Cause of Device-Related Incident
Device factors; User errors

Clinical Specialty or Hospital Department
Clinical/Biomedical Engineering; CSR / Materials Management; Facilities Engineering

Device Factors
Improper maintenance, testing, repair, or lack or failure of incoming inspection

Document Type
Hazard Reports

External Factors
*Not stated

Mechanism of Injury or Death
Exposure to hazardous gas

Support System Failures
*Not stated

Tampering and/or Sabotage
*Not stated

User Errors
Incorrect clinical use

Cartridges, Ethylene Oxide [16-612]; Sterilizing Units, Ethylene Oxide [13-740]

Improperly Connected Ethylene Oxide Sterilizer Supply Cylinder

Hazard [Health Devices Dec 1994;23(12):493]


A member hospital reported that, when changing the supply cylinders on its 15-year-old ethylene oxide (EtO) sterilizer, service personnel had been using a wrench to tighten the fitting into the valve stem of the new EtO-CFC (Freon) cylinders. Following advice from the manufacturer, the service personnel started hand-tightening the connection. Moments after a cylinder had been changed using hand-tightening, nearby employees experienced respiratory and eye irritation. On investigation, the cylinder connection was found to be spraying the EtO-CFC mixture into the air. As a result, a worker was sprayed in the face, and employees in the area were exposed to high levels of EtO.


While an excellent sterilant, EtO is also a hazardous gas, regulated by the Occupational Safety and Health Administration (OSHA). It causes irritation to eyes, skin, and mucous membranes and, in high concentrations, can cause pulmonary edema. It is moderately toxic when inhaled (causing convulsions, nausea, vomiting, and olfactory and pulmonary changes) and poisonous when ingested; it is also a suspected carcinogen. In addition, it is a fire and explosion hazard if exposed to flame. (Also see our Guidance Article on EtO sterilization.) Because of EtO's hazardous nature, OSHA requires specific precautions to prevent EtO exposure to hospital workers (see 29 C.F.R. § 1910.1047). Care must also be exercised in working with EtO containers and all devices that use EtO.


Instead of the hex-head nut typically used in many cylinder connections, the incident sterilizer fitting has a hand-wheel nut, about two to three inches in diameter, that is meant to be hand-tightened only. The fitting has a conical end with a conical gasket, made of polytetrafluoroethylene or polyethylene, that seals against the mating conical opening in the cylinder valve stem. Initial wrench-tightening of the fitting can permanently deform the gasket. Continued wrench-tightening can further deform the gasket, creating a new seal sufficient to prevent EtO leaks; however, eventually, wrench-tightening will cause the gasket to fail completely and leak.

In the reported case, the fitting gasket was probably malformed from previous wrench tightening, which allowed a small leak to occur when the valve was only hand-tightened. The leaking EtO most likely cooled the gasket and fitting, causing them to shrink and the area of the leak to enlarge.


Hospitals using EtO sterilizers or devices with hand-wheel fittings, should take the following steps to prevent this kind of accident:

  1. Inspect the fitting, cylinder valve stem, and hose for defects before installing a new cylinder. Replace any damaged fittings or hoses. Do not use cylinders with damaged valve stems. For fittings that have been wrench-tightened, continue to wrench-tighten until a replacement, hand-tightenable fitting can be installed.
  2. Check the completed connection for leaks with a handheld leak detector; such detectors typically sense between 25 and 50 ppm of EtO. (Note: Use only leak detectors that actually sense EtO to enable detecting older EtO-CFC mixtures [which are being phased out] and newer EtO-CO2 mixtures.) Shut off the cylinder and correct the cause of any leaks.
  3. Ensure that working and effective engineering controls, such as a dedicated exhaust hose or hood, are in place near the supply cylinder(s) to minimize employee exposure to EtO should a leak occur. Alternatively, position the supply in a well-ventilated room where workers are not normally present. (See 29 C.F.R. § 1910.1047 paragraph [f] and Appendix A.VII.1.d.)


  • Cartridges, Ethylene Oxide [16-612]
  • Sterilizing Units, Ethylene Oxide [13-740]

Cause of Device-Related Incident

Device factor: Improper maintenance, testing, repair, or lack or failure of incoming inspection

User error: Incorrect clinical use

Mechanism of Injury or Death

Exposure to hazardous gas

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