Silo spews cloud of dust over bus yard

A malfunctioning silo at a Charlestown cement company spewed a massive plume of dust yesterday, sending 61 bus drivers to hospitals with minor respiratory problems, coating about 60 school buses in a nearby parking lot with gray powder, and scrambling the afternoon bus ride home for thousands of students.

School officials said they could not use any of the buses in the Charlestown yard, approximately one third of the fleet. Buses had to be rerouted citywide, and buses scheduled for athletic events were redeployed to transport students home throughout the evening.

Michael Contompasis , interim superintendent of the Boston public schools, warned families to prepare for significant delays. Schools in northern parts of Boston were likely to be affected the most, officials said.

Work crews planned to clean the buses last night and alert parents by telephone if buses would be late this morning.

The dust came from Lafarge North America, whose six silos tower over the firm's Charlestown plant. According to officials, the dust collection equipment on top of one of the silos malfunctioned at about 12:45 p.m., causing it to spew onto the adjacent bus yard operated by First Student, a Cincinnati-based company that transports 32,000 students in Boston.

The air was so thick with dust that bus drivers could barely see their hands in front of them. Frank Geraidi , who emerged from Boston Medical Center wearing blue medical scrubs and carrying his clothes in a black trash bag, said he and two friends were walking in the bus yard when a huge cloud of dust dropped on them. Geraidi ran inside a school bus and waited for the dust to settle.

``It looked like snow -- gray snow," said Geraidi , 56, of East Boston.

Suffering from burning eyes and a dry throat, Geraidi was examined at the hospital and released.

Bus driver Judith Alexis , a six-year veteran, said she was inside the bus company's building at the time of the accident.

``All we heard was a noise, like a boom," she said. ``We went outside, and all we saw was white."

The substance was identified by emergency officials as crystalline silica, a nontoxic cement dust. Most of the 61 drivers taken to hospitals had minor chest, eye, and respiratory irritations, said Lieutenant Christopher Stratton of Boston Emergency Medical Services.

The dust could worsen symptoms for those who suffer from preexisting conditions, such as asthma or emphysema, medical specialists said.

``The initial effects are mostly irritants to skin, eyes, mouth, and airway passages," said Richard D. Zane , co director of the Department of Emergency Medicine at Brigham and Women's Hospital, where some 20 drivers were treated.

Because the drivers were not exposed to the dust for an extended period, Zane did not expect there to be lasting health effects.

Ted Rainha , Boston terminal manager for Lafarge, promised to help with the cleanup.

``I want to express our concern for the health and safety of those people affected and our regret at the disruption to the transportation schedule of the Boston public school system today," he said in a statement.

John R. Ellement and Maria Sacchetti of the Globe staff contributed to this report.