Many years ago I was quite used to doing odd jobs on my cars. I had an Injection Capri and it was time to change the front pads. I chocked the rear wheels with a brick for each and jacked the front up under the engine cross member - all on the tarmac pathway at the house. Sadly it had been warm and the sun was beating down. I changed one side and moved over to the other side and placed my feet on the ground either side of the disc to take out the old pads. Sadly the foot of the jack had bitten into the heat-softened tarmac of the drive and must have been leaning. The car gave a forward lurch and toppled off the jack. Fortunately my feet weren't under very far and the disc backing plate just rested on my leg above the ankle - just effectively holding it but not trapping it. I've never taken any chances since!