Pure Steam Quality Test
The testing involved in Facility Utility pure steam validation requires a continuous supply of saturated steam; preferably sourced from the actual line that supplies your sterilization systems. Too high a level of non-condensible gases will prevent the attainment of sterilization; too little moisture carried in suspension may allow the steam to become super-heated during expansion into the chamber, while excess moisture may cause damp loads. Where steam systems are either routinely or irregularly shut down, large quantities of air will be present in the distribution system on restarting. It is recommended that in such circumstances a comprehensive and validated venting procedure should be applied and testing steam quality should be routinely executed.
Non-condensible gases originate from the water
that the steam is generated from. These gases
will usually be air, although carbon dioxide
may be present, caused by certain water
treatment processes, typically water
softeners. This is exacerbated by excessive
aeration that can exist in many pharmaceutical
water treatment plants where water is
constantly recirculated and sprayed into the
top of storage vessels. The effect of such
gases being present in the steam supply to a
sterilizer can be the same as air, none
sterilization of the volume they occupy.
Superheated steam is steam at a temperature
above its boiling point for its pressure.
Superheated steam is a clear colour-less gas
that will not condense until its temperature
drops to its boiling point. Until this occurs
the moisture necessary for sterilization
cannot be produced and therefore presents a
risk to the process. Superheated steam acts as
hot air and requires sustained high
temperatures and long hold times before
sterilization can occur. It is essential in
facility utility pure steam validation to
verify that the steam being tested is not
superheated.
Wet steam is undesirable as it has less energy
than dry steam and more importantly can cause
wet loads. The packaging used for sterile
products prevents reinfection when dry, but
its bacterial retentive properties will be
adversely affected by the presence of
moisture. Wet loads can be considered to be
un-sterile. The dryness fraction describes how
dry steam is, with a value of 1 representing
steam that is 100% dry and therefore free of
entrained moisture. Steam with a dryness
fraction of 0.99 consists of 99% steam and 1%
water. If we measure the latent heat present
in steam that has a dryness fraction of 0.99
we will find that it possesses 99% of the full
quotient of latent heat.