eeh, this seems like a massive, dishonest stretch. If employees were forced out of the building and killed in the parking lot, on the highway, in their cars, etc., seems like that would be worse? Generally I'd assume if a tornado is approaching and you've got minutes to decide what to do, you should shelter in place.
It's one thing if the building doesn't meet coding standards for severe weather, or something, but honestly in natural disasters I think it's pretty hard to call someone a murderer. If a tornado is approaching my house and we've got minutes to decide what to do, and I take my family to the basement and the house collapses and someone dies, it'd be very unfair to say that I killed my family.