Critical bums

Critical bums—Second-degree bums covering more than 30 percent of the body and third-degree bums covering over ten percent. 

Artificial surfaces must be resistant to cigarette bums, vandaUsm, and other harm. Fire resistance is most critically evaluated by the NBS flooring radiant panel test (10). In this test, a gas-fired panel maintains a heat flux, impinging on the sample to be tested, between 1.1 W/cm at one end and 0.1 W/cm at the other. The result of the bum is reported as the flux needed to sustain flame propagation in the sample. Higher values denote greater resistance to burning results depend on material and surface constmction. Polypropylene turf materials are characterized by critical radiant flux indexes which are considerably lower than those for nylon and acryflc polymers (qv) (11). 

Liquid fuel is injected through a pressure-atomizing or an air-blast nozzle. This spray is sheared by air streams into laminae and droplets that vaporize and bum. Because the atomization process is so important for subsequent mixing and burning, fuel-injector design is as critical as fuel properties. Figure 5 is a schematic of the processes occurring in a typical combustor. 

Hot surfaces can produce serious bums to personnel in chemical plant operations. Surfaces tliat are witltin reach of personnel should be insulated or tlie areas shielded from accidental contact. Many critical areas in chemical plant operations should be restricted to all but e.xperienced workers. 

It is an unfortunate characteristic of propellants that they invariably bum to detonation if there is more than a critical depth of powder above the point of ignition. This depth depends greatly on the composition and on the grain size. It may vary from about 10 cm to several metres. In processing, the critical depth for the product being made is not exceeded unless full precautions for handling a detonating explosive are taken. 

Let us examine the 1300 °C criterion as a condition of flame extinction in diffusive burning to see how these critical conditions depend on oxygen and external radiation. After all, these two parameters - oxygen and radiation - are the two significant variables that make most solids bum. We will look to some data for anchoring this application. 

Hydrocarbon vapors immediately bum with flame temperatures that are considerably higher than that of ordinary combustibles. For this reason damage from a hydrocarbon fire is much more severe than an ordinary combustible fire. The objective of a fire detection for the petroleum industry is to rapidly detect a fire where personnel, high value, and critical equipment may be involved. Once detected executive action is initiated to alert personnel for evacuation and while simultaneously controlling and suppressing the fire incident. 

Levy et al. (L5) have studied the effect of eccentricity on the bum-out flux in upward vertical annular flow. Eccentricity does not affect the burn-out flux until the annular separation is about 20% or less of its concentric value. Bum-out fluxes for great eccentricities are increased about 30%, which is ascribed to poor fluid mixing pressure-drop at the same conditions is reduced. The small effect of moderate eccentricity in downward annular flow of steam-water mixtures was also reported earlier by Stein et al. (Sll) in their study of pressure-drop and critical flow. 

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