Combustibility

German test apparatus for determining combustibility at Technische Universität Braunschweig.

Combustibility is a measure of how easily a substance will set on fire, 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 needs to be reduced. Like apartment buildings, houses, offices and so on. 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:

• Combustible: A material which fails to meet acceptance criteria of CAN/ULC-S114, Standard Method of Test for Determination of Noncombustibility in Building Materials.

This leads to the definition of noncombustible:

• Non-combustible: means that a material meets the acceptance criteria of CAN4-S114, "Standard Method of Test for Determination of Non-Combustibility in Building Materials".

BS 476-4:1970 defines a test for combusibility in which 3 specimens of a material are heated in a furnace. Non-combustibile materials are defined as those for which none of the 3 specimens either:

• cause the temperature reading from either of two thermocouples to rise by 50 degrees Celsius or more above the initial furnace temperature, or
• is observed to flame continuously for 10 seconds or more inside the furnace.

Otherwise, the material shall be deemed 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 cannot support combustion and must not undergo a certain loss of mass. As a rule of thumb, concrete, steel, ceramics, in other words inorganic substances pass these tests, which permits them to be mentioned in building codes as being suitable and sometimes even mandated for use in certain applications. In Canada, for instance, firewalls must be made of concrete.

Relevance in construction

In building construction, buildings are typically divided into combustible and noncombustible ones. The code provisions and safety measures that must be taken into account in the design and construction of a building depend to a significant extent upon whether the structure is made from noncombustible elements, such as concrete, brick and structural steel, or a combustible element such as wood. Combustible structures have more stringent limits on maximum building height and area.

Combustible dust

Main article: 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. In addition to wood, combustible dusts include metals, especially magnesium, titanium and aluminum, as well as other carbon-based dusts. There are at least a 140 known substances that produce combustible dust. While the particles in a combustible dusts may be of any size, normally they have a diameter of less than 420 µm. As of 2012, the United States Occupational Safety and Health Administration has yet to adopt a comprehensive set of rules on combustible dust.

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, and other industries in NFPA Code sections 651–664. Collectors designed to reduce airborne dust account for more than 40 percent of all dust explosions. Other important processes are grinding and pulverizing, transporting powders, filing silos and containers (which produces powder), and the mixing and blending of powders.

Investigation of 200 dust explosions and fires, between 1980 to 2005, indicated approximately 100 fatalities and 600 injuries. 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. In February 2008 an explosion of sugar dust rocked the Imperial Sugar Company's plant at Port Wentworth, Georgia, resulting in thirteen deaths.

Related matters

The flammability article describes further the subcategorisations of combustible matters. Here, further fire tests are involved in quantifying the degree of flammability or combustibility.

The chemistry underlying the fire testing and resulting code classifications

The degree of flammability or combustibility depends largely upon the chemical composition of the subject material, as well as the ratio of mass versus surface area. As an example, paper is made from wood. A piece of paper catches on fire quite easily, whereas a heavy oak desk is much harder to ignite, although the wood fibre is the same in each substance, be it a piece of paper or a wooden board. Also, Antoine Lavoisier's law of conservation of mass, states that matter can be neither created nor destroyed, only altered. Therefore, the combustion or burning of a substance causes a chemical change, but does not decrease the mass of the original matter. The mass of the remains (ash, water, carbon dioxide, and other gases) is the same as it was prior to the burning of the matter. Whatever is not left behind in ashes and remains, literally went up in smoke, but it all went somewhere and the atoms of which the substance consisted before the fire still exist after the fire, even though they may be present in other phases and molecules.

See also

• Flammability
• Fire
• Fire protection
• Fire test
• Underwriters Laboratories
• Technische Universität Braunschweig
• Explosive material

External links

• CAN4-S114 CAN/ULC-S114 Abstract
• iBMB/TU Braunschweig Governmental Lab for Testing Building Materials
• BAM Abstract and Picture of Noncombustibility Test in Progress
• ASTM E136 Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750°C abstract
• "Combustible Dust: Agricultural Related Fires and Explosions Increasing, but Preventable" Division of Occupational Safety and Health, N.C. Department of Labor
• Combustible Dust: A Major Hot Work Hazard" Division of Occupational Safety and Health, N.C. Department of Labor