Fire Engineering Science
What the exam tests
Fire Engineering Science tests the physics and chemistry behind ignition, combustion and extinguishment, and your ability to turn those principles into safe fireground decisions. Expect definitions, comparisons, simple calculations and agent-selection questions.
Core rules
- Fire tetrahedron: fuel, oxygen, heat and the free-radical chain reaction. Remove any side and combustion stops.
- Flammable range: the vapour concentration in air between the lower explosive limit (LEL) and upper explosive limit (UEL). Below LEL the mixture is too lean; above UEL it is too rich.
- Flash point is the lowest temperature at which a liquid gives off enough vapour to flash when an ignition source is applied. The fire point is the higher temperature at which vapour burns continuously. Auto-ignition needs no external spark.
- Extinguishment: cooling (water), smothering (foam, CO2), starvation (isolating fuel), chemical inhibition (dry chemical).
- Class A solid fuels, B flammable liquids, C gases, D metals and K cooking oils; electrical fires are a hazard category, not a separate class in most Indian training.
Worked example
A solvent has LEL 2% and UEL 12% by volume in air. A tank headspace reads 8% vapour. Is it flammable? 8% lies between 2% and 12%, so yes; a spark could ignite it. If the reading were 15%, it is above UEL and too rich to burn, but the headspace becomes dangerous as it dilutes on opening. Reasoning: compare the measured concentration with both limits; never assume "too rich" means safe.
Traps
Reversing LEL and UEL; confusing flash point with auto-ignition; applying water to burning metals or cooking oil; treating CO2 as suitable for Class D; ignoring vapour density when judging where a flammable gas will collect.