A shelter-in-place order issued Sunday morning for portions of Texas’ most populous county was lifted by the early afternoon, local officials announced. The order applied to sections of Harris County, which includes Houston and is home to more than 4 million residents, and was ordered in response to a chemical gas leak at a 99 Cents Only Store distribution center about 30 miles west of the city.

An investigation into the warehouse leak, and what caused it, is currently underway, CBS affiliate KHOU reported. The facility, located near a freeway in the smaller city of Katy, will remain closed while the investigation is active, according to the station.

“At this time, we do feel that it is safe to lift the shelter-in-place and we will continue to work with pollution to monitor throughout the evening,” said Dr. Erika Brown, director of the community health and wellness division at Harris County Public Health, during a news conference

The chemical leak began at around 9 p.m. on Saturday night, county officials said earlier. They explained that maintenance crews were performing routine work on the warehouse refrigeration system and initially monitored the leak after it started in an overhead refrigeration line. The line itself is suspended about 16 feet in the air, said Fire Marshal Laurie Christensen, which, at first, made it “inaccessible” to the hazmat team dispatched as part of the county’s containment plan. 

Christensen said that “because of how high [the line] is and that it is an explosive product,” the hazmat team “could not go in there and do anything about that initially.”

Maintenance workers noticed that the chemical, later determined to be anhydrous ammonia, had started to leave the building at around 1 a.m. on Sunday morning, officials said. No injuries have been reported so far in connection with the leak, but the potential threats to air quality and human health prompted the Harris County Public Health department to implement a shelter-in-place order for residents within a two-mile radius of the distribution center. 

“Our landlord’s certified refrigeration contractor was performing work on the refrigeration system when the release occurred,” said 99 Cents Only Store in a statement obtained by CBS News. 

“The safety of our employees, others in the building and our community is always our first priority. The building was promptly evacuated as soon as the leak was discovered,” the statement continued. “Building operations will resume only after we have confirmed the cause of the release, the issue has been fully resolved, and state and local officials have advised that the facility is safe for normal operations.”

An ammonia leak poses dangers because of the chemical’s flammability, Fire Chief George McAteer explained, as well as its potential to cause respiratory symptoms and irritation to the nose and throat if a person comes in contact with polluted air. 

Ammonia, one of the most widely produced chemicals in the U.S., is a clear, colorless and odorous compound that is referred to as anhydrous ammonia in its purest form, the county health department said in an advisory notice shared on Twitter. Although low levels of ammonia are found in household products, like cleaning solutions, high and potentially dangerous concentrations of the chemical are “used in manufacturing, refrigeration, and agriculture (as a fertilizer),” according to the CDC.

“If anyone is experiencing watery eyes, burning eyes, irritation of the nose or throat, difficulty breathing, we are asking you proceed to the nearest emergency center to receive care,” said Brown while discussing the chemical leak on Sunday. “If anyone has any chronic medical conditions or feels they have health risks associated, we are asking that you contact your care provider to determine next steps.”