Hazardous Materials Regulations: Transportation of Compressed Oxygen, Other Oxidizing Gases and Chemical Oxygen Generators on Aircraft, 4442-4458 [E7-1487]

Agencies

• Pipeline and Hazardous Materials Safety Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 72, Number 20 (Wednesday, January 31, 2007)]
[Rules and Regulations]
[Pages 4442-4458]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E7-1487]


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DEPARTMENT OF TRANSPORTATION

Pipeline and Hazardous Materials Safety Administration

49 CFR Parts 171, 172, 173, 175 and 178

[Docket No. RSPA-04-17664 (HM-224B)]
RIN 2137-AD33


Hazardous Materials Regulations: Transportation of Compressed 
Oxygen, Other Oxidizing Gases and Chemical Oxygen Generators on 
Aircraft

AGENCY: Pipeline and Hazardous Materials Safety Administration (PHMSA), 
DOT.

ACTION: Final rule.

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SUMMARY: PHMSA (also, ``we'' or ``us'') is amending the Hazardous 
Materials Regulations (HMR) to: require cylinders of compressed oxygen 
and other oxidizing gases and packages of chemical oxygen generators to 
be placed in an outer packaging that meets certain flame penetration 
and thermal resistance requirements when transported aboard an 
aircraft; revise the pressure relief device (PRD) setting limit on 
cylinders of compressed oxygen and other oxidizing gases transported 
aboard aircraft; limit the types of cylinders authorized for 
transporting compressed oxygen aboard aircraft; and convert most of the 
provisions of an oxygen generator approval into requirements in the 
HMR. PHMSA is issuing this final rule in cooperation with the Federal 
Aviation Administration (FAA) to increase the level of safety 
associated with transportation of these materials aboard aircraft.

DATES: Effective Date: The effective date of these amendments is 
October 1, 2007.
    Voluntary Compliance: Voluntary compliance with all these 
amendments, including those with a delayed mandatory compliance date, 
is authorized as of March 2, 2007.

FOR FURTHER INFORMATION CONTACT: John A. Gale or T. Glenn Foster, 
Office of Hazardous Materials Standards, telephone (202) 366-8553, 
Pipeline and Hazardous Materials Safety Administration, U.S. Department 
of Transportation, 400 Seventh Street, SW., Washington, DC 20590-0001, 
or David Catey, Office of Flight Standards Service, telephone (202) 
267-3732, Federal Aviation Administration, U.S. Department of 
Transportation, 800 Independence Avenue, SW., Washington, DC 20591.

SUPPLEMENTARY INFORMATION:

List of Topics

I. Background
II. Safety Issues Associated with the Air Transportation of 
Compressed Oxygen Cylinders and Oxygen Generators
III. Summary of the Final Rule
IV. Comments and Regulatory Changes
    A. General
    B. Outer Packagings for Compressed Oxygen Cylinders, Other 
Oxidizing Gases, and Chemical Oxygen Generators
    1. Scope of Rulemaking
    2. Other Oxidizing Gases Aboard Aircraft
    3. Packaging Design Standards
    4. Packaging Availability and Costs
    5. Compliance Date
    C. Pressure Relief Device Settings and Authorized Cylinders for 
Compressed Oxygen and Other Oxidizing Gases
    D. Limits on Number of Oxygen Cylinders Transported on Aircraft
    E. Chemical Oxygen Generator Approval
V. Effects on Individuals with Disabilities
VI. Regulatory Analyses and Notices
    A. Statutory/Legal Authority for Rulemaking
    B. Executive Order 12866 and DOT Regulatory Policies and 
Procedures
    C. Executive Order 12988
    D. Executive Order 13132
    E. Executive Order 13175
    F. Regulatory Flexibility Act, Executive Order 13272, and DOT 
Procedures and Policies
    G. International Trade Impact Assessment
    H. Unfunded Mandates Reform Act of 1995
    I. Paperwork Reduction Act
    J. Environmental Assessment
    K. Regulation Identifier Number (RIN)
    L. Privacy Act

I. Background

    The National Transportation Safety Board (NTSB) determined that one 
of the probable causes of the May 11, 1996 crash of ValuJet Airlines 
flight No. 596 was a fire in the airplane's cargo compartment initiated 
and enhanced by the actuation of one or more chemical oxygen generators 
carried as cargo in violation of requirements in the Hazardous 
Materials Regulations (HMR; 49 CFR Parts 171 through 180). 
Recommendations issued by the NTSB following this tragedy, in which 110 
lives were lost, addressed both the initiation of the fire by the 
improperly packaged generators (which produce external heat when 
activated) and the possible enhancement of an aircraft cargo 
compartment fire (of any origin) by the oxygen produced by the 
generators or other cargo, such as gaseous oxygen in cylinders and 
other oxidizing agents. In response to the NTSB recommendations, the 
Department of Transportation has:

--Prohibited the transportation of chemical oxygen generators 
(including personal-use chemical oxygen generators) on board passenger-
carrying aircraft and the

[[Page 4443]]

transportation of spent chemical oxygen generators on both passenger-
carrying and cargo-only aircraft [61 FR 26418 (May 24, 1996), 61 FR 
68952 (Dec. 30, 1996), 64 FR 45388 (Aug. 19, 1999)];
--Issued standards governing the transportation of chemical oxygen 
generators on cargo-only aircraft (and by motor vehicle, rail car and 
vessel), including the requirement for an approval issued by PHMSA [62 
FR 30767 (June 5, 1997), 62 FR 34667 (June 27, 1997)];
--Upgraded fire safety standards for cargo compartments on aircraft to 
require a smoke or fire detection system and a means of suppressing a 
fire or minimizing the available oxygen, on certain transport-category 
aircraft [63 FR 8033 (Feb. 17, 1998)]; and
--Imposed additional requirements on the transportation of cylinders of 
compressed oxygen by aircraft and prohibited the carriage of chemical 
oxidizers in inaccessible aircraft cargo compartments that do not have 
a fire or smoke detection and fire suppression system [64 FR 45388 
(Aug. 19, 1999)].

