A TEMPEST in a teapot. That seems to be the best way to describe the Research and Special Programs Administration's current preoccupation with the safety of pressure vessel cargo tanks used to transport products such as propane. RSPA has published HM-225, an Interim Final Rule that will remain in effect from August 16, 1997, through March 1, 1999. The rule was on page 44037 of the August 18 issue of the Federal Register.
The rule applies to most pressure vessel cargo tanks. However, RSPA has specifically exempted those used to transport liquefied compressed carbon dioxide because that product poses a minimal safety risk.
The temporary rule is needed because a substantial portion of the industry failed to comply with a crucial excess-flow safety requirement that has been in place since 1941, according to RSPA officials. RSPA wants a new emergency shutoff system that will stop product discharge from pressure-vessel-type cargo tanks following a hose or piping failure.
Under the temporary rule, product delivery system integrity must be verified, new hose testing procedures must be adopted, a comprehensive emergency procedure must be printed and carried in each vehicle, and trained personnel must be on hand during all product transfer activities. Tanks with current emergency shutoff systems must be marked as operating under 49 CFR 171.5.
Among the liquefied compressed gases most commonly transported in DOT-specification cargo tanks are petroleum gases (LP-gas), anhydrous ammonia, and chlorine. The risk of personal injury due to accidental releases is high for each of these, and in the case of propane, the additional threat of fire and explosion must be considered.
RSPA officials say an accident September 8, 1996, prompted them to take a fresh look at the safety of pressure vessels used as cargo tanks, and they didn't like what they saw. In the incident, more than 35,000 gallons of propane were released during delivery to a bulk storage facility in Sanford, North Carolina. There was no fire.
Agency officials contend that the accident would not have been as severe if the emergency shutoff system had been operating properly. Currently, most MC330 and MC331 cargo tanks are fitted with an internal self-closing stop valve that incorporates an excess-flow feature. The key requirement is that the discharge valve must automatically close if any of its attachments are sheared off or if any attached hoses or piping are separated.
The emergency systems don't always function properly when pumps are used to load and unload a pressure vessel, according to RSPA officials. Along with the pumps, many operators have installed emergency shutoff valves with flow ratings well above the discharge capacity of the pump.
This arrangement assures product transfer without interruptions that could be caused by inadvertent activation of the emergency shutoff system. The pump functions as a regulator in the product discharge line, eliminating any possibility that the shutoff system will function in an emergency.
RSPA contends that the industry has known since at least 1978 that the excess flow valves are not designed to function where piping system restrictions decrease the flow rate to less than the valve's closing flow. In addition, RSPA accuses the industry of deliberately failing to report failure incidents.
In December 1996, RSPA published a safety advisory notice outlining concerns about the shutoff systems on MC330 and MC331 tanks. Operators were reminded that the equipment had to conform to the Hazardous Materials Regulations.
This brought a quick response from the industry. Applications for emergency exemptions were received from Mississippi Tank Company, National Propane Gas Association (NPGA), National Tank Truck Carriers, and The Fertilizer Institute.
In its comments, NPGA pointed out that the propane gas industry has achieved an extraordinary safety record. From 1986 to 1995, there were almost 10 million tank transport truck deliveries and almost 300 million bobtail deliveries of propane.
Those deliveries carried almost 90 billion gallons of propane to residential, commercial, agricultural, and industrial consumers in every state and county in the United States. Except for the incident in Sanford, North Carolina, NPGA is unaware of any other serious reported incident involving the emergency discharge control system during this 10-year period.
As to the smaller bobtail cargo tanks, RSPA acknowledges in the Interim Final Rule that only nine incidents of propane release have been reported during the past 10 years involving any allegation of a failure of the emergency discharge control system. None of the nine incidents resulted in fatalities.
This represents approximately one release per 30 million bobtail deliveries. It also represents one release per almost 10 billion gallons of propane delivered in the past 10 years.
Despite industry testimony and evidence that this is a relatively minor issue, RSPA has moved forward with new requirements. Existing MC330 and MC331 cargo tanks can remain in use even without certification and demonstrated performance of the internal self-closing stop valve or the excess flow feature.
The operator is responsible for verifying that the transfer system is of sound quality, is free of leaks, and has secure connections. The hose must be tested before the first delivery of the day. The pressure test must be performed at no less than 120 percent of the design pressure or maximum allowable working pressure (MAWP) marked on the cargo tank or the pressure the hose is expected to be subjected to, whichever is greater.
The pressure test must include hose fittings, and the equipment must be arranged in the configuration to be employed during transfer operations. Equipment that shows signs of leakage, significant bulging, or other defects may not be used. Hose maintenance programs must be instituted. RSPA says acceptable procedures for hose maintenance, testing, and inspection are contained in publication RMA/IP-11-2, "Manual for Maintenance, Testing, and Inspection of Hose," 1989 edition, published by the Rubber Manufacturers Association, 1400 K St NW, Washington DC 20005.
During product transfer, a qualified operator must be within arm's reach of the emergency shutoff system. The operator can be out of position for only brief periods to engage or disengage the PTO or other pump operating system.
RSPA will allow remote control systems. The operator must carry a radio transmitter that is capable of activating the emergency shutoff and must remain within the operating range of the transmitter. The operator must have an unobstructed view of the cargo tank at all times.
Comprehensive written emergency operating procedures must be developed, and employees who perform unloading functions must be trained in those procedures. The emergency operating procedure must be prominently displayed in or on the cargo tank vehicle. Training records must be certified and maintained.
New pressure vessel cargo tanks built prior to March 1, 1999, may be marked and certified as conforming to MC331 code if they meet all of the requirements of the current specification. The following statement must be added to the certification document: "Emergency excess flow control performance not established for this unit."
The tanks also must be marked as "operating under 49 CFR 171.5." The letters must be white and the background black. The marking dimensions must be six centimeters by 15 centimeters (2.4"x 6"), and the letters must be at least 1.5 centimeters (0.6") high.
Moving beyond the Interim Final Rule, RSPA has published an advanced notice of proposed rulemaking to consider amendments to the current pressure vessel cargo tank code. The agency will examine changes in the emergency shutoff systems, the possibility of a one-, two-, or three-year retrofit schedule, additional hose testing and qualification requirements, and operator safety procedures.
Written comments are due by October 17 and should be addressed to the Dockets Management System, US Department of Transportation, 400 Seventh St SW, Washington DC 20590-0001. Comments also may be submitted by E-mail to [email protected] Two copies should be submitted and should carry the docket number: RSPA-97-2718 (HM-225A).