1 

NISTIR 6941 

Review of Residential Sprinkler Systems: 

Research and Standards 

Daniel Madrzykowski, P.E. 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 

Russell P. Fleming, P.E. 

National Fire Sprinkler Association 

Patterson, NY 

January 2002 

Revised December 2002 

 Sponsored in part by: 

U.S. Department of Commerce Federal Emergency Management 

Donald L. Evans, Secretary Administration 

Technology Administration Joe M. Allbaugh, Director 

Phillip J. Bond, Under Secretary for Technology U.S. Fire Administration

National Institute of Standards and Technology R. David Paulison, Administrator 

Arden L. Bement, Jr., Director
2 

REVIEW of RESIDENTIAL SPRINKLER SYSTEMS: 

RESEARCH and STANDARDS 

Daniel Madrzykowski, P.E. 

National Institute of Standards and Technology 

Gaithersburg, MD 

Russell P. Fleming, P.E. 

National Fire Sprinkler Association 

Patterson, NY 

Introduction 

Automatic sprinkler systems have been successfully used to protect industrial and 

commercial buildings and their occupants for more than 100 years. Historically the place 

which has offered the least amount of fire protection to occupants, was and still is, their 

own home. This was brought to light in 1973 by the Report of the National Commission 

on Fire Prevention and Control, America Burning. At the time of the report 

approximately 8,000 people died in structure fires every year in the United States. Nine 

out of ten of those victims died in their home1

. 

In the 25 years since America Burning was published the number of lives lost in fires in 

the United States has decreased to approximately 4,000 per year. Unfortunately 8 out of 

10 victims still died in a residential structure fire2

. While residential sprinkler 

installations are increasing, it is estimated that less than 3 % of the one and two family 

homes in the United States have them installed3. 

In response to the information from the America Burning report, The National Fire 

Protection Committee on Automatic Sprinklers assigned a subcommittee to develop a 

standard for residential sprinkler systems. The Standard on the Installation of Sprinkler 

Systems in One- and Two- Family Dwellings and Mobile Homes (hereinafter referred to 

as NFPA 13D) was adopted in May of 1975, based on expert judgment and the best 

information available at that time. (Note the term “Mobile Homes” in the title was 

replaced with “Manufactured Homes” in the 1994 ed.). 

Significant testing and development of residential sprinkler systems has continued since 

then resulting in the evolution of NFPA 13D and the development of the Standard for the 

Installation of Sprinkler Systems in Residential Occupancies up to and Including Four 

Stories in Height, NFPA 13R. 

The purpose of the residential sprinkler system standards is to “provide a sprinkler 

system that aids in detection and control of residential fires and thus provides improved 

protection against injury, life loss and property damage” 4

. From a performance 

perspective, if the room of fire origin is sprinklered, a sprinkler system designed and 

installed in accordance with the residential sprinkler standards is expected to prevent 

flashover and improve the occupant’s opportunity to escape or to be rescued 4. 
3 

Residential sprinkler systems designed and installed in accordance with NFPA 13D or 

NFPA 13R have significantly different requirements than those for a residential 

occupancy that is required to be designed in accordance with the Standard for the 

Installation of Sprinkler Systems, NFPA 13. NFPA 13D and NFPA 13R systems have 

been optimized for specific types of residential occupancy buildings in an effort to 

minimize the cost of the system while providing fire safety.

New developments in residential sprinkler system technology continue to be made in an 

effort to increase the ease of installation and reduce the cost of installation while 

maintaining the effectiveness and reliability of the system. 

In several communities, residential sprinkler systems have been required in dwellings for 

more than a decade. Information from these communities are providing compelling data 

for installing residential sprinklers. These experiences, in addition to code requirements 

and other incentives, are increasing the numbers of sprinkler installations around the 

country. 

DEVELOPING A SPRINKLER SYSTEM IN RESPONSE TO THE 

RESIDENTIAL FIRE PROBLEM 

The development of a residential sprinkler standard with the main focus on life safety 

required a multi-faceted approach. Fire incident data had to be collected and analyzed to 

understand the nature of the residential fire safety problem. In addition, technical 

challenges had to be overcome to develop an effective, practical and economically 

acceptable design for a residential sprinkler system. 

The residential fire hazard had to be characterized in terms of area of origin (Table 1) 4

. 

Additional fire data was sought to determine which areas of the home yield the most fatal 

fires (Table 2) 4. Analysis of this data determined which rooms of the residence needed 

to be sprinklered, in order to have a cost–effective system with a positive impact on life 

safety. Based on the data presented in Table 1, 83% of all residential fires start in either a 

living room, a bedroom or a kitchen area. Table 2 shows the number of fire fatalities and 

injuries based on the area of origin. Almost 80 % of the fire fatalities and more than 70% 

of the injuries are the result of fires starting in a living room, bedroom or kitchen. The 

need for sprinklers in these locations was clear. Tables 3 and 4 show the first item 

ignited and the source of the ignition, respectively 4

. These tables show that the majority 

of residential fires involved the ignition of furniture or bedding typically by a relatively 

small heat source. This information helped characterize of the fire hazard that residential 

sprinklers would have to control. 

Another aspect of the residential fire problem involves the demographics of residential 

fire fatalities. Figures 1and 2 present the number of fire deaths per million people of a 

given age range and the relative risk of dying in a fire by age respectively3

. Both tables 

show the trends that children 4 years of age and under and adults 60 years of age and 

older are more likely to die in a fire than other segments of the population. For adults 

over 60, the risk increases significantly with age. Because these high-risk groups may 
4 

depend on assistance to exit the dwelling, “anything less than automatic suppression may 

not be enough to save them” 5. 

Another group that can benefit from the use of residential sprinklers are firefighters. The 

majority of firefighter deaths and injuries on the fire ground occur at residential fires. 

Figures 3 and 4 exhibit the supporting data from 1998 as complied by the U.S. Fire 

Administration3. Figure 4 shows that approximately 73% of firefighter fire ground 

injuries occur at residential fires. Twice as many firefighters are injured each year 

performing fire ground duties as there are fire injuries to the civilian population (43,000 

vs 23,100 in 1998) from reported fires3

. 

Once it was determined where sprinklers in a home would be most effective in reducing 

life loss, the technical challenge of developing an effective and economically viable 

sprinkler system had to be solved. The system would have to automatically activate while 

a fire was small and the smoke and heat conditions in the home were survivable. Once 

the system was activated it needed to control the fire with a small amount of water 

relative to a sprinkler system designed in accordance with NFPA 13. 

