I know that I have seen engineers design for a 250psf static UDL, but I do not personally think this is sufficient. I know the NBCC has a provision which is similar to this, with additional point loads required (I would think for exactly the kinds of outriggers you are talking about), however my copy of the NBCC is in Canada, so I can't exactly flip to the page right now...
I would suggest that you look at a combination of bridge and building codes. No matter what the minimum requirements are, the reality is that a Fire truck is not going to be pulling up nice and slow onto your slab, but screaming in and stopping pretty short.
I'll see if I can't lay my hands on a Kiwi code provision and post that for you...
Regards,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...