TABLE OF CONTENTS Hazards from processes using chemicals are assessed on the basis of:
| Toxic, flammable/explosive, reactive, unstable |
| Liquid, solid (briquette, flake, powder), gas, vapour, airborne particulate (including mist, fume, froth, aerosol, dust) |
| In storage, held up in process stages, in the working atmosphere, as wastes, etc. |
| Use of high or low temperature, high pressure, vacuum or possible hazardous reactions (polymerization, oxidation, halogenation, hydrogenation, alkylation, nitration, etc.) |
Hazards can often be foreseen from basic physicochemical principles, as summarized below.
The vapour pressure of a chemical provides an indication of its volatility at any specific temperature. As an approximation, the vapour pressure p' of a pure chemical is given by
where A and B are empirically determined constants and T is the absolute temperature.
Hence the vapour pressure of a chemical will increase markedly with temperature.
For a component 'a' in a mixture of vapours, its partial pressure p a is the pressure that would be exerted by that component at the same temperature if present alone in the same volumetric concentration. So with a mixture of two components, 'a' and 'b', the total pressure is
If an inert gas is also present, its pressure is additive:
In an 'ideal mixture' the partial pressure p a is proportional to the mole fraction y a of the component in the gas phase:
and this partial pressure is also related to the concentration in the liquid phase expressed...
