For detonation there are multiple published studies, whereas for deflagration no welladapted and rigorous method has been reported in the literature. Catlin a mathematical model of the overpressure field due to the deflagration of a point ignited ground lying vapour cloud is described. Also shown are the effects of blockage geometry on the delay time taken to. Effects of the ignition positions on the overpressure characteristics of the premixed. The information may also be relevant to the problem of assessment of the consequences of such. Flame acceleration and ddt can generate high peak pressures that may cause failure of containment. Blast injuries occur with the detonation of highorder explosives as well as the deflagration of low order explosives. Silane vce blast effects 24th icders july 28 august 2, 20 taiwan 3 given a flame speed and an average expansion ratio, the blast overpressure and impulse as functions of distance from the explosion centre can be determined see 12 for details. But unlike with a relief vent, the deflagrations overpressure, flame, and material discharge through the membrane into guidelines for choosing an explosion protection system for your dust collector part i emre ergun fenwal protection systems as appeared inoctober 2011 pbe. An overview of the effects of blast injuries at the medical level presented by. Protection against overpressure due to phenomena other than internal deflagrations e.
The temperature effect can be clearly seen by considering the overpressure at flame. Conversely, while it is certainly true that gradually increasing internal pressure increases the probability of a leak from flanges, packing, seals, and instrument connections, it is also true 328. Results of an empirical equation for the effects of initial pressure on flammability limit, is established from this study. The onway peak overpressure and flame propagation speed of gas deflagration in the tube with obstacles are important data for process safety. Possible effects of explosions on humans include blastwave overpressure effects, explosionwind effects, impact from fragments and debris, collapse of buildings, and heatradiation effects. In the absence of turbulence, under laminar or nearlaminar conditions, flame speeds are too low to produce significant blast overpressure. Explosive blast 4 explosive blast 41 this chapter discusses blast effects, building damage, injuries, levels of protection, standoff distance, and predicting blast effects. The model is based on acoustic theory with additional assumptions about the changes in the cloud.
For a given burning velocity the overpressure in a spherical cloud is larger. Also shown are the effects of blockage geometry on the delay time taken to reach these pressures. Characteristic overpressureimpulsedistance curves for. For almost 50 years, exponents engineers and scientists have investigated several thousand separate explosions that have involved a wide range of solid, liquid, and gaseous fuels. Based on carbon monoxide deflagration experiments, the paper presents a multizone integration model for calculation of onway peak overpressure, in which the tube with obstacles is considered as a series of venting explosion. By recognizing the unique features of blast injuries and by.
Regarding overpressure effects, actually pressure equilibrate quite fast in the compartment since sound velocity in air is around 340 ms, pressure between points 5 or 10 m apart will equilibrate in 0,0150,03 s. For solid fuels transported by truck or rail, the methodologies presented in regulatory guide 1. Nfpa 68, standard on explosion protection by deflagration venting addresses the design, location, installation, maintenance and use of devices and systems that vent the combustion gases and pressures from a deflagration. Safety considerations of thermal and overpressure effects article pdf available in international journal of hydrogen energy 3935 june 2014 with 77 reads. Jay wuerker, emtp ems instructor ii objectives describe the basic physics, mechanisms of injury, and pathophysiology of blast injury list the four types or categories of blast injuries list the factors associated with increased risk of primary blast injury. An acoustic model for predicting the overpressures caused. Deflagration is an explosion that propagates at subsonic velocity en 11271. Overpressure or blast overpressure is the pressure caused by a shock wave over and above normal atmospheric pressure. In the dynamic pressure this region the air pressure is below that 3. Study on peak overpressure and flame propagation speed of. An acoustic model for predicting the overpressures caused by. Study on peak overpressure and flame propagation speed of gas. Effects of initial pressure on the flammability limit of ox.
Overpressure in bleves and similar explosions, journal of hazardous materials, vol. Nuregcr5275, flame facility the effect of obstacles and. The flame propagation behaviour, pressuretime history, and flame. Blast effects of external explosions hal archive ouverte. The effects of explosive blast on structures and personnel richard w. Venting of deflagrations in buildings and equipment. If the combustion process propagates outward at subsonic speeds slower than the speed of sound, its a deflagration. Peak overpressure maximum wind speed effect on structures effect on the human body 1 psi 38 mph window glass shatters. The model calculates the tnt equivalent mass w tnt, which is the mass of tnt that would produce the same effects as the amount involved in the explosion. Deflagration and detonation are two ways energy may be released. If the explosion moves outward at supersonic speeds faster than the speed of sound, its a detonation. Pdf explosion relief panels or doors are often used in industrial buildings to reduce damages. The overpressure to be expected in the deflagration of an unconfined hydrogenair vapour cloud is in the order of 10 kpa.
After 10 seconds, when the fireball of a 1megaton nuclear weapon has attained its maximum size 5,700 feet across, the shock front is some 3 miles farther ahead. Effects of initial pressure on the flammability limit of. Protective walls against effects of vapor cloud fast. Safety considerations of thermal and overpressure effects hall, j. Introduction this appendix is a summary of the work published in the socalled green book 1989. The threshold for lung damage occurs at about 15 psi blast overpressure. Pdf the effects of obstructions on overpressure resulting. Limitations of gas explosion venting due to accelerated flame. The human body can survive relatively high blast overpressure without experiencing barotrauma. In addition to these causes of injury and death, crush injury, entrapment, and compartment syndrome magnify the devastation of blast trauma. Table 1 effect of various long duration blast overpressures and the associated maximum wind speed on various structures and the human body. Protective walls are an efficient way to protect people and infrastructures from overpressure effects due to accidental or malicious explosions detonation or deflagration. Here, two safety characteristics are essential for the design. The premixed stoichiometric methaneair deflagration is conducted in a transparent square crosssection duct.
