U.S. Fire Administration 

Backflow Protection 

for Residential 

Sprinkler Systems 

June 1993 

Homeland

Security
BACKFLOW PROTECTION FOR RESIDENTIAL

SPRINKLER SYSTEMS

By:

Frederick L. Hart, P.E., Ph.D.

Robert Till File No. 12.054

Christine Nardini June, 1993

Daniel Bisson
This document was scanned from hard copy to portable document format (PDF) 

and edited to 99.5% accuracy. Some formatting errors not detected during the 

optical character recognition process may appear. 
Notice 

This report was prepared for the U.S. Fire Administration, Federal Emergency Management 

Agency, Grant No. EMW-93-G-4191. The Project Officer for this study was Mr. Larry Maruskin 

of the U.S.F.A.. The statements and conclusions contained in this report arc those of the authors 

and do not necessarily reflect the views of the USFA or the Federal Emergency Management 

Agency. 
Table of Contents 

List of Figures .......................................................................................

List of Tables ..........................................................................................

Executive Summary ................................................................................. 1

Introduction ........................................................................................... 3

Section 1.0: Definitions ............................................................................... 7

Section 2.0: Regulations and Authorities .......................................................... 10

Section 3.0: Typical Household Water Piping Systems ......................................... 14

Section 4.0: Possible Water Quality Changes ..................................................... 17

Section 5.0: Available Data .......................................................................... 22

Section 6.0: Risks versus Benefits ................................................................. 3 3

Section 7.0: Areas Needing Additional Information ............................................. 43

Section 8.0: Recommendations ..................................................................... 46

References ............................................................................................. 47

Appendices 

1: Design Specifications for a Typical Household Potable Piping System . . . . 51

2 : Design Specifications for a Typical Household Sprinkler System . . . . . . . . . . 53
List of Figures 

Figure 1: Typical Hot & Cold Piping System for a Single Family Dwelling ..................... 15

Figure 2: Typical Sprinkler System for a Single Family Dwelling ................................ 16

Figure 3: Number of Civilian Deaths & Injuries for One & Two Family Dwellings by Year 23

Figure 4: Percent Change in Civilian Deaths from Previous Year ................................. 24

Figure 5: Percent Change in Civilian Injuries from Previous Year ................................ 25

Figure 6: Deaths & Injuries in One & Two Family Dwellings as a Percentage of Total Fire

Related Deaths & Injuries ................................................................... 26

Figure 7: Outbreaks of Waterborne Disease .......................................................... 29

Figure 8: Failure Rates for 0.75 & 1.00 Inch Devices .............................................. 31

Figure 9: Location of Sprinkler & Water Line Protection Devices ................................. 37
List of Tables 

Table 1: Number of Outbreaks & Associated Cases by Etiological Agent ........................ 30

Table 2: Failure of DCVA and SCV ................................................................... 32

Table 3: Failures of RPBD ............................................................................. 32

Table 4: Classification of Dwellings ................................................................... 34

Table 5: Units of Risk for Fire (Injury/Death) & Waterborne Illness Events .................... 42

Table 6: Normalized Risk of Fire (Injury/Death) & Waterborne Illness Events ............... 42

Table 7: Hydraulic Model Flow Testing Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53
EXECUTIVE SUMMARY 

This report addresses risk vs benefit issues associated with the installation of residential fire 

sprinkler systems. A primary objective of this assessment is to rate the risk of potable water 

contamination from a residential sprinkler system, and consequently to evaluate the need for 

installing backflow prevention devices. 

Statistics and assumptions outlined in this report show that the present risk from fire (death and/or 

injury) is 11.1 times higher than the present risk of waterborne disease (illness). This finding 

alone demonstrates a significant benefit from installing residential sprinkler systems. 

The increased risk of water contamination from unprotected household sprinklers was assumed to 

be directly proportional to the increased volume of stagnant water added to household water lines. 

This calculation assumes that potable water remaining stagnant for very long periods (e.g. 

sprinkler lines) has the same potential for biological, chemical, and physical deterioration as water 

remaining stagnant for intermittent periods (e.g. typical household plumbing lines). Although 

equating extended stagnation to intermittent stagnation could not be supported from field or 

laboratory data, a number of reasons support that conclusion. In addition, because intermittent 

stagnation may even be more detrimental to water quality, a direct volume correlation to increased 

risk may actually result in a conservative risk assessment of sprinkler lines. 

Reported failure rates of backflow preventers recommended for low hazard and high hazard cross 

connections (Double Check Valve Assemblies - DCVA and Reduced Pressure Principle Backflow 

Devices - RPBD) were used to estimate the reduction of water contamination risk when using these 

devices. An estimated failure rate of a simple and low cost alternative device (Single Check Valve ­

SCV) was used to predict the reduction of water contamination risk when using that device. 

Four installation options were selected: 

Scenario A: No protection device (SCV, DCVA, RPBD) is provided 

Scenario B: Either of the above three devices (SCV, DCVA, RBBD) are placed at the 

sprinkler line. 
Scenario C: Either of the above three devices (SCV, DCVA, RPBD) are placed at the 

sprinkler feed line and also at the potable water feed line. 

Scenario D: Same as Scenario C, but the device is placed at the feed line before 

branching to the potable feed line and the sprinkler feed line. 

A normalized risk (death & injury from fire per population base, and waterborne illness per 

population base) was calculated and presented as follows: 

Condition Fire Event 

(Injury & Death) 

Waterborne Event 

(Illness) 

Household Water Only 

(No Sprinkler) 

Scenario A 

Scenario B 

SCV 

DCVA 

RPBD 

Scenarios C& D 

SCV 

DCVA 

RPBD 

11.10 

5.84 

5.84 

5.84 

1.00 

2.50 

1.06 

1.02 

1.03 

0.10 

0.04 

0.05 

Normalized Risk of Fire (Injury & Death) and Waterborne Illness Events 

Based on this relative comparison of risk, and also noting that at no time did the risk of 

waterborne illness reach the USEPA acceptable level of risk for gastrointerstinal illness (1 x 10-4 or 

a relative risk of 12.2), the following recommendations are made: 

1) The SCV device should be considered in favor of the DCVA and the RPBD for individual 

household sprinkler systems. 

2) If a protection device is to be used for a sprinkler line, the same degree of protection should 

be considered at the potable water line. 

2
INTRODUCTION 

An estimated 478,000 residential fires occurred in the United States in 1991 accounting for 74.6% 

of all the structure fires in that year. Of these residential fires, one- and two-family dwellings 

accounted for 363,000 which represents 56.7% of all structure fires (1). In this one year, fires that 

occurred in one- and two-family dwellings are estimated for causing 2,905 deaths (65% of total 

deaths), 15,600 serious injuries (53.1% of total injuries) and $3,354,000,000 in property loss 

(40.1% of total property loss). 

Much of this suffering and financial loss could have been substantially reduced if residences were 

equipped with sprinkler systems. In a study done by Ruegg & Fuller, it was estimated from 

simulation that sprinklers in dwellings can reduce the number of fire deaths by 63% and the 

number of non-fatal casualties by 44% (2). These simulations involve scenario techniques which 

use a benefit-cost model to predict the effectiveness of sprinkler systems in residential homes. 

Equipping houses with sprinkler systems without a check valve, however, may lead to another 

problem; public water supply contamination. This potential exists because sprinkler pipe lines will 

contain stagnant water which, under certain conditions, could be reintroduced back into the public 

water network. In 1991, Regli, et. al. (3) reported that over 500 outbreaks (multiple illnesses in the 

same distribution system or area) of waterborne disease occurred since 1971. In a 1982 report (4). 

EPA reported 27,000 cases of illness from the consumption of contaminated water during the 

period 1972 through 1976 and reported an additional 11,435 cases of waterborne illness in 1987. 

In a more recent study, 26 outbreaks of waterborne disease were reported for the years 1989 and 

1990. Of the reported outbreaks for this two year time frame, 11 of the outbreaks were attributable 

to community water systems which resulted in 1,660 illnesses and four deaths (5). It should be 

noted, that none of the above mentioned cases were attributed to backflow failure from sprinkler 

systems. 

The potential for water contamination can be reduced by isolating sprinkler lines from the public 

water supply with backflow preventers. A simple and low cost version of a backflow preventer is 

the single check valve (SCV), which has been used on sprinkler systems since the early 1800’s. 

Many agencies concerned with water quality issues, however favor a double check valve assembly 

or a reduced principle backflow preventer device (RPBD) because they feel that this added degree 

3
of protection is warranted. These more sophisticated devices, however, are expensive and may 

deter people from installing household sprinkler systems. The RPBD’s may also negatively impact 

the usefulness of a sprinkler system by reducing the available pressure because of friction losses, 

and therefore lowering the deliverable flow. Finally, regulatory requirements often associated with 

sophisticated backflow preventers might also detract home owners from considering a sprinkler 

system. 

Consequently, two equally significant public health and safety issues (public safety through fire 

protection and public safety through water supply protection) are at direct odds with each other. 

This situation is unavoidable for most household dwellings because homes typically rely on the 

same water source to satisfy both objectives. These opposing viewpoints cause advocates on each 

side to often consider the other safety issue as a direct threat to their own concerns. For example, a 

requirement for sprinkler systems in individual households would satisfy fin safety concerns but, 

without the presence of backflow preventers, potable water supplies may be jeopardized due to the 

introduction of stagnant water into potable water lines. Conversely, the requirement for certain 

types of backflow preventers on sprinkler lines may make the entire household sprinkler system 

prohibitively expensive, and for retrofit systems - possibly incapable of functioning properly. 

