WAILUKU, Maui — An autopsy has determined that Punahou School science teacher Jeremiah Johnson, 36, died from accidental drowning while on an oceanography expedition with students over the weekend.

Maui County medical examiner Dr. Anthony Manoukian, who performed the autopsy yesterday, said there was no sign of natural disease that might have contributed to Johnson's death Sunday off Kaunolu Bay on the southern coast of Lana'i. Preliminary toxicology tests indicate no alcohol or drugs in his system, he said.

Johnson, an experienced diver, was one of 14 adults accompanying a group of 98 Punahou students on a weekend voyage aboard the 145-foot charter vessel Rapture.

He was diving with only a swim mask in about 40 feet of water when he apparently ran out of breath, Manoukian said.

The teacher was brought to the surface by boat crew members, who were unable to revive him.

Johnson, originally from Kaua'i, joined the Punahou staff in January 2003 and taught high school environmental science and marine biology.

A service has been scheduled for 6 p.m. today at the Punahou School chapel.