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NRC INFORMATION NOTICE 95-01: DOT SAFETY ADVISORY: HIGH PRESSURE ALUMINUM SEAMLESS AND ALUMINUM COMPOSITE HOOP-WRAPPED CYLINDERS

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert addressees to a safety concern for workers identified in the safety advisory (see Attachment 1) recently issued by the Research and Special Programs Administration of the U.S. Department of Transportation (DOT). The DOT notice advises users of certain high pressure cylinders made of aluminum alloy 6351-T6 to follow precautionary measures to prevent or mitigate cylinder ruptures. It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice are not NRC requirements; therefore, no specific action or written response is required.

On July 26, 1994, the Research and Special Programs Administration of DOT issued a safety advisory, "High Pressure Aluminum Seamless and Aluminum Composite Hoop-Wrapped Cylinders," in the Federal Register (Volume 59, No. 142, pages 38028-38030). The advisory contains a description of two catastrophic cylinder failures. The first occurred at a chemical plant in Texas, where a self-contained breathing apparatus aluminum alloy air cylinder ruptured while being filled to its rated pressure of 15.4 MPa [2216 psig]. The second failure was the rupture of a self-contained underwater breathing apparatus cylinder also made of the same type alloy that also occurred while the cylinder was being filled. The rupture caused serious injury to the attending technician. In both events, a piece of the cylinder neck separated and was blown away with great force. Ruptures like these are unexpected for aluminum alloy 6351-T6, since current metallurgical findings and modeling predict only leaking at pressures below 27.7 MPa [4000 psig]. The DOT investigation of these failures is continuing.

The DOT advisory applies to seamless aluminum cylinders marked "DOT 3AL," manufactured under one of the following exemption or special permit numbers: 6498, 7042, 8107, 8364, or 8422; composite cylinders affected are marked with one of the following exemption numbers: 7235, 8023, or 8115.

These two events are the first known ruptures of aluminum alloy 6351-T6 in the seamless (non-composite) cylinder neck and shoulder area at pressures below 27.7 MPa [4000 psig]. Previous problems with the same alloy in composite cylinders (hoop-wrapped aluminum cylinders) have been described in various National Institute for Occupational Safety and Health, DOT, and NRC generic communications, which all dealt with ruptures or cracking of cylinders rated at 31.1 MPa [4500 psig] or cracking (leaking) of cylinders with a service rating of 15.4 MPa [2216 psig].

DOT cautions users to take reasonable precautions as described in its advisory when using or handling affected cylinders, and to call the manufacturer or distributor if they have any questions about that particular unit. Anyone aware of the rupture of any DOT 3AL cylinder made of aluminum alloy 6351-T6 can call the technical contacts at DOT, as DOT is collecting information and insight on this matter, and is planning to consider additional advisories.

Licensees may wish to share this information with other potential users, such as local fire departments.

NRC Information Notice 83-68, "Respirator User Warning: Defective Self- Contained Breathing Apparatus Air Cylinders"

NRC Information Notice 84-34, "Respirator User Warning: Defective Self- Contained Breathing Apparatus Air Cylinders"

NRC Information Notice 85-48, "Respirator User Notice: Defective Self- Contained Breathing Apparatus Air Cylinders"

NRC Information Notice 86-24, "Respirator User Notice: Increased Inspection Frequency for Certain Self-Contained Breathing Apparatus Air Cylinders"

This information notice requires no specific action or written response. If you have any questions about the information in this notice, please contact one of the NRC technical contacts listed below, the DOT contacts mentioned in the subject DOT safety advisory, or the cylinder manufacturer.

1. DOT Safety Advisory, "High Pressure Aluminum Seamless and Aluminum Composite Hoop-Wrapped Cylinders"