Horizontal exit help

[Sifu]

Proposed configuration is to allow more occupants on this floor than the number of exits per 1021.2.4 and capacity per 1005.3. They propose using a horizontal exit to provide compliance. I am not an expert in the use of horizontal exits and haven't seen that many, and those I have were in I occupancies a long time ago (this is a B). I am having trouble wrapping my mind around the concept with regard to the door swings. Any thoughts? Or guidance? I think they can make it based on what I know, but I am not sure what I don't know. I have asked for confirmation of the exit discharge and 2-hr floor/clg.

 

[Sifu]

Looks like the snipping tool didn't provide a clear drawing. Basically, they are trying to cut out the large training room and put it into a horizontal assembly, accessing one of the stair cores. I think they meet the size and protection requirements. Here is a closer drawing that might help.

 

[RLGA]

Here's the article I wrote on the subject: http://www.specsandcodes.com/articles/code_corner/The Code Corner No. 24 - Horizontal Exits.pdf

It's a bit dated (based on the 2006 IBC), but the concept and most of the requirements remain the same. The only significant change was one I proposed for the 2018 edition and was accepted. The refuge area size is based on the original occupant load on refuge area side of the horizontal exit PLUS the capacity of the door(s) through the horizontal exit, meaning if the door is 40 inches wide, the capacity is either 200 occupants (40"/0.20" per occ.) or 266 (40"/0.15" per occ.) depending on whether a sprinkler system is installed with an emergency voice/alarm communication system or not. My change states that the refuge area is sized based on the original occupant load plus the capacity of the door as previously stated, but if the capacity of the door(s) is greater than the occupant load on the other side of the horizontal exit, then only the occupant load of the other side is used when determining the refuge area size.

 

[RLGA]

Sifu, the drawings are too small to read.

 

[Sifu]

Attaching the entire plan instead of a snipped shot. See if this helps? The call-outs are my observations.

 

[RLGA]

Sift:

I’m going to teach my classes now, so I’ll respond when I get back, which will be about 4+ hours.

 

[Sifu]

Ron, from your article:
Actually, the example above only provides half of the story. Side B will also require a minimum of two exits, which means that its original 250 occupants will be evenly divided so that 125 occupants will exit through the stairway exit enclosure and the other 125 occupants can egress through the horizontal exit. This creates a problem since the doors in the horizontal exit must swing in the direction of exit travel if the occupant load is 50 or more (Section 1008.1.2). Since double-acting doors are not permitted in fire-resistance-rated assemblies, two doors, each swinging in the opposite direction, will be necessary to comply with the requirements of the code

This is the source of my angst! The way I see it, this would need to be a 2-way horizontal assembly, requiring two exits from each side- one into the stair core and one through the horizontal assembly, with all doors swinging in the direction of travel. In this case, the area A refuge area has one exit through the horizontal assembly into area B directly out of the conference room, swinging in the direction of travel, and one into the stair, indirectly from the conference room. Is there a concern due to the intermediate door from the conference room into the corridor at the stair core?

Also, The horizontal exit is probably the least understood. It sure is!

 

[cda]

Will have to look at the pictures

I do not remember a horizontal exit being used to increase occupant load

Occupant load is occupant load

 

[steveray]

Single story building?

 

[Sifu]

6 story building. A horizontal exit can be used in place of a traditional exit, with some caveats, which would have the effect of increasing the allowable occupant load. I have seen it done, but usually in an "I" occupancy where the building is actually divided, but not in a case like this where they are just carving a single room out. My understanding is that it is a "protect in place" strategy that is used where evacuation of occupants to the outside is not desirable, like patients in a nursing home. (an "I" occupancy would require more area per occupant than the B occupancy, but it is the same idea.) Ron's article is an excellent one, but it, along with others seems to focus on a more clear cut division of a building instead of cherry picking a particular room. That's why I am a little confounded by the door swings and exit paths.

 

[cda]

Attaching the entire plan instead of a snipped shot. See if this helps? The call-outs are my observations.

Some reason I cannot see either drawing, says error

 

[cda]

Looks like my sawhorse expired,???

 

[RLGA]

Sifu:

1) They may be calculating the capacity of doorways incorrectly. If a door is 36 inches wide, the actual clear width determined per Section 1008.1.1 would be about 33 inches. Thus, the capacity is closer to 220 and not 240.

2) The stairway adjacent to Area A must be included within Area A and not just accessed from Area A.

3) Does the building include an emergency voice/alarm communication system? If not, they cannot use the reduced egress width factor of 0.15 inches.

4) Refuge area sizing is based on the capacity of the doorways through the horizontal exit. not how many occupants you have showing going through the doorway. There is another door at the other end of the corridor in Area A--this is also an exit door through the horizontal exit. If the doors are 36 inches (33 inches clear), then the capacity of the refuge area is based on 440 (two doors with a capacity of 220). This is per Section 1025.4: "The anticipated occupant load from the adjoining compartment shall be based on the capacity of the horizontal exit doors entering the refuge area." This will require a refuge area of 1,533 sq. ft. (440 +71 = 511 x 3 sf/occ = 1,533 sq. ft.). The area available based on square footage shown is 1,534 sq. ft., which means they barely squeak by. However, that training room can never be locked from the corridor (I assume the storage room will be locked, even though they include it in their refuge area sizing).

5) Why are they labeling it "2FW"? This is not a fire wall, so they shouldn't imply that it is.

