Important: The flash point is NOT the temperature at which the vapour will spontaneously ignite. The vapour must be exposed to a heat source at or above its Auto-ignition Temperature which is the minimum temperature required to ignite a gas or vapour in air without a spark or flame being present.
Flammable Vapours of different concentrations also react differently to heat as defined by their Flammable Range. Below the explosive or flammable range the mixture is too lean to burn and above the upper explosive or flammable limit the mixture is too rich to burn.
An open flame is not always required to ignite a gas. A hot surface like a heating element, machinery and superheated air will be sufficient to ignite HFL’s.
The flash point is an indication of how easy a chemical may burn if exposed to a temperature at or above the vapours auto ignition temperature. A Material with high flash point is less flammable or hazardous than a material with a low flash point. A material with a low auto-ignition temperature is a greater fire hazard than a material with a high auto-ignition temperature.
Fuels and their flash points for some common substances at atmospheric pressure are indicated below:
|Fuel Type||Temp (Deg C)||Temp (Deg F)|
|Diesel Fuel (1-D)||37.78||100|
|Diesel Fuel (2-D)||51.67||125|
|Diesel Fuel (4-D)||54.44||130|
|Fuels Oil No.1||37.78-72.22||100-162|
|Fuels Oil No.2||52.22-95.56||126-204|
|Fuels Oil No.4||61.11-115.56||142-240|
|Fuels Oil No.5 Lite||68.89-168.89||156-336|
|Fuels Oil No.6||65.56||150|
|Iso-Pentane||less than -51.11||less than -60|
|n-Pentane||less than -40||less than -40|
If the flash point of of a liquid is below room temperature the liquid will always constitute a major fire and explosion hazard particularly when the ambient temperature is above the auto-ignition temperature. Note that HFL substances that have flash points below the temperatures that may be found in a refrigerator or freezer will constitute an explosion hazard even when in cold storage.