Protective walls against effects of vapor cloud fast. Peak overpressure maximum wind speed effect on structures effect on the human body 1 psi 38 mph window glass shatters. Flame acceleration and ddt can generate high peak pressures that may cause failure of containment. If the combustion process propagates outward at subsonic speeds slower than the speed of sound, its a deflagration. 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. Also shown are the effects of blockage geometry on the delay time taken to reach these pressures.
The tnt equivalent mass describes the effect of the. Explosive blast 4 explosive blast 41 this chapter discusses blast effects, building damage, injuries, levels of protection, standoff distance, and predicting blast effects. In the absence of turbulence, under laminar or nearlaminar conditions, flame speeds are too low to produce significant blast overpressure. The threshold for lung damage occurs at about 15 psi blast overpressure. Study on peak overpressure and flame propagation speed of. For solid fuels transported by truck or rail, the methodologies presented in regulatory guide 1. If the explosion moves outward at supersonic speeds faster than the speed of sound, its a detonation. Appendix a explosion and fire phenomena and effects. 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. 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. Guidelines for choosing an explosion protection system for. Safety considerations of thermal and overpressure effects hall, j. Calculation of blast loads for application to structural components. Characteristic overpressureimpulsedistance curves for.
There are several currently referenced empirical correlations and emerging computer models to predict effects of. Overpressure or blast overpressure is the pressure caused by a shock wave over and above normal atmospheric pressure. The temperature effect can be clearly seen by considering the overpressure at flame. Deflagration is an explosion that propagates at subsonic velocity en 11271. 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. Our clients have included companies in the petroleum and chemical fields, defense and aerospace industry, oil and gas.
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. 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. Protective walls are an efficient way to protect people and infrastructures from overpressure effects due to accidental or malicious explosions detonation or deflagration. The effects of obstructions on overpressure resulting from. Nuregcr5275, flame facility the effect of obstacles and. In addition to these causes of injury and death, crush injury, entrapment, and compartment syndrome magnify the devastation of blast trauma. In such a case, the cloud will merely burn as a flash fire. Supersonic high pressure shock front ahead of the reaction zone i. The overpressure to be expected in the deflagration of an unconfined hydrogenair vapour cloud is in the order of 10 kpa. Limitations of gas explosion venting due to accelerated. 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. Deflagration and detonation differ in peak overpressure, in the duration of the impulse time. The flame propagation behaviour, pressuretime history, and flame.
A blast injury is a complex type of physical trauma resulting from direct or indirect exposure to an explosion. Results are shown for various obstruction types used here. 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. This paper aimed at studying the flame propagation and the overpressure effect in the process of deflagration by conducting cfd computational. Overpressure calculation for unvented partial volume. The information may also be relevant to the problem of assessment of the consequences of such. This paper focuses on the effects of a fast deflagration in the far field the. 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. 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. The effects of explosive blast on structures and personnel. For detonation there are multiple published studies, whereas for deflagration no welladapted and rigorous method has been reported in the literature. The human body can survive relatively high blast overpressure without experiencing barotrauma.
Subsonic, typically 1 ms and 7 to 10 bar starting at ambient pressure detonation. Characteristic overpressureimpulsedistance curves for the detonation of explosives, pyrotechnics or unstable substances fernando d. Characteristic overpressureimpulsedistance curves for the. Protective walls are a wellknown and efficient way to mitigate overpressure effects of accidental explosions detonation or deflagration. Protection against overpressure due to phenomena other than internal deflagrations e.
Specific blast design concerns and mitigation measures are discussed in chapters 2 and 3. Limitations of gas explosion venting due to accelerated flame. Erinrc 09203, comparison of blast pressures and effects. Pdf explosion relief panels or doors are often used in industrial buildings to reduce damages. 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. Table 1 effect of various long duration blast overpressures and the associated maximum wind speed on various structures and the human body. Sulfur pit explosion protection by deflagration venting. In the dynamic pressure this region the air pressure is below that 3. Figure 2 shows a graph generated using the apt correlations for overpressure when rocket motor segments of varying. Pdf influence of ignition position on overpressure of. The maximum reflected pressure for a fast deflagration is of order 10 bar 145 psi.
