the rust was due to off gases of materials in fire like when sewer gas has Sulfur-dioxide/ acid etc it only takes seconds to do it. can also blacken copper etc

This actually explains a great deal of how irregular some of the oxidation is, probably matching the smoke as it wended its way through everything and ruined it.  Thank you for that insight.

Yes it will do that. iron oxide is iron oxide.

wow
I too am glad no one was hurt!

also quite surprised to see the plastic front door did not melt!

I'm glad nobody was in there.  We have dogs and cats, and they sometimes liked to spend the night in there.

Fire... is weird.  It did a number on (and destroyed) a lot of my plastic drawers for holding electronic components and chips that were on the wall behind my PC (see below) , and the top shelf where I'd kept the Solidoodles had a melted plastic UPS on top of all my filament storage (That's being thrown out, as I can't trust any of it after that much heat).  Plastic bags with spare printed parts up there were charred and melted but the parts inside were fine?

my corexy seemed to get the brunt of the heat and soot though, as the soot has apparently been powder coated to the aluminum extrusion and won't come off and the ABS printed parts on the gantry were looking pretty poorly.  I've cut off my chimera, titans, and solidoodle-compatible bed off of it for re-use later and scrapped the rest

And yet, my PC was running a -a foot- from the fire (the printers were ~8-10 feet away), and other than having to pry melted drawers off of the top, still works fine with some extreme scrubbing inside and out.  CDs and -paper- in the same area were also fine, while paper on the opposite wall charred.  The printers were even still on the network after the fire!

So while they've got pretty bad  oxidative damage, the -plastic- on all three SD4s was fine.   Fire is weird, thankfully.

also quite surprised to see the plastic front door did not melt!

evapro rust is very good stuff. glad everyone is safe!!!

The only thing in there that got evaporust treatment, in the end, were the lid hinges and the grub screws on the Y carriages.  I ended up replacing the Z rods (I've never seen polished rods come back still polished after rusting and de-rusting) and the rest of the screws and the like got replaced with new ones when I realized the only way to keep them from rusting in the future would be continued oiling.  The only thing that removes any remaining oxide coating faster than fire is evaporust apparently, haha.

All of my electronics gear, hand tools, three Solidoodle 4s, one delta, and one home-built coreXY frankenprinter with a Solidoodle Z stage were in there, along with all of my spare parts and the bits needed to reassemble my i3 and my mendelmax.  Oof.

I learned something about fire:  When it doesn't directly burn something, it rusts the crap out of it, even when I lubricated it in the past.   My hand tools got hit pretty bad with soot and rust on oxide-coated components, but my printers...

on two Solidoodles, all six rods were rusted, all bearings showed rust, and every oxide-coated fastener was rust.  The delta's rails, carriages, magballs, and fasteners were the same.  If it wasn't stainless, it rusted.

This kills the printer.

Weirdly, the SD4 -frames- were good, and the third SD4 had somehow only gotten rust on the Z rods and all the bearings and fasteners.  (I swear I kept them lubricated. :B)  Side and top panels only show rust where the embers burned the paint off, too.   But the insides were also completely coated in a fine, toner-like ash that smelled to high heaven and required acts of God to remove (I still can't get all of it off the SD4 frames, ugh!). 

I'm a terrible story writer, but the part I really wanted to share was this:

(please ignore my terrible bed adhesion, this is my first print in a long while haha)

after all the evenings and weekends I've spent since the fire cleaning and reconditioning equipment, I finally got the first SD4 fully operational again.  Feels good, even if my bedroom is my lab now for the time being. 

Also, a huge mountain of gratitude to Filastruder, who still happens to sell all the bits I need to reclaim my damaged Titan extruders and pretty much the entire delta printer's motion parts.  I love that thing almost as much as I love the printer I just finished fixing, haha

tl;dr - Fire ate my stuff, rebuilding everything sucks.  Fire is weird.  Rust sucks.