Thanks, I was on a family visit, so no chance of any sort of setup!
I used the same technique as I use in a church, which is to make use of the (almost) ISO-less nature of the Fuji sensor (made by Sony). This means I can shoot at a low ISO and then bring up the shadows in pp, and have the same quality of boost to the shadows as if I had shot at a high ISO. The benefit of this is that it enables the highlights to be preserved. I did not want to blow out the window, and I definitely wanted to capture the flames and the red hot metal.
I believe Nikon sensors are also made by Sony, so the same technique may be useful with Nikons.
The main downside is that the image is almost unusable for preview purposes without some initial exposure adjustment. Here is the embedded jpeg included in the raw file with no adjustment applied.