Characteristics of Air

Abstract

An explosion in air may cause widespread damage by means of the blast wave which it creates. The pressures generated in this blast wave, although sufficient to cause extensive damage, are quite modest when compared with those within the explosion itself, and for the most part are well within the range over which air acts as an ideal gas. The characteristic equation of state describing any ideal gas may be written as

$$PV = {R_m}T$$

(3-1)

where P is the absolute pressure, V the volume of one mole of ideal gas, and T the absolute temperature. The molar gas constant R _m, in the metric units of the Système International d’Unités (SI units), has the value 8.31434 joules per mole-kelvin (J/mol-K). In this coherent system, pressures are to be expressed in pascals (newtons per square metre), volumes in steres (the stere, symbol m³, is the classic name for the cubic metre), and temperatures in kelvins. However, it is often convenient to use working metric units and express pressures in bars (one bar is 10⁵ pascals, or 14.5 psi, or 1/1.01325 standard atmospheres). The working value for the molar gas constant R _m then is 0.0831434 bar-steres per kilomole-kelvin. This is also its value in bar-litres per mole-kelvin. Table XVI gives these and other factors.