Blast wind

Blast wind (Air mass movement) Drag loading—forces on a structure resulting from the high velocity of the air particles in the blast wave flowing around the structure... 

Once the explosion occurs it creates a blast wave that has a very steep pressure rise at the wave front and a blast wind that is a transient flow behind the blast wave. The impact of the blast wave on structures near the explosion is known as blast loading. The two important aspects of the blast loading concern is the prediction of the magnitude of the blast and of the pressure loading onto the local structures. Pressure loading predications as a result of a blast, resemble a pulse of trapezoidal or triangular shape. They normally have a duration of between approximately 40 msec and 400 msec. The time to maximum pressure is typically 20 msec. 

Results from individuals being thrown by the blast wind. 

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. 

The energy of an atomic bomb is released in three violent ways as thermal radiation, as nuclear radiation, and as a combination of shock wave and blast wind. With the explosion of an atomic bomb, the maximum temperature at the burst point instantaneously reaches several million degrees centigrade, the official Japanese damage report reminds us. 

And then there are the shock wave and blast wind. The hurricane-force winds make missiles of all loose objects and can tear the clothing from a body. This unprecedented destructive power, potentially... 

As the pressure in the blast wave continues to decrease, it sinks below that of the surrounding atmosphere. In the time interval from point 3 to point 5, which may be several seconds, the negative (or suction) phase of the blast wave passes the given location. For most of this period the transient wind blows towards the explosion. As the negative phase passes, the pressure at first decreases below ambient and then increases towards that of the ambient atmosphere which is reached at the time represented by point 5. The blast wind has then effectively ceased and thedirect destructive action of the airblast is over. 

Some indication of the corresponding values of peak overpressure, peak dynamic pressure and maximum blast wind velocity for an ideal shock front in air at sea level are given in Table 9.1. 

When the pressures on different areas of a structure are quickly equalised, because of its small size, the characteristics of the structure or the rapid formation of numerous openings by the action of blast, the diffraction forces operate for a very short time. The response of the structure is then mainly due to the dynamic pressures (or drag forces) of the blast wind, e.g. for telephone poles, radio and television transmitter towers, and tall chimneys. 

Secondary blast injury - injuries due to fragmentation Secondary blast injuries are those caused by fragments energised by the blast wind. A classification is given in Box 3.8. Primary fragments are those incorporated within the explosive device itself. Improvised... 

Tertiary blast injury - injuries due to the blast wind The blast wind (dynamic overpressure) results from the motion of the combustion products of the explosion. Resultant injuries vary from total disruption to amputation and devastating injuries from impact of the displaced body on the envirorunent. 

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