How do you find leaks in a medical gas network?

Measuring leakage: the pressure decay test

Under HTM 02-01 (2026), the NHS England guidance, the carcass test on a new pipeline is meant to establish that there is no leakage from the system. It uses electronic pressure-measuring equipment with a resolution of at least 0.01 kPa in 10,000 kPa, and nitrogen as the test gas, so that a leak or cross-connection can be put right at once. Over a test period of at least two hours, once the system has filled and settled, the pressure loss should stay below 0.2 kPa for 400 kPa systems and vacuum and below 0.5 kPa for 700 kPa systems, with no allowance for temperature. If there is any doubt about the accuracy of the gauges, the test should be extended to 24 hours, and gas-law corrections for temperature should only be used on a 24-hour test with large temperature changes between start and finish. The pipeline pressure test, done later at about the normal working pressure, uses the same limits, and a vacuum system should show no loss of vacuum.

Locating the leak

Part B of HTM 02-01 lists a pipeline leak test of 2 to 24 hours at working pressure or vacuum on digital gauges (PPLx), and a leak test with leak detector fluid (PPLF), generally used for small modifications of fewer than 20 joints where every joint is accessible. The vacuum leakage test isolates the area, draws the vacuum down to a set level and monitors it on digital gauges for 15 minutes. In its precautions for changing cylinders, Part B adds that only oxygen-safe leak-detection fluids should be used, that excess spray should be wiped off with a clean damp cloth, and that a naked flame or lighted cigarette should not be used to look for leaks. In the static test of a cylinder manifold, a soap test may accompany the gauge test but not replace it, and ultrasonic leak detectors can speed up the search without replacing the static test; any pressure drop indicates a leak that should be found, put right and re-tested.

A 2004 US Department of Energy tip sheet on industrial compressed air recommends an ultrasonic acoustic detector for finding leaks and lists the usual places: couplings, hoses, tubes, fittings, pipe joints, quick disconnects, condensate traps, valves, flanges and thread sealants.

Checks during operation

• Terminal units: HTM 02-01 Part B asks for all terminal units except AGSS ones to be tested quarterly, inserting a blank probe to check gas-specificity, mechanical function and leaks.
• Exposed pipework: external runs, and internal runs in risers or corridors, should be inspected at least annually, including for leaks from fittings.
• Nitrous oxide: HTM 02-01 says nitrous oxide waste commonly occurs through leakage from the pipeline to the atmosphere before the point of delivery; given its global warming potential, an annual system pressure test should be undertaken and, where that is difficult, as in maternity, individual components should be leak-tested as part of maintenance.
• PSA plants: an operating procedure from the USAID-funded RISE programme (March 2022), written for hospitals in India, includes a monthly check of pipes and hoses for leaks, and Global Fund commissioning guidance (28 August 2024) asks for leak tests from the compressor to the bedside outlet and a 24-hour piping test at 20% above operating pressure, confirmed not to fall more than 10%.

Leaks and consumption figures

Open Critical Care warns that leaks in the oxygen infrastructure, such as an unused flowmeter left on, poorly fitted regulators or cracked tubing or piping, are a common reason for underestimating oxygen demand. For a PSA plant that supplies the pipeline directly, it suggests recording flow with a mass flow meter, which can also detect flow problems. Ways to cut these losses are on how to reduce oxygen wastage.