The effect of air with steam on the temperature of autoclave contents.

The effect of residual air on the local temperature within an autoclave has often been calculated solely from the known relationship between the pressure and temperature of steam in equilibrium with water. A system of directly measuring air is described which, together with temperature measurements, indicates that large volumes of air trapped in an autoclave load are not necessarily associated with reduced temperatures, although their presence will considerably prolong the heat-up period. It is confirmed that a restricted flow of steam into an autoclave chamber, with reliance on a 'balanced pressure' thermostatic trap as a condensate and air outlet, will not remove air efficiently, even from an empty chamber. Long heating times observed when polypropylene containers are used for laboratory discard material are probably due to retention in the container of large volumes of air. When an efficient air displacement system is employed heat-up times are considerably reduced; the conductivity of the container material being less important than the penetration of steam to its contents.