ANKARA, Turkey (AP) — An explosion at an oil refinery in northwestern Turkey on Tuesday left at least 12 employees slightly injured, the company said. A fire at the facility was quickly brought under control.

The Turkish Petroleum Refineries company, TUPRAS, said a fire broke out at its facilities in Izmit, in Kocaeli province, during maintenance work on a compressor. The company’s emergency teams responded immediately to the incident, it said in a statement.

The 12 employees sustained slight injuries and were taken to a hospital for examinations, the company said.

The company said the unit where the incident occurred “was deactivated in a controlled manner” and that other operations at the refinery were “continuing as normal.”

Earlier, Tahir Buyukakin, the mayor for Kocaeli told private NTV television that the blast occurred during a drill. The fire was quickly brought under control by the company’s own crews and no request for help was made, he said.

Video footage from the site showed smoke rising from the refinery, which is one of Turkey’s largest. Izmit is about 100 kilometers (62 miles) east of Istanbul.

The Borsa Istanbul stock exchange temporarily halted trading of TUPRAS shares, until the company provides a detailed explanation of the incident.