NFPA 13D, First Edition 1975 

Based on the review of fire incident data the committee developed a residential sprinkler 

installation standard that covered the normal use areas of a dwelling and that met the 

goals of: 1) preventing flashover, 2) providing sufficient time for safe egress or rescue, 

and 3) economical viability. 

As specified in the initial version of NFPA 13D, a residential sprinkler system would use 

a 1⁄2 in (12.7 mm) orifice, standard sprinkler, with a maximum of 256 ft2 (23.8 m2

) 

coverage, and a spray density of 0.10 gpm/ft2 (4.1 L/m2

) yielding a 25 gpm (94.6 Lpm) 

flow rate. If the system was not supplied by an adequate public water source, a 250 gal 

(946.3 Lpm) stored water supply was required to provide a 10 minute water supply. 

To keep costs down and focus the impact of the sprinklers where they were most needed, 

sprinklers were not required in bathrooms 40 ft2 (3.7 m2) or less, small closets, 24 ft2 (2.2 

m

2

) or less, attics not used as a living space, porches, carports, garages, and foyers. The 

system was to have a local water flow alarm. NFPA 13D permitted sprinklers to be 

omitted from certain areas where the incidence of life loss from fires was shown 

statistically to be low. NFPA 13 had always required complete sprinkler protection in 

order to safeguard property adequately. In departing from this ideal full complete 

protection, the 1975 edition of NFPA 13D became the first attempt at a “life safety” 

sprinkler standard. In spite of those concessions, actual installations based on this 

standard were rare, primarily due to cost. 

The initial residential sprinkler system was based on existing technology and 

improvements were needed. Jensen noted that “ much of this first edition was based on 

the collective experience of the committee members; little was based on real-world fire 

testing”6

. 
5 

Residential Sprinkler Research 

Beginning in 1976, the National Fire Prevention and Control Administration, renamed 

the United States Fire Administration (USFA) in 1979, supported a significant number of 

research programs on a wide variety of topics relating to residential sprinkler systems. 

The objective of the USFA research program was to assess the impact sprinklers would 

have on reducing deaths and injuries in residential fires.7

 The USFA working in 

conjunction with the National Fire Protection Association, Factory Mutual Research 

Corporation, Underwriters’ Laboratories and many others evaluated the design, 

installation, practical usage, and water acceptance factors that would have an impact on 

achieving reliable and acceptable systems8

, the minimum water discharge rates and 

automatic sprinkler flow required, and response sensitivity and design criteria9-11. Fullscale fire experiments were conducted to develop residential sprinkler designs and 

validate their effectiveness 12-16. In addition, standards for residential sprinklers were 

developed. These included tenability criteria that were required to be maintained in the 

room of fire origin during sprinkler operation. 

Residential Sprinkler Sensitivity and Response 

Although, researchers at the Factory Mutual Fire Insurance Companies recognized the 

need for “faster” or more “sensitive” sprinklers back in 1884, it was not until the late 

1960s that a “quick-response sprinkler” subcommittee was formed within the NFPA 13 

committee. 

The research showed that a more sensitive sprinkler was needed to respond faster to both 

smoldering and fast-developing residential fires for two reasons. First, fires had to be 

controlled quickly in order to prevent the development of lethal conditions in small 

residential compartments. Second, fires had to be attacked while still small if they were to 

be controlled with the water supplies typically available in residences, i.e., 20 to 30 gpm 

(76 to 114 L/min). 

Much of the original work in the area of measuring sprinkler sensitivity was done at 

Factory Mutual Research Corporation (FMRC) under the sponsorship of the United 

States Fire Administration (USFA) during the development of the residential sprinkler.

17,18 Important contributing research was also performed at the British Fire Research 

Station and the National Institute of Standards and Technology (NIST).19-22

The progress in this area climaxed late in 1990, when an agreement was reached within 

the working group on sprinkler and water spray equipment of the International Standards 

Organization (ISO) for a standardized approach to sprinkler sensitivity requirements and 

testing. The agreement, included in ISO 6182/1, “Requirements and Methods of Test for 

Sprinklers,” uses a combination of sprinkler test procedures developed by laboratories in 

the United States and Europe and establishes the three ranges of sprinkler sensitivity 

characteristics shown in Figure 5.23 

These ranges of sensitivity are based both on the response time index (RTI) of the device 

and on its conductivity (C). RTI is a measure of pure thermal sensitivity, which indicates 

how fast the sprinkler can absorb heat from its surroundings sufficient to cause activation. 
6 

The conductivity factor is important in measuring how much of the heat transferred from 

the surrounding air to the sensing element will be lost to the sprinkler frame and 

waterway.24 

Figure 5 shows three broad ranges of sprinkler sensitivity: standard, special, and fast 

response. Traditional sprinkler hardware falls into the standard-response category. The 

fast-response category is being used for new types of sprinklers for which fast response is 

considered important. The special-response category is being used in some countries for 

special types of sprinklers that may be installed in conformance with appropriate national 

installation standards. In the United States, this includes some of the extended coverage 

sprinklers. 

Sprinkler response time as a function of the temperature rating of the operating element is 

well understood, that is, a 165°F (74°C) rated sprinkler would operate when its 

temperature reaches 165°F (74°C), plus or minus a few degrees. Because of the “thermal 

lag” of the link or bulb mass, however, the air temperature may be significantly higher 

before the element operates. The smaller mass of the operating element of a fast-response 

sprinkler permits it to follow a temperature rise in the surrounding air more rapidly, 

resulting in faster operation. The actual sensitivity requirements of the first fast-response 

sprinklers, intended as residential sprinklers, were arrived at somewhat by trial and error 

during developmental test work. To measure sensitivity, FMRC researchers first applied 

the concept of the “tau” factor and later developed the RTI. 17,18

Both the tau factor and RTI refer to the performance of a sprinkler or its operating 

element in a standardized air oven tunnel or thermal sensitivity test. The test is known as 

a “plunge” test because a sprinkler at room temperature is plunged into a heated air 

stream of known constant temperature and velocity.17,18 In the plunge test, the tau factor 

is the time at which the temperature of the sensing element of the sprinkler is 

approximately 63 percent of the difference between the hot gas temperature and the 

original temperature of the sensing element. In other words, the tau factor is the time at 

which the temperature of the sprinkler thermal element has risen 63 percent of the way to 

the higher temperature of the heated air. The smaller the tau factor, the faster the 

sprinkler sensing element heats up and operates. Figure 6 shows a time temperature graph 

for several tau values ranging from 25 to 200.25 

The tau factor is independent of the air temperature used in the plunge test, but is 

inversely proportional to the square root of the air velocity. During the early development 

of the residential sprinkler, a tau factor of 21 seconds was considered to indicate the 

needed level of sensitivity, but this was associated with the specific velocity of 5 ft/s 

(1.52 m/s) used in the FMRC plunge test. Since the tau factor changes with the velocity 

of heated air moving past the sprinkler, it is a fairly inconvenient measure of sprinkler 

sensitivity. 

