IN THIS ARTICLE
In this article, we will take a closer look at the physical hazard classes.
Some of the classes represent materials with similar hazards (e.g., flammable liquids or flammable gases).
Examining classes with similar hazards will help you understand how to use, handle and store products with similar hazards safely.
There are many classes of flammable materials. Four of the classes are for materials that we commonly encounter at work:
- Flammable gases
- Flammable aerosols
- Flammable liquids
- Flammable solids
These materials will burn if ignited by a spark, static discharge, or a hot surface (like a hot plate).
Other classes that are not common in the workplace and use this pictogram have similar safety concerns.
- Pyrophoric liquids, solids, and gases – can readily ignite when exposed to air
- Self-heating substances and mixtures – can decompose slowly and become hot when exposed to air; they may catch fire
- Substances and mixtures which, in contact with water, emit flammable gases – can react with water to give off a flammable gas
Flammables found at work or home may include:
- Propane - heating, cooking, and car fuels
- Butane - fuel and aerosol propellant
- Acetylene - welding (in torches)
- Acetone - nail polish removers, industrial cleaners, and degreasers
- Kerosene - home heating fuel, solvent, and rocket fuel
- Gasoline - fuel, and solvent
- Toluene - industrial solvent
Examples of precautionary statements used for flammables include:
- Keep away from heat, hot surfaces, sparks, open flames, and other ignition sources
- No smoking
- Keep container tightly closed
- Ground and bond container and receiving equipment
- Take action to prevent static discharges
- Wear protective gloves/protective clothing/eye protection/face protection
There are 3 classes of oxidizing materials:
- Oxidizing gases
- Oxidizing liquids
- Oxidizing solids
Oxygen is necessary for a fire to burn. Oxidizers do not usually burn by themselves, but they will:
- Increase the intensity of a fire
- Cause materials that normally do not burn to suddenly catch on fire, sometimes even without an ignition source
Nitric acid is an example of an oxidizer. It is used to manufacture explosives. If nitric acid is spilled on cotton fabric, it can spontaneously ignite and burn when the spilled acid dries.
Remember, when handling oxidizers:
- Keep away from heat, hot surfaces, sparks, open flames, and other ignition sources. No smoking.
- Keep away from clothing and other combustible materials.
- Wear protective gloves, protective clothing, eye protection, and face protection.
- Wear fire-resistant or flame-retardant clothing.
Gases Under Pressure
These gases are stored under pressure in a container, liquefied, chilled, or dissolved in a carrier.
The main hazards are:
- The cylinder or container may explode if heated
- Leaking refrigerated liquefied gas is very cold and may cause frostbite, severe cold (cryogenic) burns, or injury if it touches your skin or eyes
- Depending on the contents, a leaking cylinder may rapidly release a high amount of gas that can displace the oxygen in the air, which leads to “oxygen deficiency” (asphyxiation) and/or releases a gas that could create a flammable atmosphere
NOTE: Your workplace-specific training should also include other hazards. For example, the cylinder may rocket or torpedo at great speeds if it is ruptured.
When exposed to high temperatures and direct sunlight, cylinders can explode. In St. Louis, Missouri, a propylene cylinder valve vented gas which ignited and caused a domino effect fire. The small fire from one propylene cylinder spread to others and then to propane and acetylene cylinders. Exploding cylinders flew 800 feet, damaged property, and started fires in the community.
Corrosive to Metals
Materials that are corrosive to metals can damage or destroy metals (steel and aluminum).
When a corrosive material eats through a container, the contents may spill out into the workplace resulting in health effects, reactivity, or fire damage.
Common corrosives are nitric acid, hydrochloric acid, and sodium hydroxide solutions.
Other Physical Hazards
Self-reactive substances and mixtures and organic peroxides are two classes that may be explosive or flammable, or both.
Self-reactive substances and mixtures are unstable materials that can cause or increase the intensity of a fire. Many organic peroxides are unstable and may be highly reactive or explosive.
These materials require specific storage and handling.
WHMIS also includes these hazards:
- Combustible dusts – a mixture or substance that is in the form of finely divided solid particles that, upon ignition, is liable to catch fire or explode when dispersed in air
- Simple asphyxiants – gases that may displace oxygen in the air and cause rapid suffocation
- Physical hazards not otherwise classified (PHNOC) – hazards that occur by chemical reaction and result in the serious injury or death of a person at the time the reaction occurs
- For example, injury or death from a violent chemical reaction like hazardous polymerization
- These hazards do not fall into another physical hazard class
Combustible dusts and simple asphyxiants do not require a pictogram. PHNOCs require a pictogram that is applicable to the hazard.