There are three necessary elements which must occur
simultaneously to cause a fire: fuel, heat, and oxygen (FHO). These elements form the three (3) parts of the
fire triangle. By removing any one of
these parts, a fire becomes impossible.
For example, if there were very little or no oxygen present,
a fire could not occur regardless of the quantities of fuel and heat that were
present. Likewise, if insufficient heat were available, no concentrations of
fuel and oxygen could result in a fire.
On the other hand, for an explosion to occur, there are five
(5) necessary elements which must occur simultaneously: fuel, heat, oxygen,
suspension, and confinement (FHO + CS or FHOCS). These form the five parts of the explosion
pentagon. Like the fire triangle,
removing any one of these parts would prevent an explosion from occurring.
For example, if fuel, heat, oxygen, and confinement occurred
together in proper quantities, an explosion would still not be possible without
the suspension of the fuel. A fire could
still occur, though, as the fuel, heat and oxygen elements are there. If the burning fuel were then placed in
suspension by a sudden blast of air, and there was still confinement present,
then all five parts of the explosion pentagon would be satisfied and an explosion
would be imminent.
Remembering the three sides of the fire triangle (fuel,
heat, oxygen) and the five sides of the explosion pentagon (fuel, heat, oxygen,
suspension, confinement) is important in preventing fires and explosions at any
facility. By eliminating the possibility of either suspension or confinement,
an explosion cannot occur, but a fire may occur. By eliminating the fuel, the
heat, or the oxygen requirements, neither a fire nor an explosion can occur.