Chemical Explosives

The vast majority of explosives are chemical explosives. Explosives usually have less potential energy than fuels, but their high rate of energy release produces a great blast pressure. TNT has a detonation velocity of 6,940 m/s compared to 1,680 m/s for the detonation of a pentane air mixture, and the 0.34-m/s stoichiometric flame speed of gasoline combustion in air.

The properties of the explosive indicate the class into which it falls. In some cases explosives can be made to fall into either class by the conditions under which they are initiated. In sufficiently large quantities, almost all low explosives can undergo a Deflagration to Detonation Transition (DDT). For convenience, low and high explosives may be differentiated by the shipping and storage classes.

A chemical explosive is a compound or mixture which, upon the application of heat or shock, decomposes or rearranges with extreme rapidity, yielding much gas and heat. Many substances not ordinarily classed as explosives may do one, or even two, of these things. For example, at high temperatures (> 2000 °C) a mixture of nitrogen and oxygen can be made to react with great rapidity and yield the gaseous product nitric oxide; yet the mixture is not an explosive since it does not evolve heat, but rather absorbs heat.

N₂ + O₂ → 2 NO − 43,200 calories (or 180 kJ) per mole of N₂

For a chemical to be an explosive, it must exhibit all of the following:

• Rapid expansion (i.e., rapid production of gases or rapid heating of surroundings)
• Evolution of heat
• Rapidity of reaction
• Initiation of reaction

Flare Gun

The most common type of flare gun is a Very (sometimes spelled Verey), which was named after Edward Wilson Very (1847–1910), an American naval officer who developed and popularized a single-shot breech-loading snub-nosed pistol that fired flares (Very flares). They have a single action trigger mechanism, hammer action, center fire pin. Modern varieties are frequently made out of brightly colored, durable plastic.

Flare Gun

The older type of Very pistol, typical of the type used in the Second World War, are of one inch bore (26.5 mm). These are still available and more recent longer barrel models can also fire parachute flares.^[3] Many newer models fire smaller 12-gauge flares. In countries where possession of firearms is strictly controlled, such as the United Kingdom, the use of Very pistols as emergency equipment on boats is less common than, for example, the United States. In such locations, distress flares are more commonly fired from single-shot tube devices which are then disposed of after use. These devices are fired by twisting or striking a pad on one end, but the contents are otherwise similar to a round from a flare gun, although the flares themselves are much larger and can burn brighter for longer.

Flare guns may be used whenever someone needs to send a distress signal. The flares must be shot directly above, making the signal visible for a longer period of time and revealing the position of whoever is in need of help.