GHS Course page 4 | Industrial & Construction Safety Solutions



Physical Hazards

In this section, we’ll 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), especially in terms of how we use, handle or store the products. Examining classes with similar hazards helps make it easier to understand.



Flammables Picture


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 and flammable solids. All of 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, examples include propane, butane, acetylene, acetone, paint thinner, kerosene, gasoline, and toluene.

Precautionary Statements for Flammables

  • 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.



Oxidizers Picture


There are 3 classes of oxidizing materials Oxidizing Gases, Oxidizing Liquids, and 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 and 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.

Precautionary Statements for 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


Gases Under Pressure Picture


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 gas can be very cold and may cause frostbite if it touches your skin. In addition, a leaking cylinder can rapidly release extremely large amounts of gas into the workplace
  • Damaged cylinders can act like rockets


  • 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


Corrosive To Metals Picture


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 & Mixtures, and Organic Peroxides 

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.

Pyrophoric Gases

Gases that catch fire spontaneously if exposed to air. Pyrophoric gases uses the flame pictogram. 

Combustible Dusts

A mixture or substance that is in the form of a powder that, upon ignition, is liable to catch fire or explode when dispersed in air or another oxidizing medium. Does not require a pictogram.

Simple Asphyxiants

Gases that may displace oxygen in air, and cause rapid suffocation. Does not require a pictogram.

Physical Hazards not otherwise classified (PHNOC)

Hazards that occur by chemical reaction and result in the death or serious injury 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. PHNOC requires a pictogram that is applicable to the hazard.


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