Medical Gas System Safety

Ernest E. Allen, ARM, CHFM, Senior Patient Safety Risk Manager, The Doctors Company

Patient injuries and deaths have occurred as a result of incidents involving the medical gas systems that supply oxygen, compressed air, carbon dioxide, nitrous oxide, nitrogen, and medical vacuum. Consider the following examples and review of requirements that support safety and compliance.

An unexpected patient death occurred on the operating table during the first procedure performed after a hospital renovated its surgery suite. An investigation revealed that the patient had received medical air instead of oxygen through the gas line. Standards now require that cross connections of medical gas lines be verified after installation before they can be used.

In another incident, several patients in an ICU died from lack of oxygen following a fire in another area of the hospital. Investigators found that oxygen to the ICU had been turned off accidentally due to unclear identification on the medical gas zone valves. Standards now require that medical gas zone shutoff valves be clearly marked.

Consequently, it is vitally important that surgery centers, hospitals, and physician offices with piped medical gas systems comply with the following National Fire Protection Association (NFPA) standards: NFPA 99, Health Care Facilities Code and NFPA 55, Compressed Gases and Cryogenic Fluids Code.

Safety Requirements

The following review focuses on the safety requirements related to NFPA Level 1 piped medical gas systems. Level 1 systems are those where any system failure would place patients in imminent danger of morbidity or mortality.

Medical Gas Manifold Rooms

  • Large H cylinders must be properly secured with either chains or angle irons. A cylinder’s flexible connection alone is not strong enough to secure it.
  • A dedicated exhaust system must be on emergency power and draw room air within one foot of the floor if there are over 3,000 cubic feet of gases in the room.
  • The light switch must be at least five feet above the floor to prevent accidental contact with the H cylinders.
  • When an H cylinder is connected, the valve must be briefly cracked open to discharge any dust and preclude it from entering the gas lines. This prevents the slight risk of the dust combusting when it enters the gas line under high pressure.

Vacuum Systems

  • Two pumps are required so that if one fails, the other can still provide vacuum.
  • Vacuum pressure must be limited with a reduction device. The high vacuum level in piped vacuum systems is hundreds of times greater than the negative pressure that the lungs can tolerate—which could result in the collapse of a patient’s lungs.

Medical Air

  • Dew point monitors: Water in the medical air system can shut down a patient ventilator. High moisture content can also lead to bacterial growth. Dew point monitoring is required, and the limit should not exceed 36°F (per the 2012 edition of NFPA 99, which is still referenced by the Centers for Medicare and Medicaid Services . Later editions have the same limits). Dryers must be maintained to properly remove moisture from the medical air.
  • Carbon monoxide monitors: Air drawn into a compressor must be monitored for the presence of carbon monoxide with a limit of 10 ppm.
  • Air intake: Air intake valves must be a minimum of 20 feet above the ground and located away from exposure to vehicle exhaust and discharge of hospital vents. Filters should be used in urban locations with high pollution levels. Another option is to mix oxygen with nitrogen to produce medical air.
  • Air compressors: A duplex system of two air compressors is required so that if one fails, the other will provide sufficient air for the patients. The compressors must be a special medical type that prevents oil from entering the air stream.

Supply and Shutoff Valves

  • Zone valve locations must show the room numbers served, not just a generic description.
  • An external sign on the wall or clear (not dark) plastic covers may ensure that the room numbers served by the valves are visible.

Intervening Walls

NFPA 99 requires an intervening wall between the zone valve and the medical gas outlets. Renovations with relocation of walls often result in noncompliance due to an existing wall being moved or eliminated. Check for compliance with this standard prior to any renovation project.

Oxygen Tank Farm

Pandemic response may require hospitals with multiple COVID-19 patients to replace the liquid oxygen on a more frequent basis. Heavy usage will also result in more condensation and ice forming around the exterior manifold. The ice buildup must be monitored and removed to prevent the oxygen line from freezing and cutting off the supply to the hospital. One method of removing the ice, especially in warm climates, is to use a large fan to blow the warm air across the manifold to help evaporate the ice and keep the line from freezing. Additional criteria include the following:

  • The tank farm must be identified with posted signs indicating the presence of oxygen tanks and that smoking and open flames are prohibited.
  • Two separate and remote entrance/exit gates must be provided in the fencing/wall surrounding the oxygen.
  • Requirements for locating the oxygen tank farm include placing it:
    • 50 feet from a wood frame structure (also consider nearby trees).
    • 10 feet from parked cars.
    • 10 feet from public sidewalks.
    • One foot from a noncombustible building.
    • 50 feet from the nearest nonambulatory patient (such as a patient room).
    • In a fenced, locked area at ground level.
  • No electrical lines must be located over the tanks.
  • A concrete pad must be used at all spill points.

Emergency Oxygen Supply Connection

Facilities must install an emergency oxygen supply connection that allows it to connect to a temporary auxiliary source of oxygen. Typically, the emergency connection is located along the exterior wall near the liquid oxygen tank. That way, if the exterior liquid oxygen tank is damaged, an oxygen supply truck can connect to the facility oxygen system and supply it until the exterior liquid oxygen tank is repaired.

Liquid Oxygen Transfilling

Rooms used for transfilling liquid oxygen from a large container to a small container must be:

  • Separated by a fire barrier that has a one-hour minimum construction rating from any portion of the hospital that houses, examines, or treats patients.
  • Mechanically ventilated, sprinklered, and have ceramic or concrete floors.
  • Identified with posted signs indicating that oxygen transfer is occurring and that smoking and open flames are not permitted in the immediate area.

Alarm Systems

  • Two master alarm panels for the medical gas system must be located remotely from each other, with one panel wired directly to sensors. A centralized computer system may now be used as one of the master alarm panels per the 2012 edition of NFPA 99. (CMS still enforces the 2012 edition.)
  • The alarm systems must be on emergency power.


  • Only American Society of Sanitary Engineering (ASSE)–certified individuals should work with medical gas systems. Certifications include ASSE 6010 for installation, ASSE 6020 for inspection, ASSE 6040 for maintenance, and ASSE 6005 for architects and engineers.
  • The inspections and testing should include the oxygen supply source, master signal panels, area alarms, automatic pressure switches, shutoff valves, flexible connectors, and outlets.
  • For new or modified medical gas and vacuum systems, NFPA 99 requires that certified individuals perform comprehensive testing before use. This includes purging lines with nitrogen to help remove impurities, pressure testing for leaks, testing cross connections, and verifying alarm systems.
  • Recommendations from inspections should be listed by priority, and corrective action must be taken within a reasonable time frame. Accreditation agencies will review medical gas system inspection reports during their surveys.

For additional information, see our article “Safe Handling of Medical Gas Cylinders” or contact the Department of Patient Safety and Risk Management at (800) 421-2368 or by email.

The guidelines suggested here are not rules, do not constitute legal advice, and do not ensure a successful outcome. The ultimate decision regarding the appropriateness of any treatment must be made by each healthcare provider considering the circumstances of the individual situation and in accordance with the laws of the jurisdiction in which the care is rendered.

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