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NOTE: This is an unformatted excerpt from our online fire protection training library.

Identifying Materials & Equipment

Liquids, Vapors & Gases

Explosion Pressure and Pressure Piling

Explosion pressures are evaluated by comparison to gasoline. Acetylene is assigned to its own group primarily because of its high explosion pressureExplosion pressure is no longer a criteria in determining Group assignments of materials. Based on the current criteria, acetylene belongs in the same group as hydrogen, and is grouped with hydrogen under the Zone classification grouping system. Acetylene keeps its own Group under the division classification system because it was historically separated based on explosion pressure, and because much of the equipment for use in acetylene areas was already available.. Pressure pilingPressure piling is related to the fact that a flame front moving through a length of conduit tends to prepressurize the mixture ahead of it, thus increasing the explosion pressure as the flame moves through the conduit. The effects of pressure piling can be reduced by dividing the overall enclosure system (of which conduit is a part) up into smaller pieces and isolating conduit runs from the most likely ignition sources in enclosures. is a related phenomenon that sometimes changes the requirements for electrical equipment or causes materials to be assigned to more than one group Butadiene, ethylene oxide, propylene oxide, and acrolein are assigned to more than one group and are permitted to use equipment designed for the less dangerous group if all conduit entries are sealed to reduce the effects of pressure piling..

NOTE: This is an unformatted excerpt from our online fire protection training library.

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