    In the August 19, 1999 final rule, ``Hazardous Materials: Chemical 
Oxidizers and Compressed Oxygen Aboard Aircraft,'' (Docket No. HM-
224A), we amended the HMR to: (1) Allow a limited number of cylinders 
containing medical-use oxygen to be carried in the cabin of a 
passenger-carrying aircraft; (2) limit the number of oxygen cylinders 
that may be carried as cargo in compartments lacking a fire suppression 
system and require cylinders to be stowed horizontally on the floor or 
as close as practicable to the floor of the cargo compartment or unit 
load device; and (3) require each cylinder of compressed oxygen 
transported in the passenger cabin or a cargo compartment to be placed 
in an overpack or outer packaging that meets the performance criteria 
of Air Transport Association Specification 300 for Type I (ATA 300) 
shipping containers. In the HM-224A rulemaking, we received more than 
55 written comments, and 14 persons made oral statements at a public 
meeting on January 14, 1998. Based on the comments submitted in that 
proceeding and our assessment of alternatives, we did not adopt the 
proposal in Docket No. HM-224A to prohibit all transportation of all 
oxidizers, including compressed oxygen, on passenger-carrying aircraft.
    In the preamble to the August 19, 1999 final rule, we explained 
that testing conducted by FAA indicated the ATA 300 container provides 
an ``incremental'' level of thermal protection for oxygen cylinders by 
increasing the time before a cylinder exposed to a fire would release 
its contents. However, FAA's testing also indicated the risk posed by a 
compressed oxygen cylinder in a cargo compartment can be further 
reduced, or even eliminated, if the cylinder is placed in an overpack 
or outer packaging providing more thermal protection and flame 
resistance than the ATA 300 containers currently in use. Accordingly, 
we announced we were ``considering a requirement that an oxygen 
cylinder may be carried in an inaccessible cargo compartment on an 
aircraft only when the cylinder is placed in an outer packaging or 
overpack meeting certain flame penetration resistance, thermal 
protection, and integrity standards.'' (64 FR 45393). In our earlier 
June 5, 1997 final rule (also in Docket No. HM-224A), we also indicated 
we were considering additional packaging requirements for chemical 
oxygen generators (62 FR at 30769).
    On May 6, 2004, we published a notice of proposed rulemaking under 
Docket HM-224B (69 FR 25469). In the NPRM, we proposed to amend the HMR 
to: (1) Require cylinders of compressed oxygen and packages of chemical 
oxygen generators to be placed in an outer packaging that meets certain 
flame penetration and thermal resistance requirements when transported 
aboard an aircraft; (2) revise the PRD setting limit on cylinders of 
compressed oxygen transported aboard aircraft; (3) limit the types of 
cylinders authorized to transport compressed oxygen aboard aircraft; 
(4) prohibit the transportation of all oxidizing gases, other than 
compressed oxygen aboard cargo-only or passenger aircraft; and (5) 
incorporate most of the provisions of an oxygen generator approval into 
the HMR.

II. Safety Issues Associated With the Air Transportation of Compressed 
Oxygen Cylinders and Oxygen Generators

    When installed on an aircraft or provided during flight for the use 
of passengers or crew members, compressed oxygen in cylinders and 
oxygen generators are subject to requirements in FAA's regulations in 
Title 14 of the Code of Federal Regulations, and are not subject to the 
HMR. When transported as cargo, cylinders of compressed oxygen and 
oxygen generators are subject to requirements in the HMR. Air carriers 
routinely transport their own oxygen cylinders and oxygen generators as 
replacement items for use on other aircraft. Some also transport 
cylinders for their passengers or other customers. Commenters to Docket 
HM-224A identified a continuing need for the transportation of oxygen 
cylinders as cargo on both passenger and cargo-only aircraft.
    As determined through testing conducted by FAA in 1999, cylinders 
of compressed oxygen release their contents at temperatures well below 
those that aircraft cargo compartment liners and structures are 
designed to withstand. When the surface temperature of a cylinder of 
compressed oxygen reaches approximately 300 [deg]F, the increase in 
internal pressure causes the cylinder's pressure relief device to open 
and release oxygen. In addition to the ValuJet tragedy, three accidents 
and ten incidents involving airplane cargo compartment fires have 
occurred between 1986 and 2002. While some of these events involved 
hazardous materials, in some instances the fire was caused by a 
malfunction of the aircraft's electrical system. The origin of other 
fires could not be determined. Regardless of the cause of the fire, the 
presence of an oxygen generator or a cylinder containing oxygen or 
another oxidizing gas creates the potential for oxygen or another 
oxidizing gas to be released and to vent directly into a fire, which 
significantly increases the risks posed by the fire.
    FAA also found that use of an outer packaging may significantly 
lengthen the time a cylinder will retain its contents when exposed to 
fire or heat. Some outer packagings meeting the ATA specification 300 
Category I extended the time by up to 60 minutes or more. However, the 
ATA 300 standard does not specifically address thermal protection or 
flame penetration. An outer packaging designed to provide both thermal 
protection and flame penetration could provide even more protection. A 
copy of the test report is available for review in the public docket.
    In additional tests conducted in 2002, FAA determined that a sodium 
chlorate oxygen generator will initiate and release oxygen at a minimum 
temperature of 600 [deg]F. However, due to uncertainties with other 
designs and the physical properties of sodium chlorate, the FAA has 
recommended that oxygen generators not be exposed to temperatures above 
400 [deg]F. A copy of this test report is also available in the public 
docket. This test report shows that an unprotected oxygen cylinder or 
oxygen generator can quickly and violently release its contents when

[[Page 4444]]

exposed to temperatures that can be expected from an aircraft cargo 
compartment fire.

III. Summary of Final Rule

    Because of safety concerns associated with the air transportation 
of compressed oxygen cylinders and oxygen generators, we are amending 
the HMR to require cylinders of compressed oxygen and chemical oxygen 
generators to be transported in an outer packaging that: (1) Meets the 
same flame penetration resistance standards as required for cargo 
compartment sidewalls and ceiling panels in transport category 
airplanes; and (2) provides certain thermal protection capabilities so 
as to retain its contents during an otherwise controllable cargo 
compartment fire. The outer packaging standard that is being adopted 
addresses two safety concerns: (1) Protecting a cylinder and an oxygen 
generator that could be exposed directly to flames from a fire; and (2) 
protecting a cylinder and an oxygen generator that could be exposed 
indirectly to heat from a fire. These performance requirements must 
remain in effect for the entire service life of the outer packaging.
    Under this final rule, an outer packaging for a cylinder containing 
compressed oxygen or another oxidizing gas and a package containing an 
oxygen generator must meet the standards in Part III of Appendix F to 
14 CFR Part 25, Test Method to Determine Flame Penetration Resistance 
of Cargo Compartment Liners. An outer packaging's materials of 
construction must prevent penetration by a flame of 1,700 [deg]F for 
five minutes, in accordance with Part III of Appendix F, paragraphs 
(a)(3) and (f)(5) of 14 CFR Part 25.
    In addition, a cylinder of compressed oxygen or another oxidizing 
gas must remain below the temperature at which its pressure relief 
device would activate and an oxygen generator must not actuate when 
exposed to a temperature of at least 400 [deg]F for three hours. The 
400 [deg]F temperature is the estimated mean temperature of a cargo 
compartment during a halon-suppressed fire.\1\ Three hours and 27 
minutes is the maximum estimated diversion time world-wide; based on an 
aircraft flying a southern route over the Pacific Ocean. Data collected 
during the FAA tests indicate that, on average, a 3AA oxygen cylinder 
with a pressure relief device set at cylinder test pressure will open 
when the cylinder reaches a temperature of approximately 300 [deg]F. 
This result is consistent with calculations performed by PHMSA. In 
analyzing PRD function, PHMSA calculated that a 3HT cylinder with a PRD 
set at 90% of cylinder test pressure will vent at temperatures greater 
than 220 [deg]F. In order to assure an adequate safety margin for all 
authorized cylinders, including 3HT cylinders, we are amending the HMR 
to require cylinders of compressed oxygen and other oxidizing gases, 
which are contained in the specified outer packaging, to maintain an 
external temperature below 93 [deg]C (199 [deg]F) when exposed to a 400 
[deg]F temperature for three hours.
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    \1\ The FAA is currently evaluating other non-ozone-depleting 
suppression agents that could eventually be used in cargo 
compartments. Some of these agents can maintain an adequate level of 
safety in the compartment, but the mean temperature may be slightly 
higher than 400 [deg]F, which is the level found during typical 
halon-suppressed fires. If an alternate agent is used, the oven soak 
temperature level may need to be adjusted accordingly.
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IV. Comments and Regulatory Changes

