SAN FRANCISCO (BCN) — A carbon monoxide leak that hospitalized four hotel guests in San Francisco Thursday night has been traced to a nearby Indian restaurant, a fire department spokeswoman said Friday.

Crews discovered a water heater leaking at Amber India restaurant at 25 Yerba Buena Lane Friday after firefighters noticed a “strange looking” pipe in the establishment, San Francisco fire Lt. Mindy Talmadge said.

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With the help of the Department of Building Inspection, crews shut down the heater and put a patch over where they believed the leak was located, Talmadge said.

The water heater was then turned on again, and carbon monoxide readings shot up again in the restaurant and neighboring Marriott Marquis, where the four people got sick on Thursday.

KCBS’ Bob Melrose Reports:

Officials discovered Amber India’s venting system was leaking carbon monoxide into a shaft between walls in the hotel. When the heater was turned on again, readings in the shaft skyrocketed.

Normal carbon monoxide levels are about 25 parts per million, Talmadge said, but readings in the hotel were well over 250 parts per million.

“Anything over 25 is not good,” she said.

A person can get sick with higher readings, but Talmadge said it’s unclear how high it needs to be for them to get sick.

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“It depends on the person, but none of the four affected were in any life-threatening danger,” she said.

Amber India no longer has hot water. The gas line that powered the heater has been shut off until officials can conduct a full investigation and repair the damage, Talmadge said.

“They’re not going to have access to this gas anymore. When the line was stopped, the readings went down to normal,” she said.

The restaurant stopped serving customers after lunch Friday because of the lack of hot water, but managers expect to resume business at about lunch tomorrow, according to an employee.

The four guests at the Marriott Marquis were flight attendants staying in four separate rooms at the hotel, located at the intersection of Fourth and Mission streets, hotel spokesman Sam Singer said.

Around 10:40 p.m., the guests complained of flu-like symptoms, and the hotel’s doctor was contacted.

The four guests were transported to San Francisco General Hospital and St. Francis Memorial Hospital, where they were doing well Friday morning, Singer said.

“Initially we believed it to be the heating system in the rooms,” Talmadge said. “But after further investigation, we determined it couldn’t be the heating system because they use a steam system, which doesn’t use carbon monoxide.”

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