PHMSA Response Letter

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December 21, 2011

Sergeant Brad C. Gibson
Texas Highway Patrol
Commercial Vehicle Training Unit
Texas Department of Public Safety
455 “B” State Highway 1
Georgetown, TX 78628

Reference No. 11-0153

Dear Sergeant Gibson:

This is in response to your July 6, 2011 letter and e-mail requesting clarification on how tube trailer motor vehicles are defined under the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180), and ask if Reference No. 10-0116 supercedes Reference No. 88-0026. You refer to two letters of clarification this Office issued under Reference Nos. 88-0026 (to Paul Horgan; 4/28/1998) and 10-0116 (to Neil Banman; 5/12/2011). Specifically, you ask under what circumstances manifolded, non-bulk packagings would be considered a single bulk packaging.

Because the two letters describe different packagings with different associated risks, which we restate later in this letter, the letter issued under Reference No. 10-0116 does not supercede the letter issued under Reference No. 88-0026. Manifolded cylinders have inherent design risks, such as exposed cylinder shells and piping, opportunities for product backflow and backflash, and are usually designed to carry larger quantities of gas. All of these factors can contribute to the loss of an entire load during an incident. Therefore, it is the opinion of this Office that:

• cylinders interconnected through manifolding that use a common outlet (e.g., a pressure regulator) operate as an integral unit;
• non-bulk cylinders that are manifolded in a tube trailer such that the aggregate capacity of the tube trailer meets the definition prescribed in § 171.8 of the HMR for a bulk packaging must be treated as one bulk packaging;
• individual non-bulk cylinders that are not manifolded and are designed to operate separately with their own stop valves are non-bulk packingings.

The Reference No. 88-0026 letter states two compartments permanently attached to a motor vehicle and used in the same manner as a cargo tank to dispense gasoline and diesel fuel to other vehicles that are manifolded together without valves to separate them are considered a bulk packaging if they have an aggregate capacity that exceeds 450 L. In addition, this letter states manifolded bulk packagings permanently attached to a motor vehicle that are designed to perform as cargo tanks contain safety features and appurtenances and are sometimes subject to different or lesser stresses than tube trailer cylinders. This letter also states if each compartment has valving that is closed during transportation, each compartment is considered a separate packaging regardless of whether the compartments have a contiguous shell. You state that based on Reference No. 88-0026 your organization has maintained the view that:

1) manifolded, non-bulk packagings with their own stop valve in the closed position are separate packagings;
2) manifolded, non-bulk packagings with their own stop valve in the open position are a single bulk packaging when their aggregate capacity exceeds 450 L; and
3) manifolded, non-bulk packagings without their own stop valve are a single bulk packaging when their aggregate capacity exceeds 450 L.

We disagree. The Reference No. 88-0026 letter concerned packagings designed to operate as cargo tanks. For the reasons stated earlier in this letter, it is the opinion of this Office that manifolded cylinders have the ability to release their entire contents during an incident regardless of whether they have individual stop valves in the opened or closed position or they are without stop valves.

The Reference No. 10-0116 letter states a tube trailer that contains non-bulk cylinders is a bulk packaging because it is a transport vehicle, and because it is designed to transport gas in an aggregate quantity greater than 3,000 L (792 gallons), which meets the definition of a bulk packaging under § 171.8 of the HMR. This letter also states cylinders in a tube trailer that each have their own shut-off valve and are connected with stainless steel tubing through a header, heat exchanger, and several additional valves to an automated valve that controls outlet pressure are also one bulk packaging under the HMR.

I hope this satisfies your request.

Sincerely,

T. Glenn Foster
Chief, Regulatory Review and Reinvention Branch
Standards and Rulemaking Division