What are the key differences between IBC and NFPA 101 for exit capacity factors?
We’ve categorized the main components of egress with exit access, exits, and exit discharge. We’ve looked at exit access – how do we physically arrange exits? Where do exits need to be located? How do we determine the number of exits?
And finally, what is an exit capacity factor? That’s what we covered in the last segment.
Here, in this video, we’re exploring what exit capacity factors look like in NFPA 101 and the difference between 101 and the IBC.
Well first, where can we find the exit capacity factors for each code? Using the latest editions IBC 2021, we go to Chapter 10 for Means of Egress, 1005 for Means of Egress Sizing, 1005.3 for Required capacity based on occupant load, and finally Section 1005.3.1 provides the exit capacity factor for stairs and 1005.3.2 for doors (called other egress components). These are listed in the code verbiage itself.
Under NFPA 101, 2021 edition, we start with Chapter 7 for Means of Egress, 7.3 for Capacity of Means of Egress, 7.3.3 for Egress Capacity, and finally to Table 18.104.22.168 which lists the Capacity Factors. This table has some similar figures to the IBC, but there are a few key differences.
DIFFERENCE #1: FACTOR INCREASES
One key difference is that IBC permits exit capacity factor increase for fully sprinklered buildings with a voice evacuation fire alarm system.
NFPA 101 does not permit this increase, meaning NFPA 101 doors are 0.2” per occupant for most occupancies, excluding non-sprinklered healthcare and high-hazard which have a different, more restrictive factor.
When it comes to stairs, IBC and NFPA 101 differ even more.
DIFFERENCE #2: STAIRS
Like doors, NFPA 101 does not recognize the exit capacity factor increase.
NFPA 101 utilizes a 0.3” per occupant factor for most occupancies (excluding Board and Care, nonsprinklered Healthcare and High Hazard which have more restrictive factors). For stairs exceeding 44” well… NFPA 101 has a formula for that.
The formula is: C = 146.7 + [(Wn-44)/0.218), where C is the capacity in persons, and Wn is the nominal width of the stair, in inches.
It’s uhhh a little clunky. It essentially means that for every inch you are over 44, the exit capacity factor is 0.218. We know that IBC has an exit capacity factor of 0.3 for stairs, which is increased to 0.2 if fully sprinklered and voice evac. NFPA 101 is 0.218 for the amount over 44 inches. So it’s kind of in-between the two.
Let’s use our 60” stair example from our last video. We have a clear tread width of 60 inches for the stair. Let’s say our building is nonsprinklered.
What is the available exit capacity for the stair?
In the IBC, this would be 60 inches divided by 0.30 inches per occupant, to get an exit capacity of 200 occupants. That sounds familiar from our last video.
If this is being evaluated under NFPA 101, we use the NFPA 101 formula.
The formula is C = 146.7 + [(Wn – 44) / 0.218].
So we have 60-44, which becomes 16, divided by 0.218, which becomes 73.4, which is added to 146.7, which gives us a capacity of 220.09, which rounds to 220. So this same stair in NFPA 101 has an exit capacity of 220 persons.
What if both the IBC and NFPA 101 apply?
In projects where both IBC and NFPA 101 must be followed, the more restrictive of the two will govern. The numbers are likely to differ in case of stairs and in cases where the IBC exit capacity factor increase is used.
In the case that a project must follow both codes, the more restrictive will govern. By more restrictive, that means the lower exit capacity applies. If our stair is under IBC and NFPA 101, we would have an available occupant load for the stair of 200 persons, not 220.
NFPA 101 doesn’t have the benefit for sprinklers and voice evacuation.
So, if our building under IBC and NFPA 101 becomes sprinklered with voice-evac fire alarm, the IBC calculation changes, but we won’t get the full benefit. Let’s look at that real quick.
In the IBC calculation, we could use an exit capacity of 0.2 inches per person from the IBC instead of 0.3 inches per person. That puts the stair exit capacity at 300 people (60 inches / 0.2 inches per person to get 300 people) – but now NFPA 101 would be the more restrictive at 220 occupants.
So even though we’re fully-sprinklered with voice evac, our available exit capacity for the stair only gets up to 220 occupants, due to NFPA 101. NFPA 101 does not have a similar benefit.
Ok, but it seems like a stretch to say that both the IBC and NFPA 101 would both ever apply. Is that ever the case?
WILL BOTH REALLY APPLY?
Yes, for Healthcare projects like hospitals the US, the IBC and NFPA 101 often apply. Typically IBC is applied at the township, city or state level and NFPA 101 is applied due to healthcare licensing requirements. Because the city, township or state requires all buildings to meet IBC, the building cannot be built without following the IBC egress requirements. Because many states require hospitals to follow NFPA 101 for licensing requirements, the building would not be able to operate as a hospital and provide care to patients, unless it was built to NFPA 101 requirements.
Similarly, the federal government requires all facilities providing Medicare or Medicaid services to be designed to NFPA 101, so this is often a requirement.
What are the key differences between IBC and NFPA 101 exit capacity factor?
One key difference is the IBC permits the exit capacity increase factor that NFPA 101 does not. The two codes also differ quite a bit in terms of calculating stair capacity. When both codes most followed, typically the more restrictive will govern.
This wraps up the video portion of our Introduction to Exits Series; before we’re done, though, we need practice. Knowledge is only half of the equation. Knowing something does not make us proficient at what we do in the real world. So, before we close out this series, we’re going to strengthen our ability to apply the knowledge by getting in practice, and building those code muscles.
I hope you’ve gained some key takeaways and a better understanding for how exits are described, arranged, and calculated. If you’re following along on the Life Safety side of things, our next series will get into more detail about Stairs.
Thanks for joining us. I’m Steven Barrett, this is MeyerFire University.
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