Decomposition Explosions

A decomposition explosion is caused by the breakdown of a compound into its various elements. The decomposition occurs with the release of tremendous amounts of heat and the expansion of tremendous volumes of gas. Chemically, the material is transformed from a solid to a gas with the emission of heat. In other words, the substance, which had previously been a solid, is converted into a gas almost instantaneously. The problem is that the volume of the solid occupies a greater physical space when converted to a gas. As the material tries to convert to the gaseous state, it expands to many times its original size. In this rapid rearrangement of molecules plus the addition of heat, the heat raises the temperature of the gas, which in turn increases the space required for the gas. At the same time, this activity increases the pressure exerted on the walls of the container, resulting in a pressure relief explosion.

TEXT 5

Explosives

Explosives are chemical compounds specifically designed, manufactured and distributed for the accomplishment of a controlled explosion. The explosion is completed through the chemical release of heat and gas, including the physical effect of creating high pressures as a result of converting a solid into a gas with the release of tremendous amount of heat. This causes expansion of the produced gas due to the heat effect. It includes explosions, which could be classified as either high or low velocity explosions.

The Department of Transportation has divided explosives into three classes, with a separate classification for blasting agents. These are listed in descending order of sensitivity to explosions.

Class A explosives possess highly sensitive detonation characteristics and include dynamite, mercury fulminate, black powder, blasting caps, detonating primers and certain smokeless propellants.

Class B explosives have highly flammable hazard rating and include the propellant materials. They are considered less hazardous than Class A explosives.

Class C explosives include manufactured articles which contain limited quantities of Class A or B explosives as one of their components. It includes detonating cords, explosive rivets or other manufactured production items. These explosives will not normally detonate under fire conditions.

Blasting agents are manufactured from an explosive material but are not easily set off by impact as are the other three classes. Blasting agents will burn, but the reaction will not reach detonation velocities.

The NFPA defines a blasting agent as any material or mixture consisting of a fuel and oxidizer, intended for blasting, not otherwise classified as an explosive and in which none of the ingredients are classified as an explosive. For reasons of safety, the construction, mining and general industry has adopted the use of fuel oxidizer systems, which do not contain explosives. The most common blasting agent is called Anfo. This is an acronym for Ammonium Nitrate Fuel Oil. The combination of ammonium nitrate and fuel oil makes a safe and very effective substitute for dynamite. Ammonium nitrate explodes by decomposition and causes the fuel oil to ignite through the combination of pressure and heat released by the ammonium nitrate. A strong detonator is required to initiate the explosion, but the additional safety found in the use of the substance makes it well worth the additional cost of detonation.

Anfo is not suited for wet applications, however, so water gels or slurries are used. These utilize ammonium nitrate and a powdered aluminium which is uninhibited by the presence of water.

TEXT 6

Поиск по сайту: