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Ignition risks can be minimized by controlling heat sources and using materials that will not ignite or will not support burning in the applicable environment. Some materials are more susceptible to ignition in oxygen-rich environments, and compatibility should be assessed before a component is introduced into an oxygen system. [ 1 ]
Because the mixture by definition is ignitable before inerting commence, it is imperative that the inerting procedure does not introduce a potential source of ignition, or an explosion will occur. NFPA 77 states [ 2 ] that carbon dioxide from high-pressure cylinders or fire extinguishers should never be used to inert a container or vessel.
A small amount of fuel in the tank leaves pumps on the floor of the tank exposed to the air-fuel mixture, and an electric pump is a potential ignition source. The explosion of a Thai Airways International Boeing 737 in 2001 and a Philippine Airlines 737 in 1990 also occurred in tanks that had a small amount of residual fuel.
The primary concept behind intrinsic safety is the restriction of available electrical and thermal energy in the system so that ignition of a hazardous atmosphere (explosive gas or dust) cannot occur. This is achieved by ensuring that only low voltages and currents enter the hazardous area, and that no significant energy storage is possible.
Alternatively, the ignition-limiting threshold is determined by performing a proper ignition test described in BSI PAS 95:2011 Hypoxic air fire prevention systems specification. [ 4 ] Smoke detectors are installed in protected volumes because, similar to gas suppression systems , hypoxic air does not prevent smoldering and pyrolyzing processes.
Cases also exist where the ignition factor is not the activation energy. For example, a smoke explosion is a very violent combustion of unburned gases contained in the smoke created by a sudden fresh air input (oxidizer input). The interval in which an air/gas mix can burn is limited by the explosive limits of the air.
Globally Harmonized System of Classification and Labelling of Chemicals uses a four category system to classify flammable liquids using flash point and boiling point temperature. [7] [8] This system is used internationally to evaluate and sort substances in industrial applications, workplaces and products distributed to consumers.
The MIE is one of the assessment criteria for the effectiveness of ignition, e.g. the discharge of electrostatic energy, mechanical ignition sources or electromagnetic radiation. It is an important parameter for the design of the protective measure of "avoidance of effective ignition sources". [2]