Students at Ambridge Area High School were evacuated to the football field for more than 2¹/₂ hours yesterday after police received a bomb threat just after 11 a.m.

A police search of the school's four floors, including the basement, by the sheriff's department and neighboring agencies using bomb-sniffing dogs found no bomb and students were readmitted to the school at 1:40 p.m.

School Supt. Dr. Kenneth Voss said that 970 students in grades nine through 12 were ushered by teachers to the bleachers at the far end of the football field.

Dr. Voss said the police and the fire department went to the school on Duss Avenue where Principal Alan Fritz and the teachers oversaw "a calm, orderly evacuation."

The sheriff's department and neighboring agencies responded with bomb-sniffing dogs and searched the school's four floors, including the basement.

Once outside, many of the students used their cell phones to contact their parents. Dr. Voss estimated that 40 to 50 percent of the students were released to parents.

Dr. Voss said it was the only time the school has had to be evacuated in his six years as superintendent.