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|Advances in Sprinkler Technology|
Issue 1: Do Quick-Response Sprinklers Provide Better Fire Protection?
By Kenneth E. Isman, P.E., National Fire Sprinkler Association
Quick-response sprinklers have been available as a tool to use in fire sprinkler systems for more than 20 years. These sprinklers have the same orifice sizes and deflectors as standard spray sprinklers, but have response elements with reduced mass (and in some cases, increased surface area) in order to decrease the time that it takes to sense the heat from a fire and activate.
NFPA 13 states that a quick-response sprinkler has to have an RTI of 50 (meters-seconds)0.5 or less. Standard-response sprinklers have an RTI of 80 (meters-seconds)0.5 or more (usually, significantly more). Although it would be tempting to assume that a sprinkler with an RTI of 50 would always react twice as fast to a fire as a sprinkler with an RTI of 100, this is not the case. Sprinkler response to a fire is not a linear relationship to the RTI of a sprinkler. The actual difference between the response time of a quick-response sprinkler and a standard-response sprinkler is a function of the fire's location, the heat release rate of the fire, and the growth rate of the fire.
During the development of the 2007 edition of NFPA 13, the NFPA Technical Committee on Sprinkler System Discharge Criteria spent quite a bit of time deliberating the concept of the reduction of the design area for sprinkler systems that use quick-response sprinklers. In listening to the deliberations of the committee, it was clear to see that no one had ever assembled in one place evidence to answer the question, "Do quick-response sprinklers provide better fire protection than standard-response sprinklers?" For additional information on this subject, see reference 1.
Field Test of a Retrofit Sprinkler System
The National Fire Protection Research Foundation2 conducted 11 full-scale hotel room fire tests collecting data in the room of fire origin including: CO, HCN, HCl, smoke obscuration, and temperature. Some of the tests were conducted with quick-response sprinklers, and some of the tests were conducted without any sprinklers at all.
In the fast-flaming fires without sprinklers, critical limits for survivability were exceeded. In eight fast-flaming fires with quick-response sprinklers, the fire was controlled, and critical limits for survivability were not exceeded.
Due to these tests and some parallel work going on in the development of residential sprinklers, the concept of protecting people in the room of fire origin with fire sprinklers was developed. Using standard-response sprinklers, the design criteria had always been protecting people in rooms outside the room of fire origin. But with quick-response sprinklers, the data was starting to show that a better level of protection was possible.
Extended-Coverage Sidewall Sprinklers in a Hotel Occupancy
Factory Mutual conducted fire tests in a simulated hotel guestroom.3 Twelve fire tests were conducted with eight flaming ignition and four smoldering ignition scenarios. Quick-response extended-coverage sprinklers protected the simulated hotel room, with quick-response sprinklers protecting the bathroom and vestibule areas. In all 12 tests, the sprinklers suppressed the fire and maintained survivability in the room of fire origin. The recommendations of this report are as follows:
"Data from this test program indicate that extended-coverage horizontal sidewall sprinklers with thermal sensitivity of RTI=53 (ft-s)0.5 [29 m-s]0.5 and temperature rating 165°F (74 °C) can provide hotels with a means of suppressing fires in the guestroom while satisfying the test program survivability criteria for occupants not in intimate contact with the fire within the guestroom. However, high gas temperatures observed during fire tests suggest that similar extended-coverage sprinklers with slower response times or lower water application densities might decrease potential for survivability of occupants."
Quick-Response Sprinklers in Chemical Laboratories
The National Institute of Standards and Technology (NIST) conducted 12 full-scale tests in chemical laboratories4 with no sprinklers, with quick-response sprinklers, and with standard-response sprinklers. Both standard- and quick-response sprinklers were able to control the fires, but quick-response sprinklers provided better overall conditions in the room of fire origin.
Quick-Response Versus Standard-Response in Control Mode
Twelve full-scale fire tests were conducted by the National Fire Sprinkler Association5 to directly compare quick-response and standard-response sprinkler performance utilizing a fuel package that would now be required to be protected as Extra Hazard Group 2. During the tests, the sprinkler system was designed to only provide a design density of 0.19 gpm per sq ft (7.7 mm/min) once several sprinklers had opened, which corresponded to Ordinary Hazard Group 3 protection at that time. The purpose of providing such a low density was to keep the sprinklers on the edge of fire control to see if additional sprinklers would open while also creating a safety factor by showing that fire control could be achieved with densities far below those required by NFPA 13.
In the tests with quick-response sprinklers, 40 percent fewer sprinklers on average opened as compared to standard-response sprinklers in the same scenario. The ceiling height in the large wide-open space was 20 ft (6 m).
Fire Experiments of Zoned Smoke Control at the Plaza Hotel in Washington, DC
NIST conducted fire tests in a hotel to evaluate the need for smoke control in both sprinklered and unsprinklered buildings.6 A number of fire tests were conducted in the building without sprinklers, with standard-response sprinklers, and with quick-response sprinklers. The tests were performed both with and without smoke control systems. In the test with quick-response sprinklers and no smoke control, CO concentrations and smoke obscuration on the fire floor were reported as "slight" and on other floors as "insignificant." The report states, "It can be concluded that such rapid fire extinction significantly reduces smoke production and that this can be considered a form of smoke protection."
Sprinkler and Detector Response in Two-Bed Hospital Patient Room Fire
NIST ran tests in a simulated hospital patient room.7 The sprinklers in these tests were not connected to any water supply. The purpose of the tests was to measure survivability conditions in the room of fire origin and report on those conditions at the time of sprinkler activation for a variety of different types of sprinklers (quick-response and standard-response) located at different places in the room. Four fire tests were conducted.
Tenability measurements included heat flux, CO2 concentrations, and CO levels in the room of fire origin. The only sprinklers to activate after the tenability criteria were exceeded in the room were standard-response sprinklers. All other sprinklers, including quick-response and concealed quick-response sprinklers, activated prior to room tenability criteria being exceeded.
Quick-Response and Dry Pipe Systems
The NFSA sponsored work8,9 to determine if there was any concern with using quick-response sprinklers in dry-pipe sprinkler systems in large open areas where the water delivery time to an inspector's test connection exceeded 60 seconds. The NFSA conducted fire modeling, water delivery tests, and full-scale fire tests with both standard response and quick-response sprinklers to help answer the question.
The water delivery tests showed that, even when the water delivery to an inspector's test connection was more than 60 seconds (around two minutes in some of the cases), water during an actual fire event got to the remote open sprinklers much faster (42 to 45 seconds) due to additional sprinklers opening and helping to evacuate the air faster. With quick-response sprinklers, the NFSA found that the first sprinklers activated much sooner than the standard-response sprinklers and helped decrease the overall delay in getting water to the fire, which in turn resulted in a lower heat release rate of the fire when water arrived.
Direct comparison of the fire tests with quick-response and standard-response sprinklers showed that the gas temperatures at the ceiling approached 1200°F (650°C) with the standard-response sprinklers, but never exceeded 800°F (430°C) with the quick-response sprinklers. The temperature of a simulated steel beam over the fire almost reached 400°F (200°F) during the standard-response sprinkler test, but never reached 200°F (90°C) in the quick-response sprinkler test.
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