So, the doubt whether your Dominant/Top will in fact keep you safe? Or might this time decide to push you beyond your limits, or might not be able to keep you safe?

Fire play is never safe. There are ways to minimize the risk, but accidents can happen. If the batons have too much alcohol in them, it can run or drip, causing a fire in an unexpected area. I've seen pictures of fire play gone wrong, and it wasn't pretty.

Would you say you experience the fear most acutely before or during the edge play?

During fire play, the fear is most acute during the scene as it gets hotter. I'm more nervous before being whipped with a single-tail than during the scene. Once it starts, I'm fine. With suspension, I'm more nervous during the scene than beforehand. Being bound is calming, but swinging around is unnerving since equipment can malfunction.

You mention subspace and it makes sense to feel that after a time in the scene... and after. But does this mean you don't have any Other physical reaction to the fear beforehand?

I may feel a little nervous, but I also feel excited. It's hard to tell which feeling is stronger. Both cause a slightly increased heart rate. I don't fear the pain I signed up for, only that something could go wrong.