These opposing views have existed for a number of years and have been debated extensively, often 

under highly emotional circumstances. Now that the need for residential sprinkler systems are 

being seriously recognized (especially for new home construction), the debate has intensified. 

Typically, those concerned with water quality issues favor a maximum degree of protection 

provided by a double check valve assembly or a reduced principle backflow device, while those 

concerned with fire protection issues favor a less expensive, low head loss single check valve 

device. Others may even favor no backflow preventers for individual households because of the 

regulations that are often associated with the installation and inspection of backflow devices. 

This paper addresses this debate by focusing on the following question: 

What is the difference in risk associated with a single check valve &vice compared to a double 

check valve assembly and a reduced principle backflow &vice for residential sprinkler system? 

To answer this question, an evaluation of risks and benefits associated with either decision is 

presented. For both options. the following assumptions are made: 

4 
All water in a household plumbing system (including sprinkler system) is from a community 

water system. 

The household is supplied with high quality municipal water that meets drinking water 

requirements at the point of delivery. 

The sprinkler pipeline is constructed of either copper (no lead solder) or PVC pipe suitable for 

potable water supplies. 

The probability of fire, backflow device failure and waterborne disease outbreak are typical 

and arc based on data reported in the literature. 

This paper is subdivided into the following sections: 

Section 1.0: Definitions

A list of terms used in this report along with their definations are presented.

Section 2.0: Background on Current Standards and Regulations 

This section identifies agencies and authorities that are associated with fire protection and public 

water supply and identifies their concerns relative to household sprinkler systems and water quality 

issues. 

Section 3.0: Typical Household Piping Systems 

This section presents typical components of a household water supply pipe system and a typical 

sprinkler pipe system. 

Section 4.0: Possible Water Quality Changes 

Water quality changes (biological. chemical and physical) reported to occur during normal 

household water flow conditions and stagnant conditions are presented. 

5
Section 5.0: Available Data 

Background data on fire incidents, disease outbreaks and backflow preventer failures are 

presented. 

Section 6.0: Risks versus Benefits 

A risk versus benefit evaluation is presented for cases where various backflow preventers are 

present and conditions of fire or water contamination occur. 

Section 7.0: Areas Needing Additional Information 

During this literature survey, some information was not available. This information, which either 

does not exist or was not found by the authors, is identified here. 

Section 8.0: Summary and Conclusions 

Based on information gathered in this study, a summary of risks and benefits associated with the 

use of single check valve, a double check valve assembly, and a reduced principle backflow 

preventer is presented. Finally a list of recommendations are given. 

6
SECTION 1.0: DEFINITIONS 

Backflow Prevenier - A mechanical device which prevents a reverse flow of water (SCV, DCVA, 

RPBD). 

Single Check Value (SCV) - A valve similar in reliability to a check valve used for a DCVA, 

which allows flow in only one direction, from the supply to the distribution system. This type of 

device is not normally referred to as a backflow preventer. However, because this report compares 

the SCV with more expensive backflow preventers, a SCV is included in the backflow preventer 

definition. 

Double Check Valve Assembly (DCVA) - A mechanical device which consists of two 

independently acting check valves with test cocks and shut-offs at both ends. This assembly is 

typically specified as a backflow device at low hazard cross connections. 

Reduced-Pressure Principle Backflow-Prevention Assembly (RPBD) - A backflow prevention 

device that consists of two independently acting, check valves together with a mechanically 

independent pressure differential relief valve located between the check valves and below the first 

check valve. These units are located between two tightly closing resilient-seated shutoff valves as 

an assembly, and are quipped with properly located resilient-seated test cocks. This assembly is 

typically specified as a backflow device at high hazard cross connections. 

Cross-Connection - Any unprotected actual or potential connection or structural arrangement 

between a public or a consumer’s potable water system and any other source or system through 

which it is possible to introduce into any part of the potable system any used water, industrial 

fluid, gas or substance other than the intended potable water with which the system is supplied. 

Residential Distribution System - A piping system which begins at the water service line 

connection and distributes water throughout the house for domestic use. 

Residential Sprinkler System - A piping system within the household that begins at the water 

service line connection and distributes water to the fire sprinklers. 
Potable Water - Water from any source which has been investigated by the health agency having 

jurisdiction, and which has been approved for human consumption. 

Community Water System - Publicly owned or investor-owned systems that serve large or small 

communities, subdivisions or trailer parks with at least 15 service connections or 25 year-round 

residents. 

Biological Contamination - The introduction of biological organisms into the potable water supply 

which is dangerous to the public’s health because it may cause sickness, disease and possibly 

death. 

Chemical Contamination - The introduction of toxic substances into the potable water supply 

which is dangerous to the public’s health because of poisoning which may cause sickness or death. 

Physical Contamination - The introduction of turbidity or color causing materials into the potable 

water supply which may contribute to biological and/or chemical contamination. 

Biofilms - Organic or inorganic deposits consisting of microorganisms, microbial products and 

detritus at a surface (6). 

Sloughing - The detachment of macroscopic patches of biofilm from a surface (pipe) (7). 

Assimilable Organic Carbon (AOC) - The portion of total organic carbon (TOC) that can be readily 

used by aquatic organisms for growth (8). 

Risk Level - The U.S. EPA adopted acceptable level of risk for gastrointestinal illness is one 

illness Per 10,000 People per year (10-4 annual risk) (9). 

Outbreak of Waterborne Disease - An incidence when at least two people experience a similar 

illness after ingesting or using water intended for drinking. Epidemiologic evidence must implicate 

the water as the source of illness (5). 

8
Stagnation - Zero to very low water velocity conditions. Intermittent stagnation is assumed to 

occur in normal household plumbing while extended stagnation is assumed to occur in a sprinkler 

system. 

9
SECTION 2.0: REGULATIONS AND AUTHORITIES 

There are a number of regulatory agencies and authorities associated with drinking water 

standards, cross connections to potable water supplies, backflow preventers and sprinkler 

systems. This section identifies and briefly outlines their relevance to the application of household 

sprinkler systems. 

Water Quality 

The United States Environmental Protection Agency (USEPA) was mandated by the Safe Water 

Drinking Act (SWDA), and later by its amendments, to establish potable drinking water standards. 

These standards are now adopted, as minimum requirements, by local authorities which have 

jurisdiction over public water suppliers. The 1986 SWDA Amendments have a direct relevance to 

sprinkler systems as they refer to water quality at the point of use in addition to the point of 

delivery from the water treatment plant. Therefore, the potential for contamination within the 

distribution systems has become a direct concern to water quality standards. These standards 

include new coliform regulations, turbidity regulations and copper regulations. 

The new coliform rule, which became effective on June 29, 1989, established a maximum 

contaminant level (MCL) goal based on the presence or absence of total coliforms, whereas, the 

original standard was based on the bacterial density. Coliform occurrences caused by bacterial 

growth in the distribution systems may cause violation of the new coliform rule even though a 

demonstrable public health risk may not exist The potential for colifotrn occurrences from the reintroduction of stagnant water within the distribution system, therefore, may be of significant 

concern to water quality standards. The USEPA does, however. allow variances for systems that 

are not at risk for fecal or pathogenic contamination (9). 

The lead and copper rule became effective in June 1991. This new rule applies to all water 

systems. Instead of setting MCL’s for lead and copper, this new regulation specifies action 

requirements consisting of corrosion control and public education. The action level for copper is 

1.3 mg/L. Because water stagnating in copper pipelines may contribute to elevated levels of 

copper, sprinkler pipelines may pose a concern with regard to this new water quality standard (10). 

10
Turbidity particles have been classified for years as a secondary standard. A secondary standard 

pertains to contaminants that adversely affect the aesthetic quality of water. With the advent of the 

Surface Water Treatment Rule (SWTR), which became effective on December 30, 1990, turbidity 

was classified as a primary standard. A primary standard relates to public health protection. This 

new rule sets a turbidity limit of 5 NTU, and typically requires 95% of all samples to have a 

turbidity of 1 NTU or lower. Turbidity particles, although not considered harmful in themselves, 

may harbor microorganism and chemicals which may be harmful. In addition, turbidity could 

contribute to corrosion reactions. Unlike the copper and coliform rules, turbidity standards are 

concerned with water leaving the water treatment plant rather than within the distribution system. 

Nevertheless, increases of turbidity within the water supply from stagnant water lines should be 

viewed as a problem from the public health perspective. 

Cross Connection Authorities and Regulations 

Individual state environmental agencies have :he highest form of authority in each state for 

regulating cross connections policy and the need for backflow preventers. The agencies mandate 

that water suppliers submit a cross connection program plan. In Massachusetts, for example, the 

plan is defined by the Drinking Water Regulations of Massachusetts (310 CMR 22.22) and 

enforced by the Department of Environmental Protection (DEP). It states that a plan shall be 

submitted by each water supplier describing the current and proposed cross connection programs 

and include information on staff training, testing, surveying, fee structure, and other areas. 

Every supplier of water is responsible for the safety of the public water system under its 

jurisdiction. They must inspect and survey all areas of a public water system to find if cross 

connections exist, record all findings, take appropriate actions to alleviate possible hazardous 

conditions and report yearly to the DEP. Some suppliers of water for the state of Massachusetts 

are delegated authority to act under code 310 CMR 22.22 and thus are a Department Designee. 

They have the responsibility to approve plans for new installations of back flow preventer devices 

and to inspect the new installations. 

