H occupancy perimeter exterior wall access

[chris macko]

I've got a building with a 2 story mixer area and related staging and support spaces that will all be classified as H-3 (Class IIIA flammable liquids), as well as an identical suite of mixers and support that will be H-4 (highly toxic) next to it, separated by a rated egress passageway. Per 415.6, H-3 and H-4 occupancies need to have 25% of the perimeter on an exterior wall. In the case of multiple rooms within the same occupancy, and multiple types of H occupancy, how would you define those areas for measurement? Is all the H area looked at as a whole compared to the overall perimeter? Are H-3 and H-4 areas broken out separately? Is each specific mixer and storage room required to have its own exterior wall access?
It matters in this case because the common walls between different H areas add to that perimeter requirement for the exterior walls, so areas that will work if treated as whole, will not work if broken out into smaller areas. I think in this case the rated egress passage between them does force a separation, but there's still a question over how much of the rest of the spaces get grouped.

 

[RLGA]

Section 415.6 states, "...25 percent of the perimeter of the occupancy..."

This would apply to the Group H3 occupancy only. So if the building has a 1,000-foot perimeter, and the Group H-3 occupancy has a 400-foot perimeter, then you would need to have 100 feet of the Group H-3 on an exterior wall.