Overpressure, effect

TABLE 26-6 Blast Overpressure Effects on Vulnerable Refinery Parts... 

Overpressure effects due to the vessel failure appear to be determined by gas expansion, not by flash vaporization. 

Smaller explosions occurred until about 6 00 a.m. There was no evidence of strong overpressure effects, although a television news broadcast showed broken windows at 3.5 km (2 miles) from the plant. 

On the basis of an extended experimental program described in Section 4.1.3, Harris and Wickens (1989) concluded that overpressure effects produced by vapor cloud explosions are largely determined by the combustion which develops only in the congested/obstructed areas in the cloud. For natural gas, these conclusions were used to develop an improved TNT-equivalency method for the prediction of vapor cloud explosion blast. This approach is no longer based on the entire mass of flammable material released, but on the mass of material that can be contained in stoichiometric proportions in any severely congested region of the cloud. 

The solid lines in Figure 4.5 represent extrapolations of experimental data to full-scale vessel bursts on the basis of dimensional arguments. Attendant overpressures were computed by the similarity solution for the gas dynamics generated by steady flames according to Kuhl et al. (1973). Overpressure effects in the environment were determined assuming acoustic decay. The dimensional arguments used to scale up the turbulent flame speed, based on an expression by Damkohler (1940), are, however, questionable. 

This appendix is a summary of the woiit published in the so-called Green Book (1989). Possible effects of explosions on humans include blast-wave overpressure effects, explosion-wind effects, impact from fragments and debris, collapse of buildings, and heat-radiation effects. Heat-radiation effects ate not treated here see Chapter 6, Figure 6.10 and Table 6.6. 

Typical Damage Caused by Overpressure Effects of an Explosion... 

U.S. Army Corps of Engineers. "Overpressure Effects on Structures." HNDIR-75-23-ED-SR. Huntsville, AL. December 1975. 

J Pressure eyeing Equipment malfunc making Overpressure effects... 

Relief valve Prevents system from exceeding specified overpressure. Effectiveness of this device is sensitive to service and experience. 1 x 10 to 1 x 10 s 1 x 10 2... 

As indicated in Equation 3.8 and Section 3.3.2, the duration of the reflected overpressure effect, tc, should not exceed that of the free field positive overpressure,... 

Therefore, there are three main types accidents of tank area can trigger a domino effect fire, explosion, and fire—explosion occurred in both cases simultaneously cross. The first accident has devastating effects of thermal radiation, and other physical effects like overpressure effects may work on equipment close to the first unit, resulting in the close tank rupture, fire, explosion, that is the secondary accident. Under certain conditions, the secondary accident may lead to higher levels of three or more accident, causing extremely serious consequences of the accident. In simple terms is that two or more times of accidents caused by the initial Tank accident (mainly fire and explosion), and became a serious consequences phenomenon is called Tank domino effect. Figure 1 shows the mechanism of Domino effect in LPG tank area accidents. 

Explosion Effects. Explosion overpressure effects that are of interest here result either from the rapid combustion of a fuel-air mixture (confined explosion or VCE), or a sudden release of pressure energy (BLEVE). 

Flash and evaporadon Dispersion Neutral or posidvely buoyant gas Dense gas Fires Pool fires Jet fires BLEVES Flash fires Explosions Confined eiqilosions Unconfined vapor cloud explosions (UVCE) Physical explosions (PV) Dust explosions Deionadons Condensed phase detonadons Missiles Consequences Effect analysis Toxic effects Thermal effects Overpressure effects Damage assessments Community Workforce Environment Company assets... 

The major difficulty presented to anyone involved in CPQRA is in selecting the proper outcomes based on the available information and determining the consequences. The consequences of concern in CPQRA studies for explosions in general arc blast overpressure effects and projectile effects for fires and fireballs the consequences of concern arc thermal radiation effects. Each of these types of explosions and fires can be modeled to produce blast, projectile and/or thermal radiation effects appropriate for use in CPQRA studies and these techniques are described in the designated sections. 

The output of a BLEVE model is usually the radiant flux level and duration. Overpressure effects, if important, can also be obtained using a detailed procedure described elsewhere (AIChE, 1994). Fragment niunbcrs and ranges can be estimated, but a probabilistic approach is necessary to determine consequences. 

Under atmospheric conditions the stability of gas emulsions is critically dependent on their size. Surface tension effects lead to an elevated total pressure (i.e. Laplace pressure) inside the bubble, quickly leading to dissolution. For a 1 pm bubble with a = 50 mN m", the Laplace pressure, piapiKc o Jr, is nearly twice the atmospheric pressure (pam)- When injected into the bloodstream, efflux of gas from the bubbles is further enhanced by blood pressure, Pbiood-In order to overcome the overpressure effects on small gas emulsion bubbles, a... 

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