The RTI has replaced the tau factor as the measure of sensitivity and is determined 

simply by multiplying the tau factor by the square root of the air velocity at which it is 

found. The RTI is therefore practically independent of both air temperature and air 

velocity. Comparisons of RTI give a good indication of relative sprinkler sensitivity. 
7 

The smaller the RTI, the faster the sprinkler operation. Standard response sprinklers have 

RTIs in the range of 180 to 650 s1/2ft1/2 (100 to 360 s1/2m1/2), while the RTI range for 

residential sprinklers is about 50 to 90 s1/2ft1/2 (28 to 50 s1/2m1/2). 

The need to add a conductivity term to the model of sprinkler response was recognized in 

1986.24,26 This term accounts for the loss of heat from the sprinkler operating element to 

the sprinkler frame, its mounting, and even the water in the pipe. These losses can 

become significant under low-velocity conditions, particularly for some of the flush-type 

sprinkler designs with little insulation between the operating element and the sprinkler 

body. 

Full-scale tests conducted by FMRC resulted in the development of a prototype fastresponse sprinkler that could control or suppress typical residential fires with the 

operation of not more than two sprinklers. It could also operate fast enough to maintain 

survivable conditions within the room of fire origin.12 Survivable conditions were 

established as follows: 

1. Maximum gas temperature at eye level of 200°F (93°C). 

2. Maximum ceiling surface temperature of 500°F (260°C). 

3. Maximum carbon monoxide volume fraction of 0.15%. 

Thus, the sprinkler concept expanded from the traditional role of property protection to 

include life safety. Full-scale field tests were then conducted in Los Angeles to establish 

system design parameters using the new prototype fast-response 

“residential sprinkler.”13-16 The data from these tests were studied by the National Fire 

Protection Association Technical Committee on Automatic Sprinklers and used to 

establish the criteria for the 1980 edition of NFPA 13D. 

RESIDENTIAL SPRINKLER STANDARDS 

It is important to recognize that, in addition to their fast-response characteristics, 

residential sprinklers have a special water distribution pattern. Because the effective 

control of residential fires often depends on a single sprinkler in the room of fire origin, 

the water distribution pattern of residential sprinklers is required to be more uniform than 

that of standard spray sprinklers, which in large areas can rely upon the overlapping 

patterns of several sprinklers to make up for voids. Additionally, residential sprinklers are 

required to wet sofas, drapes, and similar furnishings at the periphery of the room. In 

their discharge patterns, therefore, the sprinklers must not only be capable of delivering 

water to the walls of the areas where they are installed, but high enough up on the walls 

to prevent the fire from getting “above” the sprinklers. The water delivered close to the 

ceiling not only protects the portion of the wall close to the ceiling, but also enhances the 

capacity of the spray to cool gases at the ceiling level, thus reducing the likelihood of 

excessive sprinkler openings. 

Because of their differences, residential sprinklers are not listed by product evaluation 

organizations under the same product standards as standard sprinklers. Underwriters 

Laboratories Inc., for example, has developed UL 1626 for residential sprinklers, and 

FMRC has published Approval Standard FM 2030 for residential sprinklers. Both of 

these standards include a plunge test with specific sensitivity requirements and a 
8 

distribution test that checks the spray pattern in the vertical plane, as well as the 

horizontal plane. The product standards for standard spray sprinklers do not include 

either of these two tests. 

Both UL 1626 and FM 2030 also include a fire test that is intended to simulate a 

residential fire in the corner of a room containing combustible materials representative of 

a living room environment. 

The UL 1626 fuel package and test procedure was recently revised to: 1) enhance the 

reproducibility of the tests and 2) increase the similarity between the fire performance of 

the fuel package used in the standard tests and that of the fuel packages used as part of 

the principle residential sprinkler research effort.13, 15, 16

The details of the UL 1626 simulated furniture are shown in Figure 7. The three fire test 

configurations are shown in figures 8a-c. Figure 8a shows the configuration used to test 

pendent, upright, flush, recessed pendent and concealed sprinklers. Figures 8b and 8c 

present the configurations used to test sidewall sprinklers, in the first case the sprinklers 

are located opposite the fuel package and in the second case the sprinklers are located on 

the same wall as the fuel package. 

The floor plan dimensions of the test room are dependent on the rated sprinkler coverage. 

As shown in Figure 8a, the width of the test room, w, equals the rated sprinkler coverage 

width and the length of the test room, 2L,equals twice the rated coverage length. For the 

sidewall sprinkler configurations the dimensions of the test room should be the rated 

sprinkler coverage length, L, by 1-1/2 times the sprinkler coverage width, w, plus 9 ft 

(2.7 m). The ceiling height in all cases is a nominal 8 ft (2.4 m). 

The fuel package is composed several different components: a wood crib, two simulated 

sofa ends covered with foam, 2 sheets of 1⁄4 in (6.3 mm) Douglas fir plywood, a pan with 

heptane and two heptane soaked cotton wicks. A wood crib composed of 16 pieces of 

nominal 1-1/2 by 1-1/2 in (38 x 38 mm) kiln-dried spruce or fir lumber 12 in (300 mm) in 

length and weighing between 5.5 and 7.0 lbs (2.5 to 3.2 kg). The pieces of lumber are to 

be arranged in 4 layers with 4 pieces of wood per layer. The piece of lumber should be 

evenly spaced along the length of the previous layer of wood members and stapled in 

place. The layers of lumber are to be placed at right angles to the layer below. The 

finished size of the wood crib is approximately 12 in (305 mm) on a side and 6 in (152 

mm) high. 

