Maria Young

Workers at the Catalyst Refiners site were decontaminating a tank Wednesday morning when the release occurred.

Nearby residents and schools were ordered to shelter in place.

Here's Kanawha County Emergency Management Director C.W.

Sigmund.

Sigmund says that at least 21 people were treated, including seven EMS workers.

What happened and why will likely be the subject of national, state, and local investigations.

For NPR News, I'm Maria Young in Charleston.