Hazardous Chemicals: controlling fire and explosion hazards

When you understand how a hazard is created, you are better equipped to control it. So this blog takes a closer look at flammable hazards and what causes substances to burn or explode. We then outline three important key considerations for identifying how the chemicals held at your workplace could contribute to a fire or explosion.
PLEASE NOTE: This blog is not about fire protection equipment (extinguishers, hydrants, hoses) or emergency plans. We focus instead on chemical exposure, handing, and storage issues that could cause or contribute to a fire or explosion.

1. Understanding how your chemicals can burn or explode

Let’s begin by spending a moment looking at what makes a fire or explosion, it’s amazing how many people don’t fully understand this. A fire or explosion requires three key ingredients all at the same time:

1. Fuel (any combustible substance eg, wood, petrol vapours, kerosene)

2. Oxygen (contained naturally in the air or from oxidising chemicals)

3. Ignition source (flames, static electricity, industrial heat)

But even when all three of these three materials are present in the atmosphere, it is still possible not to have an fire or explosion. The flashpoint and Lower Explosion Limits (LEL) of a chemical will determine whether the substance ignites. Here’s how:

• The Lower Explosion Limit (LEL) of any substance is the minimum air-borne concentration that is capable of igniting. The LEL is expressed as a percentage of the air — when the air contains more than 1% toluene vapours, a fire or explosion could occur if an ignition source was brought into the area.

• Flashpoint, refers to the lowest temperature that flammable vapours can be ignited — when the temperature of toluene exceeds 4.4°C it can be ignited.

So (using an example to demonstrate) in order for toluene to burn or explode there must be:

• Airborne concentrations of more than 1% toluene in the surrounding atmosphere

• Toluene at a temperature of at least 4.4°C

• An ignition source

PLEASE NOTE: This is a generic example only, do NOT use the concentrations or temperatures quoted in this example in your risk assessment.

As you can see from the illustration above, a confined space that allows airborne concentrations of a chemical to steadily increase can present a significant fire risk. It also demonstrates why outdoor spaces — where chemical vapours can disperse much more easily — are often much safer. At the same time you can see how heat (hot work, direct sunlight, or a furnace) could bring the temperature of the chemical above its flashpoint.

So when you begin to assess the flammable hazards on the job site you will be specifically looking at:

• How to keep concentrations of flammable vapours under the LEL. Eg, use a mechanical ventilation system.

• How to ensure the temperature of the chemical (and subsequent vapours) remain under their flashpoint. Eg, store chemicals away from heat.

• How to protect chemical stores and work areas from ignition sources. Eg, isolate chemical stores away from hot work and operating machinery.

REMEMBER: Incompatible chemicals and dangerous goods that contact your flammables can trigger chemical reactions lie decomposition (which produces extreme heat) — this could also trigger a fire or explosion.

2. Controlling flammable vapours and emissions

Your next step is to start looking at all the ways you could contain flammable vapours and emissions and (as much as possible) keep temperatures and concentration levels within explosive ranges. Consider things like:

• Properly ventilating chemical stores, work areas, decanting, and transfer stations.

• Regulating the temperature of store rooms and handling areas (particularly when decanting and transferring).

• Keeping the lids on chemical containers (recapping as soon as the the job is done).

• Using only the required amount of flammable liquids for the job.

• Cleaning up spills and splashes immediately.

• Using work processes that minimise splash filling.

• Installing LEV or other equipment that dissipates flammable dusts.

3. Identifying ignition sources

Finally consider all possible ignition sources — especially static electricity. Here are some possibilities to consider, but take a deeper dive and examine the work processes, equipment, and clothing used in your chemical handling and storage areas.

• Sparks from electrical installations - faulty equipment and loose fittings or connections can create sparks. Most especially in generators, faulty light bulbs, failed insulation, and from equipment that isn’t earthed.

• Machinery and plant - manufacturing plant and vehicles can create friction between metals or have hot surfaces.

• Static Electricity - can be generated by mobile phones, keyless remote controls, thermostats, clothing, incorrectly earthed equipment.

• Hot work - any work processes that create heat or a generate a stream of sparks. Things like welding and grinding, metal cutting, brazing, heat treatments, soldering.

• Industrial heat - industrial machinery and work areas that contain fires, furnaces, boilers, heaters, stoves and ovens, kilns, steam pipes, radiators.

• Autoignition -  some chemicals have an autoignition temperature; meaning they will spontaneously ignite without an ignition source after reaching a specific temperature. Eg, some toluene concentrations will ignite at 250°C.

• Organic sources - bushfires, lightning, direct sunlight.

• Flames - cigarette lighters, flame throwers, bunsen burners, blow torches, matches, candles.

Next Steps

Controlling fire and explosion hazards is an important part of your risk management plan. For a better understanding of how to identify, assess, and control chemical hazards and fire risks please download our free eBook How to manage the risk of Hazardous Chemicals in the workplace. Download and read it today to get your workplace 100% chemical safety compliant.