I was introduced to model codes as a graduate intern fire protection engineer at Schirmer Engineering (now Jensen Hughes) outside of Washington DC in 1991. Since that time, for almost 27 years (I know many of you have been doing this longer than me), I have calculated the occupant load of business use areas using a factor of 100 sq-ft/person (gross). That’s how it always was and how I figured it would always be. And it was simple. 3000 sq-ft of office area? Occupant load is 30. 10,000 sq-ft? Occupant load is 100. Simple, but perhaps overly conservative.
The 100 sq-ft/person factor first appeared in the 1934 edition of NFPA 101, which was then known as the Building Exits Code. Subsequent studies by the National Bureau of Standards (now the National Institute of Standards and Technology) and other entities found that this factor is generally conservative because it is a gross factor and does not permit any reduction for corridors, closets, restrooms, or other non-occupied spaces. Later studies performed between 1966 and 1992 found the actual occupant density in business occupancies ranged from 150 to 248 sq-ft/person. The 248 sq-ft/person factor was reaffirmed by a 1993 study of 23 federal government and private sector office buildings.
Based on these studies and a 2012 Fire Protection Research Foundation report, the Technical Committee on Mercantile and Business Occupancies floated a revision to the business factor by creating a committee input (CI) at the first draft stage for the 2018 edition of NFPA 101 to change it from 100 to 150 sq-ft/person for the purpose of soliciting public comments. A total of five public comments were received, some in favor of the revision, and some against (see the NFPA 101-2018 Second Draft Report for details). At this point, the technical committee was not convinced the revision was appropriate and did not move the CI forward as a second revision, meaning the 100 sq-ft/person factor would remain.
Representatives of the U.S. General Services Administration (GSA), however, disagreed, and took advantage of the entire NFPA process to revise the Code by submitting a notice of intent to make a motion (NITMAM) and debate the issue with the NFPA membership at the NFPA Annual Technical Meeting (sometimes called the “tech session”) this past June in Boston. The NITMAM was certified, making it a certified amending motion (CAM), and was openly debated on the floor of the tech session. The membership present agreed with the GSA reps and voted to revise the business factor from 100 to 150 sq-ft/person. In order to make the change in the Code, the technical committee got one more chance to have its say via a ballot of the amendment. At this point, the committee ballot passed, meaning they now agree with the revision, and it has been incorporated into Table 18.104.22.168.
Recognizing that the new factor will reduce the occupant loads of business occupancies, new factors have been added to address collaboration rooms, which are small meeting spaces sometimes referred to as “huddle rooms.” Traditional private offices are going by the wayside in many cases. Designers are opting for more open workspaces. Sometimes, however, there is a need for private, quiet space, and these collaboration rooms can have an occupant density greater than 150 sq-ft/person. If the collaboration room is relatively small (not more than 450 sq-ft), the occupant load factor is 30 sq-ft/person. If it is larger than 450 sq-ft, it is treated like a conference room and the factor is 15 sq-ft/person. Although the Code doesn’t specify these are “net” factors, I would apply them in that way. For example, if I have a 10,000 sq-ft floor of office space that includes five collaboration rooms, each 200 sq-ft in area, I would calculate the occupant load of the floor as follows:
- Collaboration rooms: [(5) X (200 sq-ft)] / (30 sq-ft/person) = 33.3 people (33 using standard rounding)
- Remainder (office area): (10,000 sq-ft – 1000 sq-ft) / (150 sq-ft/person) = 60 people
- TOTAL: 33 + 60 = 93 people
Using the former business factor, the occupant load would have been 100, so there is not much of a difference in this case because of the collaboration rooms, but the difference will be greater as the floor area increases. The net effect is the reduced occupant load might impact the required number and capacity of means of egress, and might also impact the need for fire alarm systems and emergency lighting, the requirements for which are driven by occupant load in business occupancies.
Note that the owner can always increase the occupant load as long as all Code requirements are met for the greater number of occupants. The factor for concentrated business use, 50 sq-ft/person, which was introduced in the 2015 edition of the Code, also remains.
This was a good example of a proponent for a code revision successfully utilizing the complete NFPA open-consensus process to make NFPA 101 more accurately reflect real world conditions. Although I’ll miss being able to divide the floor area by 100. My calculator will now be getting more of a workout.
Thanks for reading, and as always, stay safe!
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