[Federal Register Volume 59, Number 31 (Tuesday, February 15, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-3474]


[[Page Unknown]]

[Federal Register: February 15, 1994]


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DEPARTMENT OF TRANSPORTATION
[Notice No. 94-1]

 

Safety Advisory: Service Life of Composite Cylinders Used in a 
Self-Contained Breathing Apparatus (SCBA) or in Other Services

AGENCY: Research and Special Programs Administration (RSPA), DOT.

ACTION: Safety advisory notice, correction.

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SUMMARY: This document makes a correction to a safety advisory notice 
published in the Federal Register on November 18, 1993 [Notice No. 93-
22; 58 FR 60899], by adding two DOT Exemptions, which were 
inadvertently omitted from the list of affected exemptions. Beginning 
with the summary, the notice is reprinted as follows:
    This is to notify persons using composite cylinders manufactured 
and authorized under DOT exemptions that those cylinders have a 15-year 
service life limit. The service life limitation applies to cylinders 
based on RSPA's fiber-reinforced-plastic (FRP) cylinder standards for 
metal-lined fiber-reinforced-composite cylinders which form part of an 
SCBA or are used in other services. The cylinders typically have 
service pressures of between 2,000 and 4,500 psig. Composite cylinders 
marked with a DOT exemption number that are older than 15 years should 
be removed from service. Such cylinders may have reduced strength 
without any visual indication of damage.

FOR FURTHER INFORMATION CONTACT: James K. O'Steen or Charles H. 
Hochman, telephone (202) 366-4545, Office of Hazardous Materials 
Technology, Research and Special Programs Administration, U.S. 
Department of Transportation, Washington, DC 20590-0001. Office hours 
are: 8:30 a.m. to 5 p.m., Monday through Friday.

SUPPLEMENTARY INFORMATION: RSPA has recently received numerous letters 
concerning the service life of certain cylinders used in Self-Contained 
Breathing Apparatuses (SCBAs). The letters express the concerns of fire 
departments and others with the 15-year service life limitation on FRP 
composite cylinders which form part of an SCBA. Commenters are 
particularly concerned with the cost of replacing the cylinders after 
15 years. These cylinders are manufactured and authorized for 
transportation under DOT exemptions.
    An FRP composite cylinder is composed of an inner metallic liner 
over-wrapped with fiber filaments, most commonly fiberglass or kevlar, 
bonded together with a plastic resin. The large forces produced by the 
high pressure inside such a cylinder are restrained by the inner liner 
and the thousands of fiber filaments windings around the inner vessel. 
In a composite cylinder used for an SCBA, a large portion of the 
strength of the cylinder is provided by the fiber filaments.
    Because fiber filaments provide much of the strength of an FRP 
cylinder, the useful life of an SCBA cylinder is greatly dependent on 
the properties of fiber filaments. Two of these properties are 
susceptibility to brittle fracture and stress rupture.
    Brittle fracture. Fiber filaments are very strong but brittle. Once 
a crack starts in a filament, the crack continues to grow until the 
filament breaks. Unfortunately, filaments cannot be manufactured 
without some microscopic cracks. Cracks are also caused by in-service 
damage and pressure cycling. As cracks in a filament grow and a 
filament breaks, the filament's load is transferred to adjacent 
filaments. With increasing load, cracks in other filaments grow faster, 
additional filaments break, and load transfer increases. As the process 
accelerates with time, the bursting strength of the cylinder may be 
reduced and the cylinder could rupture in service.
    Stress rupture is an actual reduction of fiber strength that occurs 
with time when the fiber is under load. Stress rupture varies greatly 
with material type; fiberglass is more susceptible to stress rupture 
than carbon fiber. In structures made of a material subject to stress 
rupture, such as fiberglass, the load level on filaments eventually 
exceeds their strength and the cylinder may rupture at the marked 
service pressure with potentially lethal consequences.
    Because brittle fracture damage and stress rupture may occur 
without any visual indication of damage, cannot be found by available 
non-destructive tests, and produce a general reduction in a cylinder's 
strength over time, a maximum life was established to prevent cylinder 
rupture in service. The 15-year restriction was based on technical data 
presented by the cylinder manufacturers in support of their exemption 
requests, and is consistent with the service life limitation found in a 
position paper, ``Basic Considerations for Composite Cylinders,'' 
developed and published by the Compressed Gas Association.
    Only one manufacturer of SCBA has requested that DOT amend its 
exemption to extend the cylinder service life from 15 years to 18 
years. RSPA technical staff performed an extensive technical review of 
the manufacturer's information that resulted in a denial of the 
request. RSPA concluded that the test data presented in support of an 
increased service life indicated a trend toward accelerated loss in 
cylinder burst strength and an increasing probability of cylinder 
failure, and did not support a service life extension.
    RSPA is aware of, and concerned about, the financial burden 
associated with limiting the service life of composite cylinders, but 
RSPA must weigh this burden against the safety risk of a cylinder 
failure to firefighters and other users. For example, a Coram, New York 
firefighter was killed earlier this year (1993) by the rupture of a 
composite cylinder which was more than 15 years old. While the cause of 
that rupture was neither brittle fracture nor stress rupture, it is an 
example of the severe consequences of a composite cylinder failure.
    Based on the above information, RSPA has retained the 15-year 
service life limitation on composite cylinders. At a minimum, persons 
finding composite cylinders that are older than 15 years should remove 
those cylinders from service. Composite cylinders are authorized for 
SCBA and other services under the following exemptions: 

DOT-E 7218               DOT-E 8391               DOT-E 9716            
DOT-E 7235               DOT-E 8487               DOT-E 10019           
DOT-E 7277               DOT-E 8718               DOT-E 10147           
DOT-E 7769               DOT-E 8725               DOT-E 10256           
DOT-E 8023               DOT-E 8814               DOT-E 10345           
DOT-E 8059               DOT-E 8965               DOT-E 10637           
DOT-E 8115               DOT-E 9634               DOT-E 10905           
DOT-E 8162               DOT-E 9659               DOT-E 11005           
                                                                        

    Issued in Washington, DC on February 10, 1994.
Alan I. Roberts,
Associate Administrator for Hazardous Materials Safety.
[FR Doc. 94-3474 Filed 2-14-94; 8:45 am]
BILLING CODE 4910-60-P