A student at the exclusive Madeira school for girls near McLean was burned around the face yesterday when a caustic liquid toilet cleaner was poured on her head in what was described as an accident during a traditional school event.

The fluid, called Valsol, was poured on the heads of nine or 10 other students, but apparently none of them was injured, a school official said.

The injured student, reportedly from the Vienna area, was not identified. She was treated at the ACCESS hospital in Reston and taken home. Jean Harris, headmistress of the school, said the student appeared to have suffered a "bad burn" but said that she expected her to return to school shortly.

Harris said the school physician looked at the other students "and said they were fine." Some showed "a couple of tiny spots we were told don't amount to anything," Harris added.

According to the headmistress, the incident occurred about 5 a.m. yesterday at a ceremony to welcome incoming pupils onto the two teams into which the school is divided for intramural competition.

Harris said that the ceremony is traditionally marked by high jinks, and that it is customary for the older students to pour shampoo or something similar onto the new students' heads.

She said the student who brought the fluid to the event picked it up by accident in her dormitory room, which is provided with a connecting bath.

The event, which involved a small number of seniors and freshmen, was halted as soon as the mistake was discovered, and participants were placed under showers, Harris said.

"It was purely an accidental thing," she said. "We've never had anyone hurt [at the event] before."