Basics of Fires & Blasts

While simplistic, the fire tetrahedron (formerly a triangle) illustrates the
requirements for a fire: fuel, air, an ignition source, and an uncontrolled chain
reaction. The base of the tetrahedron is the chain reaction is meant to highlight
that some firefighting agents (e.g., Halon & dry chemical) act by interrupting the
chain reaction but do not secure the scene from possible reignition.

Basics of Fires & Blasts

While simplistic, the fire tetrahedron (formerly a triangle) illustrates the
requirements for a fire: fuel, air, an ignition source, and an uncontrolled chain
reaction. The base of the tetrahedron is the chain reaction is meant to highlight
that some firefighting agents (e.g., Halon & dry chemical) act by interrupting the
chain reaction but do not secure the scene from possible reignition.

The factors influencing whether a blast wave is generated is discussed in WG #3 but is generally summarized as a function of:

• Flame speed of the burning open-air fuel release often referred to as reactivity.

• Freedom of the flame front to expand in all dimensions without restrictions (3-
D), within an open frame structure (2-D), or between decks / plates (1-D).

• Turbulence created by the flame front passing over / around obstacles such as
equipment, piping, and structural members and the spacing / pattern of such
obstacles (i.e., closely spaced, multiple layers).

Inherent Safety Hierarchy:

• Eliminate – that is, removing all potential of a fire or blast hazard (e.g., no
release)

• Prevent – that is, disrupting a fire or blast from occurring by eliminating the
possibility of ignition / air or blast factors.

• Detect / Control – that is sensing a release, fire, or blast and implementing
executive actions such as facility shutdown, etc.

• Mitigate – minimizing the effects of the fire / blast such as by deluge water
spray systems, fireproofing (PFP), robust structural design (WG #3 and WG

• Establish Contingency Measures (emergency response, evacuation, etc.)

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