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Even if monitoring indicates that exposure is below an exposure standard, sensitive workers may still be at risk. Exposure standards do not represent a 'no-effect' level which makes exposure at that level safe
for all workers, therefore you should ensure that exposure to any hazardous chemical is kept as low reasonably practicable. This includes exposure to hazardous chemicals that do not have exposure standards.
Some chemicals, such as isocyanates, are known to be sensitisers and can induce an adverse reaction in workers at levels well below the exposure standard once sensitisation has occurred.
If a worker becomes sensitised to a chemical, the exposure standard for that chemical is no longer relevant and control measures such as improving engineering controls or job rotation to remove the affected worker from potential exposure to the chemical should be implemented.

For more information on how to interpret exposure standards and comply with the WHS Regulations, refer to Safe Work Australia's Workplace Exposure Standards for Airborne Contaminants and Guidance on the Interpretation of Workplace Exposure Standards for
Airborne Contaminants.

3.4 How to assess physicochemical risks
The assessment of physicochemical risks in the workplace is different in many respects from that needed when assessing health risks. Whereas health risks arise from interaction of people with the chemical, physicochemical risks arise mainly from hazardous chemicals where they come into contact with other things such as ignition sources.

Fire and explosion
Regulation 51-52: A person conducting a business or undertaking must manage the risk to health and safety associated with a hazardous atmosphere or an ignition source in a hazardous atmosphere at the workplace.

Fire and explosion can result in catastrophic consequences, causing serious injuries or death of workers, as well as significant damage to property.  They occur when the following three primary elements come together (commonly referred to as the fire triangle – see Figure 1):
    * a source of fuel (a flammable or combustible substance)
    * a source of oxygen (usually in the air)
    * an ignition source (a source of energy sufficient to cause ignition).

Figure 1 Fire triangle

When identifying hazards you should have identified all of the sources of fuel in your workplace that could contribute to fire and explosion risks.  Fuels that present the highest risk are those hazardous chemicals that are flammable (for example, flammable solids, liquids or gases, including their vapours and fumes), other fire risk substances in other hazard classes (for example, pyrophoric liquids and solids that ignite spontaneously in contact with air, substances that react with water to emit flammable gasses) and other materials that are not hazardous chemicals, like wood, paper and leaves, and other combustible materials that contribute to the fire load.
You should also identify