The DEP requires any new or existing fire system that is connected to street-water mains to be 

evaluated by the Department or its Designee for the determination of what type of backflow 

preventer is required. This may include residential sprinkler systems. According to 310 CMR, 

however, residential sprinkler systems that do not have any fire pumper connections, nor any 

11
chemical additives and are made with potable piping material would not require a backflow 

preventer. Finally, sprinkler system connections that originate within a house are not regulated by 

DEP and subsequently are under the jurisdiction of local plumbing codes. 

Codes Relevant to Backflow Preventers 

Regulatory agencies will refer to plumbing codes and manuals published by other agencies when 

specifying rules and regulations concerning backflow preventers. The following plumbing codes 

are commonly used as references: 

l. The National Plumbing Code (NPC) 

- Building Officials and Code Administrators International, Inc. 

2. The Uniform Plumbing Code (UPC) 

- International Association of Plumbing and Mechanical officials 

3. The Standard Plumbing Code (SPC) 

- Southern Building Code Congress International 

The NPC is primarily based on the AWA M-14 manual (39). The new 1993 NPC contains 

rquirements that all automatic fire sprinkler systems be protected against backflow. The code 

requires a double check valve assembly on all sprinkler systems. However, systems that use 

approved water piping materials and systems containing no fire department connections arc 

exceptions. Therefore, residential sprinkler systems that use approved potable piping and do not 

have fire department connections would not require backflow according to the NPC. 

The 1991 UPC contains requirements that piping not made of approved potable piping materials be 

separated by an approved backflow prevention device. 

In the area of fire sprinklers, the 1991 SPC specifically references the AWWA M-14 manual. The 

SPC will be updated to be in accordance with the revised 1990 edition of the AWWA M-14 

manual 

12
The AWWA M-14 Manual, The Recommended Practice for Backflow Prevention and Cross 

Connection Control, was revised in 1990. This manual provides classifications and guidelines for 

the recommended use of backflow preventers. In Chapter 3, a cross connection is defined to mean 

“any unprotected actual or potential connection or structural arrangement between a public or a 

consumer’s potable water system and any other source or system through which it is possible to 

introduce into any part of the potable system any used water, industrial fluid, gas, or substance 

other than the intended potable water with which the system is supplied.” From this definition, the 

manual classifies each case according to its degree of risk to the potable water system In Chapter 

6 of the manual; it is stated that for cross connection control, fire-protection systems may be 

classified on the basis of water source and the arrangement of supplies. A residential sprinkler 

system would fall into the category of Class 1 or Class 2. 

A Class 1 consists of direct connections from public water mains only; no pumps, tanks, or 

reservoirs; no physical connection from other water supplies; no antifreeze or other additives of 

any kind; all sprinkler drams discharging to atmosphere, dry wells, or other safe outlets. A Class 

2 is the same as a Class 1 except that a booster pump may be installed in the connections from the 

street mains. For Class 1 and Class 2 fire protection systems, an approved backflow preventer is 

not required. 

13
SECTION 3.0: TYPICAL HOUSEHOLD WATER PIPING SYSTEMS 

Introduction 

Descriptions of typical household plumbing and sprinkler systems arc presented in this section. 

With these piping systems clearly defined, a quantification of stagnant water associated with a 

sprinkler pipeline system and a typical household plumbing system is possible. The household 

system presented here consists of a 3/4 inch supply line that is branched at the house to the 

residential distribution system and the residential sprinkler systems. Both systems (potable water 

supply lines and sprinkler supply lines) are assumed to be constructed of copper or PVC approved 

for potable water use. 

Potable Water Pipe Design 

Design of the residential piping system was based on a typical 20 feet by 50 feet ranch style single 

family home. The hot and cold water piping system was designed according to plumbing codes 

and a plumbing design manual (11). A list of specifications used in the design can be found in 

Appendix 1. A schematic of the design is shown in Figure 1. 

Potable Water piping for the house consisted of two different diameters: 1/2 inch and 3/4 inch. 

The total length of pipe contained in the system was determined to be 45 feet in length for the 1/2 

inch pipe and 90 feet for the 3/4 inch pipe. Pipe lengths were estimated from the service line to the 

water use locations inside the house. The calculated volumes of the 1/2 inch and 3/4 inch pipes 

was 106 cubic inches and 477 cubic inches respectively, totalling 583 cubic inches. 

14
Figure 1 - Typical Hot and Cold Piping System for a Single Family Dwelling 

Sprinkler System Design 

The sprinkler system was designed according to the standards found in the National Fire Protection 

Association (NFPA) 13D and can be found in Appendix 2. A schematic of this system is shown in 

Figure 2. 

The diameter of the service line for the sprinkler was also considered to be the standard 3/4 inch in 

diameter. The total length of the sprinkler piping was estimated from the service line connection to 

the system connection inside the house. The total length of the sprinkler pipe line was estimated 

from the service line connection to the system inside the house and was determined to be 113 feet. 

The total volume of water contained in the sprinkler line was calculated to be 896 cubic inches. 

15
Figure 2 - Typical Sprinkler System For a Single Family Dwelling 

Household Plumbing Network vs the Sprinkler Network 

Based on the above design calculations, the total volume of water in a household plumbing system 

should be increased by 2.5 if a sprinkler system is installed. As will be pointed out later, a parallel 

projection of increased risk from this added volume may not be totally rationaL However, because 

there are a number of arguments that may be used to support suspicions that a relatively short term 

stagnant pipe system (household plumbing) represents equal or increased dangers compared to 

extended stagnant pipe systems (sprinkler systems), an assignment of equal risk is conservative. 

16
SECTION 4.0: POSSIBLE WATER QUALITY CHANGES 

Water left stagnant in a water line used for potable water delivery or for fire sprinklers will 

deteriorate in terms of biological, physical, and chemical parameters. This chapter discusses these 

changes. 

Biological Quality Changes 

Major factors that determine microbial water quality include break through, biofilm formation, and 

growth rates (6). Given the correct set of circumstances, even the most sophisticated water 

treatment systems can experience negative impacts on the quality of water in their distribution 

systems. 

Breakthrough 

Breakthrough is the increase in bacteria in the distribution system due to bacteria passing through 

the treatment system It is suspected that a significant portion of the breakthrough bacteria may be 

injured bacteria that is not detected using standard tests for treatment plant effluent. Furthermore, 

bacteria may survive disinfection and pass through the treatment system by adhering to particles, 

including macroinvertebrates, turbidity particles, algae, and carbon fines. As a rule, turbidity 

interferes with the detection and accurate accounting of bacteria allowing turbidity associated 

organisms to go undetected or under counted (6). 

Biofilms 

Microbial growth in distribution systems is largely attributed to the occurrence of biofilms on pipe 

surfaces (7). A biofilm is defined as an organic or inorganic deposit consisting of 

microorganisms, microbial products and detritus at a surface. Biofilm formation is initiated by the 

transport and accumulation of microorganisms and nutrients at an interface. followed by 

metabolism. growth, and product formation, and finally, detachment, erosion or sloughing of the 

biofilm from the surface (6). The rate of biofilm formation is dependent on the physicochemical 

properties of the interface, the physical roughness of the surface, and the physiological 

characteristics of the microorganisms (12). During a study of a New Jersey water utility, 

LeChavallier concluded that coliform bacteria found in water columns originated from biofilms in 

17
the distribution system and that the coliform levels increased 20-fold as the water moved through 

the distribution system, away from the treatment plant. Coliform species diversity also increased 

as the water flowed away from the treatment plant (9). 

Studies have also shown that stagnation in distribution systems can lead to loss of the disinfectant 

residual, thus promoting microbial growth. Water in dead end lines is consistently found to be of 

poorer quality than water found elsewhere in the same distribution system (6). An inverse 

relationship has been demonstrated between water velocity and biofilm counts (6,14). 

Furthermore, the starting and stopping of water flow in pipe systems has been shown to increase 

bacterial levels up to ten-fold (6). Emde et al. reported that microbial regrowth in distribution 

systems is linked to the recurrent sloughing of pipe biofilms into passing water (15). LeChavallier 

et al. concluded from a study of a drinking water distribution system experiencing recurrent 

coliform bacteria growth, that the majority of water quality deterioration could be attributed to the 

dead-end sampling locations. This study emphasized that short periods of water stagnation can 

have profound and adverse effects on the quality of potable water (16). 

Bacterial Growth 

LeChavallier indicated that numerous factors contribute to bacterial survival in chlorinated water 

supply systems, including: attachment to surfaces, bacterial aggregation, age of the biofilm, 

encapsulation, previous growth conditions, alterations in the bacterial cell wall, and choice of 

disinfectant (6). In drinking water distribution systems, several conditions can promote the growth 

of biofilms. Macromolecules tend to accumulate at the solid- liquid interface, creating surface area 

and protection for the attachment of microorganisms. High flow rates can transport nutrients to 

fixed microorganisms, providing the necessary nutrients for growth in otherwise low nutrient 

concentration water. Furthermore, biofilms can provide shielding of microorganisms from 

disinfectant residuals. Research has shown that low-level breakthrough of injured bacteria from 

the treatment plant combined with increases of bacterial densities by subsequent growth in the 

distribution system has caused coliform occurrences. Such breakthrough and regrowths are 

characterized by large initial occurrences of coliform organisms followed by a gradual decline in 

bacterial levels over time. The period of time between the large initial occurences and the gradual 

decline has been observed to last several months (12). 

