[Jottle]

There is another option besides combustion. You are putting this stuff in offsite storage, I assume some sort of rental unit. Maybe the place has vermin,which would be drawn to the fog juice the same way they'd be drawn to the highly toxic ethylene glycol still found in many car antifreeze brands. Once the fluid leaks, and is exposed to filthy vermin, it would decompose naturally and produce the staining you're seeing on the reaper.

Incidentally,I blame left over fog juice for a rodent infestation in my garage about 8 years ago. They go after partially used containers, but I've never seen them damage any full and still sealed containers.

I appreciate the replies Kakugori and Blarghity. I thought it might be vermin too. But I have zero evidence of any vermin. The storage unit is free of droppings, and there's not any evidence of chewing in any of my boxes. The fog machines are stored in the black and yellow tough boxes pictured in the attached. The other pictures show examples of the fog juice damage:

This is an example of the fabric "burn" marks I described.


This picture shows how the fog juice container sits in the metal fog machine housing. There's no way for vermin to get at the bottom of the container because it's all metal in the back of the machine. And there is less than 1/2 an inch clearance around the plastic fog juice bottle.


This is a picture of the burn hole (now patched with white liquid nails) in the fog juice container. You can't really tell how it looked originally, but imagine a hot poker going straight through the bottom corner. The plastic had clearly melted and burned in this corner.


This last picture shows the black and yellow storage bins that have held my foggers these past two years. The white substance on the top black box is chalk that got on the box while stacking the boxes.

 

[Jottle]

Ah! Looking at the pic of your totes - those black ones that you store the foggers in have those flip open lids with the metal hinge pins don't they? Check the pins for rust and if it's there, you've found your answer.

You were close! I took a second look at the insides of the fogger. And there is an exposed metal screw that I didn't notice before right where the hole in the fog container is! So the brown coloring is indeed rust. However, this still doesn't explain the dozen rust spots on the fabric reaper (that one was only touching plastic), and it doesn't explain how the hole got into the fog container. It could very well be that there was a ton of pressure on the fog juice container on the top and over the whole year in storage the screw eventually pushed a hole into the plastic and allowed the fog juice to leak out all over the place and induce rusting on the screw and the container. That's the most likely explanation. However, the fabric rust/burn is still a mystery to me. It seems that every year when I store foggers with fog juice in them the juice ends up leaking out SOMEWHERE all over my stuff. Does this stuff evaporate? I suspect the motors/pump leak the fluid as well over time.

 

[Jottle]

It is combustible, just not at the temperatures a fogger works at. However, for years there have been warnings that a very limited level of combustion occurs in foggers, creating a number of toxic and carcinogenic byproduct compounds. The main byproduct to worry about is acrylamide. However,we consume far more of that in fried, grilled and baked foods than we'll ever inhale from vaporized fog juice.

So given that fog juice does combust at high temperatures, I wonder what temperature is needed to get it to that point?