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 At Toyo Elementary School in Hachioji, western Tokyo, an overheated condenser in an outdated lighting unit exploded and splashed toxic powder and liquid over the heads of students attending an art class.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.