Urban fire flow: Are we shorting ourselves?
Fire flow – the amount of water needed to manually suppress a building fire – is a common discussion point among code officials
Fire flow – the amount of water needed to manually suppress a building fire – is a common discussion point among code officials, utility purveyors, professional designers, and owners. How much is enough and when should it be provided?
Fires in buildings under construction have revealed that the fire flow values derived from the model fire codes (the International Fire Code Appendix B and NFPA 1 Fire Code) may not be sufficient when the building is at its most vulnerable: having neither passive nor active fire protection features. In recent years, these construction site fires have become newsworthy because they seem to occur with regular frequency.
For the sake of using a simple means to establish minimum water supplies – a table based on building area and construction type – have we shorted ourselves in providing adequate fire flow for both the subject building and our communities as a whole?
Is there a better way to provide the needed water supply? Should the model codes modernize their approach to the volumes specified in the required fire flow tables? What is the right amount of fire flow and how is it determined?
There are numerous variables in assessing fire flow demands ranging from property insurance considerations to the local fire services’ capacity to deliver the water where and when it is needed. These are “big picture” discussions that need to occur among civic leaders who are charged with planning, funding and building infrastructure suitable for their communities.
Fire flow: The code approach
In the model fire codes, the fire code official ultimately is responsible for establishing the required “approved” fire flow. Likewise, the building code official has a key role to play: International Building Code §3313 (2021 Edition) requires “an approved water supply for fire protection, either temporary or permanent, be made available as soon as combustible materials arrive on the site, on commencement vertical combustible construction or installation of a [construction standpipe when required].”
This approach leaves it to the local jurisdiction to establish fire flow requirements based on estimated demand, infrastructure capacity or fire service capability. Unfortunately, where the codes are not adopted or enforced, the required fire flow may be “zero” or that which can be supplied by the local fire department water tenders. Because of these wide differences among rural, exurban and suburban water supply factors, they are outside the scope of this article.
Fire flow demands have been a concern among jurisdictions well before the latest model codes and standards were created. From as far back as 1889 and even to some extent today, the primary driver was the jurisdictions’ property protection insurance grading by Insurance Services Office, Inc. (ISO) now part of Verisk. That organization employs a relatively complex formula in its “Guide for the Determination of Needed Fire Flow.” Although the Guide is intended to assess available water supplies at selected location throughout a community, its mathematical formula often was applied to individual buildings during the design and permitting phase to evaluate fire flow needs.
ISO’s formula was developed based on its studies of large-loss fires where they recorded the average fire flow and other factors such as construction type, occupancy type, fire sprinkler protection, building area and exposures: nearby properties that may be threatened by a fire in a single building. ISO employs SCOPES (Specific Commercial Property Evaluation Schedule) to assess individual properties’ vulnerability to fires.
When evaluating fire flow for sprinklered commercial buildings, ISO specifies the needed fire flow is the volume demand at the base of the riser plus the inside/outside hose stream demand. For multi-family dwellings (protected in accordance with IBC/IFC §903.3.1.2 (NFPA 13R) the minimum required fire flow is 1,000 gpm for two hours. For one- and two-family dwellings (protected by IBC/IFC §903.3.1.3 (NFPA 13D) the minimum required fire flow is 500 gpm for one hour.
In 1985, a simplified method for determining the required fire flow for individual buildings was added as an appendix to the legacy Uniform Fire Code. It has continued – without significant modernization – into the current editions of both the IFC® and NFPA 1. The IFC Appendix I-B method employs an easy-to-use table based on the construction type and fire flow calculation area. Once these two factors are known, the fire flow in gallons per minute (gpm) and duration can be established. Figure 1 is an excerpt from the table.
Appendix I-B also allows the code official to reduce the fire flow requirement by 75% if the building is equipped with an approved automatic fire sprinkler system. The fire flow for a building that might otherwise require 8,000 gpm can be reduced by 75% to 2,000 gpm.
And there’s the rub
The values derived from Table B105.1(2) and sprinkler modifications are based on the building being occupied with all passive and active fire protection features in place. This may include fire separations such as fire walls or fire barriers and gives substantial credit to the installation of fire sprinkler systems because of their enviable performance records at fire control.
However, the table does not address other key fire safety factors that the ISO “Guide for the Determination of Needed Fire Flow” does: content hazards and exposures to adjacent buildings. Based on this table, a 100,000 sq. ft. Type IIIB building for storing steel beams and other non-combustible materials demands the same fire flow as a like-sized building storing rubber tires or cardboard boxes full of Group A plastics. Based on the table, without sprinklers this building would require 6,750 gpm fire flow. That figure could be reduced to 1,688 gpm with sprinklers.
Even residential buildings protected by residential sprinkler designs get credit for these systems. Residential sprinkler system design standards were never intended for property protection: they are designed to prevent flashover in the compartment where a fire occurs to buy time for occupant escape. Residential sprinklers – except in buildings more than 55 feet above the lowest level of fire apparatus access – don’t require attic protection. Consequently, we have seen many multi-family dwellings destroyed by fires that originate on the exterior, climb the exterior walls and burn the building from the attic downwards.
