Equivalent explosive charge

For these and other purposes, blast-modeling methods are needed in order to quantify the potential explosive power of the fuel present in a particular setting. The potential explosive power of a vapor cloud can be expressed as an equivalent explosive charge whose blast characteristics, that is, the distribution of the blast-wave properties in the environment of the charge, are known. 

In the shock sensitivity test using the MKTII ballistic mortar, ANFO, DPT and DNB are identified as low-sensitivity explosives of almost equivalent sensitivity 2 7 >. The sample were put into VP-30 and VP-50 tubes and ignited by 50g of Airemite and 100 g of Airemite respectively. The relationship between the length of the explosive charge and the volume of craters is shown in Fig.3.133. 

As this table indicates, suppressive shields are approved for use in hazardous operations involving explosive charge weights up to the equivalent of 57 pounds 50/50 pentollte for Group 5 and 50 pounds of lllumlnant mix for Group 5. 

Although air shock is occasionally scaled against the linear dimensions of the explosive charge (Ref 20), it is more often scaled to an equivalent weight of TNT. The TNT equivalency is based on energy of explosion obtained in various ways. The preferred method being calculation of either the hydrodynamic or the thermodynamic work function. (Recall section 26.4.) TNT weight equivalence... 

At the beginning of the seventies, the first useable FAE were developed at the U.S. Naval Air Warfare Centre Weapons Division NAWCWPNS, California. They are considered as the strongest nonnuclear chemical explosives. Primarily ethylene oxide (EO) or propylene oxide (PO) serve as fuels. These substances are atomised by explosive charges and ignited after mixing up with air. After intra-moleculare decomposition the fuel reacts with atmospheric oxygen and starts a detonation with velocities about 2000 m/s. Peak pressure under the detonating cloud reaches up to 30 bar. The effectiveness of the blast wave exceeds TNT more than five times calculated for equivalent masses. 

This correction is carried out by using the scaled distance, d , based on the similitude principle proposed by Hopkinson in 1915, according to which when two explosive charges of similar geometry and of the same explosive but different sizes, detonate in the same atmosphere, similar pressure waves are generated at the same scaled distance. This principle can also be applied to two different explosives, taking into account the fact that two types of explosion with the same overpressure give rise to the same effects. Because overpressure is a function of the distance and two different explosions do not cause the same overpressure at the same distance from the center of the explosion, the scaled distance is defined as that at which the overpressure has the same value for both explosions. The scaled distance is related to the real distance and to the equivalent TNT mass by the cubic root law. 

One of the complicating factors in the use of a TNT-blast model for vapor cloud explosion blast modeling is the effect of distance on the TNT equivalency observed in actual incidents. Properly speaking, TNT blast characteristics do not correspond with gas explosion blast. That is, far-field gas explosion blast effects must be represented by much heavier TNT charges than intermediate distances. 

Aslanov, S. K., and O. S. Golinskii. 1989. Energy of an asymptotically equivalent point detonation for the detonation of a charge of finite volume in an ideal gas. Combustion, Explosion, and Shock Waves, pp. 801-808. 

In the first approach, a vapor cloud s potential explosive power is proportionally related to the total quantity of fuel present in the cloud, whether or not it is within flammable limits. This approach is the basis of conventional TNT-equivalency methods, in which the explosive power of a vapor cloud is expressed as an energetically equivalent charge of TNT located in the cloud s center. The value of the proportionality factor, that is, TNT equivalency, is deduced from damage patterns observed in a large number of vapor cloud explosion incidents. Consequently, vapor cloud explosion-blast hazard assessment on the basis of TNT equivalency may have limited utility. 

In summary, the potential explosive power of the vapor cloud can be expressed as four equivalent fuel-air charges whose initial strengths remain to be determined. 

Equivalent charges expressing the vapor cloud s potential explosive power are now known, both in scale and in strength. Their corresponding blast effects remain to be determined. 

W = required vapor capacity in pounds per hour, or any flow rate in pounds per hour, vapor relief rate to flare stack, Ibs/hr W(. = charge weight of explosive, lb Wj. = effective charge weight, pounds of TNT for estimating surface burst effects in free air W, = required steam capacity flow or rate in pounds per hour, or other flow rate, Ib/hr Whe = hydrocarbon to be flared, Ibs/hr Wtnt equivalent charge weight of TNT, lb Wl = liquid flow rate, gal per min (gpm)... 

Determination of Relative EfSciences of Explosives By The Method of Equivalent Charges From the Degree of Expansion In a Trauzl Bomb , ZhPMTF No 2, 116-19 (1960) CA 55, 20434 (1961) 121) V.K. Bobolev ... 

An 850 kg batch of a slightly doped form of azodicarbonamide exploded violently, with a TNT equivalence of 3.3 kg, 5 minutes after sampling at the end of drying. The probable initial temperature was 65°C, the lowest self accelerating decomposition temperature 90°C, and such decomposition is not explosive. Full explosibility tests, including detonability, had shown no hazard. Further study demonstrated that slightly contained azodicarboxamide, thermally initiated at the bottom of a column or conical vessel could explode even at the 5 kg scale. The above TNT equivalence corresponds to decomposition of 4% of the available charge. The cause of the presumptive hot spot is unknown. 

The literature lists UNi as being 90% as powerful as TNT [5], Small-scale air-blast work displayed a far-field equivalency closer to 65% [12], Literature detonation velocities listed range from 3.4 to 4.7 km/s ( 11,200 to 15,400 ft/s) [13], The author has seen several different velocities in this region depending on the charge size and confinement. UNi possesses a low loading density (typically around 0.7 g/cm3). It is highly corrosive and readily attacks most metals. In terms of sensitivity, UNi is typically a tertiary explosives such as ANFO and requires a booster to be initiated. 

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