Skip to main content

Developed and maintained by the NFCC


Flammable liquids: Unignited

Hazard Knowledge

Uncontrolled flammable liquids pose a significant hazard to responders due to their low flash point (see flash point definition). In addition to posing a threat of fire, most of these materials also present a health hazard for the worker or emergency responder. This section deals only with those that directly influence their fire hazards.

The symbols that may be seen in relation to flammable liquids are:


For detailed information on classification and labelling see The foundation for hazardous materials.

Factors that increase fire risks from flammable liquids

Quantity and surface area – As the quantity of a flammable liquid increases, so does the risk; a large quantity can generate a spill with a greater surface area than a small quantity. Increased surface area supports the production of vapour and the potential size of the ignitable plume or fire. Additionally, any fire involving a large quantity of liquid can be deeper and thus last longer than one from a small quantity.

Heating – Hot materials are more reactive and volatile (produce more vapours) so a heated flammable liquid will generally be more ignitable than a cold one and more likely to exhibit rapid fire growth.

Containment – If materials are released in a poorly ventilated or confined situation then the hazard will be greater than in an open area where dispersion is possible. Toxic, flammable/explosion hazards are increased by confinement.

Pressure – Apart from the obvious danger of bursting its container, the fact that a material is under pressure means that it will be likely to give off far more vapour if it can escape. Increased vapour can exaggerate toxicity and flammability hazards. Additionally, pressure often increases the reactions of gaseous materials.

Incompatible materials – Some materials, especially oxidizing agents, are likely to react chemically with flammable liquids. The heat of the reaction and/or presence of oxidising agents will make the mixture liable to ignition and rapid fire growth.

Absorbers, adsorbers and wicks – These can be used to immobilise or contain a spill to restrict its surface area and prevent movement towards sensitive areas or other hazardous features such as ignition sources or incompatible materials. However, many materials can act as a wick, and increasing the surface area can increase vapour production and fire risk.

Mists – Flammable liquids that are aspirated to produce a mist can be ignited at temperatures significantly below their flashpoint. Fine sprays of heavy fuels or cleaning oils with a flashpoint above 300C can still ignite and produce severe explosions at room temperatures. See Control measures for Hazard – Combustible dust.

Location – Proximity to human, animals, property, sensitive or protected habitats.

Topography and meteorology – Slopes will spread a spill, depressions in the surface and trenches, etc. can collect/concentrate vapours that are heavier than air. Strong sunshine can heat materials and the surfaces they may contact. Rain can cause liquefied gases to boil and react with water-reactive materials.