Moisture in Medical Gases - Complying with HTM 2202

Medical gases are used in a variety of applications within the health industry. Hospital operating theatres, recovery rooms and intensive care units require high quality piped medical air for patients. Hospital laboratories use clean air for sample preparation and storage. Dental surgeries require clean, dry air to prepare patients' teeth prior to and during treatment.

Medical gases are essentially medicines, and because of this their quality is closely regulated. It is vitally important that they are pure and sterile at the point of delivery to the patient, and limits are specified by European Pharmacopoeia (E.P.) monographs for oxygen, nitrous oxide and medical air. Several key contaminants that could harm patients are identified, including:
· Carbon Monoxide
· Carbon dioxide
· Sulphur dioxide
· Nitrogen Monoxide/ dioxide
· Oil
· Water vapour

In practice, water vapour is the most problematic in the hospital environment, with two effects being especially dangerous to patients:

1. Condensation could occur, resulting in the presence of liquid water within the medical gas system leading to corrosion. Liquid water can also interfere with or damage vital medical equipment.
2. High moisture levels could promote the growth of harmful bacteria. This could then pose a threat to patients either through contaminated gases or during surgery when air is used to drive tools in the operating theatre.

Legislation
In the United Kingdom piped medical gas systems are subject to regulation by the Health Technical Memorandum 2022 (HTM202). This states that medical gases supplied to pipeline systems should comply with the current E.P. standards, and that the gas quality is not affected by the pipeline system. The current E.P. limit for moisture in medical gases is 67ppm(v), 0r -46°C dew point.

How Michell Instruments can help
Michell has developed a dew-point measurement instrument that is ideally suited to medical gas applications. The Cermax Portable Hygrometer is a simple to use, accurate, fast dewpointmeter that can provide a measurement to 67 ppm(v) in less than ten minutes. Cermax is factory calibrated to an accuracy of better than 1 oC dew point, with traceability to both UK and US national standards. In addition to offering ease of use and quick response, Cermax features an in-built datalogger that can record readings from a number of different air locations and subsequently be downloaded to a computer, in order to maintain traceability of quality testing protocols.

For continuous, on-line measurement of the moisture content in medical air, Michell also offers the Easidew On-line and Transmitter hygrometers. Both instruments provide real time determination of the dew-point of the air line and can immediately detect a compressor or dryer failure. Easidew Transmitter provides a linear 4-20mA output signal for connection to a datalogger or external process control system, whilst the Easidew On-line Hygrometer provides a local display, alarms and a 4-20 mA output signal.

Back to press releases