Furthermore, if the building being evaluated for fire flow is 100 feet away from the nearest exposure – or within a few feet of one or more adjacent buildings – the table value fire flow remains the same. There is no accounting for exposure protection to prevent fire spread to adjacent properties. Frankly, this makes no sense from a risk-based fire safety approach.
Content hazards and exposure threats are topics for another article: this piece is focused on fire flow deficiencies during construction. Once the code official establishes the required fire flow – based on a complete and “fully functioning” building, the infrastructure to meet the tabular and adjusted fire flow demand may be installed. But are we doing enough for a fire in a building under construction?
An informal survey
To observe some fire flow demands, 15 fires in combustible buildings under construction were examined. The sample events were gathered from a web search on the term “construction site fires.” This very non-scientific approach involved studying the available fire videos – that were either amateur or by professional news organizations – and counting the hose streams visible during the event. The jurisdictions’ existing fire flow infrastructure capabilities are unknown. The point of the survey was to see if the tabular fire flow figures – with or without sprinkler adjustments– would be adequate for a combustible building under construction.
Fire fighters learn that large-diameter hand-held hose lines (typically 2 ½-inch) can deliver between 250 and 300 gpm. So-called “master streams”—often deployed from aerial ladder equipment, the upper level of fire engines (“Deck guns”) or by ground-mounted “monitors” – can discharge up to 4,000 gpm. To be conservative, Table 1 employs the values of 250 gpm for each observed handline and 1,500 gpm for each master stream the was counted. These constants are multiplied by the number of observed hose streams to achieve the total observed flow. Great care was taken during the video review to assure hose streams were not counted more than once, but it cannot be guaranteed from these snapshots that one or more hose streams weren’t repositioned during the fire. (Normally, due to equipment operational limits, once an aerial or engine apparatus is positioned to attack a fire it is not relocated unless it is in danger of being destroyed or is relieved by another fire apparatus). Handheld hose lines were not observed in three of the fires, yet these fires were included in computing the average of all 15 incidents lowering the overall mean.
In all the observed events, the structures appeared to be damaged beyond repair and could be classified a “total loss.” In one incident the owner, while watching the fire, was quoted in the news video as saying, “I just lost $25 million in just a few hours.”
Granted, the research to support this article is not perfect nor complete – it is intended to be illustrative only. Additional research under controlled conditions is always welcome and encouraged to fully understand the fire flow required for buildings under construction.
The big “if”
The question this simple survey asks is “if we are establishing infrastructure performance based on fire flow demand for occupied and functioning buildings, are we shorting ourselves for other catastrophic events?” The answer appears to be “yes.”
The idea of assigning fire flow for an individual building may be short-sighted, especially where a community is growing. Imagine a scenario along a major transportation artery where our 100,000 sq. ft. Type IIIB building for storing steel beams and other non-combustible materials is proposed. The building will be sprinklered, so the fire code official tells the water purveyor the fire flow will be 1,688 gpm. The infrastructure is designed to meet the “required fire flow” and everyone is happy. What happens, though, when a developer announces the next-door parcel will be covered by a one-story unlimited area non-sprinklered Group F-2 factory where the required fire flow would be 8,000 gpm. Would everyone still be happy they undersized the original service without planning for enhanced capacity? What is the potential impact on upgrading the infrastructure and who is going to pay for it?
As we have seen 1,688 gpm may not be adequate to protect combustible buildings under construction. (For non-fire service readers, that is roughly the pumping capacity of a modern urban-type fire engine. One engine could deplete the entire fire flow demand for a construction site so employing other pumping equipment would be useless and could significantly damage both the infrastructure and fire equipment). Nearby buildings also could be at risk if the available flow isn’t adequate to simultaneously protect exposures while fighting the fire.
What’s the answer?
Like so many code challenges, there is no easy answer to this problem.
How do we design our infrastructure to be cost-effective while meeting current and anticipated needs? How can we predict where development will occur that may have varying fire flow demands? How can we assign a fire flow value based on an individual building’s area, construction and fire protection features and expect that flow to be effective before the building is ready for occupancy?
First, more research needs to be done and shared so policymakers understand the risks. In 2014 the Fire Research Foundation conducted a comparative study of fire flow methods, but there does not appear to be much action resulting from it. Research needs to be performed to understand the different flow requirements between fires in buildings under construction and those that are operational.
Second, once the research is robust, long-term infrastructure planning by local jurisdictions needs to occur. Building and fire code officials need to be involved in decisions among planners, utility purveyors, politicians and developers. Verisk/ISO is a critical influence on fire flow requirements as part of a community’s fire defense and property protection insurance classification.
Third, code officials need to be more assertive in enforcing the code requirements for water supplies during construction and the fire safety regulations included in the model fire codes and standards.
Finally, those who are active in code development need to take a critical look at the fire flow calculation tables to assess whether they are keeping up with current construction hazards.
1 See “Rethinking Fire Flow” March 12, 2020, by the author.
2 Fire Protection Research Association, (2014). “Evaluation of Fire Flow Methodologies,” Quincy, MA
3 “Guide for the Determination of Needed Fire Flow” (2014). Insurance Services Office, Inc. downloaded May 20, 2022, from Verisk.
4 If the fires where no handlines were observed are removed from the data, the average increases to 1.7.