A recent inspection of the city's powder fire extinguishers found that nearly half of them failed the Shanghai Fire Bureau's tests, local media reported Tuesday.

Fire inspectors randomly tested the portable dry powder extinguishers at 47 public places in the city that are required to have fire extinguishers, including hotels, office buildings, apartment buildings and construction sites, said Zhou Meiliang, an official with the bureau. The bureau found that fire extinguishers at 22 locations failed to pass inspection.

Inspectors discovered fire extinguishers at 19 of the locations didn't contain enough fire retardant, according to a report in the Oriental Morning Post. At 14 sites, inspectors found extinguishers whose canister walls weren't think enough. Extinguishers at seven locations lacked the proper pressure.

"That can be dangerous," Zhou told the Global Times. "Fire extinguishers that don't have the proper pressure or canisters can explode."

In one case, a faulty extinguisher caused a fire to flare up during a test, according to the report.

Zhou said the fire bureau would ask management at those locations to replace the faulty extinguishers. He threatened to fine them 5,000 yuan ($783) to 50,000 yuan for not complying.

According to recognized standards, fire extinguishers should always remain at least 50 percent full.

However, depleted fire extinguishers are not an uncommon discovery in Shanghai. In June, the Jiading District Fire Department found that 140 fire extinguishers at a local supermarket were effectively empty, local media reported earlier this month. "We were surprised because the faulty fire extinguishers appeared to be certificated by their manufacturers," said the security manager at the supermarket, surnamed Zhang.