Combustion burning is a process by which energy is released. If designed and sized correctly, explosion vents reduce the maximum pressure p max of a deflagration to a safe level p. There are several currently referenced empirical correlations and emerging computer models to predict effects of. The shock wave may be caused by sonic boom or by explosion, and the resulting overpressure receives particular attention when measuring the effects of nuclear weapons or thermobaric bombs. The tnt equivalent mass describes the effect of the. Deflagration and detonation differ in peak overpressure, in the duration of the impulse time. Deflagrations occur most frequently in dust collectors, conveyors, elevators, dryers, mills, storage vessels, and entire buildings or rooms. Depending on the geometric shape of the combustion area, a distinction is made between atmospheric deflagration, prevolume deflagration, and inline deflagration. Limitations of gas explosion venting due to accelerated. The effects of bombings and blast injuries are both physically and psychologically devastating.
Under extraordinary conditions, a detonation with more severe blast effects might occur. Effect of hydrogen concentration on vented explosion. The first peak on the plot represents the initial deflagration of the cloud back to the. The effects of obstructions on overpressure resulting from. Conversely, while it is certainly true that gradually increasing internal pressure increases the probability of a leak from flanges, packing, seals, and instrument connections, it. This paper evaluates current analytical methods to determine the characteristic parameters of a blast wave with respect to the pressure, impulse and duration of the positive phase of the blast. The deflagration overpressure produced by a flammable mixture that fills less than 30%50% of the enclosure volume is. Typical damage caused by overpressure effects of an explosion.
Potential for deflagration to detonation transition in trees and bushes effects of overpressure on items typical of those observed at buncefield and jaipur. Figure 2 shows a graph generated using the apt correlations for overpressure when rocket motor segments of varying. Calculation of blast loads for application to structural. The term deflagration is often confusing to users, so the committee changed the title in an effort to simplify user understanding of the application of the standard. The overpressure computed with spatial resolutions of 5cm, 7cm and 8cm shows. Appendix a explosion and fire phenomena and effects. Obtaining a tnt equiv alent for various types of explosions, such as pressurevessel burst, boilingliquid expandingvapor explosion bleve, unconfined or confined vaporcloud explosion, deflagration.
Supersonic high pressure shock front ahead of the reaction zone i. For detonation there are multiple published investigations concerning interactions of blast waves and walls, whereas for deflagration no well. Based on carbon monoxide deflagration experiments, the paper presents a multizone integration model for calculation of onway peak overpressure, in which the tube with obstacles is considered as a series of venting explosion enclosures which link each. Methodology for assessing a boiling liquid expanding vapor. Characteristic overpressureimpulsedistance curves for the. In such a case, the cloud will merely burn as a flash fire. Blast effects are usually measured by the amount of overpressure, the pressure in excess of the normal atmospheric value, in pounds per square inch psi. Characteristic overpressureimpulsedistance curves for the detonation of explosives, pyrotechnics or unstable substances fernando d. Guidelines for choosing an explosion protection system for. Our clients have included companies in the petroleum and chemical fields, defense and aerospace industry, oil and gas. Results are shown for various obstruction types used here. The deflagration characteristics of premixed lng vapourair mixtures with different mixing ratios were quantitatively and qualitatively investigated by using cfd computational fluid dynamics method. The cfd model was initially established based on theoretical analysis and then validated by a labscale deflagration experiment.
These injuries are compounded when the explosion occurs in a confined space. Overpressure calculation for unvented partial volume. This paper aimed at studying the flame propagation and the overpressure effect in the process of deflagration by conducting cfd computational. A 5 psi blast overpressure will rupture eardrums in about 1% of subjects, and a 45 psi overpressure will cause eardrum rupture in about 99% of all subjects. Fast deflagration in the intermediate stage of a fast deflagration with the flame front still travelling at subsonic speed, a preceding shock wave is developing in the still unburnt mixture. Air force that updated many of the initial relationships2. The effects of obstructions on overpressure resulting from premixed flame deflagration. Pdf blast effects of external explosions researchgate.
Protection by deflagration venting and en 14994 gas explosion venting protective systems. The maximum reflected pressure for a fast deflagration is of order 10 bar 145 psi. For detonations, there are several engineering or cfdbased design rules for barricades design in the literature, such as nota. The tnt equivalent mass describes the effect of the explosive at a certain space when it blasts rui, lizhong. Protective walls are a wellknown and efficient way to mitigate overpressure effects of accidental explosions detonation or deflagration. Specific blast design concerns and mitigation measures are discussed in chapters 2 and 3.
Sulfur pit explosion protection by deflagration venting. Deflagration is a surface phenomenon with the reaction proceeding towards the. Deflagration venting is an explosion protection measure that involves the provision of a predesigned escape route called an explosion vent for the release of the pressure and flame generated during an explosion quickly enough to prevent a dangerous build up of pressure within the vessel, pipes and ducts, or building that is being protected. This paper focuses on the effects of a fast deflagration in the far field the. Erinrc 09203, comparison of blast pressures and effects. Subsonic, typically 1 ms and 7 to 10 bar starting at ambient pressure detonation. Pdf influence of ignition position on overpressure of.
640 732 916 557 52 1132 1396 7 1450 1167 328 1496 790 1108 1617 1341 442 332 743 1525 1528 213 1568 1328 1362 210 99 1006 1338 736 896 425 1436 200 1408 1243 327 502 280 487 378 971 1414