Astronomy:Combustibility and flammability

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Combustibility is a measure of how easily a substance bursts into flame, through fire or combustion. This is an important property to consider when a substance is used for construction or is being stored. It is also important in processes that produce combustible substances as a by-product. Special precautions are usually required for substances that are easily combustible. These measures may include installation of fire sprinklers or storage remote from possible sources of ignition.

Substances with low combustibility may be selected for construction where the fire risk must be reduced, such as apartment buildings, houses, or offices. If combustible resources are used there is greater chance of fire accidents and deaths. Fire resistant substances are preferred for building materials and furnishings.

Code Definitions

For an Authority Having Jurisdiction, combustibility is defined by the local code. In the National Building Code of Canada, it is defined as follows:

This leads to the definition of noncombustible:

BS 476-4:1970 defines a test for combustibility in which a technician heats three specimens of a material in a furnace. Non-combustibile materials are those for which none of the three specimens either:

  • Makes the temperature reading from either of two thermocouples rise by 50 degrees Celsius or more above the initial furnace temperature
  • Flame continuously for 10 seconds or more inside the furnace

Otherwise, the material is classified as combustible.

Fire testing

Various countries have tests for determining noncombustibility of materials. Most involve the heating of a specified quantity of the test specimen for a set duration. Usually, the material must not support combustion and must not lose more than a certain amount of mass. As a general rule of thumb, concrete, steel, and ceramics - in other words inorganic substances - pass these tests, so building codes list them as suitable and sometimes even mandate their use in certain applications. In Canada, for instance, firewalls must be made of concrete.

Combustible dust

Main page: Chemistry:Dust explosion

A number of industrial processes produce combustible dust as a by-product. The most common being wood dust. Combustible dust has been defined as: a solid material composed of distinct particles or pieces, regardless of size, shape, or chemical composition, which presents a fire or deflagration hazard when suspended in air or some other oxidizing medium over a range of concentrations.[1] In addition to wood, combustible dusts include metals, especially magnesium, titanium and aluminum, as well as other carbon-based dusts.[1] There are at least a 140 known substances that produce combustible dust.[2]:38[3] While the particles in a combustible dusts may be of any size, normally they have a diameter of less than 420 μm.[1][note 1] As of 2012, the United States Occupational Safety and Health Administration has yet to adopt a comprehensive set of rules on combustible dust.[4]

When suspended in air (or any oxidizing environment), the fine particles of combustible dust present a potential for explosions. Accumulated dust, even when not suspended in air, remains a fire hazard. The National Fire Protection Association (U.S.) specifically addresses the prevention of fires and dust explosions in agricultural and food products facilities in NFPA Code section 61,[5] and other industries in NFPA Code sections 651–664.[note 2] Collectors designed to reduce airborne dust account for more than 40 percent of all dust explosions.[6] Other important processes are grinding and pulverizing, transporting powders, filing silos and containers (which produces powder), and the mixing and blending of powders.[7]

Investigation of 200 dust explosions and fires, between 1980 to 2005, indicated approximately 100 fatalities and 600 injuries.[2]:105–106 In January 2003, a polyethylene powder explosion and fire at the West Pharmaceutical Services plant in Kinston, North Carolina resulted in the deaths of six workers and injuries to 38 others.[2]:104 In February 2008 an explosion of sugar dust rocked the Imperial Sugar Company's plant at Port Wentworth, Georgia,[8] resulting in thirteen deaths.[9]

Non-combustible material[10] – A non-combustible material is a substance that does not ignite, burn, support combustion, or release flammable vapors when subject to fire or heat, in the form in which it is used and under conditions anticipated. Any solid substance complying with either of two sets of passing criteria listed in Section 8 of ASTM E 136 when the substance is tested in accordance with the procedure specified in ASTM E 136 is considered to be non-combustible.

Categorization of building materials

Materials can be tested for the degree of flammability and combustibility in accordance with the German DIN 4102. DIN 4102, as well as its British cousin BS 476 include for testing of passive fire protection systems, as well as some of its constituent materials.

