(CNN) -- Firefighters at the scene of a massive fertilizer plant explosion in Texas were concerned Wednesday night about anhydrous ammonia.
According to the Centers for Disease Control and Prevention, anhydrous ammonia is a pungent gas with suffocating fumes that is used as a fertilizer.
When exposed to humans, it can cause various problems:
• Anhydrous means without water
• Anhydrous ammonia can rapidly cause dehydration and severe burns if it combines with water in the body
• Symptoms can include breathing difficulty; irritation of the eyes, nose or throat; burns or blisters.
• Exposure to high concentrations can lead to death.
• Victims require treatment with large quantities of water for at least 15 minutes
• It must be stored at high pressure, according to the University of Minnesota.
• It is a low-cost, highly effective nitrogen-based fertilizer, the University of Arkansas said.
• It is one part nitrogen and three parts hydrogen.
• When released, the vapors initially move close to the ground, causing greater risk for exposure.
One of the worst disasters in U.S. history involving a form of ammonia occurred in April 1947 when a ship loaded with ammonium nitrate -- a solid fertlizer composed of ammonia and nitrogen -- caught fire while docked in Texas City, Texas, in April 1947. The fire caused an explosion that damaged more than 1,000 buildings, according to the website of the Texas Historical Association.
The blast ignited a fire on a second ship docked in Galveston Bay that was also loaded with ammonium nitrate. With most of the city's fire fighters killed in the first blast, the fire burned for 16 hours and caused another huge explosion. Volunteers fought to put out subsequent blazes.
The historical association said almost 400 people were killed and more than 175 were listed as missing. Only a few bodies in the dock area were even recovered.