Explosion overpressure study

Experimental studies have proved that the influence of vent duct with longitudinal arrangement—located on the roof—decreases markedly with increased vessel length-to-diameter ratio. The increase of the maximum explosion overpressure is at its maximum if vessel ratio UD = 1. 

Previous studies of Vapor Cloud Explosions (VCE) have used a correlation between the mass of a gas in the cloud and equivalent mass of TNT to predict explosion overpressures. This was always thought to give conservative results, but recent research evidence indicates that this approach is not accurate to natural gas and air mixtures. The TNT models do not correlate well in the areas near to the point of ignition, and generally over estimate the level of overpressures in the near field. Experiments on methane explosions in "unconfined" areas have indicated a maximum overpressure of 0.2 bar (2.9 psio). This overpressure then decays with distance Therefore newer computer models have been generated to better simulate the effects... 

This subject has received little attention in the context of pressure vessel bursts. Pittman (1976) studied it using a two-dimensional numerical code. However, his results are inconclusive, because the number of cases he studied was small and because the grid he used was coarse. Baker et al. (1975) recommend, on the basis of experimental results with high explosives, the use of a method described in detail in Section 6.3.3. That is, multiply the volume of the explosion by 2, read the overpressure and impulse from graphs for firee-air bursts, and multiply them by a factor depending on the range. 

In this section, three examples of blast calculations of BLEVEs and pressure vessel bursts will be given. The first example is designed to illustrate the use of all three methods described in Section 6.3.2. The second is a continuation of sample problem 9.1.5, the BLEVE of a tank truck. A variation in the calculation method is presented instead of determination of the blast parameters at a given distance from the explosion, the distance is calculated at which a given overpressure is reached. The third example is a case study of a BLEVE in San Juan Ixhuatepec (Mexico City). 

The explosive phenomena produced by contact of liquefied gases with water were studied. Chlorodifluoromethane produced explosions when the liquid-water temperature differential exceeded 92°C, and propene did so at differentials of 96-109°C. Liquid propane did, but ethylene did not, produce explosions under the conditions studied [1], The previous literature on superheated vapour explosions has been critically reviewed, and new experimental work shows the phenomenon to be more widespread than had been thought previously. The explosions may be quite violent, and mixtures of liquefied gases may produce overpressures above 7 bar [2], Alternative explanations involve detonation driven by phase changes [3,4] and do not involve chemical reactions. Explosive phase transitions from superheated liquid to vapour have also been induced in chlorodifluoromethane by 1.0 J pulsed ruby laser irradiation. Metastable superheated states (of 25°C) achieved lasted some 50 ms, the expected detonation pressure being 4-5 bar [5], See LIQUEFIED NATURAL GAS, SUPERHEATED LIQUIDS, VAPOUR EXPLOSIONS... 

Few in-depth studies have been made of actual furnace smelt-water explosions and, therefore, it is difficult to delineate expected overpressures and impulses. One case history is presented to indicate in a qualitative fashion the type of damage in a large explosion. 

Information gained from simulations can reveal key insights that explain gaps or contradictions in information. The time line is a useful tool in this development. For incidents of unexpected chemical reactions, it is common to attempt a lab scale simulation of the conditions involved in the exotherm or explosion. Many chemical processes can be modeled and duplicated dynamically by computer algorithms. Accelerated rate calorimeters (ARC) have proven to he highly useful tools for studying exothermic or overpressure runaway reactions. 

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 ... 

The flame path is reconstructed from the signals of ionization probes located along the system and correlated to pressure time records t en in the vessel and at several locations along the duct. First, the explosion in the vented but unducted (L=0) chamber is studied for increasing size of the hole. Then, in the ducted cases, the changes in the amplitude and in the rate of increase of the overpressure in the vessel are examined in connection with the flame history through the duct, which depends on the... 

With the introduction of potent and costly drug substances, the 2 bar design is being replaced with a 10 bar design and higher, based on the specific mixtures of the product(s) being processed. These units can withstand explosions up to 10 bar. Most of the pharmaceutical dust explosions studied (143) show the overpressure reaching... 

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 focus of the present work is on the peak overpressure profile generated by the explosion of a vessel containing a pressurized gas. To this end, the previous models are applied to a number of study cases, changing the values of the parameters appearing in the model equations and comparing the calculated peak overpressure profiles. 

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