The simulated sofa ends are composed of a wood frame support and a 1⁄2 in (12.7 mm) 

thick piece of plywood, 33 by 31 in (840 x 790 mm) high in a vertical position. The 

plywood has 3 in (76-mm) thick uncovered urethane foam cushions 30 in (760 mm) high 

by 32 in (810 mm) wide attached to the side facing the crib. The foam has a density of 

1.70 to 1.90 lbs/ft3

 (27.2 to 30.4 kg/m3). 

The walls of the test room are covered with 4 ft by 8 ft by 1/4 in. (1.2 m × 2.4 m × 6.4 

mm) Douglas fir plywood paneling (flame spread rating 130 ± 30) attached to wood 

furring strips. The ceiling of the test room is 8 ft (2.4 m) high and covered with 2 ft × 4 ft 
9 

× 1/2 in. (0.61 m× 1.20 m × 12.7 mm) thick acoustical panels (flame spread rating 25 or 

less) with a density of 13.5 ± 1.5 lb/ft3 (216 ± 24 kg/m3) attached to wood furring strips. 

Flame spread rating or index is a relative ranking from Steiner Tunnel Test results when 

conducted and analyzed in accordance with NFPA 255, Standard Method of Test of 

Surface Burning Characteristics of Building Materials, where inorganic cement board has 

a flame spread rating of 0 and red oak has a flame spread rating of 100. 

A 12 x12 x 4 in (305 x 305 x 104 mm) high steel pan containing 16 oz. (0.5 l) of water 

and 8 oz. (0.24 l) of heptane is positioned under the wood crib and ignited to start the test. 

To meet the UL 1626 test criteria, residential sprinklers, installed in a fire test enclosure 

with an 8 ft (2.4 m) ceiling are required to control a fire for 10 minutes with the following 

limits: 

1. The maximum gas or air temperature adjacent to the sprinkler—3 in. (76.2 mm) below 

the ceiling and 8 in. (203 mm) horizontally away from the sprinkler—must not exceed 

600°F (316°C). 

2. The maximum temperature—5 ft, 3 in. (1.6 m) above the floor and half the room 

length away from each wall—must be less than 200°F (93°C) during the entire test. This 

temperature must not exceed 130°F (54°C) for more than a 2-min period. 

3. The maximum temperature 1

/4 in. (6.3 mm) behind the finished surface of the ceiling 

material directly above the test fire must not exceed 500°F (260°C). 

4. No more than two residential sprinklers in the test enclosure can operate. 

The enclosure is kept at an initial ambient temperature of 80°F (27°C) ± 5°F (3°C), and it 

is ventilated through two door openings on opposite walls. 

The fire test is conducted for 10 minutes after the ignition of the wood crib. The water 

flow to the first sprinkler that operates and the total water flow when the second sprinkler 

operates are specified as part of the listing limitations for the sprinklers in the test. The 

total water flow for two sprinklers must be a minimum of 1.2 times the minimum flow 

for a single sprinkler. 

The water distribution test requirements are based on the distribution pattern of the 

prototype residential sprinkler used in the Los Angeles test fires.16 The distribution 

requirements involve collections in both the horizontal and vertical planes. 

All residential sprinklers in the test must discharge water at the flow rate specified by the 

manufacturer for a 10-minute period simulating one sprinkler operating and two 

sprinklers operating. The quantity of water collected on both the horizontal and vertical 

surfaces is measured and recorded. 

Sprinklers being tested are required to discharge a minimum of 0.02 gpm per sq ft 

[0.8(L/min)/m2

] over the entire horizontal design area, with the exception that no more 

than four 1 foot square (0.09 m2

) areas shall be allowed to be at least 0.015 gpm per sq ft 

[0.6(L/min)/m2]. They must also wet the walls of the test enclosure to a height not less 

than 28 in. (711 mm) below the ceiling with one sprinkler operating. Each wall 
10 

surrounding the coverage area is required to be wetted with a minimum of 5 percent of 

the sprinkler flow.

In May of 2000, a Tentative Interim Amendment was issued by the NFPA Standards 

Council to the 1999 edition of NFPA 13 that requires residential sprinklers installed in an 

NFPA 13 system to be used at a minimum water spray density of 0.1 gpm/sq. ft. (4.1 

L/m2

). In 2002, the NFPA Technical Committee on Residential Sprinkler Systems 

proposed a minimum water spray density of 0.05 gpm/sq.ft. (2.0 L/m2) for sprinklers 

used in NFPA 13D and 13R systems, based on research conducted by FM and UL (add 

refs). This proposal was accepted at the NFPA Annual meeting in May of 2002. UL 

changed their testing requirements in accordance with the proposed standards. 

 

Revised NFPA 13D Design Requirements 

The design criteria in the 1980 edition of NFPA 13D included for the first time the 

requirement that all sprinklers be “listed residential sprinklers”. Other initial basic design 

requirements in the revamped NFPA 13D were as follows: 

Performance criteria: To prevent flashover in the room of fire origin, when sprinklered, 

and to improve the chance for occupants to escape or be evacuated. 

Design criteria: 

1. Only listed residential sprinklers to be used. 

2. Minimum 18 gpm (68 L/min) to any single operating sprinkler and 13 gpm (49 L/min) 

to all operating sprinklers in the design area up to a maximum of two sprinklers. 

3. Maximum area protected by a single sprinkler of 144 sq ft (13.4 m2

). 

4. Maximum distance between sprinklers of 12 ft (3.7 m). 

5. Minimum distance between sprinklers of 8 ft (2.4 m). 

6. Maximum distance from a sprinkler to a wall or partition of 6 ft (1.8 m). 

Application rates, design areas, areas of coverage, and minimum design pressures other 

than those specified above were permitted to be used with special sprinklers listed for 

such special residential installation conditions. 

Sprinkler coverage: Sprinklers to be installed in all areas with the following exceptions. 

Exception No. 1: Sprinklers allowed to be omitted from bathrooms no larger than 55 sq ft 

(5.1 m2). 

Exception No. 2: Sprinklers allowed to be omitted from closets where the least dimension 

does not exceed 3 ft (0.9 m), the area does not exceed 24 sq ft (2.2 m2), and the walls and 

ceiling are surfaced with noncombustible materials. 

Exception No. 3: Sprinklers allowed to be omitted from open-attached porches, garages, 

carports, and similar structures. 

