A chemical leak at a PEMEX oil refinery in Deer Park, Texas, on Thursday killed two workers and injured several others, prompting temporary shelter-in-place orders for residents across the city, officials said.

The leak happened around 4:20 p.m., sending hydrogen sulfide – a colorless and potentially toxic gas – seeping into the air at the plant, according to Harris County Sheriff Ed Gonzalez.

Two bodies have been found at the scene and at least 35 others were “triaged,” the sheriff said at a Thursday night news conference. It is unclear how many were treated on-site or brought to a medical facility.

PEMEX, a Mexico-based oil company, said in a statement in Spanish that operations were halted once the leak was detected and local authorities were notified.

Shelter-in-place orders were issued for the city of Deer Park, as well as some residents of neighboring Pasadena, as emergency officials told residents to stay indoors, close all windows and doors, and turn off their air-conditioners. The orders have since been lifted after air monitoring determined no hazardous chemicals had permeated the surrounding community, city officials said.

“We’ve not gotten any air monitoring reports to show that anything has gotten into the community that would be a concern to any constituents in Deer Park,” Deer Park Mayor Jerry Mouton said, noting air monitoring will be ongoing.

Hydrogen sulfide, commonly used in oil and gas refining, has a pungent “rotten egg” smell that may linger in the air, Mouton said.

The local utility, CenterPoint, has received several calls reporting possible gas leaks as the scent wafts into neighborhoods, the mayor said. He reiterated that no hazard has been detected outside of the plant.

“Other than the smell, we have not had any verifiable air monitoring to support that anything got outside the facility,” Mouton said.

Investigators have yet to enter the facility because hazmat and fire marshal personnel are still working to lower chemical levels inside the plant, Gonzalez said. The process will likely last through the night, he added.

State Highway 225 was briefly closed near Beltway 8 but has since been reopened, the sheriff said.

The sheriff’s office will lead an investigation into the incident, Gonzalez said. PEMEX also said an investigation is underway to determine the cause of the leak.

Just last month, the residents of Deer Park contended with a pipeline fire that erupted when an SUV slammed into a liquid natural gas valve along its border with La Porte. The days-long blaze damaged nearby homes, melted vehicles and led to the evacuation of about 100 homes southeast of Houston.