Incidents detonation

A combustible vapor explodes under a very specific set of conditions. There are two explosive mechanisms that need to be considered when evaluating combustible vapor incidents - detonations or deflagrations. A detonation is a shock reaction where the flames travel at supersonic speeds (i.e., faster than sound). Deflagrations are where the flames are traveling at subsonic speeds. 

Flat metal plates and cylinders driven by tangentially incident detonation waves were examined by Hoskin et al (Ref 5) using a 2-D steady state characteristic code. Their computations for plates or cylinders indicate that metal compressibility has little effect on the terminal velocity imparted to the metal by the expl. Thus the Gurney treatment is found to give essentially the same terminal states as their more sophisticated characteristics computation. This... 

Fig. 8.15 Dependencies of pressures 1 - calculated for explosion at constant volume 2 - behind the incident detonation wave 3 - behind the reflected detonation wave and comparison with the experimental data [49], HOM atPo = 0-1 MPa...

A low incidence of explosions has been reported when precipitation is effected without a nucleating agent and during the screening process. Precautions must be taken during detonator loading to prevent dusting and to maintain a scmpulously clean operation. 

S. Gordon and B. J. McBride, "Computer Program for Calculation of Complex Chemical Equilibrium Composition, Rocket Performance, Incident and Reflected Shocks, and Chapman-Jouget Detonations," NASA SP-273, Interim Revision, NTIS, Springfield, Va., Mar. 1976. 

Nitromethane [75-52-5] is produced in China. Presumably a modified Victor Meyer method is being employed. Nitromethane is transported in dmms or smaller containers. Two tank cars of nitromethane exploded in separate incidents in the 1950s. Both explosions occurred in the switching yard of a railroad station. In both cases, essentially adiabatic vapor compression of the nitromethane—air mixture in the gas space of the tank car resulted in the detonation of the Hquid nitromethane. Other nitroparaffins do not, however, detonate in this manner. 

The characteristic magnitudes of detonation cells for various fuel-air mixtures (Table 3.2) show that these restrictive boundary conditions for detonation play only a minor role in full-scale vapor cloud explosion incidents. Only pure methane-air may be an exception in this regard, because its characteristic cell size is so large (approximately 0.3 m) that the restrictive conditions, summarized above, may become significant. In practice, however, methane is often mixed with higher hydrocarbons which substantially augment the reactivity of the mixture and reduce its characteristic-cell size. 

Furthermore, accidental vapor cloud explosions are anything but detonations of the full amount of available fuel. Therefore, practical values for TNT equivalencies of vapor cloud explosions are much lower than the theoretical upper limit. Reported values for TNT equivalency, deduced from the damage observed in many vapor cloud explosion incidents, range from a fraction of one percent up to some tens of percent (Gugan 1978 and Pritchard 1989). For most major vapor cloud explosion incidents, however, TNT equivalencies have been deduced to range from 1% to 10%, based on the heat of combustion of the full quantity of fuel released. Apparently, only a small part of the total available combustion energy is generally involved in actual explosive combustion. 

Nitryl perchlorate reacts with organic matter with a violence ranging from slight explns to sharp detonations accompanied by fire. Incidents have been reported with acet, benz eth (Ref 2)... 

Three operations were carried out without causing any incident and by sticking to the operating rules and quantities recommended in the literature. A fourth attempt caused the equipment to detonate. 

It was decided to increase the reagent quantities after carrying out the reaction three times without any incident. This time there was a detonation that was explained by the polymerisation of the halogen derivatives, whose exothermicity could not be controlled. 

As a heavy metal azide, it is considerably endothermic (A// +279.5 kJ/mol, 1.86 kJ/g). While pine silver azide explodes at 340°C [1], the presence of impurities may cause explosion at 270° C. It is also impact-sensitive and explosions are usually violent [2], Its use as a detonator has been proposed. Application of an electric field to crystals of the azide will detonate them, at down to — 100°C [3], and it may be initiated by irradiation with electron pulses of nanosecond duration [4], See other catalytic impurity incidents, irradiation decomposition... 

Rayner, P., Safety Digest Univ. Safety Assoc., 1991, 40, 14 A methyl but-3-enylimidate ester hydrochloride, was charged to a tenfold excess of stirred 14% hypochlorite solution cooled in ice. After 50 min the flask was removed to replenish the ice. Shortly after returning the flask to the icebath a violent explosion shattered both flask and icebath. This was attributed to thermal runaway (although available energy is scarcely sufficient to boil the water in the flask). It seems more likely that trichloroamine was generated by the excess hypochlorite, settled when removed from the magnetic stirrer, and detonated from friction when this restarted. The reaction is said to have been performed many times previously without incident. 

Interaction of chlorine with methane is explosive at ambient temperature over yellow mercury oxide [1], and mixtures containing above 20 vol% of chlorine are explosive [2], Mixtures of acetylene and chlorine may explode on initiation by sunlight, other UV source, or high temperatures, sometimes very violently [3], Mixtures with ethylene explode on initiation by sunlight, etc., or over mercury, mercury oxide or silver oxide at ambient temperature, or over lead oxide at 100°C [1,4], Interaction with ethane over activated carbon at 350°C has caused explosions, but added carbon dioxide reduces the risk [5], Accidental introduction of gasoline into a cylinder of liquid chlorine caused a slow exothermic reaction which accelerated to detonation. This effect was verified [6], Injection of liquid chlorine into a naphtha-sodium hydroxide mixture (to generate hypochlorite in situ) caused a violent explosion. Several other incidents involving violent reactions of saturated hydrocarbons with chlorine were noted [7],... 

Mechanical impact on a road surface on to which liquid oxygen had leaked caused a violent explosion [1], Anecdotal evidence that there have been several like incidents is given [2], Mixtures of asphalt and liquid oxygen were shown to be impact-sensitive on the small scale, but on the larger scale a detonator was necessary to initiate mild explosion of liquid oxygen on a layer of asphalt [3], Oil,... 

Repair and Reuse After Explosion. Although the risk of a high order detonation of a munition during disassembly is low, this hazard does exist. In the event of such an incident, it is a design requirement for the containment rooms to suffer only minimal damage and allow rapid refurbishment. To assure this capability, the containment room structural design criteria are more conservative than Department of Defense Explosive Safety Criteria would normally require. This is considered appropriate since vapor containment is so critical in this facility. 

BLAST ATTENTION. Shields used to provide protection from accidental detonation, are to be designed to prevent exposure of operating personnel to peak, positive incident pressures above 2.3 psi or peak positive normal reflected pressure above 5.0 psi. 

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