Many workers are confronted daily with the risks of dust inhalation! This is also a topic discussed on the Arrive Alive website and various other information portals. How is this problem perceived and evaluated by our health and safety officers? The World Health Organization has provided some invaluable assistance:
If any dusty process is being carried out, an assessment should be made to establish if people are at risk from dust exposure. This requires looking systematically at the workplace to see whether there is a problem and in general terms what could be done to prevent risk. The assessment should determine which hazardous materials are in use, in what amounts, and how much dust of which fraction may become airborne and lead to exposure, among other factors.
Walk-through Surveys
An initial “walk-through” survey of the workplace should be conducted. The controls in use should be examined to determine their effectiveness, and the eventual need for other or additional controls should be considered.
Maintenance and cleaning procedures should be examined, to ensure that they are effective and do not give rise to excessive exposure. The position of workers and the organization of their tasks should be appraised in view of the location and nature of the dust sources. The level of training and information of the workforce should also be assessed. It should be ensured that management favours work practices which reduce or eliminate risks.
Advice from competent professionals, preferably occupational hygienists, should be sought; this is indispensable whenever dealing with complicated situations, or with hazardous substances.
The walk-through survey will not usually include detailed measurements, although direct-reading instruments may be used to gain a rough picture of the risks present. Obvious and avoidable risks can be dealt with immediately, and schemes exist for using the basic substance and using the information to decide what controls are appropriate.
Quantitive Evaluations
Quantitative evaluations of airborne dust may be performed for a number of reasons, for example: to assess workers’ exposure in relation to an adopted standard, to determine the need for control measures or to assess the effectiveness of control strategies.
The results of quantitative evaluations are usually compared with occupational exposure limits either of the country concerned, of an international agency or of some other authority. The evaluation strategy and methods should be those laid down by this authority.
The determination of the dust air concentrations to which workers are exposed involves air sampling and further analysis of the collected dust sample, chemically, gravimetrically or microscopically.
Sampling for Dust
Sampling for exposure assessment is usually carried out by means of a personal sampler, attached to the worker, which consists of a pump (air mover) and a sampling head located in the worker’s breathing zone. The sampling head consists of a filter holder, with a filter where the dust sample is collected, preceded by a pre-collector to separate the fraction of interest.
Sampling heads should be designed to collect either the inhalable or respirable fraction of the airborne dust. The worker’s average exposure during a shift or part of a shift, as laid down in the exposure limits, can then be estimated.
Other Measurements
Other measurements may be helpful to understand where dust is coming from, or at what moment(s) of the work cycle it is being emitted. These measurements may rely on fast-response direct-reading instruments, but simpler qualitative means such as forward light scattering (dust lamp) techniques to illuminate the dust, or smoke tubes to trace air movement, may be all that is needed.
Often, but not always, the workers involved may be able to say where and when the dust is emitted. There are systems that combine video imaging with dust concentration measurements, thus allowing the visualization of how exposure changes as workers perform their tasks. This is useful to evaluate the effectiveness of control systems and also to compare different controls (e.g. exhaust ventilation or wet methods).
If the situation is unsatisfactory, control strategies should be designed and implemented, as will be discussed in later chapters. Afterwards, the situation should be re-assessed, and a programme of periodic re-assessment should be planned and carried out.
It is important for the Health and Safety of Workers that the risks be clearly identified and that dust suppression techniques be used to illuminate or reduce these threats!
