In a Black Saturday context, over 90% of the pumping systems for houses that were supplying water for active defence or spray systems failed during the peak of the event.

And that was everything to do with ingestion of embers into the filter, fuel lock because the pump itself got too hot, embers and debris landing on the electrical systems and burning it out, and/or simply the air was too hot that was ingested into the pump and the pump simply stopped functioning either temporarily and needed to be manually restarted.

Pumps failed quite prolifically because the petrol and diesel powered pumps couldn't handle the heat of the day, and in some cases the heat of the day and the heat of the fire.

Really dense smoke that has most of the oxygen consumed will cause the pump to drop significantly in power and possibly cut out, but it won't permanently immobilize the pump.

Diesel doesn't experience vapor lock like the petrol ones, so the vapor doesn't create the problem in the carby. So, they're a bit less heat affected and can run to a slightly higher ambient temperature than the petrol ones.

However, the diesel ones are just as susceptible to ember attack or surface fire as the petrol one. So, if the diesel pumps suck in embers into their paper air cleaners, it'll cause a flaming ignition of that paper air cleaner and that will snuff out the diesel motor, just the same as it would a petrol one.

The diesel ones do have a slight advantage, and that is around the prospects of safely refuelling them mid-fire.

A lot of pumps are supplied with enough fuel to operate for an hour, possibly two, and they’re often connected to a water supply that can last much, much longer than that. And having that tank full in the first place is step one, but the prospects of refuelling a hot pump motor while there's active embers in the air isn't very exciting, particularly if it's a petrol pump.

I'd encourage that approach (of having a larger external fuel container) and actually to remotely mount the tank, like off the pump itself. That certainly avoids the additional risk of heating from the pump and the heat feedback, which is one of your problems with vapour lock for your petrol pumps. And it also solves the issue of vibration.

Poly pipe prolifically fails when it's above ground and exposed to direct flame.

It's actually quite challenging to find spray systems that worked and persisted throughout because they're quite rare. But where they do show up as being quite effective are metal pipework, wherever it's above ground. And very frequent spray heads either mounted on the house or in that perimeter array projecting back onto the house using an impact sprinkler are the other key ones that really do work.