I wonder if it’s feasible to keep a drum of this in the garage and spray it yourself around your property and home if a fire is approaching.(obviously actual fire prep like removing flammable material from around your home is better).

SDS for Phos-Chek (there are a few different Phos-Chek's)

https://www.fs.usda.gov/rm/fire/wfcs/products/msds/retard/ph...

I assume iron oxide is the red.

I wondered if the red dye I used for herbicides was the same, it's not, it's Rhodamine B from the SDS. It also makes poisoning far easier once I started using it.