Are Aluminum Oxygen Regulators Safe?
FAQ [Health Devices Mar 1999;28(3):118]
Question. We have heard that aluminum oxygen
regulators are now considered to be a fire hazard. What are the issues?
Answer. A recent advisory issued by the U.S. Food
and Drug Administration (FDA) and the National Institute for Occupational Safety
and Health (NIOSH) has created a lot of interest in this topic. Under certain
conditions, aluminum will burn in oxygen, and the February 1999 FDA/NIOSH
advisory cites several instances in which aluminum oxygen regulators used with
high-pressure cylinders have caught fire.
In these instances, the fires have been initiated through either of two mechanisms: 1) particle ignition, in which debris is blown from the cylinder into the high-pressure side of the regulator with sufficient energy to ignite the aluminum in the regulator, or 2) adiabatic compression ignition, in which the gas in the regulator is recompressed as the high-pressure oxygen enters the regulator; this creates a transient high temperature that ignites flammable materials in that space, resulting in the ignition of the regulator. Adiabatic compression ignition is less of a concern in the hospital setting because regulators are not likely to become contaminated with ignitable materials, such as oil and dirt, during use or maintenance in this environment. This form of ignition is more of a concern in the prehospital setting (e.g., for emergency medical services).
In light of the incidents referenced in their advisory, both FDA and NIOSH now recommend that aluminum regulators be replaced with brass regulators, which are much less likely to ignite when used with high-pressure compressed oxygen. While replacing aluminum regulators with ignition-resistant brass is a prudent measure and may eventually be required in U.S. facilities (as is implied by the FDA/NIOSH advisory), facilities can continue to use aluminum regulators for the time being, provided that they follow simple safety precautions to reduce the likelihood of fire. For example:
- Particle ignition can typically be avoided by
following basic compressed-gas safety practices. These include clearing the
cylinder valve stem (by "cracking" the cylinder valve to release a
short burst of gas) before attaching a regulator and ensuring that the
regulator is in a no-flow state before attaching it to the cylinder. In the
aluminum regulator fires that ECRI has investigated, such basic safety
practices were violated. Also, while not a sure preventive measure, the use
of a sintered inlet filter disk rather than an easily displaced mesh screen
inlet filter can help reduce the fire risk. (One major regulator
manufacturer has made this change to its regulators.)
- The risk of adiabatic compression ignition can be
minimized both by keeping all regulators free of oils, dirt, and other
combustible substances and by opening the cylinder valve slowly, rather than
For the time being, we recommend educating users in the safe practices for compressed gases while planning to replace aluminum regulators with brass ones in a prudent manner. For a detailed list of safe practices, refer to the Compressed Gas Association's (CGA) pamphlet P-2, Characteristics and Safe Handling of Medical Gases
(CGA, 1725 Jefferson Davis Highway, Suite 1004, Arlington VA 22202-4102; Phone:  827-5242,  412-0890).
Regulators, High-Pressure Gas [13-323]