Secrets of Convergence Explained
According to IBC 2018 1005.6, convergence from a base-building perspective is very explicit in the code.
From an interiors perspective, convergence is hard to explain within the code because it’s not explicitly written, see IBC 2018 1007.1.1.
Did you see that? No? That’s because the term “convergence” is not used, however, this is the code excerpt that is used for the basis for interior egress convergence.
The idea is that once the Exit Access Travel paths diverge from a Point Of Decision they should never reconvene. Think of a large conference room with two exits, to satisfy the Remoteness of Egress Doors, they are separated a specific distance apart. As those two independent paths leave the conference room the measurable distance, when measured as a straight line, should never be less than the original specific distance. Otherwise, it would be considered a convergence issue.
This position is completely substantiated in 2015 NFPA 101 7.5.1.3.
In real life, this is typically measured at the suite level as front and rear suite doors egress into the common corridor. An extreme case of convergence would be if the front and rear Exit Access Travel paths ran parallel in the corridor before reaching the first available exit stair. See figure 5.
Figure 5.
There are three solutions to resolve this:
Alter the design so that the Point Of Decision occurs right in front of the first available exit stair.
2. Alter the corridor to create a vestibule to the stairway so the stairway door is closer to one of the Exit Access Travel paths. Note that the vestibule would have to be rated and match the stairway’s protection rating and no other services, MEP, can penetrate this vestibule.
3. Rate the corridor between the stairways to 1-hour rating to abide by code 2018 IBC 1007.1.1 Exception 1.
