A flash fire is the non-explosive combustion of a vapour cloud resulting from a release of
flammable material into the open and which after mixing with air, ignites. A flash fire results from the
ignition of a released flammable cloud in which there is essentially no increase in combustion rate. The
ignition source could be electric spark, a hot surface and friction between moving parts of a machine or
an open fire.
Thus flash fire means a release of flammable gas under unconfined condition in the presence of
air and ignition source. Dispersion process occurs between LEL and UEL with no increase in combustion
rate.
A jet fire occurs when flammable gas releases from the pipeline (or hole) and the released gas
ignites immediately. Damage distance depends on the operating pressure and the diameter of the hole or
opening flow rate.