Methyl hydrate is probably methanol aka methy alcohol. That interpretation is based on the context and chemistry.

Another possibility is a clathrate of methane and water, which is found in deep oceans and wells. Basically, that is a crystalline form of methane (which is normally a gas) that forms under pressure with water. It is relatively stable and has been considered as a way to transport methane easily. Methane hydrate (not methyl hydrate) is a more appropriate name for the clathrate.

As for the carcinogenicity of burning acetone, think of all the other things that are being burned in our engines, such as nitromethane, methanol, oil, and various additives to the oil. All of those things produce active chemical species when burned and should not be enhaled continuously. Just don't run them in a closed room. Even toasting bread produces carcinogens.

John