Exception No. 4: Sprinklers allowed to be omitted from attics and crawl spaces that are 

not used or intended for living purposes or storage. 

Exception No. 5: Sprinklers allowed to be omitted from entrance foyers that are not the 

only means of egress. 

In the twenty years, following the development of the residential sprinkler, special 

listings involving expanded protection areas and reduced flows proliferated to the point 
11 

that the original flow and spacing criteria have become all but obsolete. Residential 

sprinklers are now listed for coverage areas up to 400 sq ft (37.2 m2) per sprinkler. 

Since 1985, the use of residential sprinklers has also been permitted under some 

conditions in accordance with NFPA 13. Essentially, NFPA 13 allows residential 

sprinklers in dwelling units located in any occupancy, provided they are installed in 

conformance with the requirements of their listing and the positioning requirements of 

NFPA 13D. A dwelling unit is defined as one or more rooms arranged for the use of one 

or more individuals living together, as in a single housekeeping unit normally having 

cooking, living, sanitary, and sleeping facilities. Dwelling units include hotel rooms, 

dormitory rooms, sleeping rooms in nursing homes, and similar living units. Occupancies 

encompassing dwelling units include apartment buildings, board and care facilities, 

dormitories, condominiums, lodging and rooming houses, and other multiple-family 

dwellings. 

For NFPA 13 applications involving residential sprinklers in dwelling units, the design 

area is required to consist of the four most hydraulically demanding sprinklers. 

Other areas, such as attics, basements, or other types of occupancies outside of dwelling 

units but within the same structure, are required to be protected in accordance with 

regular provisions of NFPA 13, including the appropriate water supply requirements. The 

decision as to which areas are to be protected with sprinklers is also regulated in 

accordance with the normal provisions of NFPA 13. This means, for example, that 

combustible concealed spaces generally require sprinklers. Although the four-sprinkler 

design area can be used in the dwelling units when protected with residential sprinklers, 

any sprinklers installed within such concealed spaces would have to use a different 

design approach. 

Residential sprinklers installed in systems designed to NFPA 13 requirements are spaced 

and positioned in accordance with their residential listings, not with the spacing 

requirements of NFPA 13. The water demands for the residential sprinklers are the same 

as in NFPA 13 applications, except that the multiple sprinkler flow requirement is 

extended to four sprinklers rather than the two stipulated for one- and two-family 

dwellings and manufactured homes in NFPA 13D. The less restrictive piping, 

component, hanger, location, and water supply duration allowances of NFPA 13D are not 

permitted in these systems. 

Beginning in 1996, NFPA 13 required residential sprinklers or fast-response sprinklers in 

residential areas. 

Development of NFPA 13R 

In 1989, a new standard was developed to bridge the gap between NFPA 13 and NFPA 

13D. The new standard is NFPA 13R, Standard for the Installation of Sprinkler Systems 

in Residential Occupancies up to and Including Four Stories in Height (hereinafter 

referred to as NFPA 13R). 

Like NFPA 13D, NFPA 13R is oriented toward economical life safety protection. 

Sprinklers are omitted from building areas that have been found to have a low incidence 
12 

of fatal fires, including combustible concealed spaces, small bathrooms and closets, and 

attached porches. As with NFPA 13D, residential sprinklers are required throughout 

dwelling units, with some minor exceptions. A four-sprinkler design area is required 

unless the largest compartment contains fewer sprinklers. 

In recognition of the greater risk associated with multifamily occupancies, however, 

NFPA 13R is more conservative than NFPA 13D, in some areas. Requirements for plans, 

hydraulic calculations, and system acceptance certificates parallel those of NFPA 13. 

Unlike NFPA 13D, NFPA 13R requires a consideration of the likelihood that 

simultaneous domestic flows might occur through combined service piping. In addition, 

pumps and other key equipment are required to be listed. In NFPA 13R systems, areas 

outside dwelling units can be protected with standard spray sprinklers, using NFPA 13 

design criteria. 

 

NEW TECHNOLOGY IN RESIDENTIAL SPRINKLER SYSTEMS 

Multi-purpose piping systems 

Although NFPA 13D has had the option for a combined or multi-purpose piping system 

for many years, in 1999 the committee further encouraged the use of this option by 

allowing non-listed pipe to be connected to the sprinkler system for the purpose of 

supplying plumbing fixtures and by specifying a working pressure requirement of not less 

than 130 psi (8.9 bar) at not less than 120 oF (49 oC). The combined system may be a 

means to integrate the sprinkler system into new homes as a standard feature instead of as 

an option. 

The multi-purpose system uses the cold water piping to serve as a supply for both the 

domestic fixtures, i.e. sinks, showers, etc, and the fire sprinklers. Given the potential for 

a reduced amount of pipe and fittings, there is a potential for reduced system cost. 

 

Supplying the sprinklers from the domestic water system can provide increased system 

reliability since any impairment to the water supply would be more quickly recognized. 

In addition a combined system eliminates the need for back flow prevention devices. 

This also helps to reduce the cost of the system and eliminates any water pressure losses 

that would be incurred by a backflow prevention device. 

New piping materials composed of cross-linked polyethylene have recently been listed by 

UL for use in residential sprinkler systems. 27 This piping is similar to piping already 

used in domestic plumbing systems and therefore is easily used in combined systems. 

Residential Water Mist System 

Residential fire suppression/control systems are also being developed under NFPA 750, 

