The fumes can go on fire. I know a house where it happened.
You have a toxic mix of the flue gas mixing with the burnt silicone gases which can create a highly dangerous flammable mixture.
Silicone is not HETAS approved for use on sf stoves. And good job too!
If you have been advising its use then take a step back.
I didn't say I would or do. The stuff may give off noxious fumes, but I would be surprised if they were any more than unpleasant. If the stove is fitted with required clearances, I don't se how the dwelling will burn down - even if the silicon went aflame. I would expect it to shrivel thus failing to do the job required. I shall google.