The helmet is made of a material that is strong enough to withstand the impact of the force exterted by on some falling objects upon contact, without breaking apart/disintegrating.

This causes the falling object to be deflected and land elsewhere.

So it prevents the falling object from directly landing on/hitting the worker's head and also absorbs some of the impact/force.

The worker's head avoids the full impact/force and therefore the physical injuries/trauma sustained is reduced, as compared to not wearing a helmet.

For these type of questions energy conversion is important they award marks for that. Then one can continue on to talk about the impact on the helmet. These type of questions have become trending questions in the PSLE

http://www.livephysics.com/tools/mechanics-tools/solve-problem-related-impact-force-falling-object/

This link shows you the relationship between kinetic energy and force.

So you can mention that the object which possesses kinetic energy woulld therefore have an impact force upon in contact with the helmet

agree with Banana Republic Of Ireland

Energy conversion is important , but link between KE and impact force has to be drawn in the answer i.e explain how KE translates to having impact force. Having KE doesn't say anything about what happens to the worker or helmet unless you link it to the force part