Crews at the Hanford Nuclear Site worked overnight after a tunnel, full of highly contaminated materials, in a plutonium uranium extraction (PUREX) plant collapsed Tuesday morning.

In a Facebook live video Wednesday, spokesperson Destry Henderson said several employees remained on scene overnight to begin preparing the area to fill the hole inside the tunnel.

Henderson said overnight air monitoring showed no sign of radiological release and no employees have been injured.

Officials said a collapsed patch of ground above the tunnel was larger than first believed, which contributed to the collapse. The U.S. Department of Energy said the collapse covered about 400 square feet (37.1 square meters) instead of the 16 square feet (1.4 square meters) first reported.

Hundreds of workers were told to go into a “take cover” position after the tunnel collapsed.

“We’re going to approach this slowly, safe and methodically,” said Henderson.

Henderson added that all non-essential employees that work north of the Wye-Barricade have been asked to stay home while crews work to repair the tunnel.