Flammability of Liquids and Gases

Understanding the combustion characteristics of flammable liquids, vapors
and gases is an essential aspect of a process safety review and regulatory
compliance. Combustion properties of importance include:

• Closed cup flash point is the lowest temperature of a liquid in a
  small closed cup at which the vapors above a liquid surface reach
  a concentration in air that is above the lower flammable limit,
  as determined by a specific test method. See ASTM D93.
  
  
• Open cup flash point is the lowest temperature of a liquid at which
  the vapors near the unconfined liquid surface reach flammable
  concentration as determined by a specific test method. See ASTM D1310.
  
  
• Fixed-temperature flash point test is an open cup test to
  assess the development of ignitable liquid vapors at a specified
  temperature. See ASTM D4206.
  
  
• Sustained burning at a fixed temperature. This data point is
  determined from a fixed-temperature flash point test where an
  observation is made as to the duration of burning after an initial
  flash ignition (sustained burning). See ASTM D4206.
  
  
• U.S. DOT packaging classification for liquids is derived from
  a sustained burning test conducted at temperatures specified
  in 49CFR173 Appendix H.
  
  
• Fire point is the open cup test temperature at which, after flash
  ignition occurs, burning continues for a specified time.
  
• Auto ignition temperature is the lowest temperature at which
  a vapor-air mixture will spontaneously ignite at specified test
  conditions. See ASTM E659.
  
  
• Limiting oxygen concentration is the determination of the lowest
  oxygen concentration achieved in a fuel-air mixture that is diluted
  with an inert.. See ASTM E2079.
  
  
• Flammable limits of gases and vapors, both lower flammable limit
  (LFL) an upper flammable limit (UFL) represent critical safety limits
  where flammable gases and vapors are present.
  
  
• Flammability diagram of a fuel-air-inert gas system is a more
  general representation of the flammable composition space where fuel,
  air and an inert gas are mixed.