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Fast Fill, Slow Fill, Does It Make A Difference?

Several years ago, MSA (Mine Safety Appliances) and Interspiro, manufacturers of SCBA cylinder systems, introduced policies that encourage extraordinarily rapid fill of their brands of fully wrapped composite SCBA cylinders.  The potential value of filling a cylinder in a minute or less is obvious.  Emergency personnel can get back on line much more quickly than either having to change out cylinders or wait for a air fill that conforms to the more common gas industry standard of 600 psig or less.  The disadvantages are less apparent and, in some cases overlooked.

MSA in a well-written guideline, points out that its cylinders are well made and thoroughly tested.  Selected new cylinders are even cycled at much faster fill rates to hydrostatic test pressure thousand of times with no ruptures.  Temperature sensing devices affixed to the aluminum liner of a composite cylinder show that internal temperatures, generated by rapid compression of air, at about 116 degrees F. are well within the allowable limits for safety.  Even in-service use of the fast filling methods for several million fills contributes to the view that fast filling techniques are safe.

The process of fast filling, that is charging a 4,500 psig full-wrap composite cylinder in 45 seconds, is reported to be so routine that it can be used for non-emergency filling as well as emergency fills even though the original purpose was for emergency fills. That rate of fill may also be used on steel SCBA according to MSA and Pressed Steel Tank Co.(PST).

PSI, Inc. personnel are neither metallurgists nor engineers.  We do not dispute the policy statements made that indicate new and otherwise well maintained full wrap composite SCBA cylinders can safely withstand such rapid fill and resulting expansion.  Apparently they can and emergency conditions may well support the need for such speed.  We do however know something about in-service cylinder condition and their level of care.

We know that within the 15year life of a composite cylinder many receive unusually harsh treatment.  Some are not hydrostatically retested at the required three-year interval. And, there is some question as to the actual value of the hydrostatic retest to determine the overall quality of the cylinder. A few fire departments have been found using composite cylinders past the mandatory retirement age of 15 years.  A small percentage of SCBA cylinders are kept like new in storage cases at factories, aboard vessels, and at other locations where they are not regularly used.  Most SCBA in fire department inventories are used regularly and often harshly.

We at PSI, Inc. are concerned that many operational SCBA are in far less than Ideal Condition.  OSHA (Occupational Safety and Health Act), DOT (Department of Transportation) and NIOSH (National Institute for Occupational Safety and Health)  all direct or recommend frequent visual inspections.  NIOSH places considerable emphasis on both the quality of the inspection and the qualification of the inspector.  In a December 7, 1999 NIOSH notice signed by Richard W. Metzler, Chief Respirator Branch, seven policy statements are made.  In that document, NIOSH recommends filling cylinders (without regard to type) at a rate below 600 psig per minute and refrain from over-pressurizing or fast filling.  Cylinders are to be inspected frequently, at least annually, by trained inspector conducting proper inspections.  Inspections should be conducted by trained, qualified and competent visual inspectors.  Unfortunately, many government officials and fire department technicians don’t know what constitutes a proper inspection.  OSHA requires the employer to be responsible for safe cylinders based upon visual inspection and directs that SCBA shall be inspected every 30 days and after each use.  DOT in its notice RSPA-99-5143 (notice no. 99-11) advises those who own or fill certain 3AL or aluminum lined composite cylinders to have annual technical internal and external visual inspections.  The notice further advises,  “for additional information on SCBA/SCUBA cylinders contact PSI, Inc. and Luxfer Gas Cylinders”.

The problem with fast fills is that there are a great many cylinders in use that have not had frequent inspections by trained, competent technicians with a technical protocol to follow.  So, while there appears to be nothing wrong with the concept of rapid cylinder filling, even while the cylinder is on the fire fighter’s back, many cylinders may not qualify for the dramatic stresses generated by a 45 second fill to 4,500 psig.  Since 90 percent of cylinder failures occur during the fill process and, every year numerous cylinders of various designs rupture, great care should be given to ensure the cylinders are not damaged.   Technical visual examinations should only be conducted by trained inspectors who understand the significance of various damage types.  Fire fighters in Detroit didn’t understand the effect of damage nor did the fatally injured New York fireman or the California department that filled chemically damaged cylinders.  It is interesting that several agencies recommend all fills take place in some form of protective container which contradicts the logic of routine fast fills on the back of a fire fighter.

A policy of routine fast fills might also prompt technicians to fast fill other cylinders that have not been recommended for filling faster than 600 psig per minute.  Many fire departments use solid wall 3AL SCBA and SCUBA. One manufacturer specifies these cylinders are not to be filled faster than 600 psig per minute.  While Pressed steel Tank Co. states that its steel cylinders may be fast filled, we know that many of those cylinders used by divers have significant damage and might not withstand a fast fill protocol.

All fill station operators who chose to fast fill cylinders should be trained and qualified to identify any questionable cylinders and to ensure the cylinders they fill receive frequent, technical visual inspections, the cylinders are in excellent condition and eligible for fill rates beyond 600 psig per minute.

Professional training for cylinder inspectors is offered throughout the U.S. and Canada and at some international locations.  Contact PSI, Inc. at: telephone 425-398.4300, fax 425.482.0160 e-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it.