A. General

    PHMSA received comments from 24 entities in response to proposals 
and specific questions in the NPRM concerning outer packaging, PRDs, 
authorized cylinders, oxidizing gases aboard aircraft, and chemical 
oxygen generator approvals. These comments were submitted by 
representatives of trade organizations, hazardous materials shippers, 
carriers, and packaging manufacturers, including Airbus, Air Line 
Pilots Association (ALPA), Air Products and Chemicals, Air Transport 
Association (ATA), Alaska Airlines, Aviation Excellence, Aviation 
Mobility, Aviosupport, BE Aerospace, Carleton Technologies, Continental 
Airlines, Draeger Aerospace, Federal Express (FedEx), International 
Federation of Air Line Pilots Association (IFALPA), Intertechnique, 
National Transportation Safety Board (NTSB), Northwest Airlines (NWA), 
Satair, Scott Aviation (Scott), SR Technics Switzerland, United Parcel 
Service (UPS), Viking Packing Specialist (Viking), and two individuals.
    Commenters generally noted our continued efforts to enhance the 
safe transportation of hazardous materials by air. For example, ALPA 
applauds our efforts to address the potential hazards associated with 
oxidizing chemicals, oxygen generators, and gaseous oxygen. Relevant 
portions of these comments are discussed in the following sections of 
the preamble.

B. Outer Packaging for Compressed Oxygen Cylinders, Other Oxidizing 
Gases, and Chemical Oxygen Generators

    In the NPRM, we proposed to require an outer packaging for an 
oxygen cylinder and a package containing an oxygen generator to meet 
the standards in Part III of Appendix F to 14 CFR Part 25, Test Method 
to Determine Flame Penetration of Cargo Compartment Liners. We proposed 
to require the outer packaging to conform to these performance 
requirements with no deterioration for its entire service life. We also 
proposed to prohibit cylinders of compressed oxygen contained in an 
outer packaging from reaching an external temperature of 93 [deg]C (199 
[deg]F)--which is below the temperature at which its PRD would 
actuate--when exposed to a 205 [deg]C (400 [deg]F) temperature for 
three hours. We proposed to add a thermal resistance test for 
packagings for oxygen cylinders and oxygen generators in appendix D to 
Part 178. We further proposed to remove the limits in Sec.  175.85(i) 
on the number of oxygen cylinders that may be transported in cargo 
compartments not equipped with sufficient fire suppression systems. We 
proposed to allow outer packaging to be built either to the ATA 
Specification 300 standard or to a UN standard at the Packing Group II 
performance level. We proposed to authorize only rigid outer packagings 
for compressed oxygen cylinders. In addition, we proposed one year 
after publication of the final rule as the mandatory date to comply 
with the thermal resistance and flame penetration standards for outer 
packagings for oxygen cylinders and oxygen generators transported on 
board aircraft.
1. Scope of Rulemaking
    FedEx and NWA ask PHMSA to reconsider its approach to this 
rulemaking and begin a more comprehensive assessment with other Federal 
agencies (including FAA and NTSB), equipment manufacturers, and the air 
carrier industry. NWA states the requirements on compressed oxygen 
cylinders proposed in the NPRM are not adequately justified. It 
differentiates oxygen cylinders from oxygen generators because the 
latter provide their own heat source and, once initiated, release an 
uncontrolled flow of oxygen. FedEx suggests the origins and results of 
cargo compartment fires should be examined in a more comprehensive 
manner before this rulemaking is implemented. Continental states PHMSA 
should seek input from both the International Air Transport Association 
(IATA) and International Civil Aviation Organization (ICAO) regarding 
the potential impact of the proposed packaging requirement on 
international regulations and international carriers serving the United 
States.

[[Page 4445]]

