been focused on general workplace dust, as this article will consider.
General workplace dust
General workplace dust is the dust defined in the Control of Substances Hazardous to Health Regulations 2002 (COSHH) (SI 2002 No. 2677) as a dust of any kind, except dust which is a substance which is classified under the Chemicals (Hazard Information and Packaging for Supply) Regulations 2009 as very toxic, toxic, harmful, corrosive or irritant; or has a Workplace Exposure Limit (WEL); or is a biological agent and is present at a concentration in air equal to or greater than:
10mg/m3, as a time-weighted average over an 8-hour period, of inhalable dust, or
4mg/m3, as a time-weighted average over an 8-hour period, of respirable dust.
If the concentration of dust in a workplace exceeds these figures, then the requirements of COSHH will apply, including the need to assess the risk to workers and to ensure exposure is prevented or adequately controlled.
These levels were taken from figures developed over 50 years ago by the American Conference of Government Industrial Hygienists (ACGIH), based on expert opinion, rather than any health-based criteria. It is important to recognise that these concentrations are not Occupational Exposure Limits (OELs) or WELs; rather they are the levels at which the COSHH Regulations come into effect.
What’s in a name?
General workplace dust as a name does not convey the nature of the dust. The range of names used illustrates the confusion about this material. The names used include “inert”, “biologically inert” and “low toxicity” dusts. The Working Group on Action to Control Chemicals (WATCH), a Government Scientific Advisory Committee, used the term “poorly soluble dusts of limited cytotoxicity” and the German Maximum Allowable Concentrations list the term “biodurable dust”.
General workplace dust has also been known as “nuisance dust”, but this term is used for the coarse fraction of airborne particulates that is visible dust and that creates annoyance and soiling. There are no standard definitions, or universal monitoring methods for nuisance dust, but it is now becoming accepted as dust above 10µm. Nuisance dust can be long-term such as the long-term soiling of paintwork, or short-term such as a short-lived dust cloud. Consequently, to avoid confusion, the term “nuisance dust” should not be used when considering occupational exposure.
Calls for a dramatic reduction
There have been calls for a dramatic reduction in the levels at which COSHH comes into effect by the TUC and the Institute of Occupational Medicine (IOM). The TUC claims that there is now clear scientific evidence which suggests that the current UK limits for inhalable and respirable dust should be much lower. This claim is based on a study that concludes that there is a wide range of research that shows that a considerable number of the cases of cancer and COPD caused by dusts are caused by exposure to “a range of so-called low toxicity dusts” that is below the official limit of 4mg/m3 for respirable dust. The TUC claims that the research shows that for some dusts, even a 1mg/m3 limit was not protective.
The IOM considers that the current British OELs for airborne dust are unsafe and employers should attempt to reduce exposures to help prevent further cases of respiratory disease amongst their workers. The IOM points out that the studies, most of which were carried out at the IOM, suggest that if there is a threshold for adverse effects, it may be lower than the current limit values. The IOM recommends that employers should aim to keep exposure to respirable inert dust below 1mg/m3 and inhalable inert dust below 5mg/m3.
The study of the health effects of exposure to non-toxic, low solubility dusts is complex. The dust particles can vary in size, surface area and density. Minerals such as coal, kaolin and talc can vary in composition from place to place.
The IOM carried out a study for the Health and Safety Executive (HSE) in 2006 to help it judge the adequacy of the current COSHH position on dusts that are otherwise not classified. This study considered investigations into exposure to five kinds of low solubility dusts: coal dust, talc, kaolin and PVC and the dust to which wool and textile workers are exposed. The study was confined to epidemiological data and aimed to summarise published and available information on the exposure–response relationships between cumulative dust exposure and lung function in coalminers and workers exposed to other poorly soluble dusts.
The study concluded that exposure to 4mg/m3 of poorly soluble respirable dust over a working lifetime would cause a loss in forced expired volume in 1 second (FEV1) of 178ml in the majority of individuals. Although this is a relatively small loss compared to the effect of ageing, a moderate proportion (approximately 12%) of workers would develop larger losses in FEV1 as a result of the dust exposure, which are losses of such a magnitude that they raise concern for respiratory health. However, it was not possible to identify a “threshold” level of exposure below which there would be no dust-induced decline in lung function.
After considering data on the consequences of exposure for respiratory function, WATCH who provides advice to the HSE, suggested that further research work was needed, and whilst recognising the variability in the data, noted that a significant effect on lung function with exposure to 4mg/m3 was apparent.
The HSE’s response
In 2011 the HSE Board considered the case for a change to the dust concentration levels outlined in COSHH or to establishment of a WEL via the EU process. The Board agreed that at this time, the HSE would not pursue any change to the dust concentration levels outlined in COSHH or to establishment of a WEL via the EU process, as such an approach would require a considerable amount of resource that the HSE would have to divert from other priority work. Furthermore, the HSE had already stated that only limited health benefit would accrue from reducing the exposure threshold. However, the Board did request that work in this area should be kept under review and noted that at that time, the German the Maximal Arbeisplatz-Konzentration Committee was proposing a new national scientific limit value on inert dusts.
Developments in Germany
Germany has its own workplace OEL system; based on maximum allowable concentrations (MAKs). In 1997 the German MAK-Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area established a "general threshold value" of 4mg/m3 for the inhalable fraction and 1.5mg/m3 for the respirable fraction of poorly soluble dusts. This was mainly based upon a re-analysis of data from the Deutsche Forschungsgemeinschaft (DFG) Chronic Bronchitis study (1965–1977), which indicated inhalation of inert dust is one of the important variables for the development of chronic bronchitis. In recent years several studies have shown tumorigenic responses of rats after exposure to poorly soluble low-toxicity particles. In 2011 the Commission set a new MAK value of 0.3mg/m3 for respirable biodurable dust and also classified such dust as Carcinogenicity Category 4. This German classification identifies cancer-causing materials that do not increase cancer risk in humans, provided the corresponding MAK value is not exceeded.
According to Health and Safety Executive: Annual Statistics Report: 2010/11, which was based on about 30,000 workers, these workers currently have breathing/lung problems caused or made worse by their work. Campaigners for a reduction in the COSHH thresholds have used these figures to back their case. However, these figures are likely to include health problems caused by vapours, fumes and toxic dusts, etc, while the effect of inert, non-toxic dusts is not clear.
The Hazards magazine points out that even if the COSHH threshold is reduced, it will be “equally important that any standards are adhered to, and that will become far more difficult as the HSE cut pro-active inspections and reduce access to guidance”.