The diving boat that caught fire on Labor Day off Southern California, killing 34 people, was among hundreds of small vessels exempted by the U.S. Coast Guard from stricter safety rules designed to make it easier for passengers to escape, according to a newspaper report Monday.

The Conception was one of 325 boats built before 1996 and given exemptions from standards imposed on new vessels, according to records cited by the Los Angeles Times. The newer rules required escape hatches at least 32 inches wide and illuminated exit signs.

The Conception, built in 1981, had a 24-inch hatch and no illuminated signs.

It’s unclear whether such measures would have made a difference on the Conception, the newspaper said. Crew members on deck said they were unable to reach passengers trapped in the hull below because of intense flames. It was the worst maritime disaster in modern California history.

U.S. authorities are conducting criminal and safety investigations into the fire that killed all 33 passengers and one crew member sleeping in stacked bunks below deck. The blaze’s cause has not been determined.

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