Trade Union Congress Representatives on ACTS
(Advisory Committee on Toxic Substances)
Proposed Interim Dust Standard
Scientific evidence considered by the UK Health and Safety Executive's (HSE) Advisory Committee on Toxic Substances (ACTS) suggests that the current UK limits for inhalable and respirable dust of 10 mg/m³ and 4 mg/m³ respectively , are not safe.x
In 2004 the HSE commissioned the Institute of Occupational Medicine (IOM) in
When assessing the effects of exposure to dust the most robust data is where there are actual measurements of lung function. The two measurements usually used are the volume of air exhaled in one second (called FEV1) and the total lung capacity (referred to as FVC). Smoking, obesity, exposure to dust, and diseases like asthma will all reduce FEV1. Our height and age also affects FEV1 and as we age the value falls; height increases it. So a reference height of 1.75 metres is commonly employed. At this height, a non-smoking man aged 60 will have an FEV1 of between 3,100 and 3,300 millilitres (ml) according to the American Thoracic Society.
Dust particles reach different parts of the lung according to their size. Inhalable particles only reach the nose and upper parts of the respiratory tract. Respirable particles on the other hand, are small enough to penetrate deep into the lungs.
According to the IOM, exposure of UK miners to 4 mg/m³ of respirable coal dust over a 40 year working life led, on average, to a reduction of FEV1 of 178 ml y. This was the effect on non-smokers and it may seem a small value as it represents only 6 % of the average FEV1 at age 60. However, this was the average reduction, with some registering a smaller effect and others a larger one. The data show that 37% of the miners would have a reduction of 627 ml, and in 17%, the reduction would be 993 ml, or almost a third of their lung function. This larger reduction, added to the effect of aging, will have a profound effect on a person's physical activity.
Comparing other dusts with coal dust the data showed the following reductions in FEV1 at exposures of 4 mg/m³ for 40 years :
Cumulative exposure to dust Equivalent loss of FEV1 ( ml/sec )
4 mg/m³ for 40 years for a man of 1.75 metres in height
Coal dust 178
Carbon black 386
These figures provide a guide to the likely effects of exposure to other dusts. The data for these other dusts is less robust that that for coal dust as far fewer workers have been monitored and far less dust measurements carried out. But it also needs to be pointed out that many of these studies are, what is called, cross sectional studies. This means that it is generally an assessment of those actively working with the dust. It is quite possible that those with the worst respiratory function had already left their industry because they were too ill to work in it. This would have the effect of underestimating the consequences of exposure to the dust.
The size of particles may also have profound effects on the lung. Carbon black, for example, has some tiny (nanometre) particles and this may mean that it is not truly representative of other dusts.
Coal dust is a mixture of coal dust, other dusts from the surrounding geological strata (usually clays) and quartz. However,
Symptoms of chronic bronchitis such as cough and phlegm usually arise from changes in the bronchial airways whereas changes to FEV1 are caused by changes in the smaller airways deep in the lung. Individuals may have changes in FEV1 but no symptoms and vice-versa. Bronchial symptoms may occur before lung function impairment. However, individuals with severe reductions in FEV1 are almost certain to have symptoms.
Given the large amount of data on coal dust it was possible to assess effects on lung function at exposures as low as 1 mg/m³ for 40 years and even at this value there were sizeable reductions in FEV1. Thus, if there is an exposure to coal dust that has no effect on lung function, it is below a concentration of 1 mg/m³.
The data from other dusts is clearly worrying. The four dusts which were compared with coal dust all showed more severe effects on the lung at the same exposure levels. It is highly likely that for these dusts there will also be a spectrum of effect with some men having lesser reductions in lung function and others much greater ones at the same exposures. HSE data suggests that at least 12 % of workers could develop significant reductions in FEV1, with profound results for their respiratory health.
This variation in response to dust has implication for the current
As an interim measure therefore, the TUC reps on ACTS are recommending to unions that they should follow a precautionary standard of 2.5 mg/m³ for inhalable dust (as opposed to the current 10 mg/m³ standard) and 1 mg/m³ for respirable dust (as opposed to the current 4 mg/m³ standard).
This measure should continue until such time as the
There are some specific dusts which have an HSE standard, or limit, above what we are recommending. In these circumstances we urge members to insist that employers use the limits we recommend. .
Similarly, the Control of Substances Hazardous to Health Regulations (COSHH Regs) reference to substantial quantities of any dust should be defined by the interim standard of 2.5mg/m³ for inhalable dusts and 1mg/m³ for respirable dust. (see Appendix 1 and Appendix 2)
In pressing for the better control of all dusts, trade unions should refer to any guidance on specific dusts, or specific to dust reduction in the sector where they are operating, or to the general dust guidance produced by the HSE, Guidance Note EH44, 3rd Edition, 1997, 'Dust: General principles of protection'.
x These measurements refer to the weight of dust in one cubic metre of air. The average worker inhales 10 cubic metres of air every 8 hours )
y To put this in context: on average, men lose between 25 and 30 ml in their FEV1 capacity every year from their mid 20s to age 70
The TUC representatives on ACTS are Alastair Hay, Bud Hudspith and Susan Murray
From HSE Guidance Note EH44, 1997 'Dust General Principles of Prevention'
'The COSHH Regulations apply to 'substances hazardous to health' and these include dusts of any kind, when present in a substantial concentration in air (COSHH regulation 2). The General COSHH ACOP6 states that a substantial concentration of dust should be taken as a concentration of 10 mg.m-3, 8-hour time weighted average (TWA), of total inhalable dust or 4 mg.m-3, 8-hour TWA, of respirable dust. This means that any dust will be subject to the COSHH Regulations if people are exposed to 8-hour TWA concentrations exceeding these values.'
From EH40/2005 'Workplace exposure limits' HSE
42 The COSHH definition of a substance hazardous to health includes dust of any kind when present at a concentration in air equal to or greater than 10 mg.m-3 8-hour TWA of inhalable dust or 4 mg.m-3 8-hour TWA of respirable dust. This means that any dust will be subject to COSHH if people are exposed above these levels. Advice on control is given in EH44 Dust: General principles of protection and in the great majority of workplaces reasonable control measures will normally keep exposure below these levels. However, some dusts have been assigned specific
43 Most industrial dusts contain particles of a wide range of sizes. The behaviour, deposition and fate of any particular particle after entry into the human respiratory system and the body response that it elicits, depend on the nature and size of the particle. HSE distinguishes two size fractions for limit-setting purposes termed 'inhalable' and 'respirable'.
44 Inhalable dust approximates to the fraction of airborne material that enters the nose and mouth during breathing and is therefore available for deposition in the respiratory tract. Respirable dust approximates to the fraction that penetrates to the gas exchange region of the lung. Fuller definitions and explanatory material are given in MDHS14/3 General methods for sampling and gravimetric analysis of respirable and inhalable dust.
45 Where dusts contain components that have their own assigned workplace exposure limits, all the relevant limits should be complied with.'
Issued: 1 September, 2011