Three members of a cruise-ship crew were killed by toxic sewer gas yesterday as they repaired a waste pipe aboard the ship that had just...

LOS ANGELES — Three members of a cruise-ship crew were killed by toxic sewer gas yesterday as they repaired a waste pipe aboard the ship that had just returned to the Port of Los Angeles.

No passengers were injured, but 19 other crew members from Royal Caribbean’s Monarch of the Seas were examined for possible exposure to the toxic gas, authorities said.

Passengers were leaving the ship at the time of the incident, the company said.

The crew members were removing a pipe from the sewage system at about 9:15 a.m., apparently believing the pipe was empty. But when they removed it, about five gallons of sewage and an unknown amount of gas in a propeller-shaft tunnel leaked, Royal Caribbean officials said.

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Officials first identified the gas as methane but later determined it was hydrogen sulfide, which occurs in sewage, said Barbara Yu, a supervising hazardous-materials specialist for the Los Angeles County Fire Department.

The crew members were not wearing protective clothing or masks.

Coast Guard Lt. j.g. Tony Migliorini said the repair crew could have worn special masks but they usually are not required for such operations.

Fire officials said the repair was being done in an isolated, enclosed space and most of those who later reported feeling nauseated had not been in the space but decided that they wanted to be checked out.

The incident occurred after the ship returned from a cruise with about 2,500 passengers and 850 crew members, said city Fire Department Battalion Chief Lou Roupoli. The ship makes regular trips down Mexico’s Pacific coast.

Paramedics took seven injured crew members to hospitals. Two of the injured were ship physicians who performed CPR on the crew, said Melissa Kelley, a fire department spokeswoman.

Authorities said they were removing passengers from the ship, which had just docked after a trip to Baja California.

Royal Caribbean’s Web site described the ship as recently renovated and able to carry 2,744 passengers and 856 crew members.

Royal Caribbean said the Coast Guard and local authorities were immediately notified and the cruise line “will fully assist in the investigation of the incident.”

Passenger Yvonne Powers of Sacramento said she was about to disembark with her daughter when she saw men in hazardous-materials protective gear going downstairs. “Nobody said anything to us,” Powers said.

Later, after they had left the ship, there was a public-address announcement that there had been a mishap and that “we’ve got it under control,” she said. The 14-year-old Monarch of the Seas is based in Los Angeles harbor and registered in the Bahamas.