Fire Escape Rusting

Not IME.

Well, grit blasting is probably the best idea. It depends on how much the OP has to do.... it might cost a few hundred, I'd imagine. It would get all the fiddly bits done nicely...

Ah.. you may well be right, in which case I have been talking bollocks..

Phosphides and tannates. At least you get tannates if you use the good stuff (usually white) rather than Jenolite or plain phosphoric acid.

Not bad as a preparation of existing rust you can't remove, but it has limited resistance to rusting in the future. In particular it doesn't have the electrolytic protection that zinc coating (plate or paint) offers.

Chromates are useful for aluminium (the yellow-green stuff) but they're horribly toxic.

A wire brush on an angle grinder is a lot more effective than a slower one on a drill. But use a good quality knotted brush, a thick apron and a faceshield (not just goggles) or you get peppered.

Grit blasting is certainly the best, and the only practical way to get into the corners - but a portable rig is messy and far from cheap to hire. Even a larger "hobby" compressor would struggle with this sort of work too.

I've used jenolite FIRST to stabilise the rust, then a zinc primer.

Having used a grit blaster attachment many many moons ago, I have already ruled that out.

The Balcony thing is just too big and fiddly. The amount of grit required and the mess on the floor would be a nightmare. It's about 9m x 3m. See following