Following are Fire hazards & percentage loss
(a) Direct cost 30%.
(b) Protection of building 30%.
(c) Cost of emergency services 15%.
(d) Cost of insurance 15%..
(e) Indirect cost 5%.
(f) Human losses 5%.
(g) Cost of research & information negligible.
The plume of hot gases above a fire having following constituent parts.
(i) Hot vapours & gases given off by the burning material.
(ii) Unburnt decomposition & on condensation matter.
(iii) A quantity of air heated by the fire entrained in to the rising plume makeup of flammable tars & small particles of carbon suspended in gas.
Smokes are clouds of particles each too small to be normally visible but in aggregate, they scatter light & air, opaque to visible light.
Particle diameter less than one micron & can be suspended in a gas. All other particles size more than one micron is dust. Unrelated carbon molecules agglomerate on leaving the combustion zone forming long chains of carbon particles that is known as soot.
Density reduces vision perhaps by the presence of irritant gases which causes a person to lose all sense of direction & contribute to osculation of exit ways. Smoke irritate the eyes & hard passages similar blinding & or chocking of peo- Smoke is not as much harmful as it become by impairing visuality to occupants.
Observing exit signs affects other senses. Asphysation caused by smoke Smoke kill more people than fire.
Smoke control depends on following:
(i) Volume of Smoke.
Rate of production of smoke kg/sec = 0.188 x P x Y 3/2 Where P = Perimeter of fire in m
Y = Distance between floor & bottom of smoke layer under ceiling.
(ii) Quality of smoke.
Obscurity – Reducing the visibility of human eyes.
(iii) Visibility & obscuration.
(iv) Smoke density.
(v) Light obstruction.
(vi) Optical density.
(vii) Smoke movement.
(viii) Wind action.
Heat of fire produces air pressure & buoyancy that aid the spread of smoke well beyond the scene of the fire itself.
Most passive design responses to smoke i.e. try to confine to the fire area itself.
For a limited time a fire at early stage. The dilution of smoke with 100% outdoor air makes condition bearable during occupant’s evacuation.