At least 8" thick unless poured on virgin ground. A recently back filled area you should dig to a solid base under lift.
I have and ALM I have it since 1997 it is a very dangerous lift. The arm locks are threaded slip rods which wore out .Make sure you buy a lift with auto locking arm so they do not swing free once the car is in the air. Note the free swinging arms below . If the arms were gear locked once raised they may have survived.
I’m always very safe while under a car and agree I need one with auto locks.
I don’t think I would have grabbed onto the car like that. The one guy did the right thing and GTFO
