Medical gas supply testing

This was the subject of the nightmarish Question 2 from the second paper of 2005; it interrogated the candidate's intimate knowledge of Australian Standard 2896 1998 – "Medical gas systems – installation and testing of non-flammable medical gas pipeline systems".

The question itself reads as follows:

"A new level three Intensive  Care Unit has been built  in your hospital.   Patients  are going to be admitted next week.  The Director of Intensive Care Services gives you the job of testing that the gas supplies and suction that have been installed are appropriate and working satisfactorily.  How will you do this?"

In brief summary;

• Make sure all bed spaces have
  • 3 × oxygen outlets
  • 2 ×air outlets
  • 3 ×suction outlets
• Make sure all the outlets have the right gases in them
  • check labels
  • check colour coding
  • check the gas (i.e. ensure its oxygen)
  • sniff the outlets, like some kind of weirdo.
• Make sure the gases are at the correct static pressure (~ 400kPa)
• Make sure the gas pressure does not drop more than 10kPa when the flow is turned up to 40L/min.
• Make sure the low pressure alarms are working.

A more detailed exploration of this issue can be found in the famous textbook of anaesthesia equipment by Dorsch and Dorsch. Specifically, Chapters 1 to 4 are dedicated exclusively to medical gas supply and distribution systems. Their recommended steps for gas supply testing can be summarised as follows:

Installer-performed tests

• Initial blow-down: After installation, the line must be blown clear of foreign material by using oil-free dry nitrogen.
• Initial pressure test: Each section of the piping system must be subjected to a test pressure of 1.5 times the normal system working pressure (i.e. about 600kPa)
• Cross-connection test: The installer must make sure that the right gas is delivered at each wall outlet, i.e. there are no "cross-connections". Each wall outlet is tested to ensure that the correct gas emerges only from the outlets being tested, rather than from some extra random outlets somewhere.
• Pipeline purge: a high-pressure gas purge of each outlet; "until no discoloration is produced on a white cloth that is held over the outlet".
• Standing pressure test: the entire system is subjected to a 24-hour test with a pressure 20% above the normal operating line pressure, and with all the valves closed. The next day the pressure should still be the same. This test is to identify leaks.

System verification tests

• These should be performed by somebody competent who is not associated with the installer.
• Standing pressure test: just like the 24 hour test, except for 10 minutes.
• Cross-connection test: more or less identical to the installer's version
• Valve test: to ensure all the valves actually work
• Alarm test: one must ensure that gas failure alarms are actually working
• Piping purge test: again, observing the appearance of blown out particulate matter on a piece of white cloth.
• Piping particulate test: again, a test of particulate matter - except instead of a white cloth this time at least 1000L of gas must be allowed to escape though a 0.45micron filter.
• Piping purity test: a test whereby the outlet gas is tested for dew point, methane, and halogenated hydrocarbons.
• Final tie-in test: this is performed when you have commissioned the entire system, and then decide to add extra pipes. The new system extensions must be tested for leaks at normal system pressure.
• Operational pressure test: The outlets must all deliver a certain flow, and they must all d this without a significant drop in pressure. The specifics are:
  • Flow rate no less than 100 L/min (and 140 L/min for nitrogen)
  • Pressure drop no more than 35 kPa for any gas
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• Malodorous gas outlets are important. In spite of all my childrish giggling about the perversity of gast outlet sniffing, Dorsch and Dorsch report that "pipeline odors should always be taken seriously", and that "All medical gases should be odor-free."