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Title: Introduction to Explosions and Explosion Safety
Department: Mechanical Engineering
Author: Prof. K. Ramamurthi
University: IIT Madras
Type: WebLink
Abstract: Starting with the definition of the word explosion, the conditions for which disruption of things at the site of the explosion would occur and examples of the different categories of explosions are discussed. The mechanism of formation of shocks and blast waves are investigated and predictions for a blast wave using the Buckingham Pi theorem are given. The equation for a shock Hugoniot is derived from the conservation equations and the jump in pressure, temperature, density across a constant velocity shock wave is calculated. The impulse and overpressure across a blast wave is thereafter modeled and the scaling laws arrived at for determining overpressure and impulses. Explosion length is introduced as an appropriate scaling parameter. Since the energy release rates must be fast enough to drive an explosion, methods of predicting energy release and energy release rates are dealt with. Induction time is defined and a long induction time or equivalently a high value of activation energy is seen to be essential for an explosion to occur.
The theory of thermal explosion is derived in the context of heat release rates and heat loss rates. Flames and detonations are thereafter discussed following a discussion of one dimensional combustion waves. Limits of flammability and limits of detonation, limiting oxygen concentration and fire point and flash point temperatures of volatile liquids are examined in the context of fire and explosion safety.
Confined and unconfined gaseous explosions, dust explosions and condensed phase explosions are thereafter considered. Different condensed phase explosives and their chemical structure are discussed. Physical explosions and cryogenic explosions and the TNT equivalence of the non-ideal explosions are discussed. Since atmosphere plays a major role in dispersing gaseous substances and mixing them with air to form an explosive, the role of atmospheric dispersion is also discussed. The course concludes with quantification of damages, some basics of risk analysis, acceptable risks and use of Fault Tree and Event Tree analysis for predicting the probability of an explosion.
 
   
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