Poisons in the News: Anhydrous Ammonia

By Wafa Unus

Poisons in the News: Anhydrous Ammonia

Last night, an enormous explosion shook the small town of West, Texas when a fertilizer plant caught fire and exploded. At least 5 people were killed and an estimated 150 more were injured. The blast leveled nearby homes and businesses, with its impact visible within a five block radius of the blast site.

As emergency personal continue their search and recovery efforts, poison center experts are prepared to respond to the health impact of the release of anhydrous ammonia, a potentially poisonous gas released by the fertilizer plant. While the explosion was massive and uncommon, poison center experts don’t expect exposure to the gas to be the primary cause of injury, according to Henry Spiller, managing director of the Central Ohio Poison Center. “Most of the injuries were from the actual blast,” he said.

What is Anhydrous Ammonia?

Anhydrous ammonia is a gas used as a low-cost nitrogen-based fertilizer. Its effectiveness makes it a popular choice for industrial plants. However, exposure can cause serious danger in certain conditions.

Anhydrous means “without water.” When used as a fertilizer, it is injected into soil in a liquid form. When it makes contact with the moisture in the soil, the water combines with the ammonia rapidly and becomes a gas. This gas is then easily absorbed into the soil.

When the anhydrous ammonia mixes with water, it becomes the highly corrosive compound ammonium hydroxide. It’s the exposure to ammonium hydroxide that poses a potentially serious danger when inhaled.

Low levels of exposure are generally more an annoyance than anything else. Those exposed may feel irritation in their throat or eyes. However, high exposures to anhydrous ammonia can be fatal. The highly corrosive nature of ammonia can cause the body to physically close airways, ultimately leading to severe and potentially fatal respiratory distress.

Exposure Risks

A number of factors contribute to the danger of exposure to anhydrous ammonia. Distance and concentration are primarily responsible for severe reactions. Because of the nature of the anhydrous ammonia vapors to move closer to the ground, low-lying areas such as valleys can see a fatally high concentration of the gas in the event of a chemical release.

Exposure to high concentrations of the gas is also not highly likely in situations like the one in West, Texas where, the geography of the region is fairly flat. “[Anhydrous ammonia] is a highly reactant gas…It becomes another substance once it combines with water. It doesn’t stay at high concentrations,” said Dr. Cynthia Lewis-Younger, medical director at the Florida Poison Information Center in Tampa. “The main concern is [for] people who already have respiratory concerns.”

Those who have been exposed to anhydrous ammonia may begin to have difficulty breathing, irritation of the eyes, nose and throat as well as see burns and blisters.

“In very rare cases [the effects of exposure] can be long term. It can cause an asthma-like disease process. That’s pretty infrequent [and] is only if there was really severe exposure. Ninety-nine percent of [those exposed] will get better,” Spiller said.

Poison center experts encourage those in the affected regions to stay indoors with windows and doors closed to cut down on exposure and limit activity that would contribute to an increased respiratory rate such as running.

For more information about anhydrous ammonia or if you think you may have been exposed to anhydrous ammonia please contact your local poison center at 1-800-222-1222.



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