    ATA states thermal protection of oxygen cylinders and oxygen 
generators does not increase the level of safety under the extreme 
conditions assumed in test protocols. ATA also states passenger 
carriers no longer transporting oxygen generators on passenger aircraft 
due to post-1996 regulations must transport oxygen generators by 
ground, and ground transportation of oxygen generators in compliance 
with post-1996 regulations has not resulted in any incidents involving 
oxygen generators. ATA recommends PHMSA thoroughly review all incidents 
pertaining to burned aircraft in order to investigate the condition of 
any oxygen cylinders or oxygen generators that were on board.
    Aviation Excellence, an aircraft parts distributor holding a 
Competent Authority Approval to ship oxygen generators (UN3356) 
questions why the transportation of oxygen generators has become a 
critical concern, and, along with other commenters, cites ValuJet as 
the only accident of note involving oxygen generators. This commenter 
asserts the ValuJet incident was likely due to improper marking and 
loading, not improper packaging standards, and that thick smoke was the 
likely cause of the ValuJet incident. Aviation Excellence suggests 
PHMSA should address the reasons a fire occurred in the cargo bay, 
rather than what effect the fire had on oxygen, and notes non-hazardous 
materials, such as rubber and plastic, generate deadly gases and smoke 
when exposed to fire.
    Scott notes chemical oxygen generators are currently transported by 
air as either components or as larger assemblies. When transported as 
components, the commenter states chemical oxygen generators are 
cylinders ranging from 2 \1/2\ to 4 inches in diameter and 5 to 11 
inches in overall length. The commenter states the size of chemical 
oxygen generator outer packaging would depend on whether the shipping 
requirement is for individual generators or a group of generators.
    Intertechnique also suggests the exception in Sec.  175.501(c) of 
the HMR allowing a limited number of oxygen cylinders to be transported 
in the aircraft cabin should recognize that oxygen cylinders used for 
carrying supplemental oxygen on board frequently have a large capacity, 
up to 213 cubic feet. Intertechnique states these cylinders must be 
transported from their respective manufacturing sites to the aircraft 
manufacturing facility, as well as to and from maintenance facilities, 
and restrictions on air transportation would increase turnaround times 
and operational costs when surface transportation is required. 
Intertechnique also notes that equipment containing an oxygen cylinder 
must be considered an oxygen cylinder, even when the cylinder is not 
apparent as in the case of the large number of protective breathing 
equipment units used on aircraft.
    We disagree with the commenters' assertions that PHMSA did not 
conduct a comprehensive assessment before initiating this rulemaking 
and that the requirements proposed in the NPRM were not effectively 
justified. The safe transportation of hazardous materials by air is an 
ongoing area of significant concern for the Department. We regularly 
assess methods to increase the safe transportation of hazardous 
materials, and incorporate input from other Federal agencies (including 
NTSB), equipment manufacturers, and the regulated community as we 
develop new or revised regulatory requirements. This process was 
applied to this current rulemaking as well.
    The FAA and PHMSA have taken a number of steps to reduce the 
likelihood of a fire on board an aircraft. These include limiting the 
transport of known flammable materials; imposing restrictions on 
aircraft systems likely to increase the risk of a fire, requiring 
increased inspection and maintenance of wiring systems; and 
incorporating designs to prevent the spread of fire from highly 
flammable zones. Despite all these measures, it is not possible to 
totally eliminate fires aboard aircraft. In addition to the risks 
presented by hazardous materials (whether shipped in violation or 
conformance with the HMR), structural failures, improper maintenance, 
and the ignition of non-hazardous materials remain possibilities. For 
these reasons, we cannot accept claims that PHMSA and the FAA did not 
conduct a sufficient assessment before initiating this rulemaking.
    We also disagree with the commenter that suggested we only 
addressed the reasons a fire occurs in a cargo bay, rather than what 
effect a fire has on oxygen. A fire in cargo compartments aboard an 
aircraft can result from several causes, some of which cannot be 
controlled through regulations, including illegal shipments of 
oxidizing agents, heat- or fire-producing chemical interaction between 
certain goods damaged during shipment, or human error. FAA concluded 
that the use of an outer packaging may significantly lengthen the time 
an oxygen cylinder or chemical oxygen generator will retain its 
contents when exposed to fire or heat. The provisions of this final 
rule will reduce the risk that a fire on board an aircraft will be 
significantly worsened by the presence of compressed oxygen cylinders 
or chemical oxygen generators.
    Because the possibility of fire in a cargo compartment cannot be 
completely eliminated, the FAA has adopted requirements to mitigate 
risk and increase the likelihood that a fire can be suppressed and 
contained long enough to land the aircraft. The FAA has upgraded fire 
safety standards to require inaccessible cargo compartments on 
passenger aircraft to have a fire detection and three-hour suppression 
system, by minimizing the available oxygen (e.g., 14 CFR 25.857(c), 
25.858, 121.314(c)). In addition, flame penetration and fire resistance 
requirements apply to cargo compartments on both passenger and cargo-
only aircraft (e.g., 14 CFR 25.855, 121.314(a)). However, these 
requirements do not, and cannot, address those situations where a fire 
is actually fed by oxygen provided by other cargo, such as cylinders of 
compressed oxygen or other oxidizing gases or oxygen generators.
    Accordingly, as discussed in the ``Background'' section above, we 
have prohibited the transportation of chemical oxygen generators on 
board passenger-carrying aircraft and the transportation of spent 
chemical oxygen generators on both passenger-carrying and cargo-only 
aircraft, and we issued standards governing the transportation of 
chemical oxygen generators on cargo-only aircraft, including the 
requirement for an approval issued by PHMSA. We have also imposed 
additional requirements on the transportation of compressed oxygen 
cylinders by aircraft; and prohibited the carriage of chemical 
oxidizers in inaccessible aircraft cargo compartments that do not have 
a fire or smoke detection and fire suppression system. The amendments 
adopted in this final rule are a continuation of our ongoing objective 
to reduce the risk of another catastrophic event like the ValuJet 
crash.
    Because fires on aircraft cannot be totally eliminated, and the 
consequences of fire in air transportation are far greater than those 
in highway transportation, an absence of incidents involving ground 
transportation of oxidizing gases and oxygen generators does not 
justify postponing these actions. The fact that an oxygen cylinder or 
generator did not release oxygen during a particular aircraft fire does 
not diminish the potential for enhancement of a cargo compartment fire 
by the release of oxygen and the likely consequences. For

[[Page 4446]]

these reasons, we disagree with the comment that PHMSA should only 
address the reasons a fire occurs in a cargo bay, rather than what 
effect a fire has on oxygen.
    We accept the suggestion that international carriers and 
international regulations should be considered when undertaking any 
rulemaking potentially affecting international commerce. The escalating 
quantity of hazardous materials transported in international commerce 
necessitates the harmonization of domestic and international 
requirements to the greatest extent possible. However, we cannot wait 
for an international agreement when it is necessary to address a known 
safety hazard. Therefore, we intend to submit a paper to the ICAO 
Dangerous Goods Panel proposing that the ICAO Technical Instructions be 
amended consistent with this final rule.
    We also considered this proposal based on its overall impact on 
transportation safety and the economic implications associated with its 
adoption into the HMR. Our goal in this rulemaking is to increase the 
level of safety for the transportation of oxygen cylinders and oxygen 
generators currently in the HMR in the most cost-effective manner 
possible. We believe the adoption of this final rule contributes to 
meeting that goal.
    Larger cylinders used as part of an aircraft's supplemental oxygen 
system (up to 213 cubic feet) makes it impractical for them to be 
transported (as cargo) in the aircraft cabin under the exception in 
Sec.  175.501(c). As noted above, when these cylinders are installed on 
the aircraft, they are not subject to the HMR, nor are Protective 
Breathing Equipment (PBEs) that are part of the required equipment on 
board the aircraft--but alternate packagings may be used for these 
cylinders and PBEs when carried or shipped as replacement items (or 
company material), ``provided such packagings provide at least an 
equivalent level of protection to those that would be required by 
this'' final rule. 49 CFR 175.8(a)(3) (as adopted at 71 FR 14605 [March 
22, 2006]).
    We disagree with the commenter's opinion that thick smoke was the 
likely cause of the ValuJet incident. First, that view has little 
support in the NTSB's findings (at p. 134 of the accident report) that 
``[o]nly a small amount of smoke entered the cockpit before the last 
recorded flightcrew verbalization * * * including the period when the 
cockpit door was open,'' and the ``loss of control was most likely the 
result of flight control failure from the extreme heat and structural 
collapse,'' although ``the Safety Board cannot rule out the possibility 
that the flightcrew was incapacitated by smoke or heat in the cockpit 
during the last 7 seconds of the flight.'' Moreover, even if the 
commenter were correct, that circumstance would support the measures we 
are adopting to prevent the enhancement of a cargo compartment fire 
(and the associated smoke) caused by the release of oxygen from a 
cylinder or an oxygen generator.
    BP Aerospace and Intertechnique recommend an exception from the 
proposed packaging requirements for cylinders that are nominally empty, 
with only a small amount of residual pressure, on the ground that the 
hazards of these ``empty'' cylinders are negligible. BP Aerospace 
states it is a common practice to transport such cylinders in order to 
avoid possible contamination of the cylinder from inward leakage. 
Intertechnique notes many cylinders are shipped before filling (new or 
repaired cylinders) or after being emptied (for maintenance).
    Oxygen is a Division 2.2 gas and, as such, is only subject to the 
regulations when the pressure in the container (cylinder) equals or 
exceeds 280 kPa (40.6 psia) at 20 [deg]C (68 [deg]F) (see Sec.  
173.115(b)(1)). Therefore, oxygen cylinders where the pressure has been 
reduced to less than 280 kPa (40.6 psia) are not subject to the 
regulations and are considered to have been purged to the extent 
necessary for the purposes of Sec.  173.29(b)(2)(ii). In addition, a 
completely empty cylinder (either new and never filled or purged of all 
its contents) is not subject to the packaging requirements adopted in 
this final rule (or to other transportation requirements in the HMR).
2. Other Oxidizing Gases Aboard Aircraft
    Several commenters also addressed our proposal to prohibit the 
transportation of all oxidizing gases (other than compressed oxygen) 
aboard both passenger and cargo-only aircraft. In the NPRM, we 
discussed our concern that cylinders containing these materials, if 
exposed to a fire, could intensify the fire to the extent that it would 
overcome the compartment's halon fire suppression system, penetrate the 
cargo compartment sidewalls, and cause severe damage or destruction of 
the aircraft. We stated we had no information to support the need for 
the following materials to be transported aboard aircraft: ``Air, 
refrigerated liquid, (cryogenic liquid),'' ``Carbon dioxide and oxygen 
mixtures, compressed,'' ``Nitrous oxide,'' ``Nitrogen trifluoride, 
compressed,'' ``Compressed gas, oxidizing, n.o.s.,'' and ``Liquefied 
gas, oxidizing, n.o.s.''
    Air Products expressed agreement with the Department on the need to 
increase the level of safety in the transportation of oxidizing gases 
by aircraft, and it states the list should not be limited to oxygen. 
Air Products suggests materials in Division 2.2 with a subsidiary risk 
of 5.1 can be transported safely by aircraft and pose no great risk to 
the aircraft unless the oxidizing material is exposed to abnormally 
high temperatures over an extended period of time. This commenter 
suggested packaging performance requirements can be met by limiting the 
fill density pressure of the oxidizing material and configuring the 
cylinder so that oxidizing material cannot escape at temperatures up to 
and including 205 [deg]C (400 [deg]F). Air Products submitted 
alternative wording for a new section under Sec.  173.302a that would 
pertain to nitrogen trifluoride and nitrous oxide.
    Alaska Airlines opposes the proposal to ban Division 2.2 gases with 
a 5.1 subsidiary risk for transportation by air, stating it is not 
aware of any experience indicating a safety problem. According to the 
Alaska Airlines' comments, consumers in Alaska use some of these gases, 
and in many cases, could not obtain them if not via air transportation. 
One Anchorage vendor of gas products estimates 20,000 to 50,000 pounds 
of cylinders of compressed oxygen and nitrous oxide are transported by 
air every month to medical facilities around the State, with empty 
cylinders constantly being returned for refilling and return to the 
hospitals. Alaska Airlines states DOT needs to consider the impact of 
this proposed rule on the health and welfare of Alaskans, not to 
mention the subsequent increased cost of medical care. This commenter 
also notes international regulations identify two additional materials 
classified as Division 2.2 materials with a 5.1 subsidiary hazard that 
are permitted on passenger aircraft: ``UN2037, Receptacles, small, 
containing gas (oxidizing) without a release device, non-spillable,'' 
and ``UN2037, Gas cartridges (oxidizing) without a release device, non-
spillable.'' The commenter concludes that if PHMSA does ban oxidizing 
gases, it will create additional variances between United States and 
United Nations dangerous goods regulations DOT has been working to 
harmonize.
    The comments summarized above indicate a continuing need for air 
transportation of most of the oxidizing gases we had proposed to 
prohibit on

