Introduction of oxygen into a confined area that is pressurized with super-heated, flammable gases, deficient in oxygen, resulting in an explosive force.
II. FIRE PHASES
A. 1st Phase - (Incipient or Growth)
1. 02 = 21%
2. Temperature is slightly elevated
B. 2nd Phase - (Free Burning or Fully Developed)
1. 02 = 17%
2. Fire burns at slower rate
3. Temperature is above 1300oF.
C. 3rd Phase - (Smoldering or Decay)
1. 02 = 15%
2. Temperature is above 1000oF.
3. Gas/smoke are heated, expand, causing pressure inside structure
4. Internal pressure forces smoke/gases from all cracks/openings
5. If 02 introduced at this stage = prime opportunity for backdraft
III. CAUSE
A. Fire in a confined space
1. Winter
2. Sealed building
B. 02 content is reduced to 15% and visible fire ceases
C. Combustibles continue to produce heated flammable gases and pressurize the room
D. 02 is introduced into this environment and it ignites with explosive force
IV. WARNING SIGNS
A. Fires that are restricted or confined by structure
B. Smoke:
1. Under pressure, “puffs,” escaping and expanding
2. Heavy black smoke becoming grey/yellow
3. Turbulent, “boiling,” escaping and expanding
4. Smoke being drawn back into building
C. Windows
1. Dark, black, “oily”
2. High heat
D. Weak, feeble fire
E. Muffled sounds
V. PREVENTION (if warning signs are present)
A. Vertical ventilation
1. To remove heat and flammable gases upward
2. Done before attack team advances or forces entry
3. Last resort - vent horizontally
B. Coordinated operations with hose lines and ventilation
C. Recognition, communication, timing between ground and roof personnel