How often should medical air dew point and CO sensors be calibrated?

HTM 02-01 (2026) deals with two sets of instruments for medical air: the hygrometers that watch each dryer continuously, and the analysers the Quality Controller (MGPS) uses to test the delivered air, including for carbon monoxide.

Plant dew point hygrometers

Under the HTM, each dryer assembly should have its own dew point sensor and test point after the bacteria filter, so that the dryer can be tested before it is brought online and the product can be monitored continuously. The dryer control unit should contain hygrometers and displays with a minimum accuracy of ±3 °C over a range of at least −20 °C to −80 °C, set to −46 °C atmospheric dew point, and an automatic changeover to the standby dryer when the duty dryer fails on dryness or pressure. For compressor plant, Part B of the HTM says the testing and servicing procedures supplied by the manufacturer should be followed.

Quality control analysers, including carbon monoxide

Carbon monoxide is not in the HTM 02-01 list of plant faults; it is checked by quality control testing of terminal units, with a limit of 5 ppm (v/v). The HTM asks for electronic equipment for these tests because of its repeatability, resolution and accuracy, calibrated on site before testing with certificated calibration gases. If readings drift during testing, the analyser calibration should be checked and recalibrated and the Quality Controller should consider repeating a sample of tests; calibration should also be carried out once all tests are completed, and records should be kept of all calibrations. The Quality Controller (MGPS) should ensure that all equipment used for medical gas testing is maintained and serviced according to the manufacturer's recommendations and local protocols.

Contractor test equipment

Separately, HTM 02-01 Part B makes the maintenance contractor provide the test equipment for its tasks, identified in the method statement and in Chapter 19 of Part A. That equipment should be calibrated in accordance with the manufacturers' recommendations, and in any case against recognised national standards at a frequency of no less than annually, with calibration records kept by the contractor and produced for inspection by the Authorised Person (MGPS).

How often the air itself is tested

Quality control testing is carried out on new installations and after repairs and modifications, and the HTM sets quarterly testing for medical and surgical air compressor plants. Water vapour should not exceed 67 vpm, about −46 °C atmospheric dew point; the HTM says the test at the compressor plant confirms dryer performance, and failure to achieve the minimum dew point standard should not be accepted.

On Ultra Controlo equipment

The ULTRAAR ME has two integrated ULTRAGEST systems for continuous monitoring and control of the dew point. The ULTRAMED treatment unit accepts a digital dew point indicator for continuous outlet monitoring, which is not included as standard, and has a low dew point indicator alarm.