Flammable Liquid Fires

 

Flammable Liquid Fires

A flammable liquid is a liquid which has the potential to ignite at temperatures below 62°C. The ignition temperature is commonly known as the liquids' flash point (see below). Flammable liquids are more easily ignited than most common solid materials.

Every year in Australia, about

  • 7 % structural fires are caused by flammable or combustible liquids;
  • 15 % of industrial fires involve flammable or combustible liquids;
  • 10 % of $$ losses are due to flammable or combustible liquid fires.

Spills

Flammable liquid spills include spills without fire and any remaining fuel after a fire has been extinguished. In both of these cases, the liquid must be protected to prevent ignition until it can be picked up or removed. The use of a foam "blanket" covering the liquid surface will greatly reduce the the possiblity of ignition.

All crew working around spills must wear full protective clothing to afford protection in case of possible ignition. SCBA must be used in vapour areas. A Hazardous Materials Response Team should be dispatched in high vapour atmospheres.

In a diffusion flame, oxygen and fuel diffuse into each other; where they meet the flame occurs. A candle flame, for example,(a diffusion flame) operates through evaporation of the gaseous wax, which then mixes with surrounding oxygen and combusts.

Terminology

Flash Point — is the minimum temperature at which a liquid produces a sufficient concentration of vapour above it that it forms an ignitable mixture with air. At the flash point, the vapour may cease to burn when the source of ignition is removed.

The fire point, a slightly higher temperature, is defined as the temperature at which the vapour continues to burn after being ignited. Neither the flash point nor the fire point is related to the temperature of the ignition source or of the burning liquid, which are much higher.

Auto Ignition Temperature — of a substance is the temperature at or above which a material will spontaneously ignite (catch fire) without an external flame or spark. The flammable range is the range of a concentration of a gas or vapour that will burn if an ignition source is introduced. Below the flammable range, the mixture is too lean to burn and above the upper flammable limit, the mixture is too rich to burn. The limits are commonly called the "Lower Flammability Limit" (LFL) and the "Upper Flammability Limit" (UFL).

  Lower Flammability Limit Upper Flammability Limit Flash Point °C Auto Ignition Temperature °C
Acetone 2.6 % 13 % −17 465
Diesel Fuel 0.6 % 7.5 % > 62 210
Ethanol
3.3 % 19 % 12.8 365
Petrol
1.0 % 6.0 % <−140 230 °C — 450
Kerosene 0.7 % 5 %    

At the Scene

  • Positioning of appliance and crew uphill and upwind.
  • Size up - will you use offensive, defensive, and preventative strategies?
  • Protect people and property from a liquid fire, and take preventative action including foam blankets.
  • Contain flammable liquid spills – equipment carried – containment of liquids when alight and not.
  • Use of “sweeping” branch techniques using water to separate flame from surface of burning liquids to extinguish.
  • Which liquids can be safely allowed to evaporate – how to dispose of spilled flammable liquids.
  • Cleaning of spill scenes – disposal of used absorbent materials.
  • Managing the safety of bystanders in the village environment.