Given the general toxicity of handling flamable liquids, let alone their potential for toxic outgasses, I would assume this is a major part of the issue, not counting the possiblity of contact burns and the like.
Like you, I didn’t find anything specifically regarding these heaters, but those are my first impressions. You may find an electric space heater (like the ceramic heaters) to be a safer alternative.
Good luck in your search…
