Not all code revisions are more conservative.
The 2018 Edition of NFPA 101 has updated the long-held occupant load factor of 100 sqft per person to 150 sqft per person. If you don’t live in the life safety arena, this change allows the calculated occupant load for a business space to be notably less, thereby requiring less exit width, stair width, potentially the number of exits, and other means of egress requirements.
The 1934 Building Exit Code first incorporated the density of 100 sqft per person, which was based upon a 1922 recommendation from the Building Exit code committee. It has since carried through over eight decades of code revisions and has lasted through many differences in office design.
Concentrated Business Use Introduced in 2015
The Life Safety Code introduced the Occupant Load Factor for “Concentrated Business Use” at 50 sqft per person in the 2015 Edition.
The goal with determining occupant loads has always been to provide the means of egress for a maximum probable number of occupants, and the introduced higher density was intended to address higher-density spaces than would normally be expected in a business occupancy. Annex material in NFPA 101 states that this should be applied where occupant concentrations are maximized, such as business call centers, trading floors, or data processing centers.
Modern open office concepts have changed the way we congregate and occupy buildings
Challenges with High Occupant Loads
This 2015 Edition change, according to testimony in committee hearings for 2018, has brought increased scrutiny and sometimes higher occupant loads to business occupancies by review authorities.
Increased occupant loads impact egress capacity, additional exiting, and can be very difficult to achieve higher occupant loads in existing buildings. Without additional horizontal exiting or plumbing fixtures, many existing office buildings cannot accommodate redesigns under higher occupant loads.
Open office concepts have also introduced new challenges. Collaborative spaces are sometimes being reviewed as assembly, even though these small rooms are intended and often used by the same people that are no longer at their workstations. The occupant load could effectively double-count the same occupant for two different work areas.
While terminology for the collaboration rooms is not entirely defined, modern office buildings are often labeling these as huddle rooms, quiet rooms, focus rooms, enclave rooms, or other owner-specific terms. These type spaces appear to meet the intent for the new collaborative room load factors identified below.
Collaboration rooms, often labeled as huddle, quiet, focus, or enclave rooms, are often used for smaller group activities by people who otherwise occupy the open office space. These smaller spaces function differently than traditional conference rooms.
Researching New Load Factors
The NFPA Fire Protection Research Foundation sought to study the appropriateness of the business occupant load factor for modern buildings in 2012.
Two studies stemmed from their initiative; a WPI Student Research project studies office building designs, modern changes in the workplace, and occupancy impacts of flexible employee scheduling and telecommuting. This study suggested it would be reasonable to increase the load factor to 150 sqft per person.
The second study, by Gilbert Group at the University of Canterbury in Spain, found average load factors for modern office buildings averaged 181 sqft per person. Both studies summarized that the 100 sqft per person occupant load was considered conservative.
Further testimony in the committee hearings suggested that at least ten research studies on office buildings conducted since 1935 have indicated that the Occupant Load Factor for businesses was conservative at 100 sqft per person.
The research, motions, and resulting voting brought a few major changes to the 2018 Edition of NFPA 101. Business use occupant load factor has increased from 100 sqft to 150 sqft per person; the “Concentrated Business Use” load factor has remained from the 2015 edition; and lastly small collaboration rooms and large collaboration rooms (with a threshold at 450 sqft) are given occupant load factors of 30 sqft and 15 sqft per person, respectively:
NFPA 101 Updates to Business Occupancies by Year
The new occupant load factors use the more modern net square footage (square footage inside the perimeter of exterior walls with deductions for hallways, stairs, closets, interior wall thickness, columns, and other features, NFPA 101-2018 18.104.22.168.2) instead of gross square footage.
While the discussion above considers the process for NFPA 101 Changes, the International Building Code has similar provisions for the 2018 Edition for Business Occupant Load Factors as well as definitions of net and gross floor areas (Table 1004.1.2 and Chapter 2 Definitions, respectively).
Lastly, occupant loads of 50 people or more in a single space would still consider the space to be assembly and not a business occupancy. Large presentation rooms, training areas, or lecture halls can quickly introduce assembly occupancy requirements that are unaffected by these changes.
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Roughly 160 years ago the development of the industrial revolution brought together people and production into a far greater density than had ever been experienced in history. What was once individual merchants and small productions gave way to the centralized factory. With it came new and larger fire hazards not realized before.
Early Manual Systems
Early attempts at suppression for fires in these environments (other than manual intervention by responders) included manual piped systems, which fed water to different zones of a building and ended with permeated pipes. These crude systems still required intervention to activate, only provided water after fire had grown, and had issues with plug-holing due to rust or debris in the pipe network.
The next iterations involved coating the pipe with tar that melted in a fire, opening holes in pipe that allowed water to arrive near where it was needed. The delivery of water in the manual system was still delayed, and a remaining issue remained concerning water distribution.
