DELTA, B.C. -- Poor ventilation at a Delta, B.C., greenhouse is to blame for sending dozens of workers to hospital for carbon monoxide exposure, a fire chief said.

Delta fire battalion chief Neil Shuster said an emergency call came in Saturday afternoon that at least 12 people at Windset Farms were suffering from inhalation of a suspected cleaning product.

Three fire crews and a hazmat crew were dispatched along with police and BC Ambulance Services.

Once on scene, Shuster said crews determined there were high levels of carbon monoxide in the building.

Approximately 43 people required treatment on site.

The workers had been inside a greenhouse while a gas-powered pressure washer was running without adequate ventilation, he said.

"I believe they were working at the time and it was maintenance, regular maintenance I guess they were doing at the time," he said

Representatives from Windset Farms did not immediately respond to requests for comment.

Provincial workplace safety officials are investigating the incident.

Carbon monoxide is a colourless, odourless gas that's produced whenever fuel is burned.

It can cause health problems -- and eventually death -- because breathing it reduces the body's ability to carry oxygen in the blood.

BC Emergency Health Services tweeted that 13 ambulances responded to "a major incident" with 10 in serious to critical condition and 32 others in stable condition.

Linda Lupini, the services' executive vice president, said on Sunday that response to the incident was swift and followed protocols for mass casualty events with those most seriously injured receiving priority care.

Those exposed to carbon monoxide were treated with oxygen and given blood tests to ensure they were recovering, she said.

No additional crew or other staff were affected by carbon monoxide.

"The entire event as we know could have had a very different ending," she said. "There's no doubt this was an incredibly well executed response."

She said everyone who was taken to hospital has been released. She added that a few people who were more seriously affected may need follow up treatment such as being placed in a hyperbaric chamber to replenish their oxygen levels.