Ammonia, also known as anhydrous ammonia, is well known to be a dangerous chemical capable of inflicting severe chemical burns on a person’s air system and causing death. On May 11, 1976, people along US 59, or the Southwest Highway, and Interstate-610, or the Loop, received firsthand information about the dangers of ammonia.

At around 11 a.m. on May 11, 1976, a Transport Company of Texas tanker truck carrying 7,509 gallons of anhydrous ammonia, or ammonia, struck a bridge rail on an overpass connecting the Southwest Expressway and the Loop . The truck went through the guardrail and ended up falling approximately 15 feet onto the Southwest Expressway.

After impact with the road below, the damaged truck released the vast majority of its cargo into the atmosphere. When the ammonia was released, there were about 500 people within a quarter mile of the spill. The ammonia in question evaporated almost immediately. It must not have been very humid that morning as the wind, at 7 miles per hour, gradually decreased the concentration at ground level. This is possible when there is no humidity since ammonia is less dense than air. When water is present in the air, ammonia mixes with it and stays near ground level. Within 5 minutes, the liquefied ammonia evaporated and the vapor cloud completely dispersed.

As a result of the accident, 6 people lost their lives, 78 people were hospitalized with serious injuries, and 100 more sought medical attention for less serious injuries. Of the 6 deaths, 5 of them were attributed to inhalation of anhydrous ammonia. The 178 injuries were also attributed to inhalation or exposure to ammonia. All of the spill victims were within 1,000 feet of the ammonia release site.

Because of this accident, those who stayed in their cars or office buildings were less likely to be seriously injured by ammonia. All of the people who were injured were out of their vehicles or buildings. They started out of their cars or came out to help. For this reason, it is recommended that people not rush into an ammonia spill without protective equipment. Also, when helping people who have been injured by ammonia, it is recommended that rescuers approach from upwind. This ensures a better chance that the ammonia has already left the area.