Not really associated with horizontal exits, but do you allow spaces used for assembly purposes to be classified as Group B when the occupant load is greater than 49? They show this 1,362 sq. ft. training room (68 occupants) as a Group B.

 

[cda]

Attaching the entire plan instead of a snipped shot. See if this helps? The call-outs are my observations.

Interesting code bending, I do not think you have an horizontal exit.

Can they reference the 2018 IBC??? and use the 150 as the factor for business ??

 

[cda]

Also, My concern would be that everyone has access to both stairwells!!!!

 

[RLGA]

Interesting code bending, I do not think you have an horizontal exit.

You may have a point in regard to interpretation. The last paragraph of Section 1025.2 states, "Horizontal exits constructed as fire barriers shall be continuous from exterior wall to exterior wall so as to divide completely the floor served by the horizontal exit."

The drawing shows the horizontal exit extending "from exterior wall to exterior wall," but does it "divide completely the floor served"? My first thought is no, it doesn't. But what does "divide completely" really mean--two equal parts, wall to opposite wall, etc.?

Does the impact of the horizontal exit really change if it separates a 1600 sq. ft. chunk from the side of the building or a 1600 sq. ft. chunk off the end of the building? It's going to come down to interpretation by the building official. I think a horizontal exit can be done in a more traditional way, but the owner will have to forgo the large open office concept and provide two smaller open office areas.

 

[RLGA]

Also, My concern would be that everyone has access to both stairwells!!!!

Everyone is supposed to have access to both stairways. The areas on each side of the horizontal exit must have access to a stairway. The one stairway is only accessed from the corridor within Area A (see my comment about encompassing that stairway within Area A).

 

[steveray]

The horizontal exit separation shall extend vertically through all levels of the building unless floor assemblies have a fire-resistance rating of not less than 2 hours with no unprotected openings.

Can you ever really meet this in reality? Always seen it with a FW, not a FB......

 

[cda]

What you have is a failure to communicate.



You have a highly protected room, and that is all.


I am thinking revaluate the occupant load, provide us a layout out with showing occupant load per room.

Possibly use the 2018 IBC 150 sq ft, and or count the number of seats, throughout the entire space.


all you have to do is knock out 19 people, looks like

 

[Sifu]

All good points. The over-riding concern I have is in the intent of a horizontal exit. In my experience, they have always done what the section says, divide the building and protect in place. The use of the horizontal exit in this case is less true to the intent than I am accustomed to.

To answer some specifics:
RLGA,
The capacity of the door is a valid question, and I will point that out.........I don't know why they don't include the other door.
Not sure what the point of including the stair in area A is, unless it is just to add it in the area calculation?? It is a 2-hr concrete shaft.
If the occupant load of the refuge area (B) is based on the capacity of the two doors combined, and they show it as 240 each, and then add the 71, they would not have an area large enough. But if they show the actual width, say 33" they would. I don't know why they don't include the capacity of the other door, because if they don't they may go over the capacity of the stair in area A.
I brought the "fire wall" designation along with the question about the exterior wall being rated. It has been my experience that most folks don't know the difference or just express it as a generic term. I always try to get them to fix it, and since this is just a preliminary "throw it against the wall to see if it sticks" inquiry, I will get it fixed when they are ready to submit.
No, I do not allow a B designation unless they meet the specifics of 303.1.2, and as a prelim I am not worried about it since they got the occ load correct. (I know some don't like the 20 net but that is a different argument for another thread)

CDA,
Not going to offer up the 2018 code at this point, we still do not have it adopted, and there is no guarentee it will be adopted by city council. If they want to push that they can do so with the CBO. I have expressed my surprise that they are doing all of this for a few people, but they want what they want.
By my reckoning, they meet the requirement for access to exits. Code says each area must have access to at least one stair, and they do. The third required exit is the horizontal exit. BUT I may not fully understand RLGA's comment about the stairway in area A.
The floor is a 2-hr assembly, so no need to worry about fire barriers underneath it.

Again, the technical details will need to be ironed out, it is the concept I am unsure about. I will present my work (and all of yours) to the CBO. Thats what they pay him for (I think).

 

[Sifu]

BTW, just got another full floor remodel for the same building, tenant and DP. This time they have creatively named a bunch of rooms to try and usurp the occupant load issue. If they call them conference or training rooms they exceed the allowable occupants for the floor with just the two exits. So they called them "collaboration rooms" and calculated them at 100 gross. This tenant occupies at least 3 entire multi-story and high rise buildings, and this six story building is going to have every floor remodeled, so I want to set a good precedent on this first one.

 

[RLGA]

I don't know why they don't include the capacity of the other door, because if they don't they may go over the capacity of the stair in area A.

The capacity of the stair in Area A is supposed to be based on the original occupant load of Area A and not the added occupant load (See the last paragraph of Section 1025.4 [not the exception]).

 

[cda]

“”””All good points. The over-riding concern I have is in the intent of a horizontal exit. In my experience, they have always done what the section says, divide the building and protect in place. The use of the horizontal exit in this case is less true to the intent than I am accustomed to. ”””

Maybe in hospitals

I mainly see it as a side bar to dividing a building, to increase area

 

[cda]

“””The third required exit is the horizontal exit.””

Ah NO!!!



“””Code says each area must have access to at least one stair,“””

Access to both stairs so look at door swing and such, so unhendered access.