Feb. 18 (UPI) — A massive fire caused heavy damage to a warehouse in Abington Township, Pa. Monday night but all 60 of the employees inside the building were accounted for.

Witnesses said they heard an explosion at SPS Technologies when the fire started, and the blaze continued to smolder Tuesday morning.

“It’s still actively burning,” Thomas McAneney, Abington Township emergency management coordinator said, according to WCAU-TV.

The four-alarm blaze led to officials calling on residents within a one-mile radius to shelter in place because of the particulates generated from the fire.

Three school districts — Abington, Jenkintown and Cheltenham — all closed Tuesday along with private and religious schools in the area because of the fire. The Southeastern Pennsylvania Transportation Authority said the fire had affected services on two lines, Doylestown and Warminster.

Abington Township’s Fire Marshal’s Office is investigating the fire but a cause has not been determined.

SPS Technologies supplies aerospace fasteners and fittings. The company started as Standard Pressed Steel Company in Jenkintown in 1903.