Despite years of warnings and growing criticism, potentially hazardous fluorescent lighting units in the classroom are likely to hang above students' heads for a while to come.

A high-profile incident in October exemplified the dangers of this mode of illumination. At Toyo Elementary School in Hachioji, western Tokyo, an overheated condenser in an outdated lighting unit exploded and splashed toxic powder and liquid over the heads of students attending an art class.

A series of similar incidents across the country have since come to light, including two in Hachioji -- one at another elementary school in May and one at a junior high school two years ago.

Many Japanese schools still use florescent lighting units, which contain condensers that use toxic polychlorinated biphenyl as insulation, despite repeated warnings of their danger by an electric appliance industry group. The production of PCBs -- a carcinogen and an endocrine disrupter -- has been banned for nearly 30 years.

Students involved in the October incident were immediately taken to a shower to wash off the toxic material. They, along with the other students in the classroom at the time, have since undergone medical checks and have shown no signs of related illness.

Education authorities are increasingly coming under fire for failing to heed the warnings of the industry group and exposing children to potential health risks.

It could also be some time before the lighting units are phased out in classrooms because of the fiscal constraints local governments currently face.

"We lacked proper recognition of the dangers of PCBs," said Masataka Nishiki of the Hachioji Municipal Board of Education. "We did not report the previous two incidents because we did not think they were grave."

But they had been warned. The Japan Luminaires Association sent letters to municipal boards of education nationwide in 1988 and 1997, urging that PCB-laden florescent lighting units be replaced.

"Some schools replaced them, but most left old appliances untouched," said Atsuo Koyama, the association's executive managing director.

An Education Ministry survey in April also found that about 25 percent of responding municipal education boards said at least one of the schools in their respective districts still use the units.

About 18 million florescent lighting units with PCB insulation were produced between 1957 and September 1972, when the production of such appliances was terminated, Koyama said.

Even without considering the years of ignored warnings, Koyama said he is especially appalled that such outdated equipment is still used in schools.

"The duration of lighting appliances is about 10 years, 15 years on the outside," he said. The unit that exploded at Toyo Elementary School was made in 1967.

Dai-hachi Elementary School in Kashiwa, Chiba Prefecture, was the scene of a similar incident in September. Schoolmaster Hiroshi Ota said: "At the time of the incident, we had no idea it was PCBs. We did not even know that such a chemical substance was used in the appliances.

"I have no recollection of receiving any warning about such a danger."

Central government officials are also quick to deflect blame. Despite the meticulous control the Education Ministry usually exerts over schools, the ministry claims that local authorities are primarily responsible for school maintenance.

"Basically, it is the responsibility of those who set up the facilities. That is, in the case of municipal schools, municipal authorities," one ministry official said. "At a time when the central and local governments are placed on an equal footing, we have no authority to order them to replace their appliances."

Municipal authorities receive no monetary assistance from the central government to address the problem, however.

Currently, there are some 4,300 PCB-laden lighting units in 34 municipal schools in Hachioji. Their replacement, which is scheduled by the end of the month, will cost around 95 million yen, a city official said.

While that may not appear an outrageous amount, city officials still had to scramble to raise the sum, which accounts for roughly 25 percent of the city's annual maintenance budget for its 106 schools.

"It's tight," said Nishiki of the municipal board of education. "We have to postpone other repair work to foot the bill. We also have to ask for a supplementary budget."

Noting that other municipalities face the same problem, Nishiki said, "We wish the central government would provide financial assistance."

The Education Ministry, however, remains intransigent. It says central government subsidies are for large-scale reconstruction projects and the replacement of hazardous lighting units does not qualify.

"Do we have to give money when glass breaks? No," one ministry official said. "It's the same thing (for the lighting units). . . . It's a job for municipal authorities."

Yet, Miyako Okabe, president of Toyo Elementary School's parent-teacher association, said the central government should share the responsibility for years of negligence and provide financial assistance to facilitate quick replacement.

"It has to because it is mandatory education and children have no choice but go to those classrooms. Their safety should be given top priority," she said.

Masaaki Hosomi, a professor at the Tokyo University of Agriculture and Technology, played down the potential danger and urged children and their parents not to overreact.

"If it is wiped away quickly from the skin, I don't think it will cause any serious problems," he said.

One drop of liquid inside a condenser has about 50 micrograms of PCBs -- about 25 times what people naturally ingest through food in the course of a day, he said. He added that unless PCBs are swallowed in large quantities, there is no cause for concern.

Having said that, however, Hosomi still expressed anger that authorities have failed to rectify the problem.

"Although the risks are relatively small, there are still risks," he said. "Children are not responsible for their exposure to danger."