SVMS Steam Quality
Non-Condensable Gases

The Non-Condensable Gas Test demonstrates that the attainment of sterlisation conditions in all parts of a steriliser load (particularly for porous load items) is not impaired by the presence of non-condensable gases.

The measurement of non-condensable gases is made by cooling a steam sample with an efficient condenser, using water siphoned from a tank at 200ml per minute. Minimum requirements are: one metre head and water temperature below 28 degrees centigrade. Pressurised water is not required.

When the sampled steam is condensed any non-condensable gases present are released and separated from the cooled condensate into two sight glass columns. Gas and steam condensate volumes are measured by 'zero-adjustable' calibrated scales mounted behind the sight glasses. The temperature of the condensate is maintained above 80 degrees centigrade by controlling the steam flow through the inlet needle valve while measuring the condensate temperature from a thermocouple probe on the outlet of the condenser.

To carry out repeated tests a return to the 'zero scales' position is made by opening the condensate drain and gas bleed valves. The valves are then closed when a new sample is is required. Volumes up to 14ml gas and 140ml condensate are possible for each sample.

The non-condensable gas test is considered to be acceptable for sterilisation purposes on clinical sterilisers if the percentage of gas to condensate is less than 3.5%.

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