18 
Bacterial growth has been attributed to several conditions affecting a distribution system including: 

environmental factors (e.g. temperature and rainfall), nutrient concentrations, ineffectiveness of 

disinfectant residuals, corrosion, and hydraulic effects (12). 

Microbial activity is reported to increase with temperature, with significant activity commencing at 

temperature of 15°C and higher. Temperature has been found to influence both the growth rate, 

the lag phase, and cell yield (12). In a year long study of bacterial growth in a distribution system, 

LeChavallier et al. found that coliform organisms occurred most frequently during warm weather 

periods (8). Donlan and Pipes concluded a strong relationship between water temperature and 

attached microbiological population density (17). 

Heterotrophic bacteria require carbon, nitrogen, and phosphorous in a ratio of 100:10:1, 

respectively; therefore, organic carbon may often be the growth-limiting nutrient in drinking water 

(8). Assimilable organic carbon (AOC) is the portion of total organic carbon that is usable by 

microorganisms as nutrient for growth. AOC levels have been found to decline in drinking water 

as it flowed through the distribution system (6). LeChavallier reported the results of AOC on 

bacterial growth as waters containing greater than 50 pg/L showed bacterial growth. Specifically, 

E.coli was demonstrated to be inhibited at AOC levels of less than 54 pg/L (12). 

Physical Quality Changes 

Water pipes experiencing stagnation are prone to tuberculation. This phenomenon, which is a 

result of chemical and biological reactions, is characterized by deposits on the interior pipe wall 

(7). Tuberculation can severely restrict waterflow and contribute to water quality deteriorations if 

settled deposits are re-suspended from flow surges. Tubercule growth initiates from iron oxide 

blisters on ferrous pipe walls. This phenomenon, therefore, is not expected to be prevalent in 

copper or PVC lines. 

The primary form of physical water quality deterioration is turbidity increases due to a resuspension of deposited materials. Turbidity particles, although not necessarily harmful 

themselves, can contribute to bacterial growth and corrosion reactions. For potable water lines 

made of copper or PVC, the accumulations of turbidity causing scales or deposits should be a 

function of the raw water quality rather than potential tuberculation reactions. Water lines that 

19
experience intermittent stagnation (such as dead ends in potable supplies) may be more prone to 

resuspension occurrences than water lines experiencing extended stagnation. The degree of 

intermixing at the extended stagnant sprinkler line to the intermittent stagnant potable water line is 

not clearly understood at this time. 

Chemical Water Quality Changes 

Chemical water quality changes resulting from stagnation will occur from corrosion reactions. 

Conditions that influence these reactions include: water quality, pipe material, and flow conditions 

(18). Of the two materials considered in this paper (copper and PVC), only copper corrosion is 

feasible, as the PVC will not support the necessary electrical reactions. 

Water Quality 

The primary parameters that will influence corrosion are pH, oxygen levels, carbon dioxide levels, 

water conductivity, and temperature. Low pH conditions will prevent protective scale build-up and 

consequently result in uniform copper corrosion (19). This type of reaction may cause copper 

leaching to the water which results in a quality deterioration. The presence of oxygen and high 

carbon dioxide levels will promote pitting, which results in a corrosion reaction that causes pipe 

failure. Elevated conductivity and temperature conditions will increase corrosion reactions (20). 

Pipe Material 

Copper corrosion is low compared to other pipe materials because a protective CuO2 film will form 

on the pipe wall. In the absence of oxygen, this protective film may break down, causing pitting 

(20). Copper pipe is generally considered to be corrosion resistant (21). 

Flow Conditions 

During intermittent stagnation conditions, products of corrosion may be flushed, exposing new 

pipe material. In addition, the extent of corrosion may be more uniform throughout the pipe line 

with flowing water conditions. Extended stagnation, however, will cause corrosion to be more 

localized (21). 

20 
Summary - Water Quality Changes 

The literature does indicate that biological, physical, and chemical water quality changes will occur 

in water lines if stagnation or low velocity conditions exist. An examination of these phenomena, 

however, supports a suspicion that extended stagnation conditions may not be as detrimental to 

water quality as intermittent stagnation conditions. For example, a large volume of information is 

available that clearly shows the probability of bacterial growth in stagnant water lines. But data 

supporting this conclusion is based on potable water lines that are subjected to intermittent 

stagnation. Resupplies of needed nutrients and oxygen will be provided in that type of 

environment, but may not be available under extended stagnation conditions. Biofilm sloughing 

and nutrient replenishment should occur at local zones where sprinkler lines arc attached in the 

absence of any flow reversal protection, but the degree of intermixing at these connections is 

unknown. Similarly, corrosion reactions that can occur in water lines supplied with oxygen and 

particles may be more prone to chemical and physical water quality deterioration conditions than 

water lines that very rarely (or never) experience water flow. 

One could take this argument to an extreme and conclude that extended stagnant water is actually 

safer than intermittent water. A more conservative approach, however, would be to conclude that 

they have equal degrees of risk associated with them. Potable water lines within a household 

(intermittent stagnation), therefore, is assumed to be equal in risk as sprinkler lines within a 

household (extended stagnation) if both lines arc fed with the same initial water and arc made of 

PVC or copper approved for potable water delivery. 

21
SECTION 5.0: AVAILABLE DATA 

Introduction 

This section presents data pertaining to fire incidents, disease outbreaks and backflow preventer 

failures currently available in the literature. Deaths and injuries related to fires was readily available 

from existing databases and is presented as historical information on occurrences in one and twofamily dwellings. Information pertaining to fire-related deaths and injuries occurring in one and 

two-family dwellings quipped with sprinkler systems was statistically insignificant; therefore, 

simulated data is presented. Data pertaining to the historical occurrences of illnesses and deaths 

associated with waterborne disease is available, however, much of this data does not identify the 

source of the contamination (treatment plant failure, cross-connection, etc.). One recent study that 

provided waterborne disease outbreaks identified by source of contamination is presented. Data 

pertaining to the performance reliability of backflow preventers was based on actual field studies 

conducted by a large community water authority over a period of three years, representing 

approximately 6,000 tests. 

Fire-related Deaths 

The total number of civilian deaths in one and two family dwellings by year is shown below in 

Figure 3 (22). Since 1977-78. some trends arc worth noting. Deaths in one and two family 

dwellings peaked in 1978, where 5,213 occurred. Deaths then decreased steadily during the 

1979-82 period to 3,969 by the end of 1982. the only exception being the year 1981. 

22
Figure 3 - Number of Civilian Deaths and Injuries for One and Two Family 

Dwellings by Year 

From 1982 to 1988, the number of home fire deaths remained relatively constant in the 3,780 to 

4,125 range. The only exception was 1984, when 3290 deaths occurred. In the past three years, 

home fire deaths moved well below the 1982-1988 plateau. There were 3,545 in 1989, 3,370 in 

1990, and 2,905 in 1991, the last year for which information is currently available. The percent 

changes from the previous year are shown below in Figure 4 (22). It should be noted that 1978 

data is not included, due to a change in NFPA survey methods. The year 1991 was the third year 

of a home fire death total that was significantly lower than the 82-88 plateau. This shows that 

progress in limiting the number of fire deaths in the home is currently being made, possibly due to 

increased use of home smoke detectors, increased public fire safety education, and increased use of 

more fire safe products (23). 

23
Figure 4 - Percent Change in Civilian Deaths From Previous Year 

Reported Fire-related Injuries 

Estimates of civilian injuries in one and two family dwellings tend to be low. because many civilian 

injuries are not reported to the fire service. For example, many injuries occur at small iires that fire 

departments do not respond to. In addition, sometimes when departments do respond they may be 

unaware of injured persons that were not transport to medical facilities (24). 

It can be seen from the data in Figure 3 that the total number of injuries per year is in the 15,000 

range, with slightly higher numbers in some years, particularly in 1978 and 1988. The per year 

percent changes in these numbers is shown below in Figure 5 (22). Data for 1978 is missing, due 

to changes in NFPA survey methods, as noted above. 

24
Figure 5 - Percent Change in Civilian Injuries From Previous Year 

In 1991, 65 percent of all reported fin deaths occurred in the one and two family dwellings. As 

shown in Figure 6, consistently about two-thirds of all fire deaths occurred in one and two family 

dwellings. Also shown in Figure 6, consistently roughly 50 percent of all reported fin related 

injuries occur in one and two family dwellings. 

25
Figure 6 - Deaths and Injuries in One and Two Family Dwellings as a Percentage 

of Total Fire Related Deaths and Injuries 

This information suggests that one and two family dwellings account for the majority of deaths and 

injuries attributed to all fires in the United States. The wider use of residential sprinklers have been 

suggested to reduce the number of fire deaths and injuries occurring in the home (24). 

Data on Effects of Residential Sprinklers 

A number of studies have been performed attempting to determine the effectiveness of residential 

sprinkler systems. These include studies that apply information concerning standard commercial 

sprinkler systems to residential occupancies, such as the study performed by Melinek (25). They 

also include studies using information that strictly concerns residential systems, such as those 

performed by Ruegg and Fuller (2.27) and Harmathy. Automatic sprinklers are thermosensitive 

devices designed to react at predetermined temperatures by automatically releasing a stream of 

water and distributing it in specified patterns and quantities over designated areas (28). Residential 

fast response sprinklers differ from standard response sprinklers for a number of reasons. These 

26
sprinklers have a higher thermal sensitivity than standard response sprinklers, which allows for 

quicker activation than standard response sprinklers. In addition to their fast response 

characteristics, residential sprinklers have a special water distribution pattern. This pattern must be 

more uniform than the pattern of standard spray sprinklers, because in large areas standard spray 

sprinklers can rely on the overlapping patterns of several sprinkler heads to make up for voids 

(28). For these reasons, and others, information concerning standard sprinkler systems as applied 

in residential environments, such as that produced by Mclinek (25) is not readily applicable to 

residential fast response sprinkler systems. 

