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By Connor Mannion

One person was dead and two other people were treated at a hospital after an apartment building linked to the University of Texas was exposed to the poisonous gas hydrogen sulfide.

The Austin Fire Department responded to a reported gas leak at 2:30 p.m. (3:30 p.m. ET). It found a sign on an apartment door that read "Danger: Watch out, hydrogen sulfide," along with a person inside who was in cardiac arrest. That person was pronounced dead at the scene, according to officials.

Firefighters respond to a haz-mat situation at the West Campus apartment complex in Austin, Texas.Tom Rapp / KXAN-TV

First responders in haz-mat gear took the initial patient out and tried to decontaminate him while checking to make sure others in the building were evacuated, NBC station KXAN reported.

Hydrogen sulfide, also known as "sewer gas," is a poison that is often described as smelling like rotten eggs. Short-term, high-level exposure can cause immediate collapse, with a high probability of death, according to the U.S. Centers for Disease Control and Prevention.

"Crews quickly started ventilation and going door to door to make sure everyone was OK," Austin fire Division Chief Palmer Buck told KXAN.

Six people in all were exposed to the gas, said Cmdr. Mike Benavides, a spokesman for Austin-Travis County Medical Services. The three other people were treated and released at the scene.

Police are still investigating, but authorities said the poisoning might have been intentional. "This is not an uncommon method of chemical suicide," Emergency Services Division Chief Eric Jakubauskas.

Hydrogen sulfide can be created by mixing common household chemicals. In August 2009, a 23-year-old California man was found dead in his car behind a Pasadena shopping center. The car's doors were locked, the windows were rolled up and a warning sign had been posted in one of the windows.

Carolina Gonzalez contributed.