[[Page 4447]]

aircraft, including Compressed gas, oxidizing, n.o.s.; Nitrogen 
trifluoride, compressed; and Nitrous oxide. Based on those comments, we 
conclude we should not prohibit air transportation of these oxidizing 
gases; however, the same outer packaging standards adopted for 
cylinders of compressed oxygen and oxygen generators should also be 
required for these other oxidizing gases. The only exception is that 
Air, refrigerated liquid (cryogenic liquid), which is already 
prohibited on passenger aircraft, will also be prohibited on cargo-only 
aircraft.
3. Packaging Design Standards
    In the NPRM, we proposed to require a cylinder of compressed oxygen 
to remain below the temperature at which its PRD would activate, and an 
oxygen generator not actuate, when exposed to a temperature of at least 
205 [deg]C (400 [deg]F) for three hours. ALPA recommends the design 
standards be raised to 260 [deg]C (500 [deg]F), instead of 205 [deg]C 
(400 [deg]F), and to 3.5 hours, instead of three hours, in cargo 
compartments required to have an active fire suppression system, and 
maintain the knock-down fire status to allow for a safety margin for 
temperature in excess of the expected mean of 205 [deg]C (400 [deg]F). 
In addition, Aviation Mobility states there is no aircraft that would 
survive the extreme conditions for the three-hour duration which the 
rule would require the cylinder to survive without the actuation of the 
PRD.
    We disagree. We continue to believe that these requirements for 
outer packagings are the most appropriate means to prevent the release 
of oxidizing gases from a cylinder or chemical generator, which could 
feed an aircraft compartment fire. The U.S. DOT/FAA Report titled 
``Evaluation of Oxygen Cylinder Overpacks Exposed to Elevated 
Temperature'' (included in the docket of this rulemaking), found that: 
``In a Class C compartment, the fire would be detected and agent 
discharged to extinguish the fire. In the event of a suppressed but not 
fully extinguished fire, which would be the case if the origin were a 
deep-seated fire, the temperatures in the compartment could reach 205 
[deg]C (400 [deg]F).'' For a deep-seated fire in a Class C cargo 
compartment, a temperature of 205 [deg]C (400 [deg]F) is the estimated 
mean temperature of a cargo compartment during a halon-suppressed fire.
    The FAA test results support our conclusion that a temperature of 
at least 205 [deg]C (400 [deg]F) is sufficient for the flame resistant 
penetration test method. In addition, the conditions noted in the NPRM 
are a worst-case scenario, and were based on a deep-seated fire in a 
Class C cargo compartment, the duration of which would be the maximum 
estimated diversion flight time for an aircraft flying a southern route 
over the Pacific Ocean. However, limiting the requirement for overpacks 
capable of meeting the three-hour suppression performance standard to 
overseas flights would be impractical, since this rulemaking 
anticipates in most instances the overpacks will be provided with the 
containers, rather than purchased and maintained by an air carrier. 
Since the initial shipper may not know the final destination of its 
product, it would also be unable to reliably determine when to use a 
three-hour overpack as opposed to a one-hour overpack. In any case, 
applying a lesser fire penetration and thermal protection standard to 
overpacks because of the shorter flight times to diversion airports in 
geographic areas other than the South Pacific would undermine the 
existing rationale behind our requirements that Class C cargo 
compartments on airplanes be equipped to meet the three-hour fire 
suppression standard. Therefore, we are amending the HMR to require 
each cylinder of compressed oxygen remain below the temperature at 
which its PRD would activate, and that an oxygen generator not actuate, 
when exposed to a temperature of at least 205 [deg]C (400 [deg]F) for 
three hours.
    We also received comments on the proposal to require an outer 
packaging to be built either to the ATA Specification 300 standard or 
to a UN standard at the Packing Group II performance level. One 
commenter (Aviation Mobility) states it encloses oxygen cylinders in a 
manner that provides safe delivery to the gate and use of the cylinder 
in the passenger compartment without altering the outer packaging. The 
commenter notes that, under Special Provision A52 of the HMR, an oxygen 
cylinder may be carried in the passenger compartment or an inaccessible 
cargo compartment on a passenger aircraft if it is in ``an overpack or 
outer packaging that conforms to the performance criteria of Air 
Transport Association (ATA) Specification 300 for Category I shipping 
containers.'' The same commenter states its specific outer packaging 
meets the ATA 300 definition of a ``rigid pack'' and questions whether 
PHMSA intended any difference in its use of the term ``rigid'' in the 
NPRM.
    For clarification, we proposed requiring an outer packaging to be 
built either to the ATA Specification 300 standard or to a UN standard 
at the Packing Group II performance level to provide greater 
flexibility in the design of outer packaging for oxygen cylinders. In 
the NPRM, we proposed to authorize only rigid outer packagings in order 
to clarify our original intent to ensure outer packaging provides an 
adequate level of safety. In addition to meeting the flame penetration 
and thermal resistance protection requirement, we will continue to 
require the outer packaging for compressed oxygen cylinders to meet 
certain performance criteria. Therefore, we are amending the HMR to 
allow the outer packaging be built either to the ATA Specification 300 
standard or to a UN standard at the Packing Group II performance level. 
In addition, we are amending the HMR to authorize only rigid outer 
packaging for compressed oxygen cylinders.
4. Packaging Availability and Cost
    Commenters expressed concern about the availability and cost of the 
proposed outer packaging, and the number of different types of outer 
packagings meeting the proposed thermal resistance and flame 
penetration requirements. For example, Continental states because this 
packaging is not yet available, any cost estimate is subject to 
significant error. Continental estimates the initial cost to provide 
outer packagings meeting the required flame and temperature penetration 
standards will exceed $850,000. The same commenter estimates costs of 
at least $500,000 to modify its medical oxygen service.
    Scott states it would need a minimum of nine (9) different-sized 
ATA 300 specification containers to accommodate all of the high-
pressure oxygen cylinders it currently supplies, and additional size 
packages may be required to adequately accommodate high pressure oxygen 
cylinders supplied by other entities or to accommodate cylinder 
configurations for new aircraft development programs. This commenter 
estimates the average cost of currently used outer packagings would 
range from $300 to $500 per container. Scott recommends PHMSA conduct 
additional analyses to determine the number of different outer 
containers that would be required to accommodate chemical oxygen 
generators.
    Scott also disputes our statement in the NPRM that only a few small 
aviation entities will require flame and heat protective reusable 
packaging and suggests PHMSA did not consider the major potential 
impact of this rule on small entities. According to Scott, ``many small 
aircraft operators do not provide their own oxygen system maintenance 
or have extensive spare part inventories but, rather, rely on the 
shipping of these components to specialized oxygen repair stations, by 
air, in order to maintain their aircraft in

