This happened on one of my ships.

The fitter and myself were working in the boiler flat. It was hot and sultry and we were sweating profusely. An oilman was working on the cylinder head platform right below the boiler flat.

While working with a spanner, it slipped out of the fitter's sweaty hands and after bouncing on the cylinder head hit the oilman's head. Unfortunately, he was not wearing a helmet.

But fortunately for him the spanner's impact was reduced as it had bounced on its way down and then hit him. A swelling on his head and some rest brought him back to his job.

Goes to show the importance of helmets.
hindustan institute of marine training chennai