The safety of medical compressed air systems is worth learning about*

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Medical gas systems, also known as life support systems, are used to sustain the lives of critically ill patients and facilitate their recovery. The two most popular standards in the world, HTM 2022 and NFPA 99, which are widely recognized by the industry, have a history of several decades; China’s latest regulations for medical gases are also about to be issued. Life support systems established in accordance with authoritative standards will play an increasingly important role in maintaining the orderly operation of the entire hospital. Medical compressed air is one of the most important medical gases in central gas supply systems; it is the only \"drug\" that is produced on-site in hospitals (with the exception of some hospitals that use oxygen generators). The European Pharmacopoeia lists compressed air as a drug and specifies its components in detail. Therefore, the managers of gas supply equipment in various hospitals bear a great responsibility. The following is a brief analysis of how to ensure safe gas supply. Medical compressed air is primarily supplied to various wards, intensive care units, emergency rooms, operating rooms, and other areas for use in patients’ breathing. For example, many patients sensitive to oxygen need to use medical air as a substitute, and many other patients require high-precision ventilators. So, what kind of medical compressed air is safe and reliable for patients? I. Ensure continuous gas supply; in other words, the gas supply must not be interrupted under any circumstances. To ensure continuous gas supply, it is necessary to consider backup or safety designs for every component in the system, including the electrical control section. At the same time, self-startup after a power outage must also be considered to ensure continuous gas supply in the event of an instantaneous power failure. This issue has been recognized by the vast majority of current hospital managers, and domestic hospitals are relatively well-equipped in this regard. II. In medical compressed air systems that ensure the quality and safety of gases, the quality of the gases must meet the requirements for safe use by patients. And the most troublesome issues in compressed air are oil and water in it. (1) Addressing the issue of oil in the air: External air, after being processed by old-fashioned oil-containing air compressors, often contains trace amounts of oil molecules. When oil-contaminated medical gases are mixed with oxygen and supplied to ventilators, the combination of oxygen and oil can lead to localized explosions and fires, which is extremely dangerous. In developed Western countries, it is explicitly stipulated that the oil content in medical gases must be less than 0.1 mg/m³. Now, generally we use two methods to address oil-containing problems. One option is to purchase an oil-free air compressor directly, but in that case, oil removal equipment is still required ； Another method is to use compressed air oil removal equipment to remove the oil from oil-containing air compressors. If an oil-based compression system is used, the procurement cost is lower, but a reliable oil removal device must be available to ensure the stability and safety of oil-free compressed gas. The gas quality not meeting the requirements can affect patient health or damage the terminal equipment. Especially for hospitals with inadequate equipment management, it is recommended to ensure the stability of the gas supply system. Minimal maintenance throughout the year is sufficient to ensure the continuity and reliability of gas supply. (II) Solving the problem of moisture content in air: The moisture content in air is an issue that is often easily overlooked. Moisture is not filtered out by the air filter like other dust particles. It can enter the air supply pipelines, **machines, ventilators, and other end devices through filters. Liquid water, or water vapor mixed with **agents**, can cause mechanical failure in sprayers. Water damage to a ventilator can result in expensive repair costs or even render the equipment unusable. In low-temperature environments, water in medical gas supply pipelines may freeze and block the pipes, affecting gas flow. Furthermore, water can also cause oxidation of copper pipes, leading to a sharp geometric increase in the amount of harmful impurities contained within the pipes. All these have caused significant economic losses to the hospital. Some hospitals use small, portable compressors to power ventilators; this solves the problem posed by water, but it is costly. In large hospitals with a large number of ventilators, the costs can be much higher than those associated with centralized air supply. Moreover, water serves as a medium for bacterial growth, which can lead to cross-infection among patients. It is particularly noted that the operating noise of small compressors can also cause irritation in patients. 1. The use of cold dryers is not recommended. The US NFPA 99 standard specifies that the dew point temperature must be below 0°C at any flow rate. Currently, most hospitals that rely on centralized gas supply use two different drying technologies: cryogenic dryers (hereafter referred to as cold dryers) and adsorption dryers (hereafter referred to as adsorption dryers). The dew point temperature of a cold dryer is generally at +3°C. In previous cases where cold dryers were used, the biggest problem was that the dew point temperature rose sharply at low flow rates, preventing the removal of water molecules. Subsequent studies found that this is because, at low flow rates (20% of the rated flow), the condensate water in the water separator cannot be removed in time, resulting in the formation of a large amount of saturated water molecules within the separator; these molecules are then carried along with the gas to subsequent equipment and pipelines, where they accumulate as liquid water. Therefore, the use of cold dryers in medical air systems is generally not recommended abroad. However, at present, many systems use a combination of cold dryers and desiccants to achieve stable drying air. 2. Advantages and disadvantages of desiccants. Desiccants achieve drying by using the van der Waals forces between adsorbent particles (alumina) and water molecules; therefore, they do not suffer from the problems associated with cold dryers at low flow rates. Industrial desiccators generally have a dew point temperature of -40°C; in reality, it is impossible for patients to inhale air that is too dry, and the air must be re-humidified before it can be supplied for the patient’s breathing. Therefore, medical air does not require a particularly low dew point; moreover, the lower the dew point, the more electrical energy is consumed. Therefore, it is suggested that the key issue in medical air is not to achieve a certain dew point, but rather to ensure that no liquid water appears at the endpoints under any conditions. Based on practical examples, the selected desiccant dryer operates at a temperature of -12°C, which not only meets the usage requirements but also offers good cost-performance. Of course, the easy damage to the switching valve is the main drawback of desiccators; it not only increases maintenance costs but also poses safety risks due to the requirement for continuous air supply to the system. To this end, it is recommended to use specially designed dedicated switching valves. With the upcoming introduction of **medical gas standards, domestic companies will gradually develop specialized medical gas equipment to provide safer and more reliable medical air