doug - i think you hit the nail on the head when you stated people have stopped looking out for f/lifts - I agree that yes the opertaor MUST sound the horn- however as you stated in your own work place - not all sounds can be heard!
Perhaps the staff may need to be reminded before its not too late as to the danger's of Flifts and remind them that they too need to look out for their own safety also - after all the operator can only do so much! (Sound horn/ slow down)
A team effort is needed on both operator and pedestrian - Mirrors etc are fine - as long as pedestrians remember to use / look at them!