Standard on Water Mist Fire Protection Systems. A water mist system uses very fine 

water sprays “... to control or extinguish fires by cooling of the flame and fire plume, 

oxygen displacement by water vapor, and radiant heat attenuation” 28. 
13 

Water mist systems typically use smaller amounts of water at significantly higher 

pressures when compared to a NFPA 13D residential sprinkler system. The spacing of 

water mist nozzles tends to be smaller than the spacing of residential sprinklers, hence 

more nozzles are needed to provide fire protection for a given area. Studies sponsored by 

the U.S. Fire Administration showed that in some cases water mist systems could provide 

equivalent levels of fire safety relative to a residential sprinkler system, however at a 

significantly higher cost. 29,30

RESIDENTIAL SPRINKLER EXPERIENCE 

Scottsdale AZ, Case Study 

Due to the proven effectiveness of residential fire sprinklers, communities in 25 states 

require sprinklers in 1 and 2 family homes.31 One of these communities, Scottsdale, AZ, 

has conducted a detailed 10 year study on the impact of residential fire sprinklers on their 

community. In June of 1985, the City of Scottsdale passed a comprehensive fire 

sprinkler ordinance which required all new multi-family and commercial structures to be 

protected by sprinklers beginning in July of 1985 and all new single family homes 

beginning in January of 1986. 32 

The results of the study held some surprises. The average installation cost of a residential 

sprinkler system decreased significantly over the ten year period. In 1986, the average 

installation cost was $1.14/ ft2. By January of 1996, the average cost was $.59/ ft2, a 

decrease of approximately 45%.32 Surveys of the home insurance companies in the 

Scottsdale area yielded an average discount of 10% for homes with residential sprinkler 

systems installed. 32 

The Scottsdale study also examined the issue of water usage during a fire incident. The 

first 38 sprinklered fire incidents, a combination of fires in commercial, multi-family and 

single family units, were investigated. Based on the incident timelines, the water flow 

times for the sprinkler systems were determined and the total water flow was calculated. 

The average amount of water used per fire was 357 gallons. Assuming that manual 

suppression could be accomplished in the same amount of time as the sprinkler flow 

time, the average amount of water used per fire incident by the fire department would 

amount to more than 4,800 gallons. 32

In 1996, a review of the 109 fires that had occurred in sprinklered buildings in Scottsdale 

included 44 residential fires. In more than 90% of the incidents, the fire was controlled 

with 1 or 2 sprinklers activated. The average amount of water flowed by the sprinklers 

was 299 gallons per fire vs. an estimated manual suppression usage of approximately 

6,000 gallons per fire. Most importantly, the study indicates that at a minimum 8 lives 

were saved in these fires by the residential sprinkler systems. 32

This study is yet another measure that demonstrates with real world experience how 

sprinklers can decrease the amount of property damage from both the fire and the 

suppression of the fire, while providing improved life safety. 

 
14 

INCENTIVES TO MORE WIDESPREAD USE OF RESIDENTIAL 

SPRINKLERS 

There are certain incentives that can stimulate interest in residential sprinklers. These 

incentives are discussed in the following paragraphs. 

Reduction in Government Spending 

Reduction in all forms of government spending, resulting from public pressure to reduce 

property taxes, is a prime factor in the future growth of the residential sprinkler concept. 

Many fire departments are forced to protect larger areas and more subdivisions with the 

same number of, or even fewer people, in several communities since financial restrictions 

hamper a fire department’s ability to grow with the community. As a result, alternates to 

traditional fire-fighting techniques must be found. One of them is the use of residential 

sprinklers. 

San Clemente, CA, was the first community in the United States to pass a residential 

sprinkler ordinance in 1980 as part of the fire department’s master plan. This ordinance 

requires automatic sprinkler systems to be installed in all new residential construction. 

The prime motivation for the passage of this ordinance was San Clemente’s cutbacks in 

government spending brought about by Proposition 13, the state’s tax-capping measure. 

Many communities across the country face similar situations. Automatic sprinklers in 

residences may be the answer to fewer fire fighters and longer response times from the 

fire department. 

Insurance Savings 

Although the greatest benefit from widespread installation of residential sprinklers will 

be the lives saved and injuries prevented, lower property losses will be a secondary and 

substantial benefit. An ad-hoc committee from the insurance industry sponsored a 

number of the test fires in Los Angeles and concluded that residential sprinklers have the 

potential for reducing homeowners’ claim payment expenses.33 As a result, the Insurance 

Services Office (ISO) Personal Lines Committee recommended that a 15-percent 

reduction in the homeowner’s policy premium be given for installation of an NFPA 13D 

residential sprinkler system. While this would not pay for the system over a short period 

of time, as is the case in many commercial installations, the continuing increases in the 

cost of insuring a single-family home make this a significant incentive nonetheless. 

Real Estate Tax Reductions 

In 1981, the State of Alaska enacted into law a significant piece of legislation that has a 

dramatic impact on the installation of sprinkler systems throughout that state. The law 

provides that 2 percent of the assessed value of any structure is exempt from taxation if 

the structure is protected with a fire protection system. The word “structure” is significant 

in the law, since it also applies to homes. In effect, if a home were assessed at $100,000 

for purposes of taxation, the assessed value would be computed at $98,000, provided that 

it contained a fire protection system. 
15 

Buyers’ Attitude 

While one study indicated that 30 percent of the people interviewed perceived no need 

for a residential sprinkler system,8 a 1980 survey published by the National Association 

of Home Builders on luxury features that buyers want in a new home showed that 14.3 

percent indicated “fire suppression systems” as a choice. For potential buyers with 

incomes over $50,000, the percentage rose to over 20 percent. 

Zoning 

Greater land use may be possible with zoning changes that would permit fully sprinklered 

residences to be built on smaller parcels of land. The assumption is that the space 

between houses will not be as important from a fire protection standpoint if an entire 

street or neighborhood is fully sprinklered. One could argue, however, that if the 

sprinkler system fails, the resultant fire involving a number of residences could be much 

greater. 

Sprinkler Legislation 

In addition to the San Clemente ordinance, a number of other California communities 

have passed residential sprinkler legislation, including Orange County and Los Angeles 

County. By 1993, more than 4 million Californians lived in communities in which 

residential sprinklers were mandated in all new homes.34

Since 1982, Greenburgh, NY, and several surrounding communities have enacted 

sprinkler ordinances that require the installation of automatic sprinklers in virtually all 

new construction, including all new multiple- and one- and two-family dwellings. A 

similar law went into effect in Prince Georges County, Maryland, in 1992. 

The State of Florida in 1983 passed a law requiring that all public lodging and time-share 

units three stories or more high in the state be sprinklered. It also required that all existing 

units be sprinklered by 1988. 

In 1983, the City of Honolulu, HI, adopted legislation that required all new and existing 

high-rise hotels, which are those more than 75 ft (23 m) above grade, to be sprinklered. 

In the late 1980s, additional jurisdictions, including Atlanta, GA, the State of 

Connecticut, and the Commonwealth of Massachusetts, acted to retroactively require the 

installation of sprinkler systems in high-rise residential buildings. 

In 1990, the federal government enacted the Hotel and Motel Fire Safety Act, which 

contains strong incentives for complete sprinkler protection of hotels, since only hotels 

with satisfactory levels of fire protection are eligible for federal employee travel. 

