Fireboxes waiting for a roof

This is a rather sad image, copied from an out of focus print, but it shows the construction at an interesting stage. The gaps at 1 and 2 are the apertures through which all the flames must enter the chamber and although the numbers looked OK the small physical width bothered me. There is not much chance of the bricks visible here moving to close these apertures, but care must be taken to make sure the bagwalls do not lean out and effectively close the gaps. Loose bagwalls always lean out towards the flames, so accidental restriction of these apertures is a real danger. The next step is to put the floor arch over the two fireboxes.