Here's a picture of the bomb rooms in the Red Zone. I had to draw in the marker for the final room since the markers disappear once you place them all.

Once you're in the rooms, just look for sections of the level with a full wall behind it (like a wall panel instead of the gears and machinery) and use the scanner. Make sure you're using the scanner and not the Unknown Device you get from one of the soul rewards.

This ♥♥♥♥ drove me nuts, hope this helps if you're stuck too.