Information about 201,417 fins that occurred in 1990 in one and two family dwellings is available 

from the National Fire Incident Reporting System (NFIRS) database. Data is collected by each of 

the participating states and gathered together by the Federal Emergency Management Agency 

(FEMA). This data is coded in accordance with the appropriate NFPA standards. The NFIRS 

database showed that less than 0.5 percent of one and two-family dwellings arc equipped with 

sprinkler systems. Furthermore, it is unknown if these systems complied with NFPA 13D. Since 

the number of fires in sprinklered homes is not statistically significant, we must depend on the 

results of research studies consisting of field tests, experiments. and expert judgement, to 

determine the reduction of deaths and injuries that will occur due to the installation of residential 

sprinkler systems. 

Ruegg and Fuller prepared a cost benefit analysis of residential sprinkler systems in which they 

adopted death and injury information from an unpublished report by Gomberg, Hall, Stiefal, 

Offensend, and Pacey. Gombcrg et al. conducted a study of the loss reductions offered by fast 

response sprinklers. Their work was planned to be published by the National Bureau of Standards 

(29). According to the study, sprinkler effectiveness was based on expert judgement and 

“extrapolations applied to the results of laboratory and field tests”. The percent reduction in human 

losses due to sprinklering was determined in this report to be an 80.4 percent reduction in fire 

deaths, and a 45.9 percent reduction in fire injuries. 

Ruegg/Fuller obtained results by subtracting the predicted deaths and injuries per fire assuming 

smoke detectors and sprinklers, from the average deaths and-injuries assuming the use of smoke 

detectors alone. Reliabilities of 84 percent and 92 percent for smoke detectors and sprinkler 

systems, respectively, were assumed (2). This information, combined with the effectiveness 

27
measures cited in the unpublished report, yielded a 63 percent decrease in life loss due to sprinkler 

presence, and a 44 percent decrease in fire injuries. 

Harmathy adapted the percent reduction values in fire deaths and injuries and used the 

Ruegg/Fuller report to determine the number of deaths and injuries that would occur in sprinklered 

occupancies. However, his reference case for no sprinklers made use of 1985 NFIRS data and 

information from a fire protection consultant, therefore causing his results to differ from those 

presented by Ruegg/Fuller. According to Harmathy, there was a 75 percent decrease in life loss 

due to sprinkler and detector presence and a 46 percent decrease in fire injuries (27). 

Waterborne Disease Outbreaks 

Sobsey et al. reported that the total number of potentially pathogenic microorganisms in water is 

unknown and increasing (30). Pathogens in drinking water arc associated with acute risks that 

vary greatly in clinical manifestation and severity. The manifestation and severity are dependent on 

the microorganisms and the degree of exposure. Pathogens arc defined as either frank or 

conditional. Frank pathogens produce infectious disease in both healthy and compromised 

individuals, whereas, conditional pathogens produce disease only when conditions in the 

environment and the compromised host provide opportunity. Reliable detection methods do not 

currently exist for many of the pathogens commonly found in water. In addition, the mechanisms 

of pathogenicity are known for very few microorganisms and is virtually non-existent for many 

conditional pathogens (30). Microbial risk assessment modelling has indicated that exposure to 

low concentrations of microorganisms in water (one infectious microorganisms per 1,000 liters) 

may result in significant risks of infections, illness and mortality in a community. Sobsey et al. 

reported that the risk of microbial infection is commonly known to most individuals as nearly all 

children experience rotavirus and most Americans contract hepatitis A during their lifetime. 

Gastrointestinal illnesses am. on the average, experienced once or twice a year by most Americans 

(30). 

Data on the occurrence of outbreaks of waterborne disease is collected and tabulated by the Centers 

for Disease Control in conjunction with the USEPA. Outbreaks arc reported on a voluntary basis 

and have been tracked since 1920. It is assumed that only a fraction of the total number of 

outbreaks are reported, however, the level of under reporting is not known. Source water is 

28
categorized into community water systems, noncommunity water systems and non-public or 

individual systems (typically individual wells). Community and noncommunity systems are 

classified as public systems and constitute 31 percent and 69 percent, respectively of the 189,600 

public systems in the United States. Community systems service approximately 91 percent of the 

U.S. population (5). 

Reported Outbreaks 

The number of reported outbreaks associated with potable water for the years 1987, 1988, 1989 

and 1990 were 15, 13, 12 and 14, respectively. The minimum number of reported outbreaks for 

each year from 1971 through 1986 was 20 (5). This data is presented in Figure 7. 

Figure 7 - Outbreaks of Waterborne Disease 

Herwaldt et. al., recently studied the outbreaks of waterborne disease in the United States for the 

years 1989 and 1990 (5). For this two year period, 26 outbreaks of waterborne disease were 

reported and concluded to have resulted from the consumption of water intended for drinking. As 

a result of the outbreaks, illnesses inflicted 4,288 people and 4 people died. The number of 

outbreaks associated with community systems was 11, resulting in 1660 illnesses (39 percent of 

29
the total reported illnesses) and four deaths (100 percent of total reported deaths). In the 

waterborne outbreaks caused by community water, several etiologic agents were identified; 

including Giardia lambio, Hepatitis A, Norwalk-like, and E. coli. Table 1 summarizes data 

repeated by Herwaldt et al. (5) in the U.S. for 1989-1990. 

Etilogical Agent outbreaks Cases 

AGI 

Giardia 

4 

4 

894 

503 

Hepatitis A 

Norwalk-like 

E. coli 0157:H7 

CLB (possible) 

Total 

0 

1 

1 

11 

0 

243 

21 

1664 

Table 1 - Number of Outbreaks and Associated Cases by Etiological Agent (5) 

Based on this most recent data, an average of 830 illnesses and 2 deaths per year can be assumed 

to occur in the United States for the 1989-90 population level. This average rate will be used to 

identify present risks associated with waterborne disease. 

Backflow Preventer Failures 

The effectiveness of any backflow preventer in maintaining the integrity of potable drinking water 

is directly related to its expected rate of failure. In a field study (31). the AWWA - Pacific 

Northwest. Section reported data on the tested failure rates for double check valve assemblies 

(DCVA) and reduced pressure principle devices (RPBD). A breakdown of these data are shown in 

Tables 2 and 3, and in Figure 8. For this report, failure of the No. 1 check valve in the DCVA is 

used to estimate the probability of a single check valve failure. Such an assumption, of course, 

assumes that the single check valve device uses the same technology, or has an equal degree of 

reliability, as the first check valves placed in the DCVA. Failure of the DCVA and RPBD &vices 

is assumed to occur when both checks fail. 

This breakdown of expected failure rates according to different backflow devices is presented 

because each device has distinct advantages and disadvantages. A SCV represents a low cost 

alternative to both the DCVA and the RPBD devices. A disadvantage of the SCV is that is has not 

been approved for low hazard or high hazard crossconnections. Based on information presented 

30
in this report, however, such a high degree of protection can not be justified for household 

sprinkler systems. The DCVA represents a higher cost backflow protection alternative and has the 

advantage of being approved for low hazard cross-connections. Another advantage of this device 

(and also the RPBD) is that it is supplied with test cocks and shut-off valves for periodic checking. 

The RPBD backflow preventer represents a high cost and high protection alternative (suitable for 

high hazard crossconnections). A distinct disadvantage of this backflow preventer is the potential 

for head loss, which may cause a sprinkler system to be ineffective, especially in retrofit situations. 

Based on data printed in Tables 2 and 3, the average reported failure rate of DCVA’s and RPBD 

and the estimated failure rate of a SCV in the 0.75 -to- 1.00 inch range is as follows: 

DCVA - 1.6% 

RPBD - 1.8% 

SCV - 4.0% 

The 0.75 -to 1.00 inch range is selected because it represents the typical household supply line. 

These failure ratings will be used in the next section to predict expected rates of risk when selecting 

each of these backflow protection devices. For example, if the risk of illness without any 

backflow protection device is 1.0 x 10-6 (one person out of one million will become ill), this risk 

will be reduced to 4.0% (.04 x 10-6 or 4.0 x 10-8) if a SCV is used for protection. 

Figure 8 - Failure Rates for 0.75 and 1.00 inch Devices (31) 

31 
Table 2 - Failures of DCVA and SCV (31) 

Table 3 - Failures of RPBD (31) 

32
SECTION 6.0: RISKS VERSUS BENEFITS

Introduction 

Risk is considered the likelihood or probability that a particular event will have either a direct or 

indirect adverse effect on human health and welfare (32). Two risks are the subjects of this study: 

the adverse effects on human life/health due to fires, and the adverse effects on human illness due 

to waterborne disease. The overall objective of this study is to answer the question: 

What is the difference in risk associated with a single check valve device, a double check valve 

assembly, and a reduced pressure principle device for residential sprinkler system? 

This section explains how risk is quantified for this report, identifies conditions commonly 

assumed for both risk assessments, calculates risks associated with fire and water contaminations, 

and finally, compares these risks. 