[[Page 4448]]

a timely manner.'' Scott states these companies would be required to 
obtain outer packages meeting the requirements of this proposed rule in 
order to ship oxygen cylinders and valve and regulator assemblies to 
oxygen service shops for maintenance. These outer packages ``would then 
be used to return these items to the operator in the same manner that 
the present rule has required the operators to purchase ATA 300 
specification containers for that purpose.''
    ATA contends the requirement for carriers to comply with the 
proposed outer packaging requirements would be costly and prohibitive 
to air carriers of oxygen generators, forcing carriers to refuse 
passengers or cancel flights because of the lack of generators 
supplying emergency oxygen to aircraft passenger seats. It states it 
conferred with vendors and found neither existing packaging, nor a 
design amenable to the proposed requirements in the developmental stage 
of manufacturing. ATA estimates replacement packaging costs of 
approximately $2,200,000 to $3,350,000 for its members, without any 
substantial improvement in safety. This commenter states this cost 
could effectively double as existing ATA Specification 300 packaging, 
acquired in response to the final rule in HM-224A, could not be 
converted for other uses.
    NWA states it uses seven cylinder types and estimates four separate 
sized boxes will be required for its seven cylinder types to meet the 
proposed packaging requirement. NWA foresees the replacement of 1,400 
boxes at twice the cost necessary to replace the boxes that were 
required by HM-224A. In addition, the commenter says it would be forced 
to scrap the boxes purchased in compliance with HM-224A before the 
exhaustion of their useful life. FedEx notes the proposed outer 
packaging is neither currently available for purchase, nor does it know 
when it will be available, or at what cost. It estimates the required 
packaging will range between $600 and $900 per unit, for an estimated 
cost imposed on its operations of between $360,000 and $540,000.
    Intertechnique states the introduction of the packaging proposed in 
the NPRM will lead to added costs for shipping cylinders from the 
cylinder manufacturer to aircraft manufacturers and airlines, and to 
and from airline maintenance sites. Intertechnique asserts there are 
approximately 500 new cylinders per year requiring outer packagings and 
those packagings delivered to aircraft manufacturers may be sent back 
for future shipment (with an estimated loss of 20% per year). It says 
the outer packagings of cylinders shipped to airlines will be retained 
by the airlines for their own shipment or repair, and new packagings 
will have to be bought for each shipment. Intertechnique estimates a 
replacement rate of 10% per year, with a best estimate need of 300 new 
outer packagings per year, leading to an average cost increase of the 
oxygen cylinders and repairs of 10 to 15% depending on the final cost 
of packaging not yet available on the market.
    Satair states it is currently spending approximately $50,000.00 on 
packaging and other materials to facilitate the shipping of chemical 
oxygen generators. It estimates a ten-fold increase in packaging and 
other material costs needed to implement the requirements in the NPRM, 
for a total of approximately $500,000.00. This commenter considers this 
to be a significant impact on its business and would have to bill and 
recover this expense from its customers, the airlines. Aviation 
Excellence states the additional cost for packaging and return 
shipments will impose a prohibitive financial burden.
    Many of the commenters indicate they do not provide medical oxygen 
service to persons with disabilities, and, therefore, do not address 
whether the proposals would increase the cost to transport medical 
oxygen. However, Continental and ATA state they offer this service and 
this requirement would have to be evaluated for the cost impacts and 
feasibility of this service. Aviation Mobility states it is not aware 
of any outer packaging in existence that would meet the fire resistance 
criteria proposed in the NPRM. The commenter states the cost of this 
service would become too expensive to pass along to customers, or for 
carriers to absorb. This same commenter asserts that, as a result of 
the costs to acquire the outer packaging specified in this rulemaking 
and the added weight of such a packaging, most carriers transporting 
medical oxygen to passenger air carriers will discontinue this service. 
Further, this commenter states all cost speculations with regard to 
such a packaging are merely theoretical. ATA recommends PHMSA 
reconsider this rulemaking action to consider possible disadvantages to 
disabled passengers requiring medical oxygen.
    We considered possible cost increases and the availability of outer 
packaging for oxygen generators and cylinders containing compressed 
oxygen and other oxidizing gases. At least one packaging manufacturer 
(Viking) appears to have addressed the flame penetration and thermal 
penetration standard and states it is able to produce the required 
packaging. That manufacturer provided estimates of costs for the 
existing ATA specification 300 packagings and the new outer packagings, 
and those estimates were used in our complete analysis of the 
associated costs to implement this final rule in the regulatory 
evaluation (available for review in the public docket for this 
rulemaking).
    In that regulatory evaluation, we specifically discussed cost 
figures provided by other commenters and the basis on which we 
estimated a total cost of $10.8 million ($7.6 million discounted to 
present value) over 15 years, for the transport of oxygen cylinders; 
and $27.0 million ($16.9 million discounted to present value) over 15 
years, for the costs associated with the transport of chemical oxygen 
generators. While some of the cost figures provided by other commenters 
are higher, those figures are reasonably close to the estimates used in 
the regulatory evaluation; moreover, the estimates used in the 
regulatory evaluation do not reflect the likelihood that, when this 
requirement becomes effective, additional manufacturers will produce 
the required packaging, thereby reducing purchase prices. With 
competitive packaging pricing available in the marketplace, air 
carriers will be in a better position to make cost-effective business 
decisions to continue providing medical oxygen service to the disabled 
community and will continue to do so. Even if we were to assume the 
industry commenters were correct, and the cost of this rule was to 
double, the benefits would still outweigh the higher costs. Thus, the 
agency has carefully weighed these comments in deciding to proceed with 
this rulemaking initiative.
    We also estimated benefits of this rule over the next 15 years 
range from $30 million, if a single cargo aircraft accident is averted, 
to $357 million, if a single passenger aircraft accident is averted. 
This indicates a significant potential to improve the level of safety 
associated with the continued transportation aboard aircraft of 
packages of chemical oxygen generators and cylinders containing 
compressed oxygen and other oxidizing gases.
    PHMSA continues to believe that only a few small entities will be 
affected by this rulemaking. For example, we learned from container 
manufacturers that only ten small air carriers transport cylinders of 
compressed oxygen. Outside of Alaska, air shipments of other oxidizing 
gases are very infrequent, according to the comment of Air Products, 
and most small entities will be able to utilize ground

