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Many chemicals are flammable depending on the environmental conditions. Understanding when these conditions are met is needed to work safely.
Definitions
Flashpoint
The lowest temperature at which a chemical gives off sufficient vapour to ignite in air, if given an ignition source.
Fire point
The lowest temperature at which the vapour will continue to burn after the ignition source has been removed (usually higher than the flashpoint).
Auto ignition temperature
The lowest temperature at or above in which a substance will spontaneously ignite (catch fire) without an external source of ignition, such as a flame or spark.
Flammability limit
The minimum to maximum concentration range in which the vapour from a flammable substance/ gas can produce a fire or explosion when an ignition source (such as a spark or open flame) is present. The concentration is usually expressed in percent by volume.
- Above the upper flammable limit (UFL) the mixture of substance and air is too rich in fuel (deficient in oxygen) to burn. This is sometimes called the upper explosive limit (UEL).
- Below the lower flammable limit (LFL) the mixture of substance and air lacks sufficient fuel (substance) to burn. This is sometimes called the lower explosive limit (LEL).
Any concentration between the upper and lower limits can ignite or explode.
Flashpoints
Flammable liquid or vapour: Flashpoint equal to or higher than (≥) 23°C 73.4°F and lower or equal to (≤) 60°C 140°F
Highly Flammable liquid or vapour: Flashpoint lower than (<) 23°C 73.4°F and a boiling point higher than (>) 35°C 95°F
Extremely Flammable liquid or vapour: Flashpoint lower than (<) 23°C 73.4°F and a boiling point lower than (≤) 35°C 95°F
Non-flammable chemicals
Concentrations outside both limits are considered to be non-flammable. Flammability limits vary with temperature and pressure. However, the normal expression is in terms of % of volume at 25 °C at 1013.25mbar (mean sea-level atmospheric pressure (MSLP)).
This information can be found on the Safety Data Sheet (SDS) for the substance.
Flammable chemicals
Any work with flammable chemicals may affect the fire risk assessment for the lab or even the building. For further information please read the relevant fire technical notes. The standard fire extinguisher for UCL is water mist- this may not be suitable for some chemicals.