Mass of Explosives

Critical Mass of Explosive. The minimum quantity of an expi required for development of detonation it varies widely for different types, being only milligrams for sensitive primary expls and pounds or tons for non-detonating expls like colloided proplnts and AN Ref Dunkle s Syllabus (1957-58), 157-58 

Critical Phenomena.This includes critical temperature, pressure and volume 

Critical temperature is the maximum temperature at which a gas or vapor can be liquefied by application of any pressure, however great, such as the critical pressure which is the pressure at its critical point . Critical volume is the volume occupied by unit mass (one mole) of a substance at its critical temperature and critical pressure  

Critical Phenomena in the Detonation of Gases. This subject was discussed in two papers published by J.E. Lennard-Jones A.F. Devonshire in ProcRoySoc 163A, 53-70(1937) and 165A, 1-11(1938). Abstracted very briefly in CA 32, 1533 6118(1938) 

Equation of state discussed in these papers is given in this Volume under Detonation (and Explosion), Equations of State , as Lennard-Jones Devonshire Equation of State  

---

If the seat of a condensed phase explosion and an associated crater can be located, this can be quite helpful. Measurement of crater dimensions can enable an approximate estimate of the amount of explosive involved, and also may focus questioning of witnesses or examination of video footage from security cameras. Crater size depends on the mass and nature of the explosive, the nature of the substrate, and the position of the explosive charge relative to the substrate surface. As a first approximation, the diameter of a crater in a uniform substrate varies as the cube root of the explosive mass for a charge on or above the surface. For charges buried just below the surface, the diameter of the crater is proportional to the mass of explosive raised to the power 7/24 this factor allows for the effect of backfilling of the crater by ejected material. Intuitively (and practically), the diameter of the crater in the surface also decreases with distance of the charge above or below the surface. 

NEC Net Explosive Content. The mass of explosive composition within a firework. 

There are two basic ways to look for explosive material. They differ in their point of focus. Some sensors seek the mass of explosive material within a device. These are particularly useful when the device is well sealed and its surface is well cleaned of stray explosive molecules, or when the explosive being used is nonaromatic, that is, it does not readily release molecules from its bulk. We will refer to these as bulk sensors. They include X-ray techniques, both transmission and backscatter neutron activation in several techniques y -ray excitation, in either transmission or backscatter modes and nuclear resonance techniques, either nuclear magnetic resonance (NMR) or nuclear quadrupole resonance (NQR). Bruschini [1] has described these thoroughly. They are also described by the staff of the Jet Propulsion Laboratory [2], The following forms a very brief synopsis. 

Since little or no heat is evolved during the induction period, the initial energy input in the "hot spot is not immediately related to the heat of decomposition of the explosive. In such cases, thermal instability is not conditioned by the heat of explosion or the mass of explosive but by other less obvious factors which apparently are related to the nature and amount of the autocatalyst... 

B) Deton velocity is equal to the speed of movement of hot products of reaction thru the mass of explosive (See Note 3)... 

D) The presence of pores in the mass of explosive facilitates the penetration of hot gaseous products of deton along the charge... 

If the products of explosion behave as ideal gases with a constant ratio of specific heats y and are further assumed to undergo adiabatic changes, the pressure-volume relation is P(V/W)Y= k, where W is the mass of explosive products in grams and k is a constant. The internal energy E(a) is then given by... 

It appears that transition of deflagration into detonation is almost discontinuous and may be caused by mechanical shock waves formed within the mass of explosive by the hot product gases that stream from the surface undergoing very rapid deflagration (Ref 9a)... 

Explosives may reside on a person in the form of trace (residue from handling explosives, exposure to explosives, or hidden explosives) and/or bulk (a large mass of explosives). The portal technologies that enable the detection of these two forms of explosives may be categorized as trace and anomaly. The detection methods utilized by these two types of portals are substantially different in the signature of the material detected and the... 

Trace portals could also be used for bulk detection because of the likelihood that a mass of explosive concealed on the person would present an adequate chemical signature. The combination of a trace and anomaly portal would provide a powerful multi-sensor platform that would offset the limitations of the individual technologies. Currently, a commercially available multi-sensor explosives detection personnel portal that combines trace and anomaly methods does not exist. 

S = signal output from the detector (red light/green light depending on alarm thresholds) M0 = initial mass of explosives residue or traces on a person (vapor and/or particles)... 

The preconcentrator is a mechanical system used to concentrate the limited mass of explosive delivered from the sample collection subsystem [8], From the sample collection subsystem airflow, the preconcentrator adsorbs explosives (vapor or particulate). The adsorbing surface is then heated to desorb the explosives into the airflow stream for delivery either to a detector or another preconcentration stage. Concentration of the explosives sample occurs because the explosive contained in the sample collection airflow prior to adsorption is now contained in a smaller volume after desorption. Equation 2 shows the relationship between concentration and volumes related to the preconcentrator. 

A mass of explosive material prepared for use in bulk form without packaging. 

Fig. 3.134 Crater volume vs mass of explosive from the explosion test in sand PVC tube with d=50cm, inner dia. 50mm...

Since detonative explosives are kept in various types of vessels used for different objectives such as warheads, bombs, and industrial mines and civil engineering, the performance of the explosives is dependent not only on the chemicals and mass of explosives but also the physical shape of explosives. When a detonation is initiated at a point in an explosive charge, the detonation wave propagates spherically in all directions. When a detonation is initiated at a point at one end of an explosive charge, the detonation wave propagates semi-spherically in the charge. Thus, the... 

Just as different explosives have different detonation rates, the same explosive under varying conditions will have a range of detonation rates. For a solid explosive such as RDX or PETN, this rate depends largely upon how dense the mass of explosive is. For example, if the charge consists of finely crystalline material, its detonation rate will be quite a bit less than if it has been melted together into one solid rock. This is because the finely powdered material is less dense than the rock form. Those... 

Other balloon tests with up to 15 m volume and tests in plastic tubes with ethylene-air gas mixtures were found to detonate by means of 8 g of an explosive, however, not with a 100 J heated wire. Minimum mass of explosive is 80 g for propane-air mixtures, and as much as 22 kg for methane-air mixtures. For real gas clouds, the required explosive mass is even higher 300 g did not initiate a detonation of a flash-depressurized propylene gas cloud, where 20 g would suffice for a stoichiometric mixture. 

Detonator is a device, containing a very small amount of sensitive explosive, which can be initiated remotely (by electric current, a fuse or detonating cord) and safely to detonate a larger mass of explosive (see primer). 

---