By Laura Sanicola

(Reuters) -A “noxious” gaseous smell coming from St Croix’s recently reopened refinery that caused schools to close was caused by excess emissions of hydrogen sulfide, U.S. Virgin Islands officials said on Friday.

The Department of Planning and Natural Resources (DPNR) is advising people with respiratory ailments such as allergies, lung disease and asthma to consider taking protective actions such as staying indoors or relocating to less affected areas.

The U.S. Occupational Safety and Health Administration describes hydrogen sulfide “as a colorless gas known for its pungent ‘rotten egg’ odor at low concentrations. It is extremely flammable and highly toxic.”

The odor was caused by an “operating upset” overnight and into the early morning hours which has been corrected, according to a Limetree Bay spokesperson.

“The executive management of Limetree Bay sincerely apologizes for the impact to the public,” the spokesperson said, adding that the company would continue to monitor impact to the outside community.

The Department of Planning and Natural Resources told Reuters it is investigating to what extent Limetree exceeded permitted hydrogen sulfide levels.

Local grammar schools and a career and technical education center closed in-person learning after students and staff reported feeling nauseous due to a “noxious odor” affecting air quality on the campuses on April 22, according to a notice from the U.S. Virgin Islands Department of Education.

A St. Croix community coronavirus vaccination center was also closed on Friday due to the odor, a representative told Reuters.

The smell has been observed west of the island in Fredricksted for several days and has prompted citizen complaints, according to the DPNR.

The refinery recently resumed producing fuel following an entire plant shutdown earlier this month due to an undisclosed operational issue.

(Reporting by Laura SanicolaEditing by Chizu Nomiyama and Aurora Ellis)