Confined explosions

A basic distinction is made between confined unconfined explosions. Confined ex occur within some sort of containment such as a vessel pipework, or a building. Explosio open air are unconfined explosions. 

Process plants are categorized into different hazard classifications, according to the potential explosion energy available from vessel rupture, condensed-phase explosion, confined vapor (building) explosion, or VCE. 

Fia 6 Effect of A on shock sensitivity of various explosives. NQ-f is low-bulk-density nitroguanidine with hollow-needle crystals of about 5 n diam X 60-65 it long. NQ-h is the high-bulk-density material made up of solid particles of about GO-65 n diam. DATB, TNT, and Tetryl are, respectively, dia-minotrinitrobenzene, trinitrotoluene and trinitro-phenylmethylnitramine. RDX is cyclotrimethyl-enetrinitramine which contains 2.5% lubricant. Measurements were carried out with a standardized test (Ref 16) in which a 3.65-cm-diam test explosive confined in 0.55-cm-thick steel is the acceptor and polymethyl methacrylate is the gap material MGl = NCro filt ro uasiM i ... 

J. Savitt, "Effect of Acceptor Explosive Confinement upon Acceptor Sensitivity , NavOrdRept 2938(1953)... 

Venting of gases generated by the explosion (for explosions confined in vessels or other structures) ... 

When occasions demand, there are cases in each of which a fairly small vibrator is applied to the base of the closed cell in order that the high explosive confined in the cell may come closely in contact with the glass capillary tube. 

Confined Explosions. Confined explosions occur when a flammable mixfure in a confined space is ignited. A typical example is the case of a flammable liquids tank. When these tanks are emptied, residu liquid may evaporate and form a flammable mixture in the tank. If ignited, a confined explosion would be produced. The modeling of confined explosion effects is analogous to the modeUng of BLEVEs. Here the explosion energy released is obtained from the enthalpy of combustion. 

Combustion is an exothermic reaction in which reactants are converted to principally gaseous products. Because the reaction is exothermic, the product gases heat up and expand. In a fire, such as arson, this expansion generates plumes with predictable behaviors that leave distinctive markings at the crime scene. In contrast, propellants rely on expansion of hot gases to drive a projectile forward, while explosives confine the expansion as long as possible to generate a destructive shock wave. Because of this confinement, a detonation is a... 

Flash and evaporadon Dispersion Neutral or posidvely buoyant gas Dense gas Fires Pool fires Jet fires BLEVES Flash fires Explosions Confined eiqilosions Unconfined vapor cloud explosions (UVCE) Physical explosions (PV) Dust explosions Deionadons Condensed phase detonadons Missiles Consequences Effect analysis Toxic effects Thermal effects Overpressure effects Damage assessments Community Workforce Environment Company assets... 

The shocks interact with the walls and the explosive confinement and send reflected shocks back into the detonation products, resulting in additional heating and varying amounts of additional chemical reaction. Because the gas-analysis studies give such varied results, not the products along a C-J isentrope but rather the products many steps removed are being measured. The equation of state described in this section is inadequate to account for the additional reaction of the ammonium nitrate and detonation products that apparently occurred in the Hershkowitz experiments. 

The numerical model used to interpret cylinder wall expansion experiments must include a realistic description of build-up of detonation, Forest Fire burn and resulting detonation wave curvature. A problem in numerical simulation of long cylinders of explosive confined by thin metal walls is to obtain sufficient numerical resolution to describe the explosive burn properly and also to follow the simulation of long cylinders. The NOBEL code includes the necessary physics and will numerically model cylinder tests as described in Chapter 6. 

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