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IBC 2009 Table 508.4 Required Separation of Occupancies

R

Rudag

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Sep 27, 2014
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New Mexico
I am having difficulty understanding this table. I am reviewing a 5,000 square foot type III B mixed use building. Half of the building is and occupancy class B, office, and the other half is a class F-1.

While using table 508.4 to determine the fire separation between the Office use the F-1 occupancy no fire separation is required.

This is where I get confused, the fire separation between an Office and a F-2 occupancy requires a 1-hour separation for a sprinkled building and a 2-hour separation for a non-sprinkled building.

A F-1 occupancy is a Low to Moderate-hazard occupancy. A F-2 occupancy is a Low-hazard occupancy. F-1 should be more restrictive than F-2. Logic tells me that fire protection between an Office and F-1 should be greater than the fire protection between an Office and F-2.

I do not understand why a use that is a has a greater likelihood of causing a fire or feeding a fire because of its flammable contents does not require a fire separation, yet the use that has a lower likelihood of causing a fire does. Shouldn't a Low to Moderate-hazard use offer more fire protection than a Low-hazard use?

I must be missing something simple, please point me in the right direction.

Thanks.
 
First, welcome aboard.As with non-separated mixed use the separation is not required until the lesser of height and area in Table 503 is exceeded for the occupancy. In other words allowed a larger fire area for B/F-2 before the separation is required; F-1 in this respect is more restrictive owing to the smaller tabular fire area.
 
I agree, the separation is due to the B........the protection is for the F-2, from the B. The F-1 to the B is a push.
 
Tend to agree with the above comments. With the B occupancy there is typically a large volume of paper that contributes significant fuel to a fire (some might know or remember the term 'fire load'), also lots of furnishings - you know the plastic and foam stuff - which contribute to fire load as well.

The height and area allowances are a little deceiving as the B allowances are generally closer to the F-2, but where they differ the B moves closer to the (more restrictive) F-1 allowances.
 
JBI is correct. The Group B occupancy has a higher fire load, comparable to the Group F-1. The Group F-2 has a lower fire load; thus, the separation is actually to protect the Group F-2 (lower fire load) from the Group B (higher fire load).

However, I don't see the need for separation, anyway. A Type IIIB F-1 is allowed 12,000 sq. ft. and the Group B is allowed 19,000 sq. ft. If the building is 5,000 sq. ft., call it a Group F-1 nonseparated occupancy building per Section 508.3.
 
Interestingly enough in the link to the commentary that cda provided generally says that Group B is low hazard.

Could it be on a case by case considering how the space is used?
 
Thank you for welcoming me into the forum and for all of your comments. I now understand the plans I am reviewing are not required to have a fire separation between the two. Thank you for helping me see that.

As to the crux of my question, I am not fully there. For discussion sake, let's assume B remains the constant factor. The factor which changes is the differing fire loads of F-1 and F-2. I understand that F-1 is restricted in area and height more than F-2 and B and F-1 have a similar fire load.

What I don't understand, is why the area with a lower fire load is required to have a higher level of protection than an area with the higher fuel load. F-1 has a higher fire load than F-2 regardless of area and height.

I'm stuck and need help to connect all of the dots.

Thanks.
 
Francis Vineyard said:
Interestingly enough in the link to the commentary that cda provided generally says that Group B is low hazard. Could it be on a case by case considering how the space is used?
Click to expand...
Yes, it is a low hazard compared to other occupancies, but it is not considered as low a hazard as Group F-2. Look at the tables in IEBC Section 1012--they show relative hazard of occupancy groups for various categories. The Group B is either at or higher than the Group F-2, but is always in the lower end of the hazard levels. However, NFPA 13 lists offices as "light hazard" and it looks like most factory uses are listed as "ordinary hazard." So, there is some dichotomy in this area.
 
Rudag said:
Thank you for welcoming me into the forum and for all of your comments. I now understand the plans I am reviewing are not required to have a fire separation between the two. Thank you for helping me see that.As to the crux of my question, I am not fully there. For discussion sake, let's assume B remains the constant factor. The factor which changes is the differing fire loads of F-1 and F-2. I understand that F-1 is restricted in area and height more than F-2 and B and F-1 have a similar fire load.

What I don't understand, is why the area with a lower fire load is required to have a higher level of protection than an area with the higher fuel load. F-1 has a higher fire load than F-2 regardless of area and height.

I'm stuck and need help to connect all of the dots.

Thanks.
Click to expand...
I understand the confusion. It's like a dam: on one side you have a higher water level and on the other side you have a lower or no water level. The dam, like a separation wall, prevents the high water level from reaching the areas where there is low or no water. If the intent was to have water of equal levels on each side of the dam, there would be no need for a dam; the same concept applies to occupancy separation. If the Group B and Group F-1 have equal fire loads, why separate them? If there's a need to separate occupancies of equal fire loads, what prevents the need from separating all spaces within the same occupancy group? The fire area concept does something similar to that.
 
Not my intent to side track this discussion but how would you look at a law office on the second story that's filled with books similar to a library and the 1st floor of equal area filled office supplies and furniture for their own use?

VB construction non-sprinklered.
 
Francis Vineyard said:
Not my intent to side track this discussion but how would you look at a law office on the second story that's filled with books similar to a library and the 1st floor of equal area filled office supplies and furniture for their own use? VB construction non-sprinklered.
Click to expand...
As a former boss of mine used to say, "We can 'what-if' something to death." The world works on the so-called "law of averages." It is assumed that some offices will be highly loaded, such as the law library, and some offices will have a very low load (i.e. metal furnishings, low combustible finishes, minimal paper materials, etc.). Another factor to consider is the occupant load. A full library will tend to have a higher occupant load throughout, while the law library and the adjacent offices may have a lower overall occupant load.
 
You the man Ron!...Thanks for the dam reference! (I did really like it) We here greatly appreciate your dam knowledge and input!..... :) Long day....
 
a "B" can have fifty shades of occupancy::::

Airport traffic control towers

Ambulatory care facilities

Animal hospitals, kennels and pounds

Banks

Barber and beauty shops

Car wash

Civic administration

Clinic, outpatient

Dry cleaning and laundries: pick-up and delivery stations and self-service

Educational occupancies for students above the 12th grade

Electronic data processing

Laboratories: testing and research

Motor vehicle showrooms

Post offices

Print shops

Professional services (architects, attorneys, dentists, physicians, engineers, etc.)

Radio and television stations

Telephone exchanges

Training and skill development not within a school or academic program
 
Part of the understanding is in what is actually happening inside the space.

From a fire load standpoint the B is relatively high, but from fire risk standpoint the B is a relatively low risk. (As compared to a factory)
 
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