Isopropyl alcohol

I bought these fireplace logs and in the center of the logs is a tray that has an area for 3 cans of what they call real flame, this is a sustance which contains isopropyl alcohol and the company states that it is safe to burn in an unventilated area. I have a ventless fireplace that did contain gas logs which I have since capped the gas line and removed the gas logs. Could you tell me if this Real Flame substance is safe to burn. I did notice that I got a headache and had a little bit of trouble breathing. I didn't have a major headache but none the less I was curious.