B. Types of Explosions   

There are 4 general types of explosions;

Mechanical, 

Chemical, 

Nuclear and 

Electrical. 

However, there are only two types of explosions that the first responder or  investigator will generally encounter, Mechanical and Chemical and several subtypes within these categories. The types of explosions are generally differentiated by the source or mechanism by which explosive pressures are produced. 

1. Mechanical

Mechanical explosions are those in which a high pressure gas produces a physical reaction, vessel failure or rupture of the container. If the material that is stored in the container, is flammable, then in many instances a resultant fire occurs as long as there is an ignition source or the temperature of the product is above its autogenious ignition temperature. Key to the resultant fire is the mixing of the fuel with air or an oxygen source.

Nature of the Fuel does not change

a. Damage to the vessel

BLEVE, Boiler Failure

2. Chemical

The generation of high pressure gas is the result of an exothermic reaction resulting from the initiation of chemical explosives or fuel gases. The rate of reaction will vary, and when explosives are present, an outside oxidizer is not required.

Nature of fuel changes

a. Combustion

Flammable Gases

Vapors of Flammable and Combustible Liquids

Dusts or Fines

Backdraft (Smoke)

Carbon Monoxide and Carbon

Explosives

3. Nuclear

High quantities of heat and gas are produced as a result of the fusion or fission process.

    Photograph from CNN

4. Electrical Explosions

High energy electrical arcs may generate sufficient heat to cause an explosion. The resultant heating of the surrounding gases results in a mechanical explosion. A common example is found in residential occupancies (and others) is that the cover of the electrical panel box has been violently dislodged from the remaining box. Often this has been caused by a lightning strike or other high energy arc. This reaction may or may not result in subsequent fire.