Overpressures estimating

In each case, two different methods were used in arriving at estimates the HSE TNT-equivalency method and the multienergy method. The results, in the form of side-on blast peak overpressures for various distances from blast centers, are listed in Table 7.10. In addition, some peak overpressures estimated by Sadee et al. (1976/ 1977) from Flixborough-incident damage patterns are included. The photographs in Figures 7.6a and 7.6b illustrate the practical effects of such overpressures. 

Another important feature of mud logging and MWD/LWD, is the capability of overpressure zone detection. As was discussed previously in this section, overpressure estimates can be done during drilling with many techniques and accuracy increases with the number of parameters available. 

Pironon, J., Boirrdet, J. (2008) Petroleum and aqneous inclusions from deeply buried reservoirs experimental simirlations and consequences for overpressure estimates. Geochimica et Cosmochimica Acta, 72, 4916-4928. 

The main and works office buildings were totally destroyed, as were the laboratory and main control room. The 0.4-m-thick concrete second floor of the southeast corner of Section 27 was displaced downwards (Roberts and Pritchard, 1982), indicating an aerial flammable cloud at this location. A tanker truck (cf. Fig. 42.7) located about 150 m east of the southern end of Section 27 was completely crushed by an overpressure estimated to be about 1 MPa (Gugan, 1976). A manhole cover located on the roadway nearly in front of the main office building and midway between the gate house and section 25A was broken by a similar overpressure (Gugan, 1976). 

Protect vessel from overpressure Estimate minimum flow through emergency relief system. 

The maximum distance that a 1-psi overpressure will be felt is estimated to be 500 meters. 

Equation 12-18 gives a eonservative estimate of the vent area, and the simple design method represents overpressure (AP) between 10%-30%. Eor a 20% absolute overpressure, a liquid heat eapaeity of 2,510 J/kg K for most organies, and eonsidering that a saturated water relationship exists, the vent size area per 1,000 kg of reaetants is ... 

Answer Use the plant s PSA to determine the risk of accidents that include containment failure from overpressurization. Then make a preliminary design of a vented containment that has sufficiently low impedance to the gas at the pressure predicted for the most severe accident sequences such that the containment is not damaged. This containment bypass will include iodine and HEPA filters as well as scrubbers and a discharge through a stack. Estimate the dose that the population would get using this bypass for comparison with the PSA result for ruptured containment sequences. 

There are no clearly discernable, broadly applicable, correlations between the 6-inch and 1 S-inch deflagration and detonation experiments. Therefore, comparisons were done on a parameter-byparameter basis. However, comparisons of data taken during experiments with the two pipe sizes reveal that enough scale-related differences exist that interpolation between the two scales for an intermediate size should be done only where conditions are very similar. Then, overpressure and specific impulse can be estimated based on L/D. 

For describing structural loading functions needed for design analysis, the use of overdriven detonation data representing the net overpressure (run-up side less protected side overpressure) on the arrester element and supporting structure is preferable to data representing only the run-up side, side-on overpressure. However, the run-up side transient history of side-on overpressure for overdriven detonations should provide a conservative estimate for design purposes (see Chapter 6). 

Making a detailed estimate of the full loading of an object by a blast wave is only possible by use of multidimensional gas-dynamic codes such as BLAST (Van den Berg 1990). However, if the problem is sufficiently simplified, analytic methods may do as well. For such methods, it is sufficient to describe the blast wave somewhere in the field in terms of the side-on peak overpressure and the positive-phase duration. Blast models used for vapor cloud explosion blast modeling (Section 4.3) give the distribution of these blast parameters in the explosion s vicinity. 

Flame acceleration does not generate extremely high overpressures. That is, numerical simulation of an explosion process with a steady flame speed equal to the highest flame speed observed results in a conservative estimate of its blast effects. 

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 ... 

Once the equivalent charge weight of TNT is estimated, the blast peak overpressures in the field can be found by applying this charge weight to the scaled distance in the blast chart (Figure 4.18). 

A safe and most conservative estimate of the strength of the sources of strong blast can be made if a maximum strength of 10 is assumed. However, a source strength of 7 seems to more accurately represent actual experience. Furthermore, for side-on overpressures below about 0.5 bar, no differences appear for source strengths ranging from 7 to 10. 

If such an approach results in unacceptably high overpressures, a more accurate estimate of initial blast strength may be determined from the growing body of experimental data on gas explosions (reviewed in Section 4.1), or by performing an experiment tailored to the situation in question. 

Once the energy quantities E and the initial blast strengths of the individual equivalent fuel-air charges are estimated, the Sachs-scaled blast side-on overpressure and positive-phase duration at some distance R from a blast source can be read from the blast charts in Figure 4.24 after calculation of the Sachs-scaled distance ... 

For /f < 2, the basic method gives too high a value for blast overpressure. In such cases, use the refined method, described in Section 6.3.3.2., to obtain a more accurate pressure estimate. 

In practice, overpressures in one case might very well be only one-fifth of those predicted by the method and close to the predicted value in another case. This inherent inaccuracy limits the value of this method in postaccident analysis. Even when overpressures can be accurately estimated from blast damage, released energy can only be estimated within an order of magnitude. 

Experimental data (Section 4.1) may be used to estimate a blast s initial strength. These data indicate that deflagrative gas explosions may develop overpressures ranging from a few millibars under completely unconfined or unobstructed conditions to greater than 10 bars under severely confined and obstructed conditions. 

Once the energy quantities E and the initial blast strengths of the individual equivalent fuel-air charges are estimated, the Sachs-scaled blast side-on overpressure and... 

Figure 7.6. (a) Damage to canteen building 130 m from explosion center. Estimated peak overpressure level 0.45-0.55 bar (Sadee et al. 1976/1977). (b) Damage to row of houses 535 m from explosion center. Estimated peak overpressure level 0.10-0.12 bar (Sadee et al. 1976/1977). 

It does not seem likely that the liquid flashed explosively, because the actual overpressure at 300 m in Mexico City was estimated to be below 3 kPa. This conclusion is consistent with the findings of Pietersen, although he assumed that... 

Figure 1 shows part of a solvent phase polypropylene plant. The plant consists of three process lines, denoted A, B, and C. During a risk assessment review, a scenario was identified that involved a release of reactor contents from a location near the west end of the A line. Estimates are needed of the blast overpressures that would occur if the resulting cloud of vapor, mist, and power ignites. 

Different materials pose different hazards, including thermal radiation, explosion overpressure, and toxic and flammable vapor clouds. Some materials pose only one hazard, while others may pose all four. For the purposes of ranking facilities you will need to estimate the laigest area affected by the potential hazards. You can arrive at such an estimate by calculating the greatest downwind distance to a particular level of hazatd. The following thresholds are commonly applied ... 

Explosion calculations, 499-504 Estimating destruction, 501 Overpressure, 502 Pressure piling, 501, 504 Relief sizing, 505 Scaled distance, 502, 503 Schock from velocity, 503 TNT equivalent, 499-504 Explosion characteristics of dusts, 515 Explosion suppression, 518 Explosion venting, gases/vapors, 504 Bleves, 504 Explosions, 482 Blast pressure. 496 Combustion, 482 Confined, 482 Damage, 498-501 Deflagration, 482 Detonation, 483... 

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. 

A small engineering building is located 350 ft (107 m) from the process unit discussed in Example 8. It has an occupancy load of 500 person-hours, which exceeds the company s occupancy criteria. The building is constructed of unreinforced concrete and contains several windows. Earlier calculations estimated the incident side-on overpressure to be 0.5 psi at 350 ft (0.069 bar at 105 m). 

By the estimates shown in Table 4.8, the calculated incident side-on overpressure of 0.5 psi (0.069 bar) should not cause significant damage to the building. However, glass breakage could occur. It was determined that the windows should be eliminated or strengthened. 

Each scenario was modeled to determine the explosion overpressure at the three buildings under review. The resultant overpressures, and corresponding vulnerability estimates, for the most severe scenario in each process area are tabulated below. 

It should be noted that consequence screening is performed without regard to the likelihood of an event s occurring. As a result, consequence screening does not determine risk. Furthermore, the consequence evaluation performed may not represent a detailed evaluation of consequences to the process plant. Instead, it is an approximation of expected consequences, given an estimate of potential blast overpressure and anticipated response of representative building types. The user should not mistake this evaluation for a detailed consequence assessment. 

Table 5.3 may be used in conjunction with the estimate of blast overpressure contours discussed previously to conduct a qualitative site assessment for the design and siting of buildings in process plants. 

Using Table 6.11 a in Reference 5, divide Ps by an estimated (assume 0.03 adjustment factor to get equivalent Ps since the geometry effects cause longer distances to the ps endpoint overpressure conditions. 

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