How To Assess Physicochemical Risks

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 the interaction of people with the chemic the l, physicochemical risks arise mainly from hazardous chemicals where they come into contact with other things such as ignition sources.


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).

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 sources of oxygen, such as oxygen gas and compressed air in cylinders, chemical oxidisers and peroxides. Oxygen is always present in the air. A list of common fuel and oxygen sources are listed in Appendix H.

Note: Chemical reactions and other processes which generate gases can also cause explosions through an increase in the pressure in the container in which the chemical is stored if the gas cannot escape, even if that gas does not itself ignite.


Ignition sources can be any energy source that has the potential to ignite a fuel. They can be categorised into three broad types: flames, sparks and heat. Some common examples of ignition sources are provided in Table 2 below.

Common examples of ignition sources


Welding flames, gas heaters, pilot lights


Welding arcs, starters for fluorescent lighting, electric motors, electrical equipment like power points, cigarette lighters, switches and telephones

Static electricity including from friction sources


Friction from drilling, grinding, scraping of metal on concrete


Hot surfaces including light bulbs, ovens, radiators or heaters, flue pipes, vehicle engines and exhaust systems, pumps and generators

Exothermic chemical reactions (those which generate heat)

 Some electrical equipment may also be a source of ignition. However, not all electrical equipment is an ignition source if it is specifically designed so that it does not create sparks. This type of equipment is referred to as “intrinsically safe”

You must identify any ignition source in your workplace that has the potential to ignite a flammable or combustible material. You should also consider sources of ignition that are adjacent to your workplace or may periodically come into your workplace, for example, vehicles (with a hot engine and exhaust systems) making deliveries, visitors or other portable items like cordless power tools, radios and fans.

Chemical Safety Quiz

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