[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
