Sounds ok to me Archie, the key features are the travel distance and the ventilation . It doesn't matter what shape the space is, a corridor is fine. The 7.5m applies to the travel distance for people, the space, and distance to the vent can be bigger than this. As Tom points out much work has been done one this by the SVA and there is guidance available on their website. Colt and others bring alternative solutions to the table, including smoke extraction systems often working on an intelligent pull or push system depending on the location of the fire. I have seen the lobby extended as far as 45m in each direction using such a system, it was approved despite my objections to the parameters used.
When I was trained in the 1970s they used to call these distances "the 7.5m dash" and it was explained that this distance was survivable in the unlikely event of the fire service needing to assist residents to escape. Hence the dash was shorter where the lobby was unventilated. It always sounded like a load of boloney to me.
