How often should medical gas alarms be tested?

Frequencies in HTM 02-01

Part B says the frequencies in HTM 02-01 should be viewed as a minimum requirement only (para 11.75). For liquid oxygen (VIE) systems, it asks for the alarm system to be tested regularly under the hospital's documented procedures and subject to risk assessment, with each alarm condition initiated by operating a pressure switch and a built-in test facility on the control panel to check the pressure switches; the high line pressure alarm needs specialist test equipment, and the gas supplier should normally be contacted to test it (paras 11.141 to 11.143).

How an alarm panel is checked

The Part B checklists, used with manufacturers' data to prepare quarterly and annual maintenance schedules, include these alarm panel tasks:

1. Push the test button and confirm the indicators or displays are clear and visible and an audible alarm sounds.
2. Disconnect the mains supply and confirm a "system failure" indicator starts together with an audible alarm.
3. With the supply still disconnected, examine the interior for loose or damaged components and the external condition of the battery.
4. Check that remote alarms mirror the functionality of the master alarm.
5. Check the low alarm condition set points annually.

At commissioning

Part A asks for warning and alarm systems to be tested in all normal operating, fault and emergency modes, with every alarm seen and heard where it is installed, the backup battery checked, mute and audible reinstatement tested, and each panel checked for the correct two-tone signal; HTM 02-01 notes that staff may confuse a single-tone panel with some patient monitoring equipment. Local alarms are tested for the correct response to pressure changes on all gases. Plant alarm tests are recorded on form B27 and local alarm tests on form B28.

During the tests

All work is covered by a permit to work. Before manifold and medical air compressor maintenance tests, Part B asks for the staff concerned to be notified and for signage at the plant alarms warning that the system is being tested and alarms are likely. Part B notes that alarms are often triggered by necessary work, such as replacing transducers or batteries, and that it is essential that alarms reported during the work are not dismissed as spurious, as they may be unrelated faults. A temporary mute resounds after a nominal 15 minutes if the fault persists, and an internal switch allows continuous muting during maintenance, resetting automatically when the system returns to normal.