The Federal Fire Safety Act of 1992 requires automatic sprinkler systems or an 

equivalent level of safety in all federally assisted housing four or more stories in height, 

as well as in office buildings owned or leased for more than 25 federal employees. 

Perhaps the most significant legislation promoting the use of sprinkler systems, however, 

is the 1990 Americans with Disabilities Act. In 1991, the U.S. Department of Justice 

published criteria that became mandatory for places of public accommodation and 

commercial facilities designed for first occupation after January 26, 1993. Alterations to 

existing buildings must also comply. A key feature of the criteria is the need for areas of 

refuge. Floors of buildings that do not have direct access to the exterior at grade must 
16 

provide areas of rescue assistance, except those buildings that have a supervised 

automatic sprinkler system. 

Construction Incentives 

Many Authorities Having Jurisdiction have used building code modifications as an 

incentive to install sprinklers. Cobb County, GA, was one of the first communities to 

amend its Buildings and Construction Code to include such an approach for multi-family 

structures equipped with residential sprinkler systems. While these construction 

alterations can be a major incentive to install residential sprinklers, the disaster potential 

must always be considered if a fire, for whatever reason, should overpower the sprinkler 

system. This is especially true if the system is designed with the minimal water supplies 

required by NFPA 13D. 

The City of Dallas, TX, adopted a building code that requires all new buildings or those 

undergoing major renovation, having an area greater than 7,500 sq ft (697 m2

), to have 

automatic sprinklers. At the same time, this building code encourages the installation of 

sprinkler systems by allowing design options that may allow different levels of “passive” 

fire protection features in exchange for “active” automatic sprinkler alternatives. 

Code Requirements 

Beginning with the 1991 edition, NFPA 101®, Life Safety Code®, required the use of 

quick-response or residential sprinklers in new health care occupancies in smoke 

compartments containing patient sleeping rooms. This generally means all patient rooms 

and their adjacent corridors. Beginning with the 1994 edition, quick-response or 

residential sprinklers were also required in all new hotel and dormitory guest rooms and 

guest room suites. 

SUMMARY 

Since the introduction of the residential sprinkler standard, NFPA 13D, in 1975, 

residential sprinkler systems have proven themselves as life safety systems. Because of 

improvements in system design and the incentives listed above, the use of new 

technology, such as residential and quick-response sprinklers, nearly tripled in the United 

States between 1987 and 1994, even though the total number of sprinklers installed 

increased only slightly.35 While there is growing recognition of the enhanced ability of 

fast-response sprinklers to protect life and property from fires, it is estimated that less 

than 3 % of the one and two family homes in the United States have them installed3

. 

ACKNOWLEDGEMENTS 

The authors would like to thank Mr. George Laverick from Underwriters’ Laboratories 

Inc, for providing the graphics representing the revised UL 1626 fire test fuel package 

and layout. The authors would also like to thank Mr. Larry Maruskin from the U.S. Fire 

Administration for his support of the development of this document. 
17 

REFERENCES 

1. America Burning, The Report of the National Commission on Fire Prevention and 

Control, U.S. G.P.O.: 1973-O-495-792, May 1973. 

2. Karter, Michael J., 1998 Fire Loss in the United States, NFPA Journal, Vol. 93, No 5 

Sept/Oct 1999. 

3. Fire in the United States 1989-1998, 12th ed. Federal Emergency Management 

Agency, United States Fire Administration, National Fire Data Center, FA-216, August 

2001. 

4. NFPA 13D, Standard for the Installation of Sprinkler Systems in One- and TwoFamily Dwellings and Manufactured Homes, 1999 ed., National Fire Protection 

Association, Quincy, MA. 

5. Bryan, John, L. Automatic Sprinkler and Standpipe Systems, 2nd ed. National Fire 

Protection Association, Quincy, MA. 1990. 

6. Jensen, Rolf, P.E., A Brief History of Sprinklers, Sprinkler Systems and the NFPA 

Sprinkler Standards. Automatic Sprinkler System Handbook 8th ed. Supplement, National 

Fire Protection Association, 1999. 

7. Halpin, B. M., Dinan, J. J., and Deters, O. J., “Assessment of the Potential Impact of 

Fire Protection Systems on Actual Fire Incidents,” Johns Hopkins University—Applied 

Physics Laboratory (JHU/APL), Laurel, MD, Oct. 1978. 

8. Yurkonis, P., “Study to Establish the Existing Automatic Fire Suppression Technology 

for Use in Residential Occupancies,” Rolf Jensen & Associates, Inc., Deerfield, IL., Dec. 

1980. 

9. Kung, H. C., Haines, D., and Green, R., Jr., “Development of Low-Cost Residential 

Sprinkler Protection,” Factory Mutual Research Corp., Norwood, MA, Feb. 1978. 

10. Henderson, N. C., Riegel, P. S., Patton, R. M., and Larcomb, D. B., “Investigation of 

Low-Cost Residential Sprinkler Systems,” Battelle Columbus Laboratories, Columbus, 

OH, June 1978. 

11. Clark, G., “Performance Specifications for Low-Cost Residential Sprinkler System,” 

Factory Mutual Research Corp., Norwood, MA, Jan. 1978. 

12. Kung, H. C., Spaulding, R. D., and Hill, E. E., Jr., “Sprinkler Performance in 

Residential Fire Tests,” Factory Mutual Research Corp., Norwood, MA, Dec. 1980. 

13. Cote, A. E., and Moore, D., “Field Test and Evaluation of Residential Sprinkler 

Systems,” Los Angeles Test Series (A report for the NFPA 13D Subcommittee), National 

Fire Protection Association, Quincy, MA, Apr. 1980. 

14. Moore, D., “Data Summary of the North Carolina Test Series of USFA Grant 79027 

Field Test and Evaluation of Residential Sprinkler Systems, (a report for the NFPA 13D 

Subcommittee),” National Fire Protection Association, Quincy, MA, Sept. 1980. 

15. Kung, H. C., Spaulding, R. D., Hill, E. E., Jr., and Symonds, A. P., “Technical 

Report, Field Evaluation of Residential Prototype Sprinkler Los Angeles Fire Test 

Program,” Feb. 1982, Factory Mutual Research Corp., Norwood, MA. 

