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Ignitable and Explosive Atmospheric Hazards
Published in Neil McManus, Safety and Health in Confined Spaces, 2018
During an explosion, atmospheric pressure rises almost instantaneously to a peak and gradually decreases to the starting level. As the shock wave travels outward, the height of the peak of the pressure wave decreases at the shock front with increasing distance. The shock wave in air usually is referred to as a “blast wave” because it may be accompanied by a strong wind. The peak wind velocity behind the shock front depends on the peak overpressure. Overpressures generated by the blast wave can injure or kill people and damage or destroy equipment and buildings. The overpressure in the shock wave is followed by a region of negative pressure, or underpressure. The underpressure usually is quite weak and usually does not exceed about 100 kPa (760 mmHg) gauge. The high-pressure components of the shock wave move outward at higher velocities. Initially, the shock wave from a detonation travels at supersonic speed. As the intensity of the wave subsides, it becomes sonic (Lees 1980, Bodurtha 1980). Table 4.9 provides information about the effects of blast-produced overpressures.
Design Safe Processes
Published in James A. Klein, Bruce K. Vaughen, Process Safety, 2017
James A. Klein, Bruce K. Vaughen
How the equipment is arranged—its layout within the process unit—is important when flammable or combustible materials are being processed. Tightly packed equipment increases equipment confinement and congestion, adversely affecting ease-of-access by operations, maintenance, and emergency responders. With greater separation distances between equipment, the consequences of loss of containment incidents are reduced with the effectiveness of the larger distances being strongly influenced by the types of hazards and how far their impact could be. For example, greater distances help reduce the impact of fires to surrounding areas by reducing the exposure to and intensity of the thermal radiation. Or for explosions, greater distances between equipment help reduce potential equipment congestion density and thus help reduce the magnitude of the blast waves (especially vapor cloud explosions [VCE]). Greater distance between equipment and occupied buildings allows for increased blast wave decay, thus reducing potential consequences to equipment, buildings, and their occupants.
Blast, Fire, and Impact-Resistant Design
Published in Srinivasan Chandrasekaran, Advanced Steel Design of Structures, 2019
Quantum of energy, released into the atmosphere results in a pressure-transient wave or a blast wave. Further, it is important to note that the blast wave propagates outward in all directions from the source at a sonic or supersonic speed. Supersonic speed is defined as the rate of travel of an object exceeding the speed of sound. For objects traveling in dry air at a temperature of about 20°C, the supersonic speed is about 344 m/s, which is equivalent to 667 knots or about 1240 km/ho. The magnitude and shape of the blast wave depend upon the nature of the energy released and the distance of the object from the epicenter of the explosion. Blast waves are categorized into two: shock wave (S-waves) and pressure waves (P-waves).
Performance of masonry heritage building under air-blast pressure without and with ground shock
Published in Australian Journal of Structural Engineering, 2020
S M Anas, Md. I. Ansari, Mehtab Alam
A shock wave or blast wave is composed of a high-intensity pressure front that expands outward from the centre of the explosive charge into the surrounding air. As the blast wave expands, it decays in amplitude, lengthens in duration, and decreases in detonation velocity (Goel and Matsagar 2014; Joint Department of the Army, the Navy and the Air Force 1990). Figure 4 shows the typical blast pressure profile in the free air. The shock wave is characterised by two phases, namely; the positive pressure phase and the negative pressure phase. The positive phase is characterised by a sudden linear increase in pressure to the peak value at the pressure front, and followed by an exponential decrease back to standard atmospheric pressure (PO) and then a suction phase where the air is absorbed and a partial vacuum is formed (Goel and Matsagar 2014). It can be noted from Figure 4 that the maximum negative overpressure (PS-) is much smaller than the peak positive overpressure (POP), its limiting value is 1 atm (≈0.1 MPa). However, the negative phase duration is 2 to 3 times as long as that of the positive phase of the air-blast (Bureau of Indian Standards (BIS) 1968).
Numerical investigation of similarity laws for blast simulation: Open-field propagation and interaction with a biomechanical model
Published in Mechanics of Advanced Materials and Structures, 2018
When an explosive detonates, it produces a shock wave at supersonic velocity. The term “blast wave” is used to describe the shock wave resulted from the explosive charge detonation in the air [38]. When propagation is in free-air field (without any obstacle which can induce wave reflection), the blast wave due to the compression of air spreads outward from the point source to the surrounding environment and can be represented by Friedlander equation: where P is pressure as a function of time (t); P+ is the peak static or incident pressure, which is the blast load experienced by a surface parallel to the blast wave direction [12]; T+ is the positive phase duration and b is a decay constant. The modeling of static pressure in free air propagation is represented in Figure 1.
Construction and spatio-temporal derivation of hazardous chemical leakage disaster chain
Published in International Journal of Image and Data Fusion, 2021
Xinxin Zheng, Fei Wang, Wenyu Jiang, Xiaocui Zheng, Zuhe Wu, Xiaohui Qiao, Qingxiang Meng, Qingguang Chen
Li and Chen (2020) summarised 5169 hazardous chemical accidents that occurred in China from 2013 to 2019, including leakages, explosions, poisonings, asphyxiations, and fires. It was found that the most frequently occurred hazardous chemical accidents are leakages (48.1%), followed by explosions (24.47%). Explosions inflicted the highest casualties, followed by poisonings. In general, chemical explosions are easily caused by an accidental leakage of combustibles when exposed to an ignition source. The blast wave can cause serious deaths and injuries over a short period of time, resulting in destructive impacts.