Chris I would think due to the conditions and heat this must class as a dangerous occurence. Why no radio contact - this must be investigated and procedures put in place to ensure this can not happen again Only after having the findings of the investigation will a true picture appear of why failings took place

Disagree. You're not asessing within the context of the sitaution and environment. Quote - "this cannot happen again"??? Well vehicles get bogged down, radio contact can lost (it's not the middle of the city there!!) and people may have to walk out of a situation to get help. Get real. The potential for this sitaution in future should be assessed and then procedures taken to minimise it but in remote environements a certain amount of resilience is required. So are the drivers adequately trained in 4x4 driving, do they carry kit for getting out of bogged down situations (winches), do they carry survival odds and sods (food, drink etc) and skills to survive if they do get stranded, is there a log of where they went and what time they were due to return etc. A vehicle getting bogged down is not a near miss nor a adangerous occuence - it is a potential risk when driving off road but unless the vehicle actually rolled these vehciles are capable of quite lary angles. Not being able to make radio contact and walking back to base is also not a dangerous occurence nor a near miss - no one was in danger by doing it (they did not collapse, were not attacked etc) Walking 8km is hardly extreme and although we are not used to 33 degrees in the UK, I have hiked in 40 deg heat ok abroad. If you are sending employees out into the remote outback (I assume it is remote) then they should have the kit and the knowledge to deal with that. That is what you should be checking was adequate. Chris's suggestion that a vehicle should not be allowed to get bogged down and radio contact should not be lost is pure idealism.

I would suggest there are three different events that need to be investigated. 1. The vehicle becoming bogged down. If there was not damage to the vehicle it is probably a near-miss. 2. Radio failure. Given that the radio performs a critical safety function I would say this was a dangerous occurrence. 3. The Operators walking 8km. The classification of this would depend on the risk assessments you have for people working in 33*C heat. If this says death is likely, then it would have to be a dangerous occurrence. If you hadn't carried out a risk assessment you have a systems failure, which may need to be classified differently.