Is the canvas a fairly close weave or is it a loose weave like a drop cloth?
OK, I'm going to try not to bore you..... Sorry in advance
An exothermic reaction gives off heat, if that heat can't dissipate it can build up to the flashpoint of whatever materials are around.
The flashpoint of linseed oil is 206C or 402F (data sheet
Here .
If you have a bundle of cloth soaked with linseed oil and in a fairly warm environment (full sun or a heated room )then it getting over 206C is relatively easy.... However, if you take the same cloth and hang it up in cool shade the heat should dissipate as fast as it is created.
I always peg my oil rags up in a breeze in the shade and have not had any problems.
The best place to work would be something like a carport or a Dutch barn (Pole Barn?), somewhere shaded that the wind can pass through.
This is a messy job and the time it takes for the oil to cure isn't all that easy to predict, depending on a lot of factors. I've made oilcloth in a few days and other pieces of roughly the same size have taken weeks. Cold and damp slow it down, a warm breeze speeds it up.
I tend to hang cloth one edge up, pegged or pinned to a cord. ETA a taught cord, you're trying to prevent sagging.
I will either paint the boiled linseed oil on or dunk the fabric and wring it to get all the fibres wet (if you wring it you will need to smooth all the creases out of the cloth before drying ).
Then leave it hanging for a while, until it stops feeling oily and starts feeling tacky. You don't want to leave it too late as the next thing you're going to do is hang it up the other way to finish curing. This ensures that you don't end up with the bottom edge saturated and the top edge dry......... If you do end up with a dry edge , just treat it again and hang the cloth with that side at the bottom.
Use only Boiled linseed oil and don't dilute it.
The Boiled oil has additives to speed up the cure (it used to be lead oxide and a few other nasty things, its now less nasty stuff, but I still don't use it on food related stuff).
Diluting it makes it easier to apply a thin coat and can cause it to dry before its cured, this is not what you want.
You can clean up uncured linseed oil with washing up liquid, this is also the best thing to wash your hands and any brushes with. Launder your clothes as soon as you're finished otherwise you could end up with a waterproof patches on your tshirt.
Tomorrow, I'll bore you with Beeswax