Saturated steam at 1 bar gauge has just over 500 kJ/kg of sensible heat energy, but over  2,200 kJ/kg of latent heat of evaporation. Reliable saturated steam sterilisation depends the release of this latent heat into the load. To achieve this, the steam must actually condense on the load surface. For these reasons the physical condition of the supplied steam is critically important. Standardised tests are set out in HTM2010/ EN285 with acceptance limits for critical parameters:

Non Condensable Gases (“ncg’s”).
Sterilisation can be compromised by the presence of air, or of ncg’s such as carbon dioxide dissolved in raw feedwater then released during steam generation. In an autoclave chamber these can cause pockets of “dry” heat, up to temperature but without steam to condense. The maximum limit is that the non condensable gas volume must not exceed 3.5% of the volume of liquid that carried it as steam.

Superheat
Pressurised steam delivered to an autoclave will almost certainly include some moisture. As it expands into the chamber much of this moisture will evaporate, the steam will become more “dry”, further expansion will lead to superheat. This can reach the point where the steam vapour can heat the load without condensing as expected at all, the release of latent heat will be less than expected and sterilisation may be compromised. The maximum superheat tolerance in the standardised test set out in HTM2010/EN285 is 25⁰C.

Dryness Fraction
Steam that entrains too much condensed moisture (is too “wet”) may coat the load with film of water which prevents the process of vapour condensation taking place on the load surface itself. The minimum dryness tolerance in the standardised test set out in HTM2010/EN285 is 90% for porous loads and 95% for metal loads.
SteriTech technicians have the necessary training to conduct these Steam Quality Tests correctly, all the necessary test instrumentation is provided.
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