QUANTIFYING RISK 

Risk is typically reported in either time or unit activity, such as worker days lost per work year due 

to illness or number of cancer cases per capita per year due to chemical exposure (32). Commonly 

used options for risk measuring units include number of lives lost per unit time or event, qualityadjusted life-years (QALYs), and economic burden (33). In evaluating risks associated with 

bacteria in drinking water supplies versus the risks associated with unsprinklered dwellings, a unit 

of risk was chosen. Units of risk for this paper arc number of lives lost per year, occurrences of 

fire injuries per year and number of waterborne illnesses per year. For example, a risk of 1 x 10-5 

means that one person out of 100,000 will experience the cited event each year. The reader should 

note that this paper is comparing, and therefore equating, deaths and injury from fire to illness 

from unprotected water. 

Common Assumptions 

The piping and sprinkler system configurations presented in Section 3 were considered 

representative of typical one- and two-family dwelling in the United States. Water volume figures 

33
from household plumbing lines and sprinkler lines for this type of dwelling are used to estimate the 

increased amount of risk associated with sprinkler line installations. Such a direct correlation of 

risk increase to volume increase is based on the assumptions that intermittent water (household 

potable lines) have an equal probability of health risk to extended stagnant water (household 

sprinkler lines). 

The total number of people living in one- and two- family dwellings was calculated from U.S. 

Census Bureau data from 1990 and is shown in Table 4. 

Type of Dwelling Number of Units 

Single Unit 65,761,000 

2 - 4 Units 9,876,000 

Mobile homes and trailers 7,400,000 

Subtotal 83,037,000 

Total U.S. Dwellings 102.264.000 units 

Table 4 - Classification of Dwellings 

According to this table, 81.2 percent of the dwellings in the United States are one to four unit 

dwellings or mobile homes/trailers (83,037,000 divided by 102,264,000). A conservative 

assumption was made that all of these dwellings were one- and two-family dwellings and thus the 

subject of this risk assessment study. Using a total U.S. population for the year 1990 of 

252,177,000, it can be estimated that 204,764,000 persons resided in single or double unit 

dwellings in the United States for the year 1990 (81.2% of the total population). 

Waterborne Disease Risk Assessment 

The USEPA has adopted a maximum acceptable risk for gastrointestinal illness caused by 

community water supplies of one illness per 10,000 people per year (a 104 annual risk). To 

ensure compliance with this risk level for infection from hepatitis A and most other enteric viruses, 

the total enterovirus concentrations in treated drinking water should be less than 2.2 x 10-7 per liter 

(9,34). 

34
Experimental data pertaining to the concentrations or life expectancies of enterobacteria in stagnant 

lines could not be found during literature searches undertaken for this project Therefore, historical 

data was used to estimate the potential for waterborne disease occurrences. The following 

conditions were assumed in the development of waterborne disease risk assessment: 

1) The reported waterborne disease values for the years 1989 and 1990 are for all outbreaks 

associated with community water systems and include deficiencies in both the treatment 

system and the distribution system (e.g., temporary disinfection interruption, inadequate 

filtration, cross-connection, back siphonage, etc.). Because the expected degree of risk from 

household sprinkler lines will be based on estimated risks already present from household 

potable lines, a conservative approach is to assume that a.U reported outbreaks in community 

systems were the result of contamination from household piping systems. In addition, this 

risk assessment also assumes that the degree of under reporting was 50%. 

2) The increase in risk of contracting a waterborne illness from unprotected stagnant sprinkler 

lines was considered proportional to the ratio of potable water normally present in a residential 

dwelling to the combined volume of water from potable water plus sprinkler water, as 

modelled in Section 3. The estimated potable water system volume of water was 588 in3 and 

the stagnant sprinkler line volume of water was 832 in3

 or a 1:1.5 ratio. An increased risk of 

2.5 is therefore assumed. 

3) The number of reported illnesses and deaths for the year 1990 was used to represent the 

expected number of illnesses and deaths without sprinkler systems in one- and two-family 

dwellings. 

4) It was assumed that a properly functioning backflow preventer (SCV, DCVA, or RPBD) 

would isolate the stagnant water associated with a sprinkler system, thereby eliminating the 

carbon source and the possibility of biofilm sloughing. 

5) Due to the continual starting and stopping of water in household piping systems, it was 

assumed that sloughing of harmful biofilms could occur readily.in a .potable water line. It was 

also assumed that this same phenomenon would occur in the total length of in an unprotected 

sprinkler water line (e.g. complete intermixing). 

35 
6) Biofilm growths are characterized by huge initial occurrences of coliform organisms 

followed by a gradual decline in bacterial levels over time, with the period of time between the 

large initial occurrences and the gradual decline lasting several months (12). However, for the 

purposes of this risk assessment it was conservatively assumed that the stagnant water in 

sprinkler lines would be at the peak of harmful bacteria concentrations during any introduction 

to potable water lines. Possible die-off of bacteria in stagnant sprinkler lines, therefore, is not 

considered. 

Estimated Risk of Waterborne Illness 

The following equation was used to estimate the increase in illnesses/deaths that could potentially 

occur if sprinklers without a single check valve or backflow devices were installed throughout the 

United States. 

R=N*U/P 

where: 

R = the risk of illness/death due to waterborne diseases 

N = number of reported illnesses and deaths for a year or averaged years for 

which data exists 

U = degree of under reporting 

P = population of U.S. citizens living in one and two-family dwelling in data 

Year. 

For the years 1989-1990, an average of 830 illnesses and 2 deaths per year (N) were reported. 

This number is increased according to the assumed degree of under repotting. Using a total of 

204,764,000 people assumed to be living in one- and two-family dwellings (P), the probability of 

contracting an illness due to waterborne disease in those years was: 

R = 830 * 2/204,764,000 

R = 8.2 x 10-6. 

In other words, for every one million people (10), 8.2 people will become ill. 

36
To estimate the expected degree of risk associated with the addition of household sprinkler lines, 

the following scenarios were considered: 

Scenario A: No protection device (SCV, DCVA, RPBD) is provided. 

Scenario B: Either of the above three devices (SCV, DCVA, RPBD) are placed at the 

sprinkler line. 

Scenario C: Either of the above three devices (SCV, DCVA, RPBD) are placed at the 

sprinkler feed line and the potable water feed line. 

Scenario D: Same as Scenario C, but the device is placed at the feed line that branches off to 

both the potable feed line and the sprinkler feed line. 

Figure 9 shows a schematic for each of these scenarios. 

Figure 9: Location of Sprinkler and Water Line Protection Devices 

37 
The risk associated with Scenario A is found by multiplying 8.2 x 10-6 by a factor of 2.5 (the total 

increase of water volume resulting from adding a sprinkler line - see assumption 2). 

Scenario A: R = 8.2 x 10-6 x 2.5

= 2.05 x 10-5

It should be noted that this risk level is an order of magnitude lower than the level of risk that is 

considered acceptable by the USEPA for occurrences of gastrointestinal illnesses. 

For Scenario B, risk is calculated by adding the degree of risk associated with a household’s 

potable water line to the increased risk of adding a protected sprinkler line. 

Scenario B: R = 8.2 x 10-6 + R (protected sprinkler line) 

where: R (proucted sprinkler line) 

= 8.2 x 10-6 x 1.5 x % failure 

The 1.5 factor accounts for an increased water volume associated with a sprinkler system while the 

% failure relates to whatever protection device is selected SCV. DCVA, RPBD). 

Scenario B (SCV): R = 8.2 x 10-6 + (8.2 x 10-6 x 1.5 x 0.04) 

R = 8.2 x 10-6 + 4.92 x 10-7 

R = 8.70 x 10-6 

Scenario B (DCVA): R = 8.2 x 10-6 + (8.2 x 10-6 x 1.5 x 0.016) 

R = 8.2 x 10-6 + 1.97 x 10-7 

R = 8.40 x 10-6 

Scenario B (RPBD): R = 8.2 x 10-6 + (8.2 x 10-6 x 1.5 x 0.018) 

R = 8.2 x 10-6 + 2.21 x 10-7 

R = 8.42 x 10-6 

As expected. the degree of risk associated with installing any type of backflow preventer (SCV, 

DCVA, RPBD) at the sprinkler line alone is close to the degree of risk initially calculated to be 

38
present with a typical household water supply system. Also, as shown from these calculations, the 

difference in risk between these devices is not great. If total protection from household water 

backflow is to be realized, however, a backflow device should be installed at the potable water 

supply line as well as the sprinkler supply line (Scenarios C & D). 

Risk calculations for Scenarios C & D are the same if risk within the individual household is not 

considered. In other words, if the Scenario C option is chosen, backflow from the sprinkler line 

to the residential potable line is prevented. The Scenario D option does not provide this protection 

within the household, but does provide the same amount of protection to the surrounding 

community. Of course, if all homes in the community are quipped with a sprinkler system, the 

option D Scenario cannot be considered equal to the option C Scenario. Expected risks for 

Scenarios C & D are calculated as follows: 

Scenario C or D: R = 2.05 x 10-5 x % failure 

The 2.05 x 10-s factor accounts for degree of risk associated with a sprinkler system plus the 

potable water lines (Scenario A), while the 8 failure relates to whatever protection device is 

selected (XV, DCVA, RPBD). 