Air force that updated many of the initial relationships2. Depending on the geometric shape of the combustion area, a distinction is made between atmospheric deflagration, prevolume deflagration, and inline deflagration. Introduction this appendix is a summary of the work published in the socalled green book 1989. For detonations, there are several engineering or cfdbased design rules for barricades design in the literature, such as nota. If designed and sized correctly, explosion vents reduce the maximum pressure p max of a deflagration to a safe level p. An acoustic model for predicting the overpressures caused by. An overview of the effects of blast injuries at the medical level presented by. 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. Effects of initial pressure on the flammability limit of. For detonation there are multiple published investigations concerning interactions of blast waves and walls, whereas for deflagration no well. The effects of explosive blast on structures and personnel richard w. Safety considerations of thermal and overpressure effects article pdf available in international journal of hydrogen energy 3935 june 2014 with 77 reads. The effects of bombings and blast injuries are both physically and psychologically devastating. The deflagration overpressure produced by a flammable mixture that fills less than 30%50% of the enclosure volume is.
Effects of the ignition positions on the overpressure characteristics of the premixed. Blast effects of external explosions hal archive ouverte. The overpressure computed with spatial resolutions of 5cm, 7cm and 8cm shows. 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. Also shown are the effects of blockage geometry on the delay time taken to. Typical damage caused by overpressure effects of an explosion. The tnt equivalent mass describes the effect of the explosive at a certain space when it blasts rui, lizhong. Deflagrations occur most frequently in dust collectors, conveyors, elevators, dryers, mills, storage vessels, and entire buildings or rooms. Under extraordinary conditions, a detonation with more severe blast effects might occur. Possible effects of explosions on humans include blastwave overpressure effects, explosionwind effects, impact from fragments and debris, collapse of buildings, and heatradiation effects. Effect of hydrogen concentration on vented explosion. 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. The first peak on the plot represents the initial deflagration of the cloud back to the.
Overpressure as a function of reduced distance cpr, 1997. Pdf blast effects of external explosions researchgate. Calculation of blast loads for application to structural. The crosswise obstacle positions are found to have significant effects on deflagration characteristics, such as flame structure, flame front location, flame speed, and overpressure transients.
The deflagration characteristics of premixed lng vapourair mixtures with different mixing ratios were quantitatively and qualitatively investigated by using cfd computational fluid dynamics method. Deflagration is a surface phenomenon with the reaction proceeding towards the. The onway peak overpressure and flame propagation speed of gas deflagration in the tube with obstacles are important data for process safety. Here, two safety characteristics are essential for the design. 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.
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. Pdf the effects of obstructions on overpressure resulting. Catlin a mathematical model of the overpressure field due to the deflagration of a point ignited ground lying vapour cloud is described. 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. Overpressure in bleves and similar explosions, journal of hazardous materials, vol. Combustion burning is a process by which energy is released. These injuries are compounded when the explosion occurs in a confined space. Blast injuries occur with the detonation of highorder explosives as well as the deflagration of low order explosives. 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. Obtaining a tnt equiv alent for various types of explosions, such as pressurevessel burst, boilingliquid expandingvapor explosion bleve, unconfined or confined vaporcloud explosion, deflagration. The premixed stoichiometric methaneair deflagration is conducted in a transparent square crosssection duct. Potential for deflagration to detonation transition in trees and bushes effects of overpressure on items typical of those observed at buncefield and jaipur.
Protection by deflagration venting and en 14994 gas explosion venting protective systems. 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. Study on peak overpressure and flame propagation speed of gas. The value of the peak overpressure as well as the velocity of propagation of the shock wave decrease with increasing distance from the detonation center. Methodology for assessing a boiling liquid expanding vapor. Deflagration and detonation are two ways energy may be released. 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. An acoustic model for predicting the overpressures caused.
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