While propane accidents rarely happen, propane is an extremely flammable gas. The National Fire Protection Agency has included it in its 2.1 class of flammable gas hazardous materials and considers it a class 4 fire hazard (the highest level). Propane ignites easily and at room temperature, when mixed with air, can quickly form an explosive mixture. On the other hand, propane liquid is not flammable or combustible.

Propane flammability

Propane gas or vapor travels quickly and far to find a source of ignition. Propane flammability is increased when it comes into contact with oxidizing agents (e.g., peroxides), halogen (e.g., chlorine).

This is why it is crucial to avoid open flames, sparks, static discharge, heat and other ignition sources when a propane leak is suspected.

Propane combustion criteria

Technically, a certain number of criteria have to be respected for propane combustion to occur. The proportion of propane to air content must be between 2.15% and 9.16% - if there is 1% of propane for 99% of air, combustion is impossible. But propane will burn when mixed with air anywhere between its lower (2.15%) and upper (9.16%) limits of flammability.

The propane flash point, which is the lowest temperature propane has to be to continue burning on its own once it has been ignited, is -156°F. Similarly, between 920°F and 1020°F, propane will burn by itself, without needing a spark or flame to ignite (Ignition Temperature in Air).

Propane safety precautions

All this shows why, if you suspect a propane leak because you smell or hear gas:

• LEAVE your home immediately and make sure everybody else in it does the same.
• CLOSE the propane tank service valve to shut off gas supply.
• PUT OUT all open flames and sparks.
• DO NOT
  • light candles,
  • switch lights on or off,
  • use a phone indoors,
  • use equipment that is electrical,
  • turn thermostats up or down, or
  • use the controls on appliances.
• CALL your propane dealer from a neighbor’s house.