The following are the categories in order of degree of combustibility and flammability:

Rating Degree of flammability Examples
A1 100% noncombustible (nicht brennbar)
A2 ≈98% noncombustible (nicht brennbar)
B1 Difficult to ignite (schwer entflammbar) intumescents and some high end silicones
B2 Normal combustibility wood
B3 Easily ignited (leicht entflammbar) polystyrene

A more recent industrial standard is the European EN 13501-1 - Fire classification of construction products and building elements—which roughly replaces A2 with A2/B, B1 with C, B2 with D/E and B3 with F.

B3 or F rated materials may not be used in building unless combined with another material that reduces the flammability of those materials.

Important characteristics

Flash point

A material's flash point is a metric of how easy it is to ignite the vapor of the material as it evaporates into the atmosphere. A lower flash point indicates higher flammability. Materials with flash points below 100 °F (38 °C) are regulated in the United States by OSHA as potential workplace hazards.

Vapor pressure

  • The vapor pressure of a liquid, which varies with its temperature, is a measure of how much the vapor of the liquid tends to concentrate in the surrounding atmosphere as the liquid evaporates. Vapor pressure is a major determinant of the flash point, with higher vapor pressures leading to lower flash points and higher flammability.

See also

  • Explosive material
  • Fire
  • Fire test
  • Fire protection
  • Active fire protection
  • Passive fire protection
  • Flammable liquids
  • Flammable limit
  • Underwriters Laboratories


  1. I.e. they can pass through a U.S. No. 40 standard sieve.
  2. E.g. NFPA 651 (aluminium), NFPA 652 (magnesium), NFPA 655 (sulphur)


  1. 1.0 1.1 1.2 United States Occupational Safety and Health Administration (2009) "Hazard Communication Guidance for Combustible Dusts", OSHA 3371-08, Occupational Safety and Health Administration, U.S. Department of Labor
  2. 2.0 2.1 2.2 United States Chemical Safety and Hazard Investigation Board (17 November 2006), Investigation Report No. 2006-H-1, Combustible Dust Hazard Study, Washington, D.C.: U.S. Chemical Safety and Hazard Investigation Board, OCLC 246682805,, retrieved 21 August 2017 
  3. National Materials Advisory Board, Panel on Classification of Combustible Dusts of the Committee on Evaluation of Industrial Hazards (1980) Classification of combustible dusts in accordance with the national electrical code Publication NMAB 353-3, National Research Council (U.S.), Washington, D.C., OCLC 8391202
  4. Smith, Sandy (7 February 2012) "Only OSHA Has Not Adopted Chemical Safety Board Recommendations Stemming from Imperial Sugar Explosion" EHS Today
  5. "NFPA 61 Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities"
  6. Zalosh, Robert et al. (April 2005) "Dust Explosion Scenarios and Case Histories in the CCPS Guidelines for Safe Handling of Powders and Bulk Solids" 39th AIChE Loss Prevention Symposium Session on Dust Explosions Atlanta, Georgia
  7. O'Brien, Michael (2008) "Controlling Static Hazards is Key to Preventing Combustible Cloud Explosions" Newton Gale, Inc.
  8. The chief executive, John C. Sheptor, said the probable cause of the explosion was sugar dust building up in storage areas, which could have been ignited by static electricity or a spark. Dewan, Shaila (9 February 2008). "Lives and a Georgia Community's Anchor Are Lost". The New York Times. Retrieved 7 May 2012. 
  9. Chapman, Dan (13 April 2008). "Sugar refinery near Savannah determined to rebuild". The Atlanta Journal-Constitution. Archived from the original on June 29, 2011. Retrieved 7 May 2012. 
  10. "NCDOI OSFM Evaluation Services: Subject of White Paper: Classification of Building Materials According to Combustibility". 8 September 2011. Retrieved 6 December 2018. 

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