# Chart Industries — Hazardous Materials Safety Interpretation

**Citation:** 11-0046  
**Type / status:** guidance / guidance  
**Agency:** Pipeline and Hazardous Materials Safety Administration  
**Effective:** Not stated  
**Published:** 2011-04-18

11-0046 response to Chart Industries concerning 173.115, 173.320.

## Document text

<<<PAGE 1>>>

U.S. Department of Transportation 1200 New Jersey Ave, SE
Washington. D.C. 20590
Pipeline and Hazardous Materials
Safety Administration
APR 1 8 2011
Mr. Dan Bricker
Chart Industries
2800 Airwest Blvd.
PlainfieJd, In. 46168
Reference No.: 11-0046
Dear Mr. Bricker:
This responds to your letter concerning the transport of cryogenic liquids under the Hazardous
Materials Regulations (HMR; 49 CFR Parts 171-180). Specifically, you ask how the definition
of the term "service pressure" and the exceptions for cryogenic liquids provided in § 173.320 of
the HMR apply to specification DOT-4L welded insulated cylinders used to transport medical
oxygen. In your incoming letter, you state that you wish to transport medical oxygen in a 46
Liter insulated liquid oxygen (LOX) container. Your questions have been paraphrased and
answered as follows:
Q1: What is the definition of the term "Service Pressure" as it applies to the specification for
DOT 4L welded insulated cylinders specified in § 178.57?
Ai: As specified in § 173.115, the term "service pressure," as it is used throughout the HMR,
means the authorized pressure marking on the packaging. For example, for a cylinder
marked "DOT 3A1800," the service pressure is 12,410 kPa (1,800 psig). The 46 Liter
insulated LOX container you describe in your incoming letter cannot be considered a
DOT-4L cylinder unless it has a water capacity (nominal) not over 1,000 pounds water
capacity, a marked service pressure of at least 40 psig but not greater than 500 psig, and
the cylinder conforms to all other specifications required in § 178.57.
Q2: Does the 46 Liter insulated liquid oxygen (LOX) container described in the incoming
letter meet the exceptions provided in § 173.320?
A2: The packaging exceptions for cryogenic liquids are found in § 173.320 and allow for
alternative packaging methods. In accordance with § 173.320(a), atmospheric gases and
helium, cryogenic liquids, in Dewar flasks, insulated cylinders, insulated portable tanks,
insulated cargo tanks, and insulated tank cars, designed and constructed so that the
pressure in such packagings will not exceed 25.3 psig under ambient temperature
conditions during transportation are not subject to the requirements of this subchapter

<<<PAGE 2>>>

when transported by motor vehicle or railcar except as specified in paragraphs (a)(l),
(a)(2), and (a)(3) of § 173.320. Provided your container meets the requirements of
§ 173.320, it may be transported in the 46 Liter insulated liquid oxygen (LOX) container
you describe. It should be noted, however, that the 25.3 psig referred to in § 173.320(a)
is not the service pressure.
Q3: If the 46 Liter insulated liquid oxygen (LOX) container described in the incoming letter
does not meet exceptions provided in § 173.320, what packaging specifications would the
container need to satisfy in order to transport cryogenic liquids?
A3: The general requirements for cryogenic liquids in cylinders are found in § 173.316. If the
medical oxygen packaged in insulated LOX containers does not conform to the
exceptions provided in § 173.320, it must be packaged in accordance with § 173.316 and
transported in a cylinder marked as a specification DOT-4L cylinder.
I hope this satisfies your inquiry. Please contact us if we can be of further assistance.
Sincerely,
T. Glenn Foster
Chief, Regulatory Review and Reinvention Branch
Standards and Rulemaking Division

<<<PAGE 3>>>

c~
CA I R E§
MEMORANDUM
To: Mr. Duane Cassidy
D.O.T. Chief of Approvals Group
FROM: Dan Bricker
DATE: 02/21/2011
SUBJECT: Request for Guidance and Interpretation
Mr. Cassidy; Thanks for meeting with Ben Kadrlik and me on Friday. As you suggested I am making my
request in writing. Please provide us with your guidance and interpretation with respect to the following:
1. I would like a definition and better understanding ofthe term "Service Pressure" as it applies to 49
CFR 178.57 specifications for DOT 4L welded insulated cylinders.
2. Secondly, I would like to know the impact and intent of 173.320 Cryogenic Liquids; Exceptions
under the Requirements for Shipments and Packaging's.
I am working on a 46 Liter insulated LOX container for providing medical oxygen to respiratory patients. In
an effort to keep the service pressure under the 40 PSIG level which would place it within the 4L requirements
I need to know specifically what is meant by the term "service pressure." I have attached plumbing
schematics of this unit in its Standby Mode and both oxygen delivery modes. When the unit is being used by
the patient, its normal operating pressure is 22 psig which is controlled by an "economizer" valve. If it is not
being used by the patient such as when the patient is away with the mating portable unit, the system pressure is
controlled by a primary relief valve. As a safety back-up to the primary reliefvalve, we then have a secondary
relief valve. I am assuming that the "Service Pressure" relates to the primary relief valve.
My thought is to have a service pressure under the 40 psig, and then consistent with CGA S-1.1 paragraph
5.9.3, I would determine the primary relief valve setting as:
Set pressure < (1.25 X 40) - 15, or 35 psig.
Another way to look at this may be that the normal operating pressure is 22 psig and if the vacuum loading of
14.7 is added, then the service pressure would be 36.7 psia. This does not make sense because 178.57 defines
the service pressure limit as 40 psig.
The second question is related to the Requirements for Shipments and Packaging's, specifically part 173.320
Cryogenic Liquids; Exceptions paragraph (a). This states that cryogenic liquids in cylinders designed and
constructed so that the pressure will not exceed 25.3 psig during transportation are not subject to the
requirements of this subchapeter. In the case of the unit described above my assumption is that since the
pressure is in excess of the 25.3 psig (35 psig) then the it is subject to the requirements ofthe subchapter which
for a liquid oxygen cylinder would be specifically, 173.316 Cryogenic liquids in cylinders.

<<<PAGE 4>>>

Since the DOT 4L relates to the specification for the welded cylinders with service pressures> 40 psig and the
requirements for shipments and packagings has requirements for pressures exceeding 25.3 psig am I correctto
assume that cylinders with pressures between these two references can be used to ship liquid oxygen without
being DOT 4L stenciled providing thatthe requirements of 173.316 are met?
Standard Reservoir Only ---
.....
Gaseous O2
Standby

<<<PAGE 5>>>

Standard Reservoir Only ---""'l
SRV
Econ Valve
22 psig
Gaseous O2
Liquid O2
Oxygen Flow Through Economizer Circuit

## Provenance

- Official: Yes
- Source: <https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/legacy/interpretations/Interpretations/2011/110046.pdf>
- Source ID: `phmsa`
- SHA-256: `1ea594fd0d7d2a8b39e5f7313f7557ccf67a37c30c6f3755607b4c89492f15b4`
- Retrieved: 2026-08-20T00:59:31.977Z
- Exported: 2026-08-22T23:04:24.797Z
- Document slug: `phmsa-interpretation-11-0046`

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