Damage from blasts

The ear is a very sensitive and complex organ that responds to very small variations in pressure. It was argued in Hirsch (1968) that ear drum rupture is decisive as to ear damage from blast waves. Figure C-3 shows the percentage of eardrum ruptures as a function of side-on overpressure F,. 

Damage from blast waves with very long duration positive phase ( 1 sec). This would be from very large explosions, a large distance away (thousands of pounds at thousands of feet). 

Since the blast overpressure decreases rapidly as the distance from the source increases, significant offsite damage from blasts is not expected. Most studies arc directed toward on-site damage. 

Damage from the blast in the vicinity was calculated to be equivalent to a blast of 50,000 to 75,000 kg of TNT. According to Burgess and Zabetakis (1973), the Port Hudson vapor cloud detonated. As far as is known, this is the only vapor cloud explosion that may have been a detonation. 

Munday, G., and L. Cave. 1975. Evaluation of blast wave damage from very large unconfined vapor cloud explosions. International Atomic Energy Agency, Vienna. 

Pritchard, D. K. 1989. A review of methods for predicting blast damage from vapor cloud explosions. 7. Loss Prev. Proc. Ind. 2(4) 187-193. 

A BLEVE can cause damage from its blast wave and from container fragments such fragments can be propelled for hundreds of meters. If the vapor-air mixture is flammable, the BLEVE can form a fireball with intense heat radiation. Each effect is discussed in the following sections. 

In practice, overpressures in one case might very well be only one-fifth of those predicted by the method and close to the predicted value in another case. This inherent inaccuracy limits the value of this method in postaccident analysis. Even when overpressures can be accurately estimated from blast damage, released energy can only be estimated within an order of magnitude. 

In each case, two different methods were used in arriving at estimates the HSE TNT-equivalency method and the multienergy method. The results, in the form of side-on blast peak overpressures for various distances from blast centers, are listed in Table 7.10. In addition, some peak overpressures estimated by Sadee et al. (1976/ 1977) from Flixborough-incident damage patterns are included. The photographs in Figures 7.6a and 7.6b illustrate the practical effects of such overpressures. 

Further properties which a detonating fuse should have are the ability to initiate blasting explosives (tested with suitable relatively insensitive mixtures usually of TNT and ammonium nitrate) resistance to low temperatures without cracking on flexing and to hot storage without desensitisation and toughness to prevent damage from stones, etc. The fuse must always be waterproof and must often withstand diesel oil, which can separate from ANFO. 

Ultrasonic baths can be used to remove detritus from delicate moulds. This method eliminates the possibility of damage by blasting techniques and does not present the health hazard of chemical methods. 

Damage from internal blast is of course a function of the complete time history of the pressure loading. But, the duration of the shock phase of the loading is usually much shorter than duration of vented gas pressure loading, while the amplitude of the shock phase is much greater than peak quasi-static pressure. Quite often, the fundamental periods of walls or roofs are much longer than the shock... 

Various methods are available to limit the damage from the effects of an explosion. The best options are to provide some pre-installed or engineered features into the design of the facility or equipment that allow for the dissipation or diversion of the effects of a blast to nonconsequential areas. Wherever these mechanisms are used the overpressure levels utilized should be consistent with the risk analysis estimates of the WCCE incident. 

In addn to the distance of the structure from the expln, the vibration period or frequency of the structure affects its behavior in a blast. The nearer the frequency of the structure to that of the shock wave, the more likely it is to vibrate in sympathy with it and therefore to suffer more damage. Since most buildings vibrate betw 1 and 10 vibrations per second and the frequency of violent explns is usually greater than 10, the damage from shock waves due to sympathetic vibrations is not likely to be great... 

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. 

Onederra, LA. Furtney, JK. Sellers, E. et al. 2013. Modeling blast induced damage from a fully coupled explosive charge. Int. J. Rock Meek Min. Sci 58 73-84. 

Penetration or failure of blast barriers and firewalls, destroying protective area directly or allowing subsequent fire to enter protected areas. Damage could be from blast overpressure... 

Duvall, I. W., Devine, J. F. (1968). Avoiding damage by air blasts and ground vibrations from blasting, Surface mining. New York AIMMPE Inc. 

The 21,000-pound GBU-43/B Massive Ordnance Air Blast Bomb (MOAB, also known as the Mother of all Bombs) is the largest and most powerful conventional explosive bomb in the world. In December, 1917, an ammunition ship, the Mont Blanc, exploded in the harbor at Halifax, Nova Scotia, with a force of roughly 3 kilotons, the largest conventional explosion in history. The damage from the explosion devastated most of the city and caused more than 2,000 deaths. 

Hazards resulting from blast over-pressure can be from direct and indirect sources. For example, indirect sources of fatal harm resulting from an explosion can be missiles, building collapse or severe structural damage (as occurred at Buncefieid). 

Revolving drum blast machines give the best production efficiency for metals which are stout enough to resist damage from the tumbling action involved. The metal parts are tumbled on a rubber belt inside a revolving drum whilst being bombarded with the abrasive medium. 

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