In a sprinklered multi-occupancy non-separated building, If I start from an H3 occupancy and cross into a B occupancy 50 feet on my way to the exit, do I continue to count from 50' to 150' or do I now start from 0 to 300'.

The H3 is not incidental as it is over 10% of the floor area.

Original Post

You continue with the 150'.  The occupants originating in the Group B have 300'.

doesn't seem right.  the limit on distance in the group H occupancy is because of the nature (i.e. danger) of the occupancy.  once you are beyond that, past an occupancy separation (or other approved substitute), you are in a less dangerous space and should be able to travel farther.

my vote is that it becomes 250 feet of exit distance once you get into the group B occupancy.

we get to vote, right?

With the logic presented in the OP's latter option (i.e. restart at zero), then, at the end of the Group B, I could tack on a Group A to extend it another 250 ft., then tack on a Group S-2 and extend it another 400 ft., etc. etc.

Each time you tack on another occupancy, you also add the occupancy separation protection.  Seems logical to not be able to have the overall distance not exceed the least restrictive as long as you meet the most restrictive within it's own occupancy.  In an H-3, you have 150 feet to exit the building or cross to another occupancy of less hazard like a B.  In the B you keep counting but the total length would no longer be 150' but would be 300'.

Originally Posted by Dan M.:

Each time you tack on another occupancy, you also add the occupancy separation protection.

Not necessarily.  The IBC allows separated AND nonseprated occupancies.  Occupancy separations, when provided, are not exits, and the code stipulates that the travel distance is measured from the most remote point to an entrance to an exit.

In lieu of an occupancy separation, the designer can create a horizontal exit, which stops the measurement of travel distance from that point forward.

Horizontal exit puts standpipes on each side of the exit.

seperation and no seperate occupancies are area limitation sections, not exiting.  Occupancy seperation walls occur without the seperation/no seperation section.

Originally Posted by Dan M.:

Horizontal exit puts standpipes on each side of the exit.

seperation and no seperate occupancies are area limitation sections, not exiting.  Occupancy seperation walls occur without the seperation/no seperation section.

Where does it state that a standpipe is required on each side of a horizontal exit?

Separation of occupancies, if the separated method is used, uses fire barriers to separate the occupancies.  The nonseparated occupancies method does not require any fire-resistive assemblies between the occupancies--they could be included in a single large space.