Vapor ignition, flammability

Mists Althougn charged mists are unable to cause ignition of flammable vapor by self-generated sparking, it is impoi tant that the mist not impinge upon an ungrounded conduc tor. 

Ignition of condensed flammable vapor or solid deposits in ductwork/ piping. Possibility of fire/explosion. 

Eriction from contact of moving parts, tramp metal, bearings or seals initiating thermal decomposition or igniting flammable vapors. 

A logic model that graphically portrays the range of outcomes from the combinations of events and circumstances in an accident sequence. For example, a flammable vapor release may result in a fire, an explosion, or in no consequence depending on meteorological conditions, the degree of confinement, the presence of ignition sources, etc. These trees are often shown with the probability of each outcome at each branch of the pathway... 

Fire Hazards - Flash Point Not flammable Flammable Limits in Air (%) Not flammable Fire Extinguishing Agents Not pertinent Fire Extinguishing Agents Not To Be Used Not pertinent Special Hazards of Combustion Products Not pertinent Behavior in Fire Pressurized containers may explode and release toxic and irritating vapors Ignition Tenperature Not pertinent Electrical Hazard Not pertinent Bunting Rate Not pertinent. 

As a general rule, vacuum relief devices are permitted on offsite storage vessels handling clean finished products, since there is essentially no possibility of an internal ignition source. However, vacuum relief devices which permit breaking of a vacuum with inerts or flammable vapors are not permitted on process equipment, since they are not judged to be sufficiently rehable to provide adequate protection under all circumstances. Vacuum devices which permit air to enter may be considered, however, in cases where the equipment does not or cannot contain flammables e.g., some steam systems. 

Releases of flammable vapors which, if discharged to the atmosphere, would in the event of inadvertent ignition result in radiant heat densities in excess of the permissible exposure level for personnel. This maximum level is defined as 19 Kw/m at ground level. 

Flare systems are subject to potential flashback and internal explosion since flammable vapor/air mixtures may be formed in the stack or inlet piping by the entry of air, and the pilot constitutes a continuous ignition source. Flares are therefore always provided with flashback protection, which prevents a flame front from travelling back to the upstream piping and equipment. Design details are described later. 

The fireball resulting from ignition of a cloud of flammable vapor may be relatively long lasting (2-5 seconds), and represents a thermal radiation hazard to those close to the cloud CCPS (1994b). 

Even if a flammable vapor cloud is formed, ignition is necessary for a UVCE. Hov----------- ,... 

A reactor was prepared for maintenance and washed out. No welding needed to be done, and no entry was required, so it was decided not to slip-plate off the reactor but to rely on valve isolations. Some flammable vapor leaked through the closed valves into the reactor and was ignited by a high-speed abrasive wheel, which was being used to cut through one of the pipelines attached to the vessel. The reactor head was blown off and killed two men. It was estimated that 7 kg of hydrocarbon vapor could have caused the explosion. 

It would be going too far to say that no one should ever enter a cloud of flammable vapor to isolate a leak. There have been occasions when, by taking a risk for a minute, a man has isolated a leak that would otherwise have spread a long way and probably ignited, perhaps exploded. However, we should try to avoid putting people in such situations by providing remotely operated emergency isolation valves to isolate likely sources of leak. 

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