[[Page 4449]]

transportation or local companies for shipping cylinders of compressed 
oxygen or other oxidizing gases.
    Therefore, we are amending the HMR to require an outer packaging 
for an oxygen cylinder and a package containing an oxygen generator to 
meet the standards in Part III of Appendix F to 14 CFR Part 25, Test 
Method to Determine Flame Penetration of Cargo Compartment Liners. We 
are also amending the HMR to require cylinders of compressed oxygen and 
chemical oxygen generators to be transported in an outer packaging 
meeting certain flame penetration and thermal resistance requirements 
when transported aboard an aircraft. In addition, we are amending the 
HMR to require that the outer packaging be capable of meeting the 
requirements throughout its service life.
5. Compliance Date
    PHMSA received several comments regarding the proposed effective 
date of one year after publication of the final rule as the mandatory 
date to comply with this final rule. Many commenters state one year 
does not provide adequate time to resolve concerns regarding a lack of 
packaging development and availability, manufacturing lead times, 
inventory, logistics, and documentation. For instance, Scott states the 
currently proposed rule, with a proposed compliance date of one year 
after promulgation, provides neither the time necessary for an orderly 
process of ensuring compliance, nor a mechanism by which compliance can 
be readily determined. The commenter also states the demand for 
reusable flame and heat-resistant packagings required by the proposed 
rule may be much higher than PHMSA currently envisions. Another 
commenter (ATA) states a one-year effective date would impose 
additional costs on carriers by forcing the removal of aircraft from 
service to replace the outer packaging proposed in the NPRM. In 
response to our inquiries in the NPRM regarding the effective date, we 
received recommendations ranging from one to three years for 
implementation of the effective date of this final rule.
    It appears compliance with the additional overpack requirements of 
one year following the publication of the final rule as proposed in the 
NPRM may result in insufficient time or undue hardship on the affected 
parties to come into compliance with the new requirements. A compliance 
date that allows flexibility for the affected parties and sufficient 
time for various manufacturers to develop and market the necessary 
equipment would better serve the overall objectives of this rulemaking. 
Therefore, we are amending the HMR to establish a mandatory compliance 
date of two years following the effective date of the final rule.

C. Pressure Relief Device Settings and Authorized Cylinders for 
Compressed Oxygen and Other Oxidizing Gases

    In the NPRM, we proposed amendments to the HMR pertaining to limits 
on PRD settings and cylinders authorized for the transportation of 
oxygen aboard aircraft. Compressed Gas Association (CGA) Pamphlet S-
1.1, which has been incorporated by reference in the HMR, specifies the 
rated burst pressure of a rupture disk must be no greater than the 
cylinder minimum test pressure. However, CGA Pamphlet S-1.1 does not 
set a lower burst limit on the disks, increasing the risk of oxygen 
releases at elevated temperatures. To better prevent a cylinder from 
releasing its contents when exposed to a fire, we proposed to require 
an oxygen cylinder to be equipped with a PRD that has a rated burst 
pressure equal to the cylinder test pressure with allowable tolerances 
of -10 to plus zero percent.
    We also proposed to limit cylinders authorized for the 
transportation of compressed oxygen aboard aircraft to DOT 
specifications 3A, 3AA, 3AL, and 3HT in order to minimize numerous PRD 
setting requirements for oxygen cylinders aboard aircraft. Although 
numerous specifications are authorized for oxygen and other oxidizing 
gases (49 CFR 173.201, 173.202a, 173.204, 173.204a), we understand 
these four specifications account for the vast majority of the 
cylinders used to transport these materials aboard aircraft--in 
addition to cylinders made of composite materials and authorized under 
special permit. (Specification 3HT cylinders are only authorized for 
aircraft use, and specification 3A and 3AA cylinders represent 
approximately 70% of the cylinders in all service.) This proposed 
limitation was not intended to restrict the use of composite cylinders 
that are currently, or may in the future be, authorized for 
transporting oxygen and other oxidizing gases under special permits.
    Several commenters, including ATA, noted the proposed PRD setting 
for a DOT specification 3HT was incorrect. The NPRM should have stated 
the rated burst pressure of a rupture disk on a 3HT cylinder must be 
90% of the cylinder test pressure. In this final rule, we have 
corrected this error.
    ATA also asks about the proposal for replacement of PRDs 
specifically on 3HT cylinders, and whether this standard will be 
applied to other types of cylinders. Aviation Mobility expresses 
concern that raising the discharge pressure of PRDs on any gas cylinder 
will increase the potential for catastrophic failure. Continental 
Airlines states the limit on PRD settings proposed in the NPRM does not 
significantly increase the level of safety beyond current hazardous 
materials regulations. It questions the need to raise the PRD standards 
based on the lack of incidents related to compressed oxygen that meet 
existing temperature and pressure relief standards. It argues the level 
of protection of the aircraft transporting the oxygen cylinders is not 
increased even if the level of protection to the oxygen cylinders is 
increased.
    Continental also raises cost concerns and estimates the costs for 
its company to meet the new PRD settings could exceed $2,500,000, of 
which $500,000 would be required to modify its medical oxygen service. 
According to this commenter, these costs will result in additional 
expense to disabled customers via increased oxygen service fees, and 
may force airlines to consider discontinuing this service. Scott 
suggests the requirement for PRDs apply after the next requalification.
    NWA expresses concern about the cost to replace approximately 2,800 
PRDs in its current supply of cylinders. The commenter states its 
cylinder maintenance is performed by a vendor and this rulemaking will 
force cylinders out of service for an extended period of time. NWA also 
recommends PHMSA perform an analysis to determine the effects a slow 
venting cylinder will have on the concentration of oxygen in cargo 
holds.
    For cost reasons and ease of maintenance, according to 
Intertechnique, most PRDs are standard items, and changing the PRDs to 
match the new requirements will increase costs and delays. 
Intertechnique recommends that the reliability of PRDs with a smaller 
tolerance should be considered. In addition, Intertechnique states 
increasing the PRD setting does not drastically change the safety 
level. The leaking of the cylinder will be delayed until the 
temperature is higher (as will be the pressure), but the energy 
released at the moment of bursting the device will be higher, thus 
propelling oxygen with a higher flow and a larger velocity to a larger 
area. Intertechnique also states proof pressure varies from steel to 
composite cylinders, and the same PRD can be used for both types. It 
says changing the tolerance will lead to duplicating the PRD part 
numbers and cost increases, resulting in confusion within workshops 
that could lead to errors in installing PRDs. In

