Impairment vs Risk vs What Should an Employer 'Reasonably' Know...? Hi Rachael
From a health and safety perspective, the answer seems pretty simple to me. Once you know about Bob's late night activities and potential fatigue, your organisation has no choice but to deal with it.
Section 22 of the Health and Safety at Work Act defines the term "reasonably practicable". Relevantly, it requires PBUs to do "that which is, or was , at a particular time, reasonably able to be done in relation to ensuring health and safety, taking into account and weighing up all relevant matters, including....(c) what the [PCBU] concerned knows, or ought reasonably to know, about the hazard or risk".
Fatigue is an obvious hazard, and the risk you have identified (even if inadvertently) is that Bob may be fatigued when he works because he is regularly not getting enough sleep. This means you need to consider - and do - whatever can reasonably be done to ensure health and safety for Bob and people who may come into contact with him while he works.
I often finds it helpful to turn the question around, so let's take a hypothetical situation. If Bob is involved in a serious traffic incident tomorrow, and WorkSafe and the Police investigate, they will likely ask to see the E-Roads data from his vehicle for the day and, potentially, a period like perhaps 1-3 months before, the incident. How comfortable are you that you can answer questions from them about Bob, and about what your organisation did to manage the risk of him working while fatigued? My guess is "not very", and that if WorkSafe or the Police ask why the organisation allowed Bob to work knowing he regularly had only three hours sleep, especially if he only had three hours sleep the night before my hypothetical accident, then you will struggle to persuade either regulator that your organisation did all that was reasonably practicable.
I should add, for completeness, that Bob's sleep pattern may not be a concern. Some people naturally sleep less than others, and others sleep a little during the week but catch up at the weekend without it having a material affect on their performance. These are issues you could usefully explore with Bob. Does E-Roads show any "red flag' issues about his driving and work performance?
I appreciate that initiating the discussion with Bob may be awkward, and that employment or privacy issues may arise. Others have made some good suggestions about that, and if in doubt I suggest you get some legal advice so the organisation follows due process and doesn't get itself in trouble. I don't work in those fields so don't know the answer.
Ultimately, you need to think about what your organisation can do to protect Bob from the risk of fatigue. Can support be offered to help him make better sleep choices (it sounds like that's what you're currently considering)? Can his shifts start later so he can sleep longer into the morning? Can a process be agreed with Bob so that if he has a late night he notifies a manager and doesn't come to work? Others smarter than me will have more ideas on this front.
Good luck!