Common Technical Terms used in quantifying the Effects: There are numerous detailed technical terms relating to quantifying the effects of explosions. Below are terms which are used frequently and for which definitions are provided. (1) Overpressure: For a pressure pulse (blast wave), the pressure developed above atmospheric pressure at any stage or location is called the overpressure. Overpressure is sometimes used to describe exposure of equipment to pressures in excess of the design pressure, but the term over pressurisation is preferred for this purpose. (2) Peak Positive Overpressure: The maximum overpressure generated is called the peak positive overpressure. (3) Duration: The time taken for the pressure pulse to decline to zero is known as the positive phase duration, usually shortened to duration. (4) Side-On Overpressure: If a pressure-sensitive device which offered no obstruction to the passage of the blast wave was placed in its path (i.e. one which was facing sideways in relation to its advance), the device would record side-on overpressure. (5) Reflected Overpressure: If a rigi object was perpendicular to the advance of the blast wave (i.e. facing), the object would reflect and diffract the wave. Due to this reflection, the object will experience an effective overpressure of at least twice the side-on overpressure. (6) Epicentre: The ground location beneath the inferred centre of a vapour cloud explosion. (7) Explosion Efficiency: The ratio of the energy in the blast wave to the energy theoretically available from the heat of combustion, usually expressed as a percentage. (8) TNT Equivalent: The amount of TNT (trinitrotoluene) which would produce the same damage effects as those of the explosion under consideration. For nondense phase explosions the equivalence has meaning only at a considerable distance where the nature of the blast wave arising is comparable with that of TNT.