Diocesan and Catholic school officials sought yesterday to assure parents that there were "no safety or welfare issues" for students in the arrest Friday of a longtime Bishop Canevin High School teacher on charges of possessing dynamite.

In a letter yesterday from Principal Kenneth M. Sinagra, parents were told that math teacher Nicholas Borrelli, 62, had been placed on paid leave, and a full-time substitute teacher has been hired.

Mr. Borrelli and his wife, Linda, 45, were arrested Friday by Munhall police, who found dozens of boxes of rifles, handguns and bomb-making equipment, along with three marijuana plants, in the basement of their home in the 4100 block of Harvey Avenue.

Police Chief Patrick Campbell said Allegheny County's bomb squad truck recovered dynamite and bomb-making materials such as fuses, tubing, end caps, mixing powder and wicks.

Chief Campbell said even though his officers arrived at the Borrelli home Friday afternoon, they did not finish removing the evidence and clearing the scene until 2 a.m. Saturday.

The Borrellis have been charged with possession of weapons of mass destruction, causing or risking catastrophe, criminal conspiracy and possession with intent to deliver.

"We are following our policies and the provisions of the teachers' contract in regards to this matter and the reported allegations," Mr. Sinagra's letter read.

According to correspondence exchanged yesterday between Don Teti, the Pittsburgh Catholic Diocese's assistant superintendant for secondary schools, and the Rev. Kris Stubna, its secretary for education, Mr. Sinagra first notified diocesan officials about the incident on Saturday.

According to the diocese, Mr. Borrelli has taught at Bishop Canevin since 1990.