Explosive power

The explosive power of a bomb depends fundamentally on the heat evolved (Q) and the volume of gaseous products produced (V) and is expressed as the product of these two quantities. The relative power of one explosive compared with another is obtained through the power index 

The explosive index of some common explosives is given in Table 9.4 typically, the index is calculated on the basis of 1.00 gram of material. 

We have already touched upon the heat produced (Q), in a reaction, determined by AH of the reaction, the ojqrgen balance, and the pressure involved. In our discussion of flames, we started with the assumption that the flame was adiabatic and that all of the heat evolved went into heating the gaseous products. In the context of arson, this first-pass assumption is reasonable, since the question usually asked of the forensic chemist relates to the presence or absence of an accelerant. For explosives, a bit more detail is required, given the role of heat in determining blast damage which can be useful in identifying the components of explosives. 

Like all combustion, explosives produce a complex mixture of gaseous products. Part of the heat evolv is absorbed by these products as a function of their heat capacities (C). In turn, he at capacity depends on temperature, so the temperature must be taken into account. This process— the creation of products, followed by the liberation of heat and the subsequent absorption of heat—determines the 

ANFO is a high explosive made from Ammonium nitrate and fuel oil. This is the type of explosive Timothy McVeigh used to attack the Murrah Federal Building in Oklahoma City or April 19,1995. It is composed of ammonium nitrate and 6% fuel oil. A similar mixture of urea nitrate and other materials was used in the first attack on the World Trade Center in 1993. 

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When used in blasting, ammonium nitrate is mixed with fuel oil and sometimes sensitizers such as powdered aluminum. Lower density ammonium nitrate is preferred for explosive formulation, because it absorbs the oil more effectively. When detonated,these mixtures have an explosive power of 40 to 50% that of TNT (see Explosives and propellants). 

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. 

To express the maximum potential explosive power of a fuel, a safe and conservative value for TNT equivalencies of vapor cloud explosions was estimated from literature data on major incidents, after correction for virtual distance. Prugh (1987) concluded that the maximum energy-based TNT equivalency is highly depen-... 

Several methods of quantiflcation are described in Chapter 4. Chapter 4 discusses in detail two fundamental approaches to quantiflcation of explosive power, together with advantages and disadvantages. In addition, there are two different blast models, each of which has certain benefits. This chapter offers guidance on their use. Application of each method is described in Section 7.2. and demonstrated in Section 7.3. Section 7.1. offers some guidance on choosing an approach and a blast model. 

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. 

If, on the other hand, the multienergy model is employed, the total quantity of fuel present in a cloud is of minor importance. Instead, the environment is investigated with respect to potential blast-generative capabilities. Fuel-air jets and partially confined and/or obstructed areas are identified as sources of strong blast. The explosive power of a vapor cloud is determined primarily by the energy of fuel present in these blast-generating areas. 

Conventional TNT-equivalency methods state a proportional relationship between the total quantity of flammable material released or present in the cloud (whether or not mixed within flammability limits) and an equivalent weight of TNT expressing the cloud s explosive power. The value of the proportionality factor—called TNT equivalency, yield factor, or efficiency factor—is directly deduced from damage patterns observed in a large number of major vapor cloud explosion incidents. Over the years, many authorities and companies have developed their own practices for estimating the quantity of flammable material in a cloud, as well as for prescribing values for equivalency, or yield factor. Hence, a survey of the literature reveals a variety of methods. 

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. 

Determine the initial strengths of the charges. A quick, simple, yet conservative approach to estimating the initial strengths of the four charges expressing the potential explosive power of the vapor cloud follows ... 

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. 

Explosive Power of Vapor Cloud at Liquefied Hydrocarbon Storage Tank Farm... 

Windows were damaged for several miles. Reconstruct the explosive power and blast effects of the vapor cloud explosion on the basis of the available data. 

TABLE 7.6. Side-On Peak Overpressure for Several Distances from Charge Expressing Explosive Power of the Flixborough Vapor Cloud Explosion... 