16. Cote, A. E., “Final Report on Field Test and Evaluation of Residential Sprinkler 

Systems,” July 1982, National Fire Protection Association, Quincy, MA. 

17. Heskestad, G., and Smith, H., “Investigation of a New Sprinkler Sensitivity Approval 

Test: The Plunge Test,” FMRC No. 22485, Dec., 1976, Factory Mutual Research Corp., 

Norwood, MA. 
18 

18. Heskestad, G., and Smith, H., “Plunge Test for Determination of Sprinkler 

Sensitivity,” FMRC J.I.3A1E2.RR, 1980, Factory Mutual Research Corp., Norwood, 

MA. 

19. Pickard, R. W., Hird, D., and Nash, P., “The Thermal Testing of Heat-Sensitive Fire 

Detectors,” F.R. Note No. 247, Jan. 1957, Fire Research Station, Borehamwood, Herts, 

U.K. 

20. Evans, D. D., and Madrzykowski, D., “Characterizing the Thermal Response of 

Fusible-Link Sprinklers,” NBSIR 81-2329, Aug. 1981, National Bureau of Standards, 

Washington, DC. 

21. Theobald, C. R., “FRS Ramp Test for Thermal Sensitivity of Sprinklers,” Journal of 

Fire Protection Engineering, Vol. 1, No. 1, Jan.–Mar. 1989, p. 23. 

22. Beever, P. F., “Estimating the Response of Thermal Detectors,” Journal of Fire 

Protection Engineering, Vol. 2, No. 1, Jan.–Mar. 1990, p. 11. 

23. Cote, A.E. and Fleming, R.P., “Fast-Response Sprinkler Technology”, Fire Protection 

Handbook, 18th ed., National Fire Protection Association, Quincy, MA, 1997, p. 6-181. 

24. Heskestad, G., and Bill, R. G., “Conduction Heat-Loss Effects on Thermal Response 

of Automatic Sprinklers,” FMRC J.I. OMOJ5.RU, Sept. 1987, Factory Mutual Research 

Corp., Norwood, MA. 

25. Madrzykowski, D., The Effect of Recessed Sprinkler Installation on Sprinkler 

Activation Time and Prediction, Master’s Thesis University of Maryland, College Park, 

MD, November 1993. 

26. Pepi, J. S., “Design Characteristics of Quick-Response Sprinklers,” Grinnell Fire 

Protection Systems Co., Providence, RI, May 1986. 

27. www.ul.com/database category cross-linked polyethlyne (PEX) sprinkler pipe & 

fittings VIXR. 

28. NFPA 750, Standard on Water Mist Fire Protection Systems, 2000 ed., National Fire 

Protection Association, Quincy, MA. 

29. Feasibility Study of Water Mist Applications for Residential Fires, Contract No. 

EMW-93-4247. Hughes Associates, Inc., Baltimore, MD. February 9, 1995. 

30. Bill, R.G., Stavrianidis, P., Hill, E.E., Brown, W.R., Water Mist Fire Protection in 

Residential Occupancies, FMRC J.I.OY1N9.RA OZOJ1.RA Factory Mutual Research 

Corporation, Norwood, MA., November 1995 

31. Residential Fire Safety Institute, www.firesafehome.org/1-2fam.html 6/9/01. 

32. Automatic Sprinklers, A 10 year Study, A Detailed History of the Effects of the 

Automatic Sprinkler Code in Scottsdale, Arizona, Rural/Metro Fire Department, 

Scottsdale, AZ, 1997. 

33. Jackson, R. J., “Report of 1980 Property Loss Comparison Fires,” 1980, 

FEMA/USFA, Washington, DC. 

34. Hart, S., “Executive Summary Report on the 1993 Fire Sprinkler Ordinance Survey,” 

May 31, 1993, Fire Sprinkler Advisory Board of Southern California, Cerritos, CA. 

35. Viniello, J.A. NFSA Statistics, Private Communication, Oct. 2001. 
19 

Source: FIDO Database 1973-1982, NFPA Fire Analysis Department 

Table 1. Area of origin in one- and two-family dwelling fires that resulted in one or 

more deaths. 
20 

Table 2. Fires and associated deaths and injuries in Dwellings, duplexes, and 

manufactured homes by area of origin: annual average of 1986-1990 structure fires 

reported to U.S. fire departments.
21 

Source: FIDO Database 1973-1982, NFPA Fire Analysis Department 

Table 3. Causal factor in one- and two-family dwelling fires that resulted in one or 

more deaths, first item ignited. 

Table 4. Causal factor in one- and two-family dwelling fires that resulted in one or 

more deaths, source of ignition. 
22 

Figure 1. Fire deaths per million population by age. 
23 

Figure 2. Relative risk of fire casualties by age. 
24 

Figure 3. Fire fighter deaths on fire ground by fixed property use in 1998. 

Figure 4. Fire fighter injuries by fixed property use, structure fires in 1998. 
25 

Figure 5. International sprinkler sensitivity ranges, response time index (RTI) vs 

conductivity (C). (For U.S. conversion: 1 ft = 0.305 m) 
26 

Figure 6. Calculated sprinkler “tau” values responding to a step change 

temperature increase of 90 °C with a gas velocity of 2.54 m/s ( 8.33 ft/s). τ=25 would 

be equivalent to an RTI of 40 m1/2s

1/2 ( 73 ft1/2s1/2) while τ=200 would be equivalent 

to an RTI of 320 m1/2s

1/2 ( 580 ft1/2s1/2 ). For a given activation temperature of 68 °C

(155 °F), a fast response sprinkler will activate in less than 14 seconds compared to 

the greater than 100 second activation time of the slowest standard response 

sprinkler. 
27 

 

Figure 7. Simulated fuel package for UL 1626. The fuel package is composed of 

several different components: a wood crib, two simulated sofa ends covered with 

foam, 2 sheets of 1⁄4 in (6.3 mm) Douglas fir plywood, a pan with heptane and two 

heptane soaked cotton wicks. The arrangement of the fuel package within the test 

room is shown at the upper left of the figure. 
28 

Figure 8a. Fire test arrangement for UL 1626, for pendent, upright, flush recessed 

pendent and concealed sprinklers.
29 

Figure 8b. Fire test arrangement from UL 1626 for sidewall sprinklers, test 

arrangement 1. 
30 

Figure 8c. Fire test arrangement from UL 1626 for sidewall sprinklers, test 

arrangement 2.