EE WAS OPERATING THE M318 CATERPILLAR RUBBER TIRED EXCAVATOR, LOADING MATERIAL FROM THE NO. 1 SUMP INTO A M45 MACK TRUCK OPERATED BY OTHER WHEN HE HAD FINISHED LOADING THE TRUCK, HE TRAMMED TH EXCAVATOR TO THE PARKING LOT OF THE TRUCK SHOP AND SHUT DOWN THE ENGINE OF THE EXCAVATOR. HE STOOD UP IN THE CAB AND APPEARED TO COLLAPSE, FALLING OUT OF THE CAB COMPARTMENT OF THE EXCAVATOR