It’s self-evident that adequate water supplies are essential to successful fire suppression outcomes. Even with the advent of modern chemical agents, water has for thousands of years been the primary fire control medium. It is plentiful, cheap, transportable, and capable of absorbing thousands of Btu’s (joules) emitted from common fires.
As new developments occur and buildings are erected throughout the US, local building and fire officials are obligated by legally adopted construction and fire safety codes to specify how much water should be provided for fire control. Property insurance underwriters or corporate risk analysts may demand more than code-required fire flow minimums.
Unlike water supplies used to support automatic fire protection systems, fire flow is the amount of water needed for manual fire suppression. While NFPA 13, Standard for the Installation of Sprinkler Systems requires water supplies to meet minimum system and hose stream demands, the NFPA 13 technical committee makes it clear the hose stream demand is “intended to provide the fire department with the extra flow they need to conduct mop-up operations and final extinguishment of a fire at a sprinklered property. This is not the fire department manual fire flow, which is determined by other codes and standards”.1 [Emphasis added].
Many of the common fire flow values in use today are based on decades of observation and experience from the Insurance Services Office (ISO), a subsidiary of Verisk Analytics based in Jersey City, New Jersey. In recent years, however, there have been several significant changes that have resulted in fire service leaders questioning the validity of existing rating schemes.
What’s Changed?
Rapid social and technological changes have created contradictory results that make finding a single fire flow strategy challenging.
Improvements in building construction through better code enforcement and engineering approaches have been noticeable in the last 50 years. The frequency of significant and catastrophic fires has decreased dramatically since the 1970s. Conversely, there have been significant changes in construction materials – especially the move toward lightweight engineered-wood products – and remarkable changes in building furnishings and contents that have proved today’s fires burn hotter and faster than ever before.
There have been dramatic improvements in the function and design of mobile fire suppression equipment. In the US, fire apparatus water-hauling and pumping capacities have increased. Vehicles able to carry up to 3,000 gallons (11 356 liters) and pump 2,000 gpm (7570 lpm) of water are common.
Firefighting tactics have changed with the technological improvement in suppression tools and personal protective ensembles. While still subject to intense debate over safety practices, it is a source of pride among many current fire fighters to make aggressive interior attacks on building and content fires.
At the same time, due to fire service influence in the consensus-based code development process, building codes encourage fire sprinkler systems to enhance fire protection and life safety in ways unheard of 50 or 100 years ago. Almost all new buildings – other than single family dwellings2 – require some sort of built-in fire suppression.
The move toward hydraulic fire sprinkler design has influenced water supply requirements, reducing overall storage demands while making systems more affordable and efficient.
Rethinking Fire Flow in Community Fire Protection
These changes are causing some fire officials to rethink the way fire flow is provided in community fire protection. They must choose an approach that works best for the jurisdiction as well as individual protected risks.
The model codes recognize that all jurisdictions don’t have the same infrastructure capacity. This may be a result of where the jurisdiction lies, its ability to fund infrastructure improvements or the community’s desire to retain a rural, suburban, or urban character. Building and fire codes leave it to the local code official to determine what constitutes an approved fire flow water supply that best suits the jurisdiction.
The fundamental question that must be answered is “what is fire flow’s purpose”? While a consensus definition describes fire flow as the water supply available for manual firefighting, there is no articulation of what fire flow should achieve. Is it solely to confine a fire to a single building? Is it intended to suppress a fire in a single building while providing supply for hose streams to protect exposed properties? Should fire flow capacity be based on a maximum foreseeable loss scenario where one or more properties or city blocks are involved? The burden of answering that question lies with the code official.
In the US, the ISO Guide to the Determination of Needed Fire Flow provides the historic basis for most community-wide and individual risk fire flow calculations. Because of its nexus to the ISO Fire Suppression Rating Schedule, the Guide it is important to many jurisdictions that consider the ISO grading scale important to their community. The Fire Suppression Rating Schedule assesses a community’s overall fire defenses including fire services, communications, weather conditions, and fire protection water supplies that make up about 40% of the rating score. The final rating may have a significant impact reducing some property insurance premium rates.
