I've breathed fire with MCT oil (the storebought stuff that is basically liquid coconut oil). It's somewhat irritating, and I imagine if deliberately inhaled chronically it would cause harm.

C8 is really fascinating because, I reckon, it's too short to set off the inflammation cascade directly, so it would be up to macrophages to alert the body "hey this doesn't belong". However you still have the usual risk from hydrophobic product in the lung.

Personally, I would use vegetable glycerine and nothing else if you can at all avoid it. PG is a bit more irritating than VG, but any short polyol is going to be diffused away into the mucous much more easily than hydrophobic products.

100% agree with the VG (Vegetable Glycerin) recommendation, you will have to add a small 20-30% percentage of PG Propylene Glycol to decrease the viscocity (or alternately use pure VG and cut with small amount of normal saline but it won't make as nice a vapor) and then can use it in any actual vape device used for nicotine as these are meant to use water-based not oil-based mixtures.

For marijuana/hemp you can make a water-based tincture using VG as the solvent just using dried plant matter. A magical butter machine can do it, putting it in a bottle and shaking it up every day for a few months, there are likely other methods. It's similar to making a CBD/THC oil but instead using VG as the carrier.

Making your own tincture from decent-quality dried plant matter is the most economical and surefire way to know that it unadulterated and limited in contaminants.