Two Kapolei High School students were arrested, and an employee was sent to a hospital with lightheadedness and nausea after a plastic bottle exploded in a campus restroom just before noon yesterday.

The two 14-year-old males were arrested for investigation of reckless endangering and released pending investigation, a police spokeswoman said.

The explosion, caused by what firefighters described as a "chemical pressure bomb," happened in a boys’ restroom in "G" Building.

Two adults, both of whom appeared to be security guards, were treated for chemical exposure at about 1 p.m. yesterday, said Bryan Cheplic, spokesman for the city Emergency Services Department.

One of the injured, a woman in her 30s, was taken in stable condition to a hospital, Cheplic said. A man who appeared to be in his 40s was treated and released at the scene after complaining of eye irritation.

It appeared that neither person came in contact with the chemical, but they were possibly affected by the vapor, Cheplic said.

Fire Capt. Terry Seelig said it appeared several other school employees were exposed to the vapor but were not injured.

The explosion was caused by a chemical reaction from the mixing of household chemicals such as corrosives and oxidizers, he said.

"It’s a real thoughtless and definitely dangerous thing to have done," Seelig said.

It is hard to time or predict when a mixture of chemicals like that might explode, he said.

Kapolei Principal Elden Esmeralda said disciplinary action will be taken against those responsible.

"We want to provide a safe campus for everyone," Esmeralda said.

After emergency personnel identified the source of the explosion, the school released its nearly 2,100 students about five minutes early, before the scheduled 1:35 p.m. bell, so a hazardous-materials crew could wash down the affected area, Esmeralda said.

Sandy Goya, state Department of Education spokeswoman, said police were sent to the campus to investigate the incident.

"Everybody seems to be fine," she said.

The incident was similar to a chemical explosion at Aiea High School in February 2009 that caused minor injuries to two adult campus employees and two students. That incident, which also involved chemicals in a drink container, prompted a school lockdown for about an hour.

Star-Advertiser reporter Mary Vorsino contributed to this report.