March 14, 2000

The bulletin contains good information about the sustained load crack phenomena, and it gives the reader advice and recommendations regarding SCBA cylinders made from 6351 aluminum alloy. However, the bulletin does not impose new requirements on the owners of these cylinders.

1. Sustained Load Cracking (SLC): Metal cracking from the process known as sustained load cracking takes a considerable amount of time, and there is no scientific evidence to support claims of “fast-growth” cracks that you may have heard about or seen on the Internet. SLC occurs over many years-usually not less than four and in some cases as many as nine years-before the cylinder leaks. Attempting to fill a leaking cylinder can lead to catastrophic failure of the cylinder, causing injury, death, and/or property damage. Statistics show that very few cylinders made of 6351 alloy actually develop cracks. But if a crack is found, the cylinder must be taken out of service and condemned.

2. Dates of Manufacture: Luxfer produced SCBA cylinders from 6351 alloy from 1972 through 1988 in the U.S. It is easy to tell if your cylinder is made from this alloy. First check to see that you own a Luxfer cylinder. Look for “Luxfer” or “Alcan” on your SCBA cylinder. Then check for a manufacturing date. The first (oldest) hydrostatic test marking on the cylinder crown is the manufacturing date. If the SCBA cylinder was made from 1972 through 1988 and it is a Luxfer cylinder, then the NIOSH bulletin applies to your cylinder. If your cylinder was manufactured after 1988, then it is made from 6061 alloy, which is not susceptible to sustained load cracking.

3. Inspection Frequency: Luxfer recommends that all-metal SCBA 6351 cylinders be inspected once every 2.5 years (halfway between requalifications). Hoop-wrapped 6351-alloy cylinders should be inspected every 3 years at the time of the normal requalification. Please note that hoop-wrapped cylinders manufactured before 1985 have expired and are to be condemned.

4. Inspection Quality: The NIOSH bulletin suggests that owners of these cylinders make sure that they are using reputable requalification stations with current ID or station numbers (RINs) issued by DOT, RSPA. The bulletin also suggests that owners make sure that requalification inspectors do thorough jobs. The SCBA cylinders that have failed in service have done so because they were not properly inspected.

5. Use of Non-destructive evaluations: For the purposes of this bulletin, non-destructive evaluations (NDE) of cylinders means the use of eddy current devices (e.g., Visual Plus and Visual Eddy), ultrasonics and similar methods to find sustained load cracking. The NIOSH bulletin recommends NDE use. While sustained load cracks can be found by a good visual inspection, as an added safety measure Luxfer supports the use of NDE on its older cylinders and for use at requalification facilities where the inspection quality is either suspect or unknown.

6. Inspectors: As cautioned in the NIOSH bulletin, cylinder inspectors need to be diligent and competent. The extra inspection for all-metal SCBA cylinders can be performed in-house and does not need to be performed by requalification station inspectors. However, if it is done in-house, the inspectors need training and should have an inspection guide. You may obtain independent cylinder inspection training from a company called PSI (telephone 425/486-2252 or e-mail at

7. Inspection Guides: Download for free at, the path is Product Info/Americas, then click the underlined text after the directory name.

If you make sure that your Luxfer cylinders receive appropriate care, maintenance and inspection, you will be able to enjoy their safe service for a long time. Luxfer is the world’s largest manufacturer of aluminum cylinders. Our cylinders have an unmatched record for safety and reliability. Thank you for using a Luxfer product.