There are many common industrial processes which cause workers to be exposed to a wide range of toxic and harmful dusts. Although official statistics are hard to come by, John Cherrie of the Institute of Occupational Medicine has estimated that in Great Britain almost 10 million workers are exposed to dust at work.
Handling of powders usually results in significant release of airborne dust, whether this involves the manual emptying of sacks, manual scooping of powders or mechanical transfer of powders and / or into open containers.
Any tasks or processes that involve cutting or abrasion of solid materials will generate dust that will become airborne.
Most of these processes are energetic which means that the dust created will form a cloud that can extend over a significant distance.
Handling friable materials (i.e. substances that break up easily) can result in the formation of a dust cloud that can lead to significant exposure.
Common friable materials include :
- Glass and rock wool
- Refractory ceramic fibre
- Cotton, flax and other vegetable fibres
Disturbing dust settled on surfaces will normally result in at least some of it becoming airborne. Using compressed air and sweeping are particularly likely to lead to significant exposures and should be avoided .
Sometimes the problem is obvious, and the sensible thing to do is to introduce controls. But in many cases an accurate assessment requires measurement of exposure. In these cases it’s important to have a “benchmark” against which the results can be compared, otherwise they’re meaningless. In Britain we have Workplace Exposure Limits – these are legal standards and where one has been set for a substance exposure must not exceed the limit. With carcinogens, mutagens and substances that can cause allergic asthma, the requirement is tighter – exposure must be reduced as far as practicable below the limit.
Although a significant number of toxic dusts have been assigned Workplace Exposure Limits many of the dusts which can cause chronic obstructive pulmonary disease or other non-malignant respiratory disease have historically been viewed as ‘low-toxicity dusts’ and haven’t been assigned limits. In Britain, the guidelines for action to reduce airborne exposure to these dusts (10 mg/m3 for inhalable dust and 4 mg/m3 for respirable dust) are now known to be insufficiently protective. The need for a new exposure limit of 1 mg/m3 of respirable dust has been suggested by some authors and limits for dust exposure are currently under review in the EU.
The Institute of Occupational Medicine, for example, has recommended that “until safe limits are put in place, employers should aim to keep exposure to respirable dust below 1 mg/m3 and inhalable dust below 5 mg/m³”. The TUC has advised health and safety representatives that they “should try to ensure that employers follow a precautionary standard of 2.5 mg/m³ for inhalable dust … and 1 mg/m³ for respirable dust.” In Germany, the MAK commission has adopted a limit equivalent to 0.3A mg/m3 respirable, where A is the density of the substance in g/cm3. This is equivalent, for example, to 0.8 mg/m³ for many silicate minerals or 1.2 mg/m³ for titanium dioxide. All three bodies therefore regard 1 mg/m³ respirable as a more appropriate guideline than the 4 mg/m3 COSHH trigger.
A commentary in a recent edition of the Annals of Occupational Hygiene discusses the background in more detail.
It’s a controversial issue, but my personal view is that working to 10 mg/m3 and 4 mg/m3 trigger values doesn’t provide adequate protection. Some employers might be concerned that working to lower levels would be costly, but in my experience it’s possible in most cases to reduce exposures to well below the widely used “triggers” by employing standard good practice approaches.