Parmelee's Automatic Sprinkler
Cue the automatic fire sprinkler, the first modern version of which Henry S. Parmelee famously developed in 1878. The new sprinkler featured a solder-sealed cap between water-filled pipe and a perforated shell, which could more precisely relate to temperature.
The initial sprinkler still delayed in activation as the soldered element was subject to conduction with cool water from the system and a thermal lag from the brass shell. This was improved upon by Frederick Grinnell, who incorporated a soldered element which was not subject to pressures from the water, was exposed to the temperature of the room (removing the thermal lag), and had a a toothed deflector that better distributed water.
Early fire sprinklers often had small deflectors, allowing uprights to direct more spray at ceilings which were often combustible. Over half a century later with manufacturing developments and continued innovation, storage application sprinklers like the Control Mode and then Early Suppression Fast Response were brought to market.
What interests me about the early development was that we were somewhat destined to end up with fire sprinklers constructed in the way we do now. The fire sprinkler is a reliable mechanical device with far greater precision and reliability than nearly all of the public seems to know. It operates independently, simply, and reliably.
Despite so many years between the original sprinklers and now, the principles and basic premises are very nearly what was dreamed about by early innovators. I wonder if in those early years they had any concept of the impact or number of lives those basic devices would save.
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We prefer wet-pipe sprinkler systems over dry-pipe systems for a handful of reasons: lower cost, no pipe slope requirements, potentially less points of drainage, can locate inspection & testing at the riser, less maintenance, testing and inspection requirements, no power needs, less noisy, and much less potential for corrosion.
However, when dry systems are needed, there's several issues to consider for the end-user.
For owners who are not associated with the intricacies of design and maintenance of dry systems, the most frequent compliant we hear about is with the noise associated with the dry system air compressors.
Dry-pipe systems are fed with pressurized air by a compressor. The compressor run-time frequency and duration is directly attributed to the amount of leakage in the system. Some people directly attribute the leakage of the system to the quality of installation due to the final tightness of fittings.
Air injected into a leaky system develops two problems. The first is increased potential for corrosion as fresh air naturally contains water moisture and oxygen, the two ingredients for corrosion. Air that feels comfortable to us offers sufficient products to encourage corrosion, and leaky systems tend to fail with corrosive issues much earlier in their lifetime.
The second issue is noise. While it sounds trivial, noise isn't for the employee whose cubicle is next to the riser room.
If leaky systems cause issues, why don't contractors prevent or fix leaky systems?
Fixing Leaky Systems
Once a system is installed and pressure tested to meet minimum standards, finding points of leakage is very tedious and time consuming. Just finding a few leaky fittings requires inspecting every joint and adjusting connection points. Needless to say, if a system isn't installed with tight fittings it becomes a very time-intensive and costly proposition to fix.
Lessening Leakage and Noise in Design
As a designer I naturally have less impact on the quality of installation than I do of the design, and there are several ways to help lessen the impact of leakage and noise.
Leakage requirements could be mandated to be leak less than prescribed code minimums. I've found this route doesn't exactly make good friends of contractors.
Noise can be reduced in a number of ways. First is to use tank-mounted air compressors in lieu of riser-mounted air compressors. Tanks act as a pressurized reserve, where they can reduce the frequency which compressors run in order to supply the system. Mounting to the tank also vibrates the tank, and not the piping network that runs through a building. Vibration on the pipe network requires absorption by the building, which contributes to higher ambient noise. The base of the tank can be isolated with vibration isolation (often rubber pads), again helping to reduce vibration transmission to the building. The downside to tank-mounted compressors is an increased cost and needs for additional floor space.
Another important consideration is where the compressor is located. Often the allotted space for risers are determined architecturally, but upfront coordination and planning to help prevent locating dry riser rooms next to normally occupied spaces can have major benefits. If the dry riser room must be near occupied spaces, consider requesting insulation within walls or acoustic panels to help absorb sound.
Quiet-Series Air Compressors
Lastly, one of my favorite products to hit the market in the last couple years offers a major solution to the noise issue. I'll start by saying I don't have any family or friends that work for General Air Products. They have not reached out to me to offer any money (although if you're out there General Air I'd be happy to share an address for a check). That disclaimer aside I really love the Q-Series (Quiet Series) General Air Compressors for fire sprinkler systems.
The Q-Series air compressor model can be tank-mounted and is significantly quieter than standard air compressors. The noise for the Q-Series have reduced noise by 20 dBA from the previous 80 dBA of standard oil-less compressors. For drywalled, carpeted rooms the effective sound from the Q-Series compressor is only slightly higher than ambient noise levels of a typical office.
The video above (by General Air) shows the difference in compressor noise. Needless to say it would be great for applications in hospitals, schools, offices, hotels, retail, nursing homes, and other areas sensitive to noise. We've found these to be a great solution to a common and intrusive issue of noise with dry risers near occupied spaces.
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Joseph Meyer, PE, is a Fire Protection Engineer in St. Louis, Missouri. See bio on About page.