That is sort of intentional(the blast radius). There wouldn't be enough of a reason to avoid using the TNT if you survived it unscathed, and I planned on kind of having this be a sacrificial fuel option when I add co-op eventually after this jam.
I also plan on adding hallucinogenic smoke options by then, where there'll be certain hazardous fuel that doesn't exactly kill you.
But in your honest opinion, do you think it's too punishing? As in, would it be better to have a little leeway to throw it into the furnace without dying? And I also wonder if it's in accordance with the rules to chance it if it really is top punishing or frustrating