MadSci Network: Chemistry

Re: Flammability

Date: Tue Jan 20 14:23:07 1998
Posted By: John Letourneau, Lab Technician, Canadian Forestry Service
Area of science: Chemistry
ID: 884881522.Ch


   Flammability is a difficult parameter to find a definition for.  The 
most definitive answer that I could find was at a website at the following 

   In essence, the definitions supplied at this site refer to the 
flashpoints of specific substances to determite their flammability.  I hope 
that this will be sufficient in answering your question.  The following is 
an excerpt from that site which I thought to be relevant;


    CLASS         oC (oF)       oC (oF)                EXAMPLES
Flammable 1A     <37.8 (100)   <22.8 (73)              ethyl ether,

Flammable 1B     >37.8 (100)   <22.8 (73)              acetone, ethyl      

Flammable 1C         --     22.8< and <37.8 (100)      butanol, isoamyl    
Combustible 2        --     37.8(100)< and <60(140)    formalin,           

Combustible 3A       --     60(140)< and <93.3(200)    phenol,             

Combustible 3B       --         >93.3(200)             ethylene glycol,    
                                                       mineral oil 

Source: National Fire Protection Association, 1987. Flammable and 
Combustible Liquids Code, NFPA 30. 

There are a number of important definitions in the evaluation of fire 

     Flammable Solid - a nonexplosive material that is capable of producing 
fire as a result of friction, water exposure, air exposure or retained heat 
from synthesis or processing, or when ignited burns so vigorously and 
persistently so as to create a hazard 

     Flammable Gas - gases of which mixtures in air of 13 percent or less, 
by volume, form a flammable mixture; or the flammable range (explosive 
range) in air is wider than 12 percent regardless of the lower limit (U.S. 
Department of Transportation definition) 

     Boiling point - the temperature at which the vapor of the liquid is in 
equilibrium with atmospheric pressure the lower the boiling point the 
greater the fire hazard

     Flash point - the minimum temperature at which a liquid gives off 
vapor in sufficient concentration to form an ignitable mixture with air 
near the surface of the liquid - also applies to certain solids that 
evaporate or volatilize : the lower the flashpoint the greater the fire 

     Auto-ignition Temperature - the minimum temperature which will 
initiate a self-sustained combustion of liquid, gas or solid in the absence 
of a spark or flame : the lower the autoignition temperature the greater 
the fire hazard 

     Flammable or Explosion limits - the range of concentration of a gas or 
vapor in air, by volume percent in air, in which a fire or explosion can 
occur upon ignition in a confined area : the wider the range of the 
explosion limits and the lower the lower limit, the greater the fire hazard 

     Vapor Density - the weight of a volume of pure vapor or gas compared 
to the weight of an equal volume of dry air at the same temperature and 
pressure: vapor densities greater than one indicate the vapor or gas is 
heavier than air 

   Information on these physical characteristics of flammable chemicals is 
listed on manufacturer's container labels and on Material Safety Data 

For a fire to occur, three conditions must be met: (1) for gases and vapors 
the concentration of the flammable gas or vapor must be between the lower 
and upper flammable limits, (2) an oxidizing agent (e.g., the air in the 
room or a chemical oxidizer) must be available, and (3) there must be a 
source of ignition or the material is at its auto-ignition temperature. 

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