I think that is a very bad idea, because it is likely to have the opposite effect -- cool rather than scary -- so in effect you'd be teaching your kid pyrotechnics. After all, there's a reason why Hollywood flicks are full of explosions. I'm sure a 5yo doesn't understand whether it's sensible to play with fire indoors. Do you really want him to play with fire even if he only does so outside?
Why would you want to demonstrate flammability in particular? Solvents are dangerous, but not exclusively because they're flammable. To make them burn, you need several items; solvents and fire. But they can be dangerous on their own, e.g. by ingestion, and I'm sure you're not going to demonstrate that.
Have you told your child not to eat the detergent from the washing machine? You could use the same approach with any other dangerous material. Matches, detergents, any number of household and garden materials and tools.
I think demonstrations are very useful for things you want to encourage. But for discouragement, demonstrations can be impractical and counterproductive -- and potentially very dangerous on their own!
If you really want to demonstrate flammability, ask your local fire department when they do such demonstrations. That will help educate your child that only trained professionals should handle these things and that not even daddy dares it!