The Harris County, Texas sheriff said he doesn't know if any others could be dead after the leak on Thursday afternoon at a Pemex Refinery.
Emergency responders waited overnight to go into the unit at the center of the leak.
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In the last update from officials, crews said they planned to wait seven or eight hours until the chemical levels dropped low enough for investigators to safely enter. Officials have not yet said if crews were able to get in on Friday morning.
One of the main things they are checking for is to see if anyone else was killed.
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2 killed, at least 35 injured after chemical release at Pemex refinery
Authorities confirmed two employees were killed and another 35 were exposed to the chemical. It's unclear how serious those exposures were.
The chemical release happened around 4:40 p.m. Thursday.
The chemical, hydrogen sulfide, is a colorless gas known for its pungent "rotten egg" odor at low concentrations. It is extremely flammable and highly toxic and can cause mild headaches, eye irritation, unconsciousness, and death -- even at low concentrations.
Neighbors said they were smelling "rotten eggs" from miles away on Thursday.
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So far, the cause of the leak is still unknown.
"Some workers were working on a flange of some kind when there was a gas leak of H2S, which was hydrogen sulfide," Sheriff Ed Gonzalez said. "We believe, at this point, that there's two persons deceased on scene."
This was the second scare for people in Deer Park in less than four weeks. A pipeline fire last month burned for four days.
The shelter-in-place orders that were put in effect for Deer Park and Pasadena, Texas around 6:30 p.m. Thursday have since been lifted.
A Houston ABC affiliate KTRK crew could still detect a hint of a chemical smell in the air early Friday morning. By 6:30 a.m., they said it was gone.
KTRK spoke to residents of both Deer Park and Pasadena, who said they were completely unaware of what was happening and are questioning why no alerts were sent to their phones.
The city of Deer Park acknowledged in a social media post that their emergency alert system was having issues and some people may not have received the notifications.
It's still unclear some Pasadena residents claim they heard nothing.
KTRK spoke to some people at a bowling alley who were not pleased that they had no idea that a dangerous chemical had been leaked into the air.
"I was at work, and I had no idea. I found out through Facebook and I was like, 'I wonder if any of my loved ones could have been harmed or anything like that.' It kind of reminded me of the ITC fires. It kind of gave me flashbacks," one resident said.
KTRK checked into Pemex's environmental record with the U.S. Environmental Protection Agency. There appeared to be one violation from 2022, and it was for the "Lead and Copper Rule." The violation was listed as resolved.
Pemex, which is based in Mexico, has not yet said anything about how the leak happened. The refinery processes crudes from several countries. They produce a range of products including gasoline, aviation fuel, diesel fuel and ship fuel.