IIAR

There are risks involved whenever anhydrous ammonia is transferred to or from an industrial refrigeration system. Potentially catastrophic ammonia releases could occur if the transfer operations are not performed safely. While catastrophic releases are relatively rare, two ammonia-related incidents occurred in 2009 during transfer operations involving cargo tank trucks. The circumstances surrounding these incidents will be summarized below along with the precautions that should be taken whenever ammonia is transferred to or from a system using a cargo tank truck.

The first incident occurred in July 2009. During a delivery and transfer operation there was an ammonia release at an ammonia storage and distribution facility. The release occurred at approximately 8 a.m. The weather conditions were hot, humid, and overcast; wind speed was about 1 mph. The ammonia cloud from the release hugged the ground for several minutes due to the weather conditions and covered a portion of a two-lane highway adjacent to the facility.

The release occurred when a common carrier cargo trailer was delivering anhydrous ammonia to the ammonia distribution facility. The cargo trailer contained about 40,000 lbs of anhydrous ammonia. The carrier utilized a two-inch transfer hose from the trailer unit to make the delivery via a pump unloading process. The receiving tank was a 30,000 gallon capacity above-ground storage tank. About ten minutes into the delivery, the carrier’s transfer hose ruptured creating an opening in the transfer hose through which the ammonia was released. The emergency shut off for the trailer was activated by personnel on site shortly after the release. It was estimated that about 7,000 lbs of ammonia could have been released.

The investigation of the incident subsequently revealed that the carrier’s transfer hose that ruptured was not rated for ammonia service. It was an LP gas hose. Carriers using DOT MC 330/331 cargo trailers can haul and transport both ammonia and propane. Even though the cargo trailer itself is suitable for either service, hoses are constructed differently and should be maintained separately for each product. The ammonia deteriorated the LP hose since the hose’s material of construction is not compatible with ammonia, and that deterioration eventually led to the failure of the hose.

Since this incident occurred during a transportation transfer operation, the National Transportation Safety Board (NTSB) had the lead in the incident investigation. Other agencies were also involved including Federal DOT, State EPA, State OSHA as well as company officials.

The second incident occurred at a fertilizer plant in Rosemont, MN in November 2009. Anhydrous ammonia apparently was held in large tanks at the plant and then transferred to awaiting cargo tank trucks at various loading stations. At about 6:30 p.m. two drivers were filling a cargo tank truck with anhydrous ammonia when a problem developed in a connection between a pipe delivering the ammonia and the tank on the truck. A driver noticed the problem and tried to fix it. Witnesses then recalled hearing noises followed by a loud “bang.” The high-pressure piping dislodged releasing liquid ammonia. One driver died at the scene and a second driver was hospitalized and later died. An employee saw the ammonia vapor cloud and within seconds hit a button shutting down the flow throughout the entire plant. Occupational Health and Safety Administration (OSHA) officials are expected to conduct a full investigation.

Though neither of these incidents occurred at a facility operating an industrial refrigeration system they do demonstrate the importance of following proper procedures whenever ammonia is transferred to or removed from a system using a cargo tank truck. These precautions include:

• Proper training for those involved in the transfer operations. For example, Department of Transportation (DOT) HAZMAT employee training, sometimes called HM-126f training, must be provided to any employee involved in the transportation of hazardous materials. Refresher HAZMAT employee training is required every three years after initial training, or if the employee’s duties involving hazardous materials change.
• Proper attendance during transfer operations. 49 CFR § 177.834 establishes the general requirements for loading and unloading cargo tank trucks. This regulation specifies that a motor carrier who transports hazardous materials by cargo tank truck must ensure that the truck is attended by a qualified person at all times during loading or unloading. For a cargo tank with a capacity greater than 3,500 water gallons, excluding delivery hose and piping, the qualified person attending the unloading operation must remain within 150 feet of the cargo tank and 25 feet of the delivery hose when the internal self-closing stop valve is open. A person is qualified if he/she has been made aware of the nature of the hazardous material which is to be loaded or unloaded, has been instructed on the procedures to be followed in emergencies, is authorized to move the cargo tank, and has the means to do so.
• Written operating procedures describing the steps that will be taken when transferring ammonia to or from a system. The procedures should describe:
  • The appropriate personal protective equipment (PPE) that should be worn and when the buddy system shall be practiced.
  • The source of the refrigerant, i.e., charge from a cylinder or from a cargo tank truck
  • Charging point on the system.
  • Facility safe work practices and emergency response procedures applicable to the charging procedures.
  • Steps required to charge ammonia to the system.
  • Steps required to purge the charging system.
• An eye wash/safety shower capable of providing at least 20 gpm of water for at least 15 minutes should be accessible within 10 seconds or less from the transfer point.
• Ensuring that no ammonia is loaded into or unloaded from any cargo tank truck unless the handbrake is securely set and all other reasonable precautions are taken to prevent motion of the vehicle during the loading or unloading process. In addition no material should be loaded into or from any cargo tank truck with the engine running unless the engine is used for the operation of the transfer pump of the vehicle.
• Proper ammonia hoses must be used whenever transferring ammonia to or from a system. Each hose must contain a label or stamp indicating that it is suitable for ammonia service. Some transfer involving hose connections may also have backflow protection such as a check valve as part of the unloading process.
• Preventive maintenance procedures for transfer hoses. The DOT requires a hose management program for liquid transfer hoses carried on cargo tanks that transport liquefied compressed gases such as anhydrous ammonia. This program should include a visual inspection each time a hose is used (see below), a monthly inspection and an annual hose leakage test.
• Proper inspection before ammonia is transferred. The qualified person performing the transfer should check the components, including the transfer hose and piping, to assure that they are of sound quality, without obvious defects detectable through visual observation and audio awareness, and that connections are secure.

  Ammonia should not be transferred if the transfer hose has any of the following defects:

  • Damage to the hose cover that exposes the reinforcement.
  • Wire braid reinforcement that has been kinked or flattened so as to permanently deform the wire braid.
  • Soft spots when the hose is not under pressure or bulging when the hose is under pressure.
  • Loose outer covering.
  • Damaged, slipping, or excessively worn hose couplings.
  • Loose or missing bolts or fastenings on bolted hose coupling assemblies.

  In addition ammonia should not be transferred if the piping system has any of these defects:

  • Any external leak identifiable without the use of instruments.
  • Bolts that are loose, missing, or severely corroded.
  • Manual stop valves that will not actuate.
  • Rubber hose flexible connectors with any condition outlined above for hose assemblies.
  • Stainless steel flexible connectors with damaged reinforcement braid.
  • Internal self-closing stop valves that fail to close or that permit leakage through the valve detectable without the use of instruments.
  • Pipes or joints that are severely corroded.
  •  Proper emergency shutdown devices should be provided. Cargo tank trucks used in anhydrous ammonia service during metered delivery service with a capacity of 3,500 water gallons (or greater) should be provided with off-truck remote shutdown equipment per 49 CFR § 177.840. This shutdown equipment should close the internal self-closing stop valve and shut off the engine and auxiliary power upon activation by the person attending the unloading operation. Additional features may be required for obstructed view deliveries