The main principle of safety helmet is to protect workers against impact by falling objects or struck by swinging object by energy absorption. Upon hitting by an object, the helmet dissipates some of the energy in the following mechanisms:
(i) Stretching of harness inside the helmet;
(ii) Partial damage of outer shell of helmet.
The remaining energy is then evenly spread around the head to reduce the hitting stress on worker’s head.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.