One person was seriously injured and another was hurt this month in a “minor” explosion at biotech firm Amgen’s South San Francisco lab facility, a fire marshal confirmed. One employee suffered burns to their face and another employee suffered burns to their hands after an explosion that began in a “flammable liquids” cabinet in a third-floor laboratory, said South San Francisco deputy fire chief Travis Nuckolls. According to the report in the Mercury News, the explosion was reported about 3:30 p.m. Officials don’t know what caused the dangerous mixture to explode, but the cabinet in which the explosion occurred was knocked over from the force, and windows on the third floor were also blown out, fire officials confirmed. Nuckolls said at least one of the chemicals involved was ether.

According to a spokeswoman at the St. Francis Memorial Hospital burn unit in San Francisco, one patient was taken there with injuries deemed “noncritical.” She would not provide further information about the patient’s condition. The region’s other burn unit, at the Santa Clara Valley Medical Center in San Jose, reported no patients from Amgen.

All buildings in the complex in addition to the Amgen building were evacuated as a precaution. An Amgen spokeswoman did not respond to multiple calls for comment. Decontamination tents were set up for employees who may have been affected by chemicals or toxins that spread after the explosion, but Nuckolls said it had been determined early Wednesday night that nothing dangerous had gone airborne.

The incident was the second to injure a worker in the facility in the last year. In May, a worker for a waste disposal company was seriously burned while collecting waste at the facility. According to Cal-OSHA spokesman Peter Melton, the firm and two other businesses — Clean Harbors Environmental Service Inc. and Thermo Fisher Scientific Inc.’s Unity Lab Services — received “serious” citations for the May incident on Nov. 14. Melton said the most serious citation issued was in the amount of $77,400 to Clean Harbors Environmental Service Inc.

Clean Harbors, a San Jose-based company, provides hazardous waste disposal, emergency response, lab chemical packing, recycling, and vacuum services, among others. The person who was burned and hasn’t been identified was working for Clean Harbors and was attempting to collect flammable liquids from one of the labs at Amgen at the time of the incident, Melton added.

Fires and explosions at pharma manufacturing facilities are not unusual, but there are few reports of events at research facilities. An explosion in 2012 at a Teva Pharmaceutical Industries plant in Croatia killed four workers and injured 17 others. A fire in a boiler room at a Sandoz plant in Boucherville, Quebec, did not cause injuries but exacerbated a shortage of one of the products made at that Novartis plant.

Thousand Oaks-based Amgen is one of the world’s largest drugmakers, producer of popular osteoporosis drug Prolia and rheumatoid arthritis medication Enbrel.