Blast overpressure injury

Neurological Effects and Mechanisms of Blast Overpressure Injury... 

NEUROLOGICAL EFFECTS AND MECHANISMS OF BLAST OVERPRESSURE INJURY... 

Blast waves from explosions may cause overpressure injury as a result of a combination of overpressure and duration at a given distance. For instance, the threshold of lung rupture may be 70 kPa (0.7 atm) overpressure for 50 ms or 140-210 kPa (1.4-2.0 atm) overpressure for 3 ms. 

Historically, ordinary glass windows are not adequate for blast overpressures as low as 0.2 psi (1.4 kPa). Many injuries in explosion accidents result from glass fragments. Therefore, the use of windows should be discouraged. 

Table 3.5 summarizes the effects of explosion overpressure on structures. With respect to human casualties, heavy building damage usually is equated to a fatal effect, as the people inside the buildings probably would be crushed. People outside of buildings or structures are susceptible to direct blast injury (blast overpressure) and indirect blast injury (missiles or whole body translation). 

Elsayed, N.M. Gorbunov, N.V. Kagan, V.E. A proposed biochemical mechanism involving hemoglobin for blast overpressure-induced injury. Toxicology 1997,121, 81-90. 

The extent of injury and property damage from an explosion depends on both the blast overpressure and the blast impulse at the point of interest [30]. Table 17.7 presents examples of overpressure and impulse combinations as a function of distance for an explosion having an energy equivalent of 10,000 pounds of TNT, together with the approximate limits of various types of injury and property damage. 

Modeling health effects from various hazard levels is a difficult task. Risk assessments are typically based on the risk of death or serious injury. Obviously there are no experimental data available on the dose-response relationship of material concentration and exposure duration, thermal radiation intensity or blast overpressures on humans. What little there is has been inferred from actual accidents. Models that predict the impact of exposure to hazardous materials are heavily influenced by animal experiments. Typically, they have large safety factors built in. It is believed that models based primarily on exposure of experimental animals are conservative when applied to humans, especially when, on a body weight difference, the animals are much smaller than humans. In fact, many will argue that they are too conservative. These estimates are difficult to make, and unfortunately little can be done to improve the degree of uncertainty. 

Many CPQRA studies consider several types of incident outcomes simultaneously (e.g., property damage and exposures to flammable and/or toxic substances). To estimate risk, a common unit of consequence measure must be used for each type of effect (e.g., death, injury, or monetary loss). The difficulty in comparing different injury types has led to the use of fatalities as the dominant criterion for thermal radiation, blast overpressure, and toxicity eiqxisurcs. 

Exposure to blast overpressure waves can cause extensive damage to an individual. There are a variety of mechanisms through which injuries can be sustained. The transfer of kinetic energy from blast overpressure exposure t5q>ically generates primary injuries, such as the shearing of tissues. Shrapnel and other debris can impact an individual and cause secondary injury. Tertiary injuries are sustained from impact with surroxmding objects... 

FIGURE 13.2 Progression of bTBI. The sequela of events after blast overpressure exposure. Blast-induced traumatic brain injuries follow a sequence of events. Initial tissue damage from the force of blast waves lead to an evolutionary period of changes in biochemical... 

As the external pressure on the chest wall becomes larger than its internal pressure during the passage of a blast wave, the chest wall moves inward, thus causing injury. Because the inward motion takes time, the duration of the blast wave is important. Results of animal tests indicate that overpressure is only important for long durations, and impulse is important for relatively short durations (White et al. 1971). 

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. 

Blast Injuries. There are two types of blast forces that occur in a nuclear detonation blast wave direct blast wave overpressure forces and indirect blast wind drag forces. The most important blast effects, insofar as production of casualties will be those due to the blast wind drag forces. Casualties requiring medical treatment from direct blast effects are produced by overpressures between 1.0 and 3.5 atmospheres. However, other effects (such as indirect blast injuries and thermal injuries) are so predominate that patients with only direct blast injuries make up a small part of the patient workload. 

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