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level of isolation (such as a deep trap) is required to prevent the cross flow of steam between
the drains. The drip tray and water tank overflow can be connected to an open tundish if
desired. This has the advantage of making any discharge from the overflow visible, which is in
accordance with water bylaws.
Water Supplies and Back-flow Prevention
The Water Supply (Water Fittings) regulations 1999
Note: The fluid categories below relate only to the above regulations, and are in no way
connected with the containment categories previously discussed with reference to drainage
and containment of pathogens.
It is mandatory that the completed installation complies with the Water Supply (Water
Fittings) regulations 1999 – SI No 1148. This will be dependent on factors outside of the
autoclave such as the layout of the water supply provided. The location and usage of the
autoclave will determine the fluid category for which back-flow prevention measures are to
be taken, however it is suggested in the guidance notes to the above regulations that all
laboratories in industrial and commercial installations are considered category 5. Prevention
measures suitable for fluids in this category may therefore need to be considered.
The back-flow prevention measures already provided within the autoclave are as follows:
Autoclaves with Automatic Water Fill Systems and Liquid Ring Vacuum Pumps
Water is fed to the autoclave vessel and vacuum pump via a header tank with air gap and
circular overflow, which is classified type AF. This alone will provide back-flow prevention
measures suitable for fluids up to category 4. Provided that the supply to the autoclave is
delivered via a header tank with similar prevention means elsewhere in the building the
installation will form an air gap with interposed cistern of type AUK, which is suitable for fluids
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