Hey Capt. Rex
The regs that cover the hearing issue are those that come from the Commonwealth WHS Act (2011), or those that fall out of it in the state the business is registered in.
In Aviation, the responsibilities associated with WHS are often seen as an embugerance. I certainly saw it that way during my 40 odd years in aviation, but if your SMS doesn't cover the WHS requirements then your company is in for a whole world of hurt. That's why you saw COMCARE guys crawling all over the fuel truck on Channel 7 and not CASA guys.
As I understand it, the security guys have no specific rights to enforce the WHS regs UNLESS they have been delegated that task by the business. Which business, I hear someone ask? Tarmacs are complex when it comes to who has the 'duty of care' under the Act, given the number of players. If a WHS claim is made, who is accountable? - the airport operator, the airline, the business whose equipment is emitting the noise?
In all cases your employer is accountable for you, so if the security staff have been delegated to ensure your company's staff have, and use, personal protective equipment (PPE) then they have a right, but if not, tell me to f@$k off. My guess is that it is the airport operator that has delegated this to the security guys, and given you are using the airport's facilities under their conditions of use, they are likely well within their rights.
T_cas is on the money here, however, .... treating the root cause. PPE is a low level risk mitigation control. The use of higher level tools, from what is know as the 'hierarchy of controls', is the way to go in high hazard environments. The highest level is to remove the hazard altogether. If that's not possible, one should consider engineering solutions, just as the Japs have done with the use of extra glass in their truck design. Additional 'administrative' controls, such as SOPs that require a 'blind spot walker', would also add depth to the control process.
Sad thing is, many see all this as too costly (in time and money) and simply the creation of 'safety nazis'. Once implemented, humans deviate from the use of the controls because they see them as time wasting (normalisation of deviance).
As a closing thought, ask the family of the poor baggage handler, who is now in hospital, whether additional control measures would be worth it.