It seems to me that your argument points to never using PPE as it is never any use. I wholeheartedly agree that PPE is a poor risk control for all the reasons we all know and as a last resort but sometimes there is no other reasonably practicable way to control the risk. I still maintain that the severity of harm can be reduced by use of PPE. The likelihood of the brick falling is not affected by the use of the hard hat and it will still hit the first thing it comes in to contact with. The severity of harm resulting from the impact is affected. However, we are arguing about fine points and in reality, what we are all seeking to achieve is preventing the incident from causing significant harm. May we all have great success in that endeavour.

Where did I say that wearing a hard hat reduces the likelihood of getting hit? All I said was that if a brick falls and hits you the likelihood of serious injury is reduced. You seem to be saying that likelihood falls to zero. That is the bit I disagree with. OK, I am willing to accept that if a single, standard sized house brick falls and hits someone who is wearing a good quality hard hat in good condition; and that person is standing upright and looking straight ahead; and that person has no illness or condition that makes them vulnerable to a physical impact of that nature; then the likelihood of them sustaining a serious injury is probably zero. However, I assumed we were talking about risk assessment in the real world. In summary. I am very uneasy with ever saying PPE will reduce severity. It is the very bottom of the hierarchy of control, and should only be considered after all other types of control. In the real world we will never do a risk assessment for a single standard house brick hitting someone on the head, would we?

Depending on your definition of risk, and there are dozens of definitions, then both points of view regarding the brick/head can be correct. If you define risk as "the likelihood of a specified outcome occurring.." - and your specified outcome is 'serious head injury', then wearing a hard hat will reduce the likelihood of that specified outcome occurring. The specified outcome is the consequence you decide to be the plausible worst case scenario if the hazard is released, after examining which current controls are in place. In other words; if I observe that there are toe-boards, brick guards, hard hats and a potential brick fall height of only 1 meter, then my 'specified outcome/consequence' would not be serious head injury. HSE.gov.uk, ISO17776, ISO31000, OGP, etc,etc all propose different definitions of risk