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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Interpretation Response #11-0175 ([NitroxFox LLC.] [Mr. John Fox])

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date:

Company Name: NitroxFox LLC.

Individual Name: Mr. John Fox

Location State: FL Country: US

View the Interpretation Document

Response text:

September 8, 2011



Mr. John Fox

NitroxFox LLC.

P.O. Box 32091

Sarasota, Florida 34239

Reference No.: 11-0175

Dear Mr. Fox:

This responds to your letter regarding the requirements for compressed gas cylinders containing breathing enriched air (Nitrox) under the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180). Specifically, you state in your incoming letter that Department of Transportation (DOT) Specification 3AL (Aluminum) and 3AA (Steel) cylinders are commonly used for containment of Nitrox and the air in these cylinders will have elevated levels of Oxygen ranging from 21% to 100% depending on the application. Your questions are paraphrased and answered as follows:

Q1: If a cylinder is to be used to transport Nitrox, at what Oxygen percentage must a cylinder used for Oxygen service be cleaned and must the cylinder cleaning conform to the cleanliness standards specified in 173.302?

A1: Gas mixtures with Oxygen concentrations greater than 23.5% by volume should be considered to cause or contribute to combustion of other material to a greater extent than air. These gas mixtures must be described as "Compressed gas, oxidizing, n.o.s." and must be classified and labeled with a Division 2.2 (nonflammable gas) primary hazard and a Division 5.1 (oxidizer) subsidiary hazard. If the Oxygen concentration is greater than 23.5%, the conditions specified in § 173.302(b) must be met. Each DOT Aluminum cylinder, including a 3AL cylinder, must be cleaned in accordance with the requirements of General Services Administration (GSA) Federal Specification RR"C"901D, paragraphs 3.3.1 and 3.3.2 (IBR, see §171.7 of this subchapter). Cleaning agents equivalent to those specified in Federal Specification RR"C"901D may be used provided they do not react with Oxygen. One cylinder selected at random from a group of 200 or fewer and cleaned at the same time must be tested for oil contamination in accordance with Federal Specification RR"C"901D, paragraph 4.3.2, and meet the specified standard of cleanliness. The HMR does not indicate specific cleaning standards for 3AA steel cylinders used for Oxygen service.

Q2. What is the maximum pressure to which a cylinder can be filled, when charging the cylinder with enriched air containing elevated levels of Oxygen? Additionally, is this pressure the same for both aluminum and steel cylinders?

A2: For aluminum cylinders used for Oxygen service, including 3AL cylinders, the pressure in each cylinder may not exceed 3000 psig at 21 °C (70 °F) as specified in § 173.302(b). The HMR does not indicate a specific operating pressure for steel cylinders, including 3AA cylinders, used for Oxygen service, thus, the cylinder must not exceed the marked service pressure.

Q3: May a cylinder contained enriched air (Nitrox) be labeled if the cleanliness standards for Oxygen service have not been met?

A3: As provided in § 172.402, each package, including cylinders, containing a hazardous material shall be labeled with primary and subsidiary hazard labels as specified in column 6 of the Hazardous Materials Table (HMT). If a cylinder is filled with an Oxygen concentration greater than 23.5%, the conditions specified in § 173.302(b), including the appropriate cleaning standards must be met prior to being offered for shipment. There is no prohibition for labeling a cylinder which does not meet the appropriate cleaning standards specified in § 173.302(b). However, this cylinder would not be permitted to be offered for transportation until all requirements of § 173.302(b) have been satisfied.

I hope this satisfies your inquiry. Please contact us if we can be of further assistance.


T. Glenn Foster

Chief, Regulatory Review and Reinvention Branch

Standards and Rulemaking Division

173.302, 171.7, 172.402

Regulation Sections

Section Subject
172.402 Additional labeling requirements
173.302 Filling of cylinders with nonliquefied (permanent) compressed gases or adsorbed gases