It depends on the what the platform will be used for. In the material handling industry I see 100 psf used regularly but this accounts for a lot more than just personel. This accounts for material build-up, etc. I have also seen heavier loads used when the material being processed is heavier than 100 pcf. I also think that 60 psf is reasonable if you are just looking at personel and tools, etc. In short I use some engineering judgement and see what I think the platform could see then design accordingly for 60 psf, 100 psf, etc. In general we use 100 psf quite often.