Fire boarding box steel

Hi - think I put this in wrong forum before - I've had some building work done and they've taken walls down and put steels up, including some box steels with 10mm plates welded on the bottom, above the new bi-folds.

I'm fireboarding the steels before BC come to inspect again and I'm happy how to do the I-beams (wooden noggins etc) but I'm not sure how to attach the board to the side and underside of the box steels (photos below).

I've got 15mm fireboard so it only needs one layer but I don't think there's enough room to batten the steel with self-drilling screws then attach to it as it will fowl the top of the door. The builder suggested 'sticks like s***' but I think BC will want to see some mechanical fixing.

Any suggestions would be great.

 

https://www.british-gypsum.com/~/me.../White-Book-C03-Steel-Encasements-Section.pdf

 

It needs to be mechanically fixed.

 

https://www.google.com/search?q=fix...XhmFwKHZrHDzkQ_AUoA3oECB8QBQ&biw=1280&bih=521

Andy

 

Here's a better link and more helpful than a mechanical answer

https://www.diynot.com/diy/threads/casing-a-steel-i-beam.246084/