At our local pool they have a disabled swimming session, which we really enjoy.
They have an Oxford hoist and chair like in the picture. The chair splits from the wheels below the seat, to lift in and out of the water and disconnects from the lift so you can be pushed to the shower and changing room.
This week, I was strapped in the chair getting dried after showering and lent to the side slightly when the chair seat parted company from the wheels and i ended up on the floor. (unhurt, but one for the accident book!)
No one can say why it became unlatched. Has it ever happened to anyone else?