For those jurisdictions that can’t or choose not to provide the underlying infrastructure to achieve ISO guidance, there are other variables the code official can employ to establish fire flow requirements. They may include a combination of fixed and mobile assets.
According to a 2014 study3 by the National Fire Protection Association (NFPA) Fire Research Foundation, the key variables in evaluating individual building fire flow demands to estimate potential fire size are the building geometry and/or the rate of heat release/fire development that can be expected. The geometry is established literally: total height, number of stories, story height, length, width, area per floor, and total building area.
Occupancy and building construction are important parameters to establish fire growth potential. More hazardous uses and combustible construction and contents add to the fire flow demand.
Exposures are important because separate hand lines or master streams might be needed to prevent fire spread. As buildings are spaced further apart, the need for protection from radiant heat transfer lessens.
Installed suppression systems, particularly sprinklers, should be considered as a potential fire-flow reduction parameter. Both NFPA 1, Fire Code and the International Fire Code provide substantial credits for fire flow when the building under consideration is sprinklered.
Although fire department response time would influence the fire flow required at a fire scene, the Fire Protection Research Foundation report concludes this variable is difficult to independently assess. It is difficult to predict and utilize in a fire flow methodology, since the pre-notification fire size cannot readily be determined.
Fire department response time might be assessed in a gross way for a limited data set using two parameters: response time less than 15 minutes and greater than 15 minutes. Fire department response more than 15 minutes might require an increase in fire flow because of the delay in fire suppression interventions. This may encourage trade-offs for early fire detection and reporting in lieu of greater water supplies.
Fire flow methodologies used with rural and suburban buildings implicitly account for possible longer fire department response times due to the remoteness of some buildings. In addition, these methods already assume there is greater risk where there are no municipal water supplies. It is recommended that rural and remote suburban buildings be addressed separately when assessing fire department response time.
In all cases, the code official or water purveyor should take a long-term view of infrastructure development to anticipate additional water demands that may have a deleterious effect on fire flow.
Recommendations for Future Study
What should be done to address fire flow requirements?
First, fire flow training for code officials and design professionals needs to occur to obtain better understanding of what fire flow means and how to use it in conjunction with other water-based fire protection systems.
Local written policies should be adopted on which fire flow method(s) will be used so owners, designers and developers know early in the design and development phase what will be required. Written policy adds the elements of predictability, fairness and consistency in codes and standards applications.
If possible, there should be a national consensus on the fire flow calculation methods that will be used. This will involve a multi-faceted effort among many interested parties including jurisdictions, public and private water purveyors, property and inland marine insurers, developers, community advocates and any interested stakeholders.
Business, industry and government should explore incentives to encourage policy and consensus development. Incentives could range from financial to laudatory: acknowledging those jurisdictions and designers who employ best practices.
Although the ISO Guide to Determination of Needed Fire Flow is based on that organization’s historic records and analysis, there needs to be more empirical research to determine – if it is possible – how much fire flow really is needed for both neighborhood and individual property demands. The research calls for a clear expectation of what fire flow is intended to achieve.
The US’s National Fire Incident Reporting System (NFIRS) currently does not include any standard method for the incident commander to capture and record for later analysis peak flow demands and total water consumption. Efforts should be made with the National Fire Information Center, US Fire Administration and other influencing entities to make this happen.
Summary
It may be a tired maxim, but water is the “life blood” of the fire protection field and likely will stay that way for many years. It is incumbent on government and design professionals to find effective methods to provide water supply and distribution based on rational analysis of the hazards that are being protected.
For more information, contact raneale@comcast.net
References
- National Fire Protection Association. (2019), NFPA 13, Standard for the Installation of Sprinkler Systems (p. 413). Quincy, MA: Author
- While sprinklers are required by the International Residential Code, they remain politically unpalatable in many jurisdictions and are amended out by state or local legislation.
- Benfer, M.E., Scheffey, J. L. (2014). Evaluation for Fire Flow Methodologies. Quincy, MA: The Fire Protection Research Foundation.
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