west texasAP Photo/LM OteroFirefighters use flashlights to search a destroyed apartment complex near a fertilizer plant that exploded earlier in West, Texas, in this photo made early Thursday morning, April 18, 2013.

A fertilizer plant in the small town of West, Texas, blew up Wednesday night after a fire broke out. At least five people are dead, several firefighters are missing, and more than 160 victims are being treated at area hospitals.

Beyond the blast that rocked the small town, some of the victims were dealing with exposure to a highly volatile gas called anhydrous ammonia.

The West Fertilizer Co. had as much as 54,000 pounds of anhydrous ammonia on hand, Randy Lee Loftis of the Dallas News reports. 

Fears surrounding the nitrogen-based fertilizer forced firefighters to back away from the fire they were fighting before the massive explosion occurred.

Here's are some basic facts about anhydrous ammonia:

When anhydrous (which means without water) ammonia contacts water, the two combine quickly. 

It was a small fire and then water got sprayed the ammonia nitrate [the liquid form of anhydrous ammonia], and it exploded just like the Oklahoma City bomb,” Jason Shelton, a clerk at a hotel in West, told The Dallas Morning News.

• Anhydrous ammonia can rapidly cause dehydration and severe burns if it combines with water in the body.

“You can’t stand to breathe it,” David E. Baker of University of Missouri-Columbia writes. “When people receive burns or eye damage from the product, it is because of a sudden release of it where the victim is unprotected and cannot escape.”

• It is a low-cost, highly effective nitrogen-based fertilizer that must be stored at high pressure. When released, the vapors initially move close to the ground, causing greater risk for exposure.

• Symptoms can include breathing difficulty; irritation of the eyes, nose or throat; burns or blisters. Exposure to high concentrations can lead to death.

“Body tissues that contain a high percentage of water, such as the eyes, skin, and respiratory tract, are very easily burned. Victims exposed to even small amounts of ammonia require immediate treatment with large quantities of water to minimize the damage,” according to John M. Shutske of the University of Minnesota.

Loftis notes that the chemical is not considered an explosion risk when in the air as a gas, but it can explode in certain concentrations inside a container.

The cause of the boom has not been announced, but this volatile substance is by far the most dangerous chemical stored at the plant. And there was tons of it.

Waco police said that air quality in West is not an issue and the hospitals say that complaints of eye irritation have all but stopped, but the Texas Department of Public Safety spokesman D.L. Wilson told residents to remain indoors because of the threat of new explosions or leaks of ammonia from the plant's ruins.