Dr. Richard Weiland said all eight patients brought to St. Francis — six adults and two children — appeared to be suffering from exposure to a non-toxic, noxious agent such as propane or butane, and showed symptoms of coughing, congestion, weakness and light-headedness.

"Whatever happened happened to a bunch of them," said Weiland. "I don't think it was mass hysteria. But the explanations they gave — eye irritations, headache and weakness — sound like exposure to some type of volatile gas."

Weiland said the adults appeared to have been more affected than the children, possibly because they had been exposed longer by remaining in the classrooms to evacuate the children.

Twenty-three children were taken to Kapi'olani Medical Center at Pali Momi.

The Pali Momi patients, all of them children — and all found to be in good condition — were released to their parents by 12:30 p.m., said Michael Hershberger, nurse manager of Pali Momi's emergency room.

"They didn't seem to be scared," he said. "By the time they arrived, we had lots of parents waiting for them."

Classrooms at Makakilo Elementary were evacuated not long after students and staff complained that the odor made them sick, but the school was not closed.

Firefighters and paramedics were called to the school about 8:45 a.m.

According to Honolulu Fire Department spokesman Capt. Kenison Tejada, the Fire Department hazardous materials unit was at the school for nearly three hours.

"The whole time we were there, we found nothing," Tejada said. "All our tests were negative."

"Some of the kids had headaches, some had nausea, some had mild shortness of breath," said Dean Nakano, city Emergency Medical Services district chief, who was on the scene. "But some of the adults were symptomatic, so there is a strong possibility that there was something in the air — although Hazmat said they were unable to find anything."

Most of the cases came from rooms in the school's Building C, which the principal ordered evacuated, Tejada said.

Firefighters then decided to check the entire campus and see if they could find the source of the problem.

"We don't know if some cloud passed through the school or what," he said. "They don't use gas at the school. We called the gas company to see if they had been doing any kind of work in the area, and they said negative."

Greg Knudsen, a spokesman for the state Department of Education, said students were taken to the library on the school's lower campus and were being sheltered there, but that classes had not been canceled for the day.

Knudsen said the school experienced a similar problem in the past, one that was later attributed to a neighbor spraying chemicals in his yard.

Knudsen said the all-clear was issued at about 10:30 a.m. and classes resumed.

Investigators are calling it a "transient release" of a noxious substance, Knudsen said.

Because Campbell Industrial Park, the island's largest heavy industrial area, is downhill from the school, there were concerns initially that a cloud of noxious industrial gas may have floated over the Makakilo Elementary campus, Knudsen said.

But the wind was blowing toward the industrial park yesterday, which would tend to rule out the park as the source of the fumes, he said.