Fire hazards following loss of containment include pool fires, jet fires or flame jets, flash fires or vapor cloud fires, and fireballs. A pool fire occurs when a liquid pool is ignited following a liquid spill on land or water. A flame jet occurs following a pressurized release and ignition of a flammable gas or two-phase mixture. A flash fire results from the delayed ignition of a flammable vapor cloud. Flash fires can burn back to the source of release and can produce severe blast waves if flame acceleration occurs. Fireballs typically occur following catastrophic vessel failures and immediate ignition of released flammable materials. Fireballs are often observed following a boiling liquid expanding vapor explosion (BLEVE) caused by catastrophic vessel failure due to external fire heating or runaway chemical reaction heating.
In what follows, we discuss methods that can be used to assess thermal radiation hazards resulting from pool fires, flame jets, fireballs, and flash fires.
Several models are commonly used to assess the thermal radiation hazards of pool fires, vapor cloud fires, fireballs, flame jets, and flares. These models are generally divided into three classes: (a) point source or line source models, (b) solid flame models, and (c) computational fluid dynamics (CFD) models. A line source model is made up of multiple point sources. A solid flame model represents the flame and flame surfaces using idealized cylindrical and/or rectangular geometries.
The simplest model for the estimation of thermal radiation hazards from fires is the point source model. The incident flux, I, at any location is described using the following relation: where s is the distance in m from the point source to target surface receiving the incident flux, Ɵ is the angle between normal to the surface and line of sight from the point source, τ is the atmospheric transmissivity, and xr is the fraction of total combustion energy radiated by the fire in all directions to the surroundings (except to the liquid pool surface), △Hc is the total heat of combustion in J / kg, M is the mass burning rate in kg / s, xt, yt, and zt are the Cartesian coordinates of the target surface receiving thermal radiation, and x, y, and z are the Cartesian coordinates of the point source usually selected at the center of the fire.
The heat release rate, QT , represents the total combustion energy of the pool liquid or liquid mixture in J / s, and I (xt, yt, zt) is the incident thermal radiation heat flux received by the target surface in J / s / m2 or W / m2.
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