[[Page 4450]]

addition, Intertechnique states the packaging should include a pressure 
balancing device (PBD) to prevent packaging burst due to pressure 
change within the cargo compartment during ascents and descents.
    PHMSA continues to believe increasing the discharge pressure of 
PRDs on cylinders used to transport oxygen and other oxidizing gases 
will significantly increase the level of safety without increasing the 
potential for catastrophic failure of the packaging. One objective of 
this rulemaking is to prevent the actuation of the cylinder PRD so as 
to retain the cylinder's contents during an otherwise controllable 
cargo compartment fire. The outer packaging requirement proposed in the 
NPRM is designed to protect a cylinder and oxygen generator that could 
be exposed directly to flames from a fire, or indirectly, to heat from 
a fire. A new limit on the PRD settings on cylinders containing 
compressed oxygen or other oxidizing gases transported aboard aircraft 
will help ensure the contents of the cylinder are not released into an 
aircraft cargo compartment in the event of a fire. The design safety 
margin on the cylinder is high enough that the risk of catastrophic 
failure of the cylinder is not a serious concern.
    Therefore, we are amending the HMR to require a new limit on the 
PRD settings on cylinders containing compressed oxygen or other 
oxidizing gases when transported aboard aircraft to ensure the cylinder 
contents are not released into an aircraft cargo compartment in the 
event of a fire. In order to accomplish this, we are amending the HMR 
to limit the PRD to a setting that will prevent it from releasing at 
temperatures the cylinder will experience while protected by the outer 
packaging. We are also amending the HMR to require cylinders containing 
oxidizing gases, including oxygen, to be equipped with PRDs that have a 
set pressure equal to the cylinder test pressure with allowable 
tolerances of -10 to plus zero percent.
    In order to eliminate a significant portion of the costs associated 
with this requirement, we are adopting the commenter's suggestion to 
apply this requirement to cylinders beginning with each individual 
cylinder's next requalification date. Although not required, many 
cylinder owners replace the PRD during the five-year requalification as 
recommended by CGA Pamphlet S-1.1. Because relatively few cylinders are 
shipped by air, any additional costs associated with replacing the PRD 
at the next requalification date will be negligible.
    Several commenters (Airbus, ATA, Carleton, Draeger, Intertechnique, 
Satair, Scott Aviation, and UPS) ask PHMSA to reconsider the 
requirement to limit the transportation of compressed oxygen aboard 
aircraft to DOT specifications 3A, 3AA, 3AL, and 3HT cylinders. Airbus 
states this proposed restriction is based on the assumption that these 
cylinders are the most commonly used for the transportation of 
compressed oxygen aboard aircraft, and on an apparent intention by 
PHMSA to limit the number of PRD settings. BE Aerospace contends the 
large volume of these cylinders is primarily because they have been in 
existence for many years. Scott confirms that the majority of oxygen 
cylinders currently in aviation service are DOT specification 3AA and 
3HT cylinders.
    Several commenters appear to believe we were proposing to exclude 
composite cylinders on board aircraft, despite the fact that a 
significant portion of compressed oxygen cylinders are currently made 
of composite material. For example, Airbus states composite cylinders 
combine weight-saving potential with significant cost reductions; 
perform as well as steel/aluminum cylinders; are subject to the same 
qualification tests as steel/aluminum cylinders; and are likely to be 
used increasingly in the future, especially the storage of oxygen as 
part of a gaseous oxygen system and portable oxygen cylinders for first 
aid. Airbus and others suggest that, if composite oxygen cylinders are 
not allowed aboard aircraft, many airlines will experience difficulty 
and increased costs regarding the maintenance and servicing of these 
composite oxygen cylinders. Carleton recommends that 49 CFR 
173.302a(c)(1) be amended to include ``DOT Exemption Cylinders 
manufactured to the requirements of DOT FRP-1 or DOT-CFFC,'' and that 
Sec.  173.302a(e)(2) define the PRD requirements for compressed oxygen 
cylinders and be amended to include ``DOT Exemption Cylinders must be 
equipped with a PRD as required by the appropriate Specification.'' 
Carleton also recommends PHMSA amend paragraph (e)(2) to read ``90% of 
cylinder test pressure'' and change ``-10 to zero percent of cylinder 
test pressure'' to ``-10 to plus zero percent of cylinder test 
pressure.''
    Composite cylinders are lightweight, possess weight- and fuel-
saving potential, and may lead to an overall reduction in the 
associated costs for air transportation of compressed oxygen. PHMSA 
recognizes the prevalence of composite cylinders in air transportation, 
the increased use of these cylinders by industry for the transportation 
of compressed oxygen, and that these trends are likely to continue in 
the future. We acknowledge that composite cylinders are currently 
authorized for the transportation of compressed oxygen aboard aircraft 
under special permit. No change in the HMR is required to permit 
composite cylinders to be used in oxygen service. The limitation of 
cylinders authorized for the transportation of compressed oxygen and 
other oxidizing gases aboard aircraft to DOT specifications 3A, 3AA, 
3AL, and 3HT does not exclude composite cylinders from being utilized 
for the transport of compressed oxygen by air transportation under the 
terms of a special permit, which is issued only upon a finding that the 
use of a composite cylinder achieves a level of safety that is at least 
equal to that required by this rulemaking. The PRD requirements for 
composite cylinders will be updated to match the new requirements of 
this final rule. Consistent with our past practice of adopting special 
permits into the HMR, we will review these special permits to determine 
if they are suitable for inclusion into the HMR.
    Therefore, we are amending the HMR to require cylinders authorized 
for the transportation of compressed oxygen aboard aircraft to be 
limited to DOT specifications 3A, 3AA, 3AL, and 3HT.

D. Limits on Number of Oxygen Cylinders Transported on Aircraft

    In HM-224A, we adopted a limitation on the number of cylinders of 
compressed oxygen allowed to be carried on aircraft: (1) Up to six 
cylinders belonging to the aircraft carrier plus one cylinder per 
passenger needing oxygen at destination could be transported in the 
passenger cabin, and (2) no more than a combined total of six cylinders 
of compressed oxygen may be carried in inaccessible aircraft cargo 
compartments that lack a fire or smoke detection system and a fire 
suppression system. See former 49 CFR 175.10(b), 175.85(i), recodifie