This has come up twice recently and I have yet to find any reason for it.
We have a building of V-B construction going in that has a small retail(M), office(B), and storage(S2) totalling just under 2000 square feet. The office and storage are too large to be counted as an accessory use in this case. The storage fits best as an S2 due to it being very low hazard items. What is confusing here is that the code, in table 508.4, requires an S2 Low Hazard to have a 2 hour seperation from a B or M occupancy. However, the S1 Moderate Hazard does not require any seperation from those same occupancies. I have talked with other people and nobody has any idea why this is. I have read everything I can find in the code that could possibly be related to this seperation requirement and table. There are no footnotes or exception listed.
To make this a little more confusing, I also found that this is exactly the same for an F1 and F2 occupancy. You can take the paragraph I typed above and replace the S1 and S2 classification with F1 and F2 and it would still be the same question.
Any help you can give to explain this would be greatly appreciated.