I remembered there was a crash? A vehicle crashing into the wall of the Glee Club classroom? Or perhaps an earthquake? I'm not sure. But the building collapsed, injuring several of the members, but not too serious. Kurt has a metal rod impaled in his thigh.
They are trapped for a while, waiting for help.
Later, Will pulled out the metal rod to avoid risks of infection and with the help of Mercedes, they tried to stop the bleeding.
Thanks a lot to anyone who can find this!