When discussing consultation and participation of workers in clause 5.4 of ISO 45001, the standard refers to workers’ representatives, where they exist. So, the ISO standard is not dictating that you have workers’ representatives, or how you determine them. The reason for this is that the rules for worker representatives in laws around the world are very different, and you must turn to the local laws if you want a definitive answer on how many worker representatives you need and how you choose them.
If you do not have a legal requirement, and wish to put worker representatives in place anyway, then how you choose them needs to be determined by you, the ISO 45001 standard does not have any requirements around this. A general rule of thumb for setting your own rules would be to ask yourself “How many representatives do we need, and how should they be distributed across departments, so that the consultation of all workers can happen effectively?” Remember, the production department is not the only place with OH&S rules and hazards.