NIOSH Respirator User Notice

(National Institute for Occupational Safety and Health)

(This is a slightly condensed summary by Bill High, PSI, Inc. March 20, 2000 of the original notice)

December 7, 1999

This notice informs users of SCBA that certain aluminum seamless and composite hoop-wrapped cylinders are susceptible to sustained load cracking (SLC).  If such cracks are not detected during visual inspection, cylinder rupture can occur, especially during filling.

DOT and NIOSH are aware of 12 cylinder ruptures from SLC in the U.S.A.   Additional failures have occurred in other countries.  Most failures occur during the fill process.  NIOSH has determined that in order to reduce the risk of death, serious injury, or property damage, the following safety precautions should be taken with all DOT 3AL and composite cylinders manufactured of 6351-T6 alloy.

  1. Increase the frequency of internal visual inspections. Perform inspections on an annual basis by a qualified inspector in accordance with comprehensive inspection guidelines using mirror and light.

  1. Inspections should be performed by qualified individuals. Individuals inspecting for SLC or other cylinder damage must be able to follow visual inspection guidelines and should be trained by accomplished instructors experienced in visual inspection of cylinders.  These inspections are only effective when properly performed.  Therefore, emphasis should be placed on inspector training and diligence.   The inspection should be conducted by trained, qualified, and competent visual inspectors.
  1. Submit cylinders for non-destructive testing at regular intervals between the required requalification testing.
  1. Do not refill any cylinder that has lost internal pressure for no apparent reason. Unexpected loss of pressure (or sound of leaking air) may indicate a SLC defect has developed. Immediately remove from service, discharge and visually inspect interior.
  1. Cylinders should only be refilled in a manner that limits risk to personnel and property. Recommend filling in a suitable enclosure.
  1. Use proper cylinder filling equipment and procedures and refrain from fast-filling. SLC develops over several years but such growth and the likelihood of cylinder rupture are accelerated when cylinders are over-pressurized, or fast filled. Recommended fill rate is below 600 psig per minute.  (Over 90 percent of all cylinder explosions occur during the fill process).  Never fill above stamped service pressure.
  1. Check for valid re-test date before filling. NO cylinder, regardless of construction type should be filled or used if it has exceeded the valid service life or re-test dates specified by DOT (seamless aluminum cylinders re-test at 5 year intervals with no life limit.  Composite cylinders retest at 3year intervals and are limited to 15 years maximum life).

Training and information on inspecting high pressure SCBA and SCUBA cylinders can be obtained by contacting

telephone 425.398.4300     e-mail  This e-mail address is being protected from spambots. You need JavaScript enabled to view it.
web site:

PSI, Inc. is the ONLY worldwide full service SCBA/SCUBA visual inspector training company recognized by cylinder manufacturers, government agencies, fire and dive industries.  We are the industry standard.

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