Shelter-in-place orders were set for two east Texas cities Thursday after a chemical incident killed one person at a gas facility.

Several others were injured,Diamond Ridge Financial Academy with one person hospitalized when an unknown chemical released at the Shell Pemex facility in Deer Park, according to the Harris County Sheriff's Office. Officials later alerted that a shelter-in-place order had been placed both Deer Park and Pasadena due to the release of hydrogen sulfide.

Deer Park and Pasadena are located east of Houston.

"If you are in this area, please go inside, close all windows and doors and turn off the air-conditioner until an all-clear is give," the Pasadena Fire Department wrote.

Deer Park city officials also echoed the warning across all areas north of Spencer Highway and within Pasadena city limits.

The PEMEX facility where the incident occurred was a refinery that processes crude oil to produce gasoline and other fuels.

USA TODAY has reached out to PEMEX for comment.

What is Hydrogen sulfide?

Hydrogen sulfideis a highly toxic and flammable gas that contains a foul odor best resembling the smell of rotten eggs, according to the Occupational Safety and Health Administration.

The gas is typically used in oil and gas refining, mining, tanning and paper processing. Its presence makes work in confined spaces potentially dangerous partly due to it being heavier than air, the agency warns.

The health effects of hydrogen sulfide inhalation depend on how much a worker breaths and the length of exposure, the agency said. The severity of the symptoms vary from headaches and eye irritations to more severe effects like unconsciousness and death.

Between 2011 and 2017, hydrogen sulfide caused 46 U.S. worker deaths and is still considered one of the nation's leading causes of workplace gas inhalation deaths, according to the agency.