Using chemicals in room without window

[screamingatthemichaelangelo]

I need to tackle the black mould in our bathroom which is in the grouting and the sealant.

I've read a lot about HG mould spray and want to give it a try

However the bathroom is in a loft conversion and doesn't have a window, just an extractor fan. The bedroom window is some distance away.

Would it still be OK to use just with the fan running?

I used to do the same in our bathroom without a window. I'd open the nearest window and doors to it, run the fan and wear a paper mask.

Not ideal, but if you do it as quickly as you can safely and ventilate yourself straight after it's probably ok?