Monitoring the dangers from dust

Are the levels of atmospheric dust in your workplace compliant with legal requirements?

by Martin Heels

Dust is produced as a result of many different industrial processes throughout the leather and footwear manufacturing supply chain. Cutting, scouring or mixing powdered raw materials can all produce dust, exposure to which can result in both short- and long-term health effects. In many countries, there are legal requirements for the maximum levels of dust in the workplace in order to maintain a safe working environment.

Once the exposure to dust has been quantified using atmospheric monitoring, changes to working procedures or control measures may need to be implemented in order to satisfy the legal requirements in that region or to show compliance with ethical auditing standards. These are established rules that can be set by retailers to ensure adherence to good labour practices throughout the supply chain. Working conditions and protecting workers’ health in the workplace are generally the main objectives for ethical compliance.

The dangers of dust

The possible health problems caused by dust can range from mild irritation of the skin, eyes or respiratory system to the aggravation of existing respiratory problems such as asthma, as well as an increased risk of developing chest diseases – or even cancer. The classic example of long-term consequence is the well-documented exposure to airborne particles of asbestos that can lead to asbestosis. In the footwear manufacturing supply chain, both rubber process dust (dust arising in the stages of rubber manufacture) and leather dust are classified as suspected carcinogens.

The accumulation of certain types of dust can also result in an increased risk of fire or explosion.

Identifying dust hazards

A simple visual inspection of work areas can give a good indication of whether dust levels may be significant. Dust clouds may be visible when particular cutting operations are in progress, or there could be deposits on floors, ledges and tops of machines. Reliance on visual inspections alone are only part of the investigation, as respirable dust (particle size less than five microns) is often too fine to be detected by the naked eye, and very small particles may be airborne for a long time and settle over a wider area. The only sure way of establishing if a dust hazard is present is by atmospheric monitoring that will quantify both small and large dust particles.

Maximum exposure levels

In the USA, the Occupational Safety and Health Agency (OSHA) sets the maximum limits of both total and respirable dust in Standard 29 CFR. This document gives maximum requirements for specific dust sources such as talcum powder (magnesium silicate) and silica. UK regulations also refer to ‘respirable’ and ‘inhalable’ dust.

The definitions of these dust categories result from the particulate sizes: inhalable dust is typically relatively large particles of 100 micron (0.1mm) diameter that can enter the nose and mouth during normal breathing. Respirable dust is much smaller – less than five microns – and can be inhaled deeply into the lungs. Therefore, respirable dust is the most hazardous type of dust and has a lower workplace exposure limit. The American levels for individual substances such as cotton dust or talcum powder are very similar to those in the UK, where limits are set by the Health and Safety Executive (HSE) under the control of Substances Hazardous to Health (COSHH) regulations. The maximum amount of inhalable dust is 10mg/m³, with the respirable dust level set at 4mg/m³. These values are calculated on an eight-hour, time-weighted average reference period to reflect a typical working shift. Other occupational exposure limit values for European countries are listed in table 1.
 

Atmospheric monitoring

The amount of dust is quantified in mg/m³ (milligrams of dust per cubic metre of air). Personal dust monitors are used in SATRA’s standard procedure for monitoring exposure to total inhalable dust. These contain glass microfibre filters of known weight, and are attached to an operator’s clothing close to the breathing zone (around the neck/lapel area). As illustrated in figure 1, the filter head is attached to a pump which constantly draws air into the filter. This flow rate is calibrated immediately prior to use and gives a slight negative pressure consistent with normal breathing, drawing dust onto the filter. These filter heads are worn for at least four hours, during which time the volume of air sampled is calculated from the pump flow rate. The exposed glass microfibre filter is then reweighed after moisture has been removed in controlled laboratory conditions, and the amount of dust collected is calculated.

Rubber process dust and rubber fume

Rubber process dust can arise in rubber manufacture when ingredients are handled, weighed or mixed. Rubber fume can occur in the mixing, milling and blending of natural rubber or synthetic elastomers.
The term ‘fume’ can be confusing, as this normally refers to gases or vapours. Guidance from the HSE (EH40 Workplace Exposure Limits) explains that the term ‘fume’ should normally be applied to solid particles generated by chemical reactions, or condensed from the gaseous state. Both rubber process dust (EH40 exposure limit 6mg/m³) and rubber fume (EH40 exposure limit 0.6mg/m³) are carcinogenic, but due to the smaller particle size, the maximum level in the UK regulations is ten times lower than for rubber process dust. Rubber fume is determined by the amount of material collected in the filter that is extractable in the solvent cyclohexane.

Control measures

Where atmospheric monitoring has indicated the levels of rubber fume or dust are a matter of concern, and if the process causing the dust cannot be modified to reduce these levels, control measures may be necessary. These may include rotating work patterns to limit workers’ exposure to dusty environments or restricting an individual’s time spent performing a particular task. Improvements to or increased maintenance of Local Exhaust Ventilation (LEV) systems to extract dust close to its source will reduce workers’ exposure. These must be regularly monitored by measuring the air speed around the extractor vent, and by carrying out a smoke test. This involves a small quantity of smoke being created close to where the dust would be produced. If working efficiently, this smoke should quickly be extracted into the LEV. Additional control measures can also include the provision of Personal Protective Equipment (PPE), such as facemasks or respirators to remove particulate matter. However, PPE is generally considered a last resort when all elimination steps have been investigated.

SATRA can help with atmospheric monitoring to measure whether workers’ exposure is within the maximum permitted requirements. Once the levels of dust and rubber fume exposure are known, any further actions may not be particularly onerous, and this regular monitoring can form part of a company’s health and safety management system or ethical trading evidence.

Publishing Data

This article was originally published on page 40 of the September 2011 issue of SATRA Bulletin.

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