Peak side-on overpressure

Venting an explosion ahead of a flame arrester can reduce the thermal flux and the impulse to which the arrester is subjected. Test results indicate that peak side-on overpressure is halved, specific impulse is reduced by a factor of three, and the temperature is substantially reduced. However, overpressure and flame speed at the flame arrester do not appear to be changed significantly. 

In summary, an object s blast loading has two components. The first is a transient pressure distribution induced by the overpressure of the blast wave. This component of blast loading is determined primarily by reflection and lateral rarefaction of the reflected overpressure. The height and duration of reflected overpressure are determined by the peak side-on overpressure of the blast wave and the lateral dimensions of the object, respectively. The Blast loading of objects with substantial... 

Figure 4.18. Peak side-on overpressure due to a surface TNT explosion according to Marshall (1976). (TNT in kilograms.)...

The gauge records eimbient pressure Pq. At arrival time ta, the pressure rises quite abruptly (discontinuously, in an ideal wave) to a peak value Pj + Pq. The pressure then decays to ambient in total time tg + T+, drops to a partial vacuum of amplitude Pj, and eventually returns to Po in total time tg + T+ + T. The quantity P is usually termed the peak side-on overpressure, or merely the peak overpressure. The portion of the time history above initial ambient pressure is called the positive phase, of duration T+. That portion below Po, of amplitude Ps and duration T, is called the negative phase. 

Peak Side-on Overpressure, psi (bar) Consequences to Buildings Possible Building Occupant Injury Consequences... 

In the course of evaluating the risk to a nearby control room, blast parameters were calculated using the Multienergy method. At 300 ft (90 m), the peak side-on overpressure was determined to be 1.5 psi (0.10 bar). By the estimates shown in Table 3.5 and Table 4.8, at 1.5 psi (0.10 bar) sheet metal can be ripped off and internal walls can be damaged. It was felt that, at this level, the building could sustain sufficient damage to cause serious injury to the occupants, and further study evaluation should be performed. 

Peak side-on overpressure during the positive phase of the blast wave... 

Chapter 3 offers guidance on evaluating the characteristics (e.g., peak side-on overpressure, duration) of potential explosion or fire phenomena. Additional information is briefly summarized in Appendix A of this document. Information on performing more detailed evaluations of the consequences of these phenomena on buildings, structures, contents, and occupants is presented below. 

Figure 6-23 Correlation between scaled distance and explosion peak side-on overpressure for a TNT explosion occurring on a flat surface. Source G. F. Kinney and K. J. Graham, Explosive Shocks in Air (Berlin Springer-Verlag, 1985).

Use the scaling law given by Equation 6-21 and Figure 6-23 (or Equation 6-23) to estimate the peak side-on overpressure. 

The blast peak side-on overpressure and positive-phase duration are calculated from the Sachs-scaled overpressure and the Sachs-scaled positive-phase duration. The overpressure is given by... 

For shock waves weak enough that air behaves as a perfect gas, there is a fixed and well-known relation between peak reflected overpressure and peak side-on overpressure (References 5 and 11). 

It then gives a multiplier which yields the reflected pressure on the surface at this incidence angle, Pro- Figure 28 gives directly the Hopkinson-Cranz scaled reflected impulse irci, also given the incidence angle and peak side-on overpressure as inputs. By using these two curves, plots of variations of peak pressure and impulse over a wall surface can be estimated, for the first shock wave reflected from the surface. 

An important parameter for describing explosion effects is the peak side-on overpressure, ps. It can be represented by the following relationship for ps (in kPa), which stems from [57] and was scaled here to produce agreement with the Marshall curve (cf. [15])... 

Fig. 10.32 Peak side-on overpressure as a function of the scaled distance (so-called Marshall curve) according to Eq. (10.163) (Note since the curve is not defined in the region of pressures above 6.2 bar the corresponding region is set here equal to 6.2 bar as to the conditional probability of death this makes no difference, because it is already equal to 1 for 6.2 bar)...

In the plant of case study 4.2 there are 101.5 kg of the explosive hexogen during stationary production. What is the peak side-on overpressure at a distance of r = 20 m in case of an explosion What are the health effects to be expected for a person standing at this distance from the reactor and what is the probability for structural damage ... 

Figure 10.33 shows the peak side-on overpressure as a function of the distance on the ground (distance between the point of reference and the point where a vertical line through the centre of the fireball hits the ground) and the corresponding conditional probabilities of death according to Eqs. (B.22) and (2.56). 

Fig. 10. 33 Peak side-on overpressure in bar right hand side ordinate) and conditional probability of death as a function of distance for the explosion of a cloud of propane...

Example 10.26 Comparison of two production processes (reduction of inventory) Two types of plants for producing nitroglycol are compared with each other. In the first case a reactor with an inventory of 100 kg is used and in the second an injector nitration process with an inventory of 3 kg. What is the peak side-on overpressure in case of explosions at a distance of 10 m What are the TNT equivalents and what are the distance-dependent overpressures and the conditional probabilities of death for both cases ... 

This gives the following peak side-on overpressures... 

Fig. 10.34 Comparison of the distance-dependent peak side-on overpressures and conditional probabilities of death for two explosions of different quantities of nitrogycol...

The calculations are based on a set of ten empirical curves (vid. Fig. 10.35) for the peak side-on overpressure. The strength of the explosion is reflected by a number between 1 (small) and 10 (strong). 

According to Eq. (10.163) we have the scaled peak side-on overpressure... 

The energy E, also required for this model, is calculated according to Eq. (10.166) and the peak side-on overpressure according to Eq. (10.168). Concerning the remaining parameters the reader is referred to the cited literature. 

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