Scenario C or D (XV): R = 2.05 x 10-5 x 0.04

R = 8.20 x 10-7

Sceriario C cm D (DCVA): R = 2.05 x 10-5 x 0.016

R = 3.28 x 10-7

Scenario C or D (RPBD): R = 2.05 x 10-5 x 0.018

R = 3.69 x 10-7

A comparison of these options to the Scenario B option shows an increase in protection if a 

backflow device is instaIled for the household supply line as well as the sprinkler line rather than 

simply at the sprinkler supply system. Again, as shown in the option B calculations, the difference 

in protection from these devices (XV, DCVA, RPBD) is very slight 

39
Fire-related Deaths/Injuries Risk Assessment 

The Ruegg/Fuller data presented in Section 5 was based on the following assumptions: 

1) The base case for calculating the number of deaths and injuries resulting from 

fire without sprinkler systems assumes that all homes are equipped with a 

smoke detector with an associated reliability of 84 percent; 

2) The calculation for number of deaths/injuries prevented assumes that all homes 

are quipped with sprinklers and smoke detectors with associated reliability of 

92 and 84 percent respectively. 

Estimated Risk of Fire Death/Injury 

Using the Ruegg/Fuller data presented in Section 5, which had the more conservative of the 

results, and applying it to the year 1990, 2120 lives would have been saved and 6700 injuries 

would have been prevented with the widespread application of residential sprinkler systems. This 

data was based on 3370 civilian deaths and 15250 civilian injuries in 1990. 

Saved Lives = 3,370 x .63

= 2.120

Saved Injuries = 15250 x 0.44 

= 6,700 

Assuming, as before, that 204,764,000 people lived in one and two family dwellings, the present 

risk associated with death and injury if homes are not equipped with sprinkler devices are 

calculated as follows: 

Lives: R = 3,370 / 204,764,000 

= 1.65 x 10-5 

Injuries: R = 15250 / 204,764,000 

= 7.45 x 10-5 

Estimated risks if sprinkler systems are universally installed are calculated as follows: 
Lives: R = (3,370 - 2,120) / 204,764,000 

= 6.10 x 10-6 

Injuries: R = (15,250 - 6,700)/204,764,000 

= 4.18 x 10-S 

A Comparison of Risks (Fire vs Illness) 

A summary of the previous risk assessments is given in Tables 5 and 6. As can be seen from 

Table 6, the relative risk associated with fire events (death/injury) is 11.10 compared to a 1.00 risk 

associated with a waterborne illness event with the present assumed condition of no sprinkler 

systems. The level of risk associated with an unsprinklered household is expressed in terms of 

probable death (1.65 x 10-5) and probable injury (7.45 x 10-5). while the level of risk associated 

with health impacts from unprotected sprinkler lines is expressed in terms of probable cases of 

gastrointestinal illnesses (2.05 x 10-5). It is important to note that the 2.05 x 10-5 risk is still below 

the 1.0 x 10-4 USEPA target risk level. 

A relative reduction in fire related risk events to 5.84 (from the original 11.10) shows that the 

residential sprinkler systems would have a significant effect in preventing fire-related deaths and 

injuries. Even without any reverse flow prevention (Scenario A assumes no device is installed), 

the increased relative risk of waterborne illnesses (2.50) is still below the reduced risk of fire death 

and injury (5.84). 

Scenarios B and C/D illustrate the reduced risk of waterborne illness associated with the selection 

of either a SCV, DCVA. or RPBD. As can be seen from both Tables 5 and 6, very little difference 

in risk is noted between either device. Residential sprinkler systems equipped with a single check 

valve device with the same degree of reliability as detected in a more expensive double check valve 

assembly, therefore, should be as effective as the more expensive DCVA and RPBD backflow 

preventers. 

The Scenario C/D approach is included in this risk assessment study to illustrate the degree of risk 

reduction (almost ten fold from the Scenario B approach) that should be realized by also installing 

reverse flow devices at the potable water connection as well as the sprinkler water connection. 

41
Condition Death 

Fin Event 

Injury Combined 

Waterborne Event 

(Illness) 

Household Water Only 

(No Sprinkler) 

Option A 

Option B 

SCV 

DCVA 

RPBD 

Options C& D 

SCV 

DCVA 

RPBD 

1.65 x 10-5 

6.10 x 10-6 

6.10 x 10-6 

6.10 x 10-6 

7.45 x 10-5 

4.18 x 10-5 

4.18 x 10-5 

4.18 x 10-5 

9.10x 10-5 

4.78 x 10-5 

4.78 x 10-5 

4.78 x 10-5 

8.2 x 10-6 

2.05 x 10-5 

8.70 x 10-6 

8.40 x 10-6 

8.42 x 10-6 

8.20 x 10-7 

3.28 x 10-7 

3.69 x 10-7 

Table 5: Units of Risk for Fire (Injury/Death) and Waterborne Illness Events 

Condition Fire Event 

(Injury & Death) 

Waterborne Event 

(Illness) 

Household Water Only 

(No Sprinkler) 

Option A 

Option B 

SCV 

RPBD 

Options C& D 

SCV 

DCVA 

RPBD 

11.10 

5.84 

5.84 

5.84 

1.00 

2.50 

1.06 

1.03 

0.10 

0.04 

0.05 

Table 6: Normalized Risk of Fire (Injury & Death) and Waterborne Illness Events 

42
SECTION 7.0: AREAS NEEDING ADDITIONAL INFORMATION 

Although conclusions presented in the next section of this report am based on rational evaluations 

of available information, this literature study had to make certain assumptions. These assumptions 

and the need for further study are addressed below. 

A Single Check Valve Device (SCV) 

For this study, a SCV was assumed equal in performance reliability to the type of check valve 

found in a DCVA ( the No. 1 check valve). Such an assumption could not be based on field data 

as that type of data collection was not found. Backflow preventer evaluations are naturally 

concerned with DCVA and RPBD devices. It is unlikely that the location and performance 

reliability of SCV’s is even known. Information regarding the reliability of a low cost single check 

valve device, therefore, should be generated form field surveys or laboratory experiments. 

Biological Impacts 

Experimental and field related data on the effects of stagnation in piping systems has been limited 

to assessments over periods that may typically occur in potable water supply systems. This report 

refers to these conditions as intermittent stagnation, where intermittent flow or very low velocity 

flow does occur. Intermittent flow conditions will transport needed nutrients and oxygen for 

biological growth and will cause biofilm materials to slough off. Extended stagnation periods, 

where water will remain in the pipeline for periods of a year or more, may be very different. 

Under such conditions, needed nutrients, oxygen, and other trace materials may not be transferred 

to the water, causing bacterial die-off or very slow bacterial growth rates. A simple extrapolation 

of intermittent stagnation effects, therefore, may not be appropriate. Ideally, the following 

information should be available: 

- What is the degree of mixing between an unprotected (or failed protection device) 

extended stagnation line with an intermittent stagnation line as typically found 

within a household potable line/sprinkler line connection. 

- What is the degree of material diffusion (nutrients, oxygen, etc) for this type of 

connection. 

43 
- What are the life cycles, under extended stagnant conditions, for a variety of 

bacteria typically expected in a potable water network. 

- What is the level of risk contracting an illness associated with waterborne disease 

that is caused by typical starting and stopping of water in household potable water 

lines relative to the risk associated with extended stagnation in sprinkler systems. 

Chemical Impacts 

As with biological impact evaluations, chemical impacts resulting from internal pipe corrosion 

reactions has been limited to assessments over periods that may typically occur in potable water 

supply systems. The literature does describe expected copper corrosion reactions that occur under 

various conditions such as with oxygen or without oxygen, but field data describing expected 

corrosion during extended stagnation was not found. This type of data is not expected to be 

generated from experiments that are currently being required to meet the new lead/copper 

regulations (10), as only intermittent stagnation conditions will be simulated. Information 

regarding expected water quality impacts from PVC pipe materials was also not found in the 

literature. Ideally, the following information should be available: 

- How do extended stagnation corrosion conditions compare to intermittent 

stagnation conditions for copper pipes suitable for potable water supplies. 

Parameters of this evaluation should include chemical variations, including oxygen, 

carbon dioxide, pH, and conductivity, as well as the physical variation of flow. 

- Possible internal corrosion reactions that will result from the introduction of 

various lead/copper control strategies should be evaluated for extended stagnation 

conditions. These strategies should include recommended practices of flushing, 

pH adjustments, and various pipe coating approaches. 

- Impacts on water quality from extended stagnation in PVC pipelines (and various 

recommended solvents) should be evaluated from field or laboratory studies. 
Physical Impacts 

Stagnant water in a pipe system will contribute to turbidity in the water supply if intermittent flow 

conditions resuspend particles that either collected or were generated from tuberculation. As with 

biological and chemical impacts, the potential degree of physical impact from extended stagnation 

dependents on the degree of intermixing at the connection location between the potable pipe 

network and the sprinkler pipeline. Variables that should be included in the evaluation of intermixing include flow velocities and connection configurations. 

45
SECTION 8.0: RECOMMENDATIONS

Assessments presented in this report illustrate that the risk of death and injury associated with 

unsprinklered dwellings is higher that the risk of illness associated with unprotected sprinkler 

systems. This assessment alone supports the need for residential sprinkler systems. 

Calculations presented in this report also show that the three protection devices evaluated in this 

study (a single check valve device, a double check valve device, and a reduced pressure principle 

device) provide the same degree of health risk protection. Either device will adequately protect 

human health to orders of magnitude below the desired USEPA acceptable risk level of 1 x 10-4 

gastrointestinal illnesses per year per person. 

Recommendations of this report are as follows: 

1) The SCV device should be considered in favor of the DCVA and the RPBD for individual 

household sprinkler systems. 

