A. General Theory, Definitions

1. Explosion

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There are a variety of definitions that have been applied to the term explosion and while each of them are correct, they are based on the community that uses the term.

a. Explosion. The sudden and rapid production and escape of gases from a confined space accompanied by heat, shock & a noise.

b. Explosion. The sudden conversion of potential energy (chemical or mechanical) into kinetic energy with the production and release of gases under pressure, or the release of gas under pressure. These high-pressure gases then do mechanical work such as moving, changing, or shattering nearby materials. (NFPA-921, 1998 Edition)

c. Explosion. An explosion is a large-scale, noisy, rapid expansion of matter into a volume much greater than its original volume. This can be achieved by

(1.) bursting a vessel containing a pressurized fluid;

(2.) rapid heating of air and plasma by an electric arc;

(3.) a very fast burning reaction; or

(4.)detonating an explosive material.

(Introduction to the Technology of Explosives; Cooper, Paul W. and Kurowski, Stanley R.)

d. Explosion. Under the fire and explosion investigation definition, an explosion is a physical reaction characterized by the presence of four major elements or criteria:

(1.) Rapid Increase in Gas Pressure (Gas Dynamic)

(2.) Confinement of the Pressure

(3.) Rapid release of that Pressure

(4.) Damage or Change to the confining structure of the vessel

"Noise is not an element"

"Explosion Investigation and Analysis, Kennedy on Explosions"; Kennedy, Patrick M. and Kennedy, John P15-16

While this definition is more of an analysis of the results it does provide the user with an understanding of the key components of an explosion and it is useful in both response considerations and investigation.

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e. Explosion. A chemical or mechanical action resulting in a sudden bursting accompanied by a loud noise.

f. Explosion. A rapid expansion of gases.

g. Explosion. Simply, a loud boom and a sudden going away of things from where they have just been!

    2. Explosives

As with the term "explosion" there are a variety of definitions used for explosives, one would only need to look at the bibliography to have the opportunity to review the definitions used by the technical literature.

a. Explosives. A mixture of solids or solids and liquids which upon initiation cause a rapid and violent decomposition, and produce large volumes of gas. (Condensed Phase)

b. Explosives. The term explosives generally is used in reference to a wide range of energetic materials that can react chemically to produce heat, light, and gas.

"In general, an explosive has three basic characteristics:

(1.) It is an unstable chemical compound or mixture ignited by heat, shock, impact, friction , or a combination of these conditions;

(2.) Upon ignition it decomposes very rapidly in a detonation (as opposed to a deflagration, which is a slower decomposition as with ignition of gunpowder);


(3.) Upon detonation there is a "rapid release of heat and large quantities of high-pressure gases, which expand rapidly with sufficient force to overcome confining forces, e.g., the confining forces of surrounding rock formation."

Blaster’s Handbook, 16th Edition; pg. 31

c. Explosives. Department of Transportation (DOT) Definition

Explosives: An Explosive is any chemical compound, mixture, or device which is designed to function by explosion, that is substantially instantaneous with the release of gas and heat. Exception—such compound, mixture, or device which is otherwise specifically classified in Parts 171-180. (See 49 CFR 173.50)

Current Classification System

DOT Hazard Classification for explosives.

Class 1 – Explosives

Division 1.1 Explosives with a mass explosion hazard

Division 1.2 Explosives with a projection hazard

Division 1.3 Explosives with predominantly a fire hazard

Division 1.4 Explosives with no significant blast hazard

Division 1.5 Very insensitive explosives; blasting agents

Division 1.6 Extremely insensitive detonating articles

Old Classification System (Provided for reference only)

CLASS A Detonating. Maximum Hazard. The nine types of Class A explosives are defined in 49 CFR 173.53.

CLASS B Flammable Hazard. In general, functions by rapid combustion rather than detonation. Included are explosive devices such as special fireworks, flash powders, etc. (49 CFR 173.88)

CLASS C Minimum hazard. Small arms ammunition, certain types of fireworks and various types of manufactured articles containing restricted quantities of Class A and/or Class 11 explosives as components. Included are common fireworks and various types of small arms ammunition manufactured articles which contain restricted quantities of Class A or Class B explosives. (49 CFR 173.100)

BLASTING AGENT. A material designed for blasting which has been tested in accordance with 49 CFR 173.114(a)(b). It must be so insensitive that there is very little probability of: (1) accidental explosion or (2) going from burning to detonation. (49 CFR 173.114a(a))

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Photograph Copyright: Ron Hopkins

Explosives Chart Copyright: Ron Hopkins