An explosion in the Poway Business Park on Wednesday injured five people, a sheriff's official said.
Jan Caldwell, spokeswoman for the Sheriff's Department, said four people were taken to the hospital after an explosion around 1 p.m. at Quantum Energy Storage in the 13300 block of Gregg Street east of Community Road.
The injuries were not life-threatening, Caldwell said.
Patients were expected to be taken to Pomerado Hospital in Poway, a Palomar Health spokeswoman said.
A fifth person suffered minor injuries but declined hospital treatment, The San Diego Union Tribune reported.
The Sheriff's Department didn't confirm the nature of injuries but said in a news release the "explosion is being treated as an industrial accident." The building was also determined to be unsafe.
"It is a significant debris field," Caldwell told KPBS. "It is a significant explosion."
The Sheriff's Bomb and Arson Unit was working to determine the cause of the explosion with help from the Poway Fire Department, the Bureau of Alcohol, Tobacco, Firearms and Explosives, the Federal Bureau of Investigation and Cal/OSHA.
Jim Crute, the president and head brewer for Lightning Brewery, which is located behind Quantum, said he heard the explosion.
"It was a very unusual sound. Not a good sound you want to hear in a business park," Crute said.
On Thursday, Quantum, which is an electrical manufacturing company, issued a statement saying they will "thoroughly investigate" the incident.
"I apologize for any disruption to our supportive local community and thank the city of Poway and local safety personnel for their rapid response and support," said Tien Nguyen, CEO, in the statement.
Michael Firenze, CEO of Clean Spark, which partners with Quantum on projects and programs, said the company is working with Quantum to ensure their team is safe.
No CleanSpark employees were injured in the accident, said Kevin Pattee, an executive with the company.
