A truck mechanic was killed west of Phoenix, Arizona, after piping was accidentally ripped from a horizontal storage tank, discharging an estimated 4,000 gallons of deadly anhydrous ammonia. He was overcome by the massive vapor cloud and unable to escape from the area.

On arrival, emergency responders were told that the mechanic had gone down and that not all the leaking anhydrous ammonia had vaporized but was puddled in the initial discharge area. Following the extensive release, the “autorefrigeration” effect of vaporizing liquefied compressed gas cooled the remaining liquid down close to its boiling temperature, thus slowing the vaporization process.

For domestic shipments within the United States, the U.S. Department of Transportation has classified anhydrous ammonia as a Nonflammable Gas. Internationally, however, the product is classified as a Poison Gas, based on the following characteristic:

Immediately Dangerous to Life and Health (IDLH)–500 ppm.


First-due responders were not equipped with the proper personal protective equipment, which, in this case, was vapor-tight suits (EPA Level A). By the time a properly equipped hazardous materials team re-sponded to the remote county area, the incident was more than one hour old. The mechanic had been inside the vapor cloud area all of this time. Based on eyewitness accounts, the logical assumption was that he was blinded and overcome by the intensely irritating vapors and had inhaled a fatal dose. Therefore, the operation was actually a body recovery and not a rescue.

In the meantime, responders concentrated their efforts on evacuating a two-mile downwind area, comprised of light agriculture and farms, with livestock and pets. In Arizona, the county sheriff is the senior public safety official within his jurisdiction, so the sheriff`s office activated its field command post, which was maintained throughout the night. The hazardous materials team worked its way into the initial release area, checking for any additional victims. The team detected ammonia vapors significantly over the IDLH level. It was able to shut down several valves that were in the open position on the leaking tanks. The sheriff`s office investigators were not trained in the use of SCBA and Level A suits, so the determination was made not to conduct the body recovery until the following morning when vapor levels would have decreased to a safer level.

Computer modeling by the state Department of Environmental Quality determined that an evacuation perimeter of one mile was more appropriate. Plans were made with multiple local and state agencies for entry the following morning.

The following morning, a joint conference was held with a command team that now included the state Department of Environmental Quality and the state Occupational Safety and Health Administration (OSHA). Since potential violations of law or safety codes were involved in the incident, evidence protection and gathering were priorities. The entry team would also determine the existing levels of ammonia vapors and help formulate the body recovery plan.

The team included a hazardous materials specialist from the state Department of Public Safety, who would photograph the entire scene. Two fire department hazardous materials technicians were to take vapor readings from six predesignated areas within the perimeter. To facilitate the readings, a hand-carried diagram was taken into the area. A similar drawing was maintained at the command post, where readings were radioed out for recording.

The fire department hazardous materials team set up its decontamination equipment outside the company`s upwind fence line. A joint safety briefing was conducted. The entry team completed its reconnaissance within less than 20 minutes and returned through the decontamination stations for a debriefing.

The OSHA Permissible Exposure Level (PEL) for anhydrous ammonia is 50 parts per million, the level at which respiratory protection is required. At lower readings, individuals can legally work in the environment eight hours a day, 40 hours a week. Based on the entry team vapor readings, a PEL vapor cloud existed only within a very narrow area of the initial release. This was due to the anhydrous ammonia`s having seeped into the ground; it was still off-gassing.

The dramatic effect of the downwind cloud could be seen in acres of browned grapes immediately downwind. The anhydrous ammonia vapors had killed these crops. There were several reports of sickened livestock in the downwind area, but the vapors were dissipated by the wind before they could reach any inhabited structures.

The mechanic`s body was finally recovered at midmorning while sheriff`s investigators and state OSHA inspectors examined the site. As a precaution, the fire department hazardous materials technicians who recovered the victim decontaminated the body before turning it over to the medical examiner`s office.

LESSONS LEARNED and reinforced

Due to autorefrigeration, vapors from the release of a large amount of a liquefied compressed gas may take many hours to disperse.

The possibility of criminal or safety code violations must be considered at a hazardous materials incident.

Determining whether an operation will be a rescue or a body recovery sometimes is a very difficult decision. Once this determination is made, it needs to be clearly conveyed to all individuals at the scene to avoid confusion and potential frustration.

The involvement of multiple agencies in a unified command structure can add hours to an operation`s duration. n

(Left) The driver of a forklift accidentally backed into the discharge piping attached to two horizontal anhydrous ammonia storage tanks, resulting in the release of an estimated 4,000 gallons of product. (Photos by author.) (Right) Part of the discharge plumbing was ripped off one of the two anhydrous ammonia storage tanks. A mechanic working on a vehicle nearby was unable to escape from the rapidly expanding cloud of deadly anhydrous ammonia gas released in the incident.

(Left) The safety officer at the command post noted on a diagram of the incident scene the parts-per-million anhydrous ammonia readings obtained by the entry team at several predesignated sites. (Right) Entry team members prepare to take an instrument reading to determine the residual levels of anhydrous ammonia remaining on the site before determining how the body recovery operation will be conducted. The anhydrous ammonia reading in the immediate area of the release exceeded 100 parts per million more than 12 hours after the incident.

STEPHEN L. HERMANN is hazardous materials coordinator for the Arizona Department of Public Safety and Arizona`s senior state on-scene coordinator for hazardous materials emergency response. He is past national chairman of COHMED, the national organization of state and local hazardous materials enforcement officers, and past chairman of the Commercial Vehicle Safety Alliance Hazardous Materials Committee. Hermann has a bachelor of science degree in explosive technology and is a graduate of the U.S. Naval School Explosive Ordnance Disposal, U.S. Army Command; General Staff College; and the U.S. Army War College and is a hazardous materials specialist for his agency and a state Division of Emergency Services Hazardous Materials technical course graduate.

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