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Bulletin of Occupational & Environmental Health

Fire Safety At Workplace

Author(s): Uttpal B. Bhuva, M. Arshad Ansari

Vol. 1, No. 1 (2004-01 - 2004-06)

The Fire Triangle : The essential elements for combustion are fuel, oxidizer, and an ignition source. Fire or burning, is the rapid, exothermic oxidation of an ignited fuel. The fuel can be in solid, liquid or vapor form, but vapor and liquid fuels are generally easier to ignite. The combustion always occurs in the vapor phase; liquids are volatized and solids are decomposed into vapor prior to combustion. When fuel, oxidizer, and an ignition source are present at the necessary levels, burning will occur. This means a fire will not occur if

1) Fuel is not present or is not present in sufficient quantities.
2) Oxidizer is not present or is not present in sufficient quantities.
3) The ignition source is not energetic enough to initiate the fire.
Various fuels, oxidizers and ignition sources common in the chemical industry are

Fuels
Liquids Gasoline, acetone, ether, pentane.
Solids Plastics, wood dust, fibers, metal particles.
Gases Acetylene, propane, carbon monoxide, hydrogen.

Oxidizers
Liquids Hydrogen peroxide, nitric acid, perchloric acid.
Solids Metal peroxides, ammonium nitrite.
Gases Oxygen, fluorine, chlorine.

Ignition Sources
Sparks, flames, static electricity, heat.

Distinction between Fires and Explosions : The major distinction between fires and explosions is the rate of energy release. Fires release energy slowly, while explosions release energy very rapidly, typically in the order of microseconds. Fires can also result from explosions and explosions can result from fires.

Ignition Energy : The minimum ignition energy (MIE) is the minimum energy input required to initiate combustion. All flammables (including dust) have minimum ignition energies. The MIE depends on the specific chemical or mixture, the concentration, pressure, and temperature.

  • The MIE decreases with an increase in pressure.
  • The MIE of dusts are, in general, at energy levels comparable to combustible gases.
  • An increase in the nitrogen concentration increases the MIEs.

Few MIEs are given in the table below:

Combustible
Pressure (atm)

Minimum energy (mJ)

Methane
1
0.29
Propane
1
0.26
Heptane
1
0.25
Hydrogen
1

0.03

Cornstarch dust

0.3

Iron dust

0.12

Fire Prevention : The best way to deal with fires is to prevent their occurrence. The different ways to prevent fire are as follows:

  • Emergency evacuation the emergency action plan should be laid for each work area.
  • Alarm system fire alarm should be placed in the work area.
  • Fire brigades some employees should be trained to fight fire themselves.
  • Fire extinguishers the extinguishers selected should be of appropriate use and should be checked regularly for pressure.
  • Automatic sprinkler system the most suitable sprinkler system should be chosen as they affect employee safety.
  • Standpipe and hose systems this system is ancient but effective when properly installed and regularly maintained.

Bibliography:

  • Chemical Process Safety Fundamentals with Applications: - Daniel A. Crowl; Joseph F. Louvar.
  • National Fire Protection Agency.
  • Occupational Health and Hygiene Guidebook for the WHSO: - David Grantham.
  • Flammability Characteristics of Combustible Gases and Vapors, U.S. Bureau of Mines Bulletin 627 (UNST) AD 701, 576, 1965.
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