Liquid-vapor releases, flashing

Other factors that affect the discharge of a flashing, two-phase, liquid-vapor release include ... 

Behavior of Flashing, Mixed Liquid-Vapor Releases... 

Flash back The ignition of vapors and the travel of the flame back to the liquid/vapor-release source. 

In a later paper, Brasie (1976) gives more concrete recommendations for determining the quantity of fuel released. A leak potential can be based on the flashing potential of the full amount of liquid (gas) stored or in process. For a continuous release, a cloud size can be determined by estimating the leak rate. For a combined liquid-vapor flow through holes of very short nozzles, the leak rate (mass flow per leak orifice area) is approximately related to the operating overpressure according to ... 

Most combustible liquids do not present a vapor problem if accidentally released into the atmosphere. The probability of a fire, therefore, is considerably less than it would be if the spill was of a flammable material. If, however, the combustible liquid is at a temperature higher than its flashpoint, then it can be expected to behave in the identical manner a flammable liquid. One major difference between the two in a fire situation is that the potential exists for cooling the combustible liquid below its flash point by the proper application of water (generally applied in the form of water spray). In the event the liquid is burning, and if the fire forces are successful in achieving the required reduction in liquid temperature, then vapor production will cease and the fire will be extinguished because of a lack of vapor fuel. Unless this reduction in liquid temperature can be brought about, the fire will necessitate the same control considerations a low-flash liquid fire would. 

For alternative evaluations, the weight of flammable material in a vapor cloud can be calculated as the gas-release or vapor-release rate multiplied by the estimated time required to stop the release. For liquid releases, the vapor-release rate would be calculated from the liquid-release rate multiphed by twice the flashing fraction (to account for aerosol vaporization) or, for hquids released below the boiling point, as the rate of vaporization from a pool multiplied by the estimated time required to cover or dilute the pool. Also, a lower energy-conversion efficiency (such as 0.03) can be used in the calculation. 

Degree two (2) includes liquids with a flash point above 100 F but below 200°F, and solids and semisolids which easily release flammable vapors. Proprionic anhydride, ortho toluidine, methacrylic acid and dimethyl sulfate are examples of this class. 

Applies to liquids with a flash point below 21 °C. Explosive air-vapor mixtures are very likely to form if the liquid is released at normal ambient temperature (indoors or outdoors). 

If a superheated liquid is released a certain fraction vaporizes on depressurization (flash) the remainder is cooled down because it has to provide the enthalpy of vaporization. The heat balance based on the assumption of adiabatic depressurization is... 

The fraction of released liquid vaporized F ) is a poor predictor of the total mass of material in the vapor cloud, because of the possible presence of entrained liquid as droplets (aerosol). There are two mechanisms for the formation of aerosols mechanical and thermal. The mechanical mechanism assumes that the liquid release occurs at high enough speeds to result in surface stress. These surface stresses cause liquid droplets to breakup into small droplets. The thermal mechanism assumes that breakup is caused by the flashing of the liquid to vapor. 

Rain out When a superheated liquid is released to the atmosphere, a fi action of it will flash into vapor. Another fraction may remain suspended as an aerosol. The remaining liquid, as well as portions of aerosol, may rain out on the ground. 

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