Consequently, the potential explosive power of the rest of the cloud, covering a more-or-less open area, can be expressed as a fuel-air charge of... 

The fuel-air charge expressing the explosive power of the source of strong blast is assumed to be of strength number 10. 

TABLE 7.7. Characteristics and Locations of Fuel-Air Charges Expressing Potential Explosive Power of the Flixborough Vapor Cloud... 

HSE method) was based. Therefore, a TNT equivalency of 3% is a reasonable measure of expression of the explosive power of a vapor cloud under conditions similar to those at Flixborough. Such conditions may be considered typical major incident conditions. 

Methylnitropropanolnitrate readily gelatinizes collodion cotton and, to a lesser extent, higher-nitrogen NC. Its explosive power is comparable to that of TNT, and about 75% of that of blasting gelatin. It is very insensitive to detonation, and for this reason its sand test value could not be detd... 

Udupa, M. R., Propellants, Explos., Pyrotech., 1983, 8, 109-111 Unusually sensitive to initiation and of high explosive power [1], it decomposes violently at 350°C [2], The explosive properties have been determined [3], and thermal decomposition at 275-325° was studied in detail [4],... 

Attempts to follow a published procedure for the preparation of 1,3 -dithiole-2-thione-4,5-dithiolate salts [1], involving reductive coupling of carbon disulfide with alkali metals, have led to violent explosions with potassium metal, but not with sodium [2], However, mixtures of carbon disulfide with potassium-sodium alloy, potassium, sodium, or lithium are capable of detonation by shock, though not by heating. The explosive power decreases in the order given above, and the first mixture is more shock-sensitive than mercury fulminate [3],... 

The explosion limits have been determined for liquid systems containing hydrogen peroxide, water and acetaldehyde, acetic acid, acetone, ethanol, formaldehyde, formic acid, methanol, 2-propanol or propionaldehyde, under various types of initiation [1], In general, explosive behaviour is noted where the ratio of hydrogen peroxide to water is >1, and if the overall fuel-peroxide composition is stoicheiometric, the explosive power and sensitivity may be equivalent to those of glyceryl nitrate [2],... 

In the other type of test, the strength of the detonation (explosive power) is determined. Examples of methods for this type of test are the lead block test [139] and the ballistic mortar test [141]. Only the first type of test, which determines the possibility of a detonation, is discussed here. 

With pressure-time data from spontaneous deflagrations (thermal explosions), the maximum expected pressure, and the time for pressure-rise can be estimated. Furthermore, the so-called "specific energy" (F) or "explosive power" of substances [24, 31] by Equation (2-22) from experiments in which the sample mass is varied. 

Cyclotetramethylenetetranitramine or HMX (C4H8N808) is a white crystalline solid with a melting point of 285°C. HMX is superior to RDX in that its ignition temperature is higher and its chemical stability is greater. However, its explosive power is... 

The five primary threats from a nuclear explosion are the destructive power of the nuclear explosion, the intense initial heat, the initial radiation, the air blast, and fallout. Almost nothing can be done to avoid the explosive power of a nuclear blast, but an individual can take some steps to avoid exposure to the remaining factors. 

Other early names of the 1,2-diazonium oxides were based on the benzoxadia-zole cyclised structure. For a long time it was doubted that 1,2,3-Benzoxadiazoles had existence, outside the speculative mathematics of theoretical chemists, but more recent researches suggest photochemical equilibrium with the diazonium form and possible predominance in non-polar solvents. Equilibrium implies similar explosive powers though it is possible that sensitivities differ. 

In an alternative assessment of the effectiveness of these computer programs, it was concluded that explosive power was over-emphasised in relation to the more practically important aspect of sensitivity to initiation, and many compounds were being indicated as hazardous when they were not. There was also no provision for considering polymerisation as a hazardous possibility, and there was little quantitative data on this. The parameter best correlating with material sensitivity is the bond-dissociation energy. It was recommended that regulations specifying the... 

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