2) If a protection device is to be used for a sprinkler line, the same degree of protection should 

be considered at the potable water line. 

3) Areas requiring additional study (as presented in the previous section) should be seriously 

considered. 

46
References 

1. Karter, MJ. Jr., “Reports on U.S. Fire LOSS,” NFPA Journal, (September/October 1992): 

36-43. 

2. Ruegg, R.T., Fuller, SK., “A Benefit Cost Model of Residential Fire Sprinkler Systems”, 

NBS Technical Note 1203, Operations Research Division, Center of Applied Mathematics, 

National Engineering Laboratory, National Bureau of Standards, Gaithersburg, Maryland, 

November 1984; 

3. Regli, S., Rose, J.B., Haas, C.N., and Gerba, C-P., “Modeling the Risk from Giardia and 

Viruses in Drinking Water”, J. AWWA, 10/91, pp. 76-84. 

4. Seidler, RJ. and Evans, T.M., Persistence and Detection of Coliforms in Turbid Finished 

Drinking Water”, USEPA Publication No. EPA-600/82-82654, August 1982. 

5. Henvaldt, B-L., Craw, G.F., Stokes, S.L. and Juranek, D.D., “Outbreaks of Waterborne 

Disease in the United States: 198990.” J. AWWA, pp. 129-135, April 1992. 

6. LeChevallier, M.W., “Microbial Processes within the Distribution System,” American Water 

Works Association Conference Proceedings. 365-376 (1991). 

7. “Control of Biofilm Growth in Drinking Water Distribution Systems”, EPA/625/R-92/001, 

June 1992. 

8. LeChevallier. M.W..Schultz W.. Lee. R.G.. “Bacterial Nutrients in Drinking Water,” 

Applied and Environmental Microbiology. pp. 857-862, March 1991. 

9. Pontius., F.W. , “A Cement Look at the Federal Drinking Water Regulations,” J. AWWA, 

pp. 3650, March 1992. 

10 . “The Lead and Copper Rule,” Journal AWWA (July 1991): 12. 

11. Ripka, L.V.. Plumbing Installation and Design, American Technical Society, Chicago, 1978 

47
12. LeChevallier, M. W., “Coliform Regrowth in Drinking Water: A Review,” J.AWWA, 

82(11):74-86 (1990). 

13. Ibrahim, AA. and M. Sadiq, “Metal Contamination of Drinking Water from Corrosion of 

Distribution Pipes,” Environmental Pollution, 578 (1989), 167-78. 

14. Wolfaardt, G. M., Cloete, T.E., “The Effect of Some Environmental Parameters on Surface 

Colonization by Microorganisms,” Water Resources. Vol. 26, No. 4, pp. 527-537, 1992. 

15. Emde, K.M.E., Smith, D.W., Facey, R, “Initial Investigation of Microbially Influenced 

Corrosion (MIC) in a Low Temperature Water Distribution System,” Water Resources. 26(2): 169­

175 (1992). 

16. LeChevallier, M.W., Babcock, T.M., Lee, R.G., “Examination and Characterization of 

Distribution System Biofilms,” Applied and Environmental Microbiology. pp. 2714-2724, 

December 1987. 

17. Donlan, R.M. and Pipes, W.O., “Selected Drinking Water Characteristics and Attached 

Microbial Population Density," J.AWWA, pp. 70-76, November 1988. 

18. Wagner, J. and W.T. Young, “Corrosion in Building Water Systems,” J. Environment 

Treatment & Control, October 1990,40-6. 

19. Leidheiser, H, The Corrosion of Copper, Tin and their Alloys, Robert E. Krieger Publishing 

Co, Huntington, NY 1979. 

20. Mendanhall, J.H., Understanding Copper Alloys, Robert E. Krieger Publishing Co, Malabar, 

FL 1986. 

21. Alleman. J.E., and HE. Hickey, “Investigation of the Water Quality and Condition of Pipe in 

Existing Automatic Sprinkler Systems for the Analysis of Design Options with Residential 

Sprinkler Systems,” NBS-GCR-82-399, August, 1982. 

22. “Fire Loss in the United States”, Fire Journal, September issues for 1978-1990. 

48 
23. “Fire Loss in the United States”, Fire Journal, September 1991, p. 48 

24. Karter, M.J., Jr. “Fire Loss in the United States During 1991”. NFPA, Fire Analysis and 

Research Division, Quincy, MA, September 1992, p. 7. 

25. Melinek, S.J., “Potential Value of Sprinklers in Reducing Fire Casualties”, Fire Safety 

Journal 20 (1993) : 275-287. 

26. “Backflow Protection for Fire Sprinkler Systems,” NFSA, R.R. No. 17054. 

27. Harmathy, T.Z., “On the Economics of Mandatory Sprinklering of Dwellings”, Fire 

Technology, August, 1988, pp. 245-61. 

28. “Fire Protection Handbook”, Seventeenth Edition, National Fire Protection Agency, pp. 5­

190. 

29. Unpublished report by A. Gomberg et al, “A Decision Model for Evaluating Residential Fire 

Risk Reduction Alternatives”, NBSIR, National Bureau of Standards, in preparation, 1984. 

30. Sobsey, M.D., Dufour, A-P.. Gerba, C.P., LeChevallier, M.W. and Payment, P., “Using a 

Conceptual Framework for Assessing Risks to Health from Microbes in Drinking Water,” 

J.AWWA, pp 44-48, March 1993. 

31. American Water Works Association - Pacific Northwest Section, Cross Connection Control 

Committee, “Summary of Annual Test Reports Reduced Pressure Principle and Double Check 

Valve Assemblies, December 1988. 

32. Wentz, CA., Hazardous Waste Management,. McGraw Hill Book Co., New York, 1989. 

33. Putnam, S.W.. Graham, J-D.. “Chemicals versus Microbials in Drinking Water: A Decisions 

Sciences Perspective,” J.AWWA. pp. 57-61, March 1993. 

34. Regli. S., Rose, J.B.. Haas, C.N., and Gerba, C-P., “Modeling the Risk from Giardia and 

Viruses in Drinking Water,” J.AWWA, pp. 76-84, November 1991. 

49 
35. Olson, B.H. “Assessment and Implications of Bacterial Regrowth in Water Distribution 

Systems,” U.S. Environmental Protection Agency Publication Number EPA-600/S2-82-072, 

September 1982. 

36. Seidler, R.J. and Evans, T-M., “Persistence and Detection of Coliforms in Turbid Finished 

Drinking Water,” U.S. Environmental Protection Agency Publication Number EPA-600/S2-82­

054, August 1982. 

37. Gaudy, A.F., Jr., Gaudy, E.T., Microbiology for Environmental Scientists and Engineers. 

McGraw-Hill Book Company, pp. 666-682,198?. 

38. LeChevallier, M.W., Cawthon, C.D., Lee, R.G., “Factors Promoting Survival of Bacteria in 

Chlorinated Water Supplies,” Applied and Environmental Microbiology. pp. 649-654, March 

1988. 

39. “The Recommended Practice for Backflow Prevention and Cross-connection Control”, 

American Water Works Association M-14 Manual, (1990). p. 25. 

40. “Potential Value of Sprinklers in Reducing Fire Casualties”, Fire Safety Journal, (20) 1993, 

pp. 275-287. 

50
Appendix 1: Design Specifications for Typical Household Potable Piping Systems 

The following design specifications were used to design a typical household piping system. The 

resultant example design is illustrated in Figure 1. 

. 3/4-inch pipe is the minimum size water service for any building from the street to the water 

main. 

. 3/4-inch pipe is the minimum size of building supply pipe (the fast section of water 

distribution piping within the building). 

. 3/4inch pipe is the minimum size to a sill cock or lawn faucet. 

. 3/4-inch pipe is the minimum size cold water supply to a water heater. 

. 3/4-inch pipe is the minimum size for the first section of hot water pipe on the outlet side of a 

water heater. 

. 1/2-inch is the smallest size for concealed pipe. 

. A maximum of three fixtures in the same bathroom of a house may be supplied by the same 

1/2-inch pipe. 

. 1/2-inch is the minimum size fixture branch pipe, with the exception of 3/4-inch minimum size 

fixture branch pipe for the sill cock, urinal(w/ flushometer valve), and sinks and a l-inch 

minimum branch pipe for a water closet(w/ flushometer). 

51

Appendix 2: Design Specifications for a Typical Household Sprinkler System 

The following designs specifications were used to model an example household sprinkler system. 

The resultant design is illustrated in Figure 2. 

. flow requirement of at least 18 gpm is required for one head activating at the hydraulically 

most remote location; 

. flow requirement of at least 13 gpm is required for two heads activating at the hydraulically 

most remote location; 

. maximum design area of 144 sqft per head; 

. maximum spacing of 12' between heads; and

. maximum spacing of 6’ off of wall.

The hydraulic verification of a typical sprinkler system was performed using a commercially

available computer modeling program (Turbofire Z ). Boundary conditions of the water supply

were assumed as follows:

. 60 psi residual pressure; and

. 40-foot length of 3/4-inch service pipe line from main to house.

The hydraulic flow testing results are presented in Table 7. 

Required Flow 

(minimum) 

Design Flow 

(actual) 

1 Sprinkler Head @ 

Most Remote Location 18gpm 23.8 gpm 

2 Sprinkler Heads @ 

Most Remote Location 13 gpm 1st @ 13.7 gpm 

2nd @ 14.6 gpm 

Table 7: Hydraulic Model Flow Testing Results 

53