NUREG/CR-0488

SAND78-1373

RP

Nuclear Power Plant Fire Protection

Fire Detection

(Subsystems Study Task 2)

Dennis L. Berry

Manuscript Submitted: December 1977

Date Published: March 1979

Sandia National Laboratories

Albuquerque, NM 87185

Operated by

Sandia Corporation

for the

U. S. Department of Energy

Prepared for

Engineering Methodology Standards Branch

Office of Standards Development

U. S. Nuclear Regulatory Commission

Washington, D.C. 20555

Under Interagency Agreement DOE 40-550-75

NRC FIN No. A-1080

~pR REGtQzl,

CCO

NUREG/CR-0488

SAND78-1373

RP

NUCLEAR POWER PLANT FIRE PROTECTION

FIRE DETECTION (SUBSYSTEMS STUDY TASK 2)

Dennis L. Berry

Manuscript Submitted: December 1977

Date Published: March 1979

Sandia Laboratories

Albuquerque, NM 87185

operated by

Sandia Corporation

for the

U. S. Department of Energy

Prepared for

Engineering Methodology Standards Branch

Office of Standards Development

U. S. Nuclear Regulatory Commission

Washington, DC 20555

Under Interagency Agreement DOE 40-550-75

NRC FIN No. A-1080

3-4

ABSTRACT

This report examines the adequacy of fire detection in the

context of nuclear power plant safety. Topics considered are:

(1) establishing area detection requirements, (2) selecting

specific detector types, (3) locating and spacing detectors, and

(4) performing installation tests and maintenance. Based on a

thorough review of fire detection codes and standards and fire

detection literature, the report concludes that current design

and regulatory guidelines alone are insufficient to ensure

satisfactory fire detection system performance. To assure

adequate fire detection, this report recommends the use of inplace testing of detectors under conditions expected to occur

normally in areas being protected.

5-6

CONTENTS

Page

I. SUMMARY 9

II. INTRODUCTION 10

A. Background 10

B. Task 2 Description 10

III, DISCUSSION 13

A. Establishing Area Detection Requirements 14

B. Selecting Specific Detector Types 19

C. Locating and Spacing Detectors 28

D. Performing Installation Tests and Maintenance 40

IV. CONCLUSIONS 45

V. RECOMMENDATIONS 47

A. Establishing Area Detection Requirements 47

B. Selecting Specific Detector Types 48

C. Locating and Spacing Detectors 49

D. Performing Installation Tests and Maintenance 49

VI. REFERENCES 51

APPENDIX A - Confusion Over Class A System Designation 53

APPENDIX B - Abbreviated Description of Commercially Available

Detectors 55

7
Figure

1

ILLUSTRATIONS

Flow Chart for Detector Selection

TABLES

Information Sources Reviewed and Corresponding

Evaluation Categories

Page

25

Table

I

II Relationship Between Design and Maintenance Activities

and Evaluation Categories

III Area Detection Guidelines

IV Physical Characteristics of Selected Safety-Related

Plant Areas as Related to Detector Selection

V Comparison of Detector Location and Spacing Criteria

with Governing Design Guidance Quoted from NFPA 72 E

VI Advantages and Disadvantages of Performing Detector

Testing and Maintenance According to Manufacturer's

Recommendations

12

13

16

24

31

44

8
NUCLEAR POWER PLANT FIRE PROTECTION

FIRE DETECTION (SUBSYSTEMS STUDY TASK 2)

I. SUMMARY

'An uncontrolled fire in a nuclear power plant can seriously jeopardize overall plant safety. Recognizing this, the Nuclear Regulatory Commission has undertaken a broad program in fire protection research, a portion of which focuses on early fire detection. This report examines the

adequacy of fire detection in the context of nuclear power plant safety.

Because of the expanse of'a nuclear power plant and the normally

limited number of resident operating personnel, remote automatic fire

detection represents the only viable method of providing early fire

warning for most plant areas. By installing throughout a power plant

devices which are sensitive to fire and by electrically connecting these

devices to centralized alarm panels, operators can receive fire warnings

from anywhere in the plant. The reliability of such a system, however,

depends upon correct design and maintenance.

Traditionally, nuclear power plant designers have utilized a

combination of fire codes, test standards, fire consultant recommendations, insurance agency requests, and detector vendor suggestions to

formulate the design of fire detection systems. Proceeding in this

manner, designers often apply detection principles to nuclear power plants

which have been proven in residential and commercial installations.

However, because the ventilation conditions, ceiling heights, ceiling

construction, and types of combustibles existing in nuclear power plants

can differ from those used elsewhere, it is difficult to show that

traditional detection system design approaches will be adequate for

9
nuclear power plants. Also, it is doubtful whether any theory can be

developed and proven in the near future to describe the effects of

different installation conditions on detection system operation.

Therefore, it appears that the best approach to solving the uncertainties of nuclear power plant fire detection is through in-place testing

of detectors under environmental conditions anticipated to occur normally

in each area being protected. Through in-place testing, during both

initial installation and subsequent maintenance intervals, satisfactory

detection performance can be assured for the variety of conditions found

in nuclear power plants.

II., INTRODUCTION

A. Background

An earlier Sandia Laboratories fire protection system study1

concluded that much progrers can be made to enhance fire detection effectiveness in nuclear power plants by clarifying fire detection design

requirements and by adapting existing detection techniques. This conclusion had been based on both the ready availability of numerous detection

devices currently on the market and the lack of adequate design guidance

for selecting, locating, testing, and maintaining detection system hardware. Based on these findings, the Nuclear Regulatory Commission decided

to undertake a more thorough review of fire detection, as part of a second

study addressing several major areas of fire protection. Task 1 of this

new study addressed ventilation, while Tasks 3 and 4, to be completed

later, will involve fire barriers and fire hazards analysis. Task 2, fire

detectors, is the subject of this report.

B. Task 2 Description

The fire detection subsystem review was undertaken to evaluate the

following .from the standpoint of overall plant safety:

a. the technical bases for detection system design criteria,

10
b. the adequacy of detailed design guidance currently available, and

c. the effectiveness of qualification testing procedures to

simulate actual design applications.

For each of these three evaluation categories, numerous recognized fire

protection information sources were chosen for review. The assignment of

each information source to an appropriate evaluation category is shown in

Table 1 and is based upon the level of detail and scope of information

available in each source.

After establishing evaluation categories and information sources, it

was decided to.focus on the selection and use of detector sensing units,

rather than to investigate either the internal design details of the units

or the operation of each ancillary detection system component (i.e., transmitters, alarm units, satellite stations, or interconnecting wiring). This

decision stemmed from a realization that:

1. Existing detection theory lacks the ability to predict

detector performance solely from known internal sensing

unit design features.

2. Ancillary detection system components primarily function

to transmit electrical signals from detector sensing units

to various panels and alarm devices, generally through the

use of fundamental electrical design techniques which have

been accepted and used extensively throughout other nuclear

power plant systems.

*One exception to this observation is cited in Appendix A of the

report.

11
TABLE I

Information Sources Reviewed and Corresponding Evaluation Categories

Evaluation Categories

Information

Sources Design Design Qualification

Reviewed Criteria Details Tests

Nuclear Regulatory Commission

Documents x*

Insurance Agency Documents x

National Fire Protection Codes x

Underwriters Laboratories Tests x

Vendor Information and Open

Literature (where applicable) x x x

*x refers to the primary charter of the cited information source

Based on these observations, the following design and maintenance

activities related to the selecting and use of detector sensing units were

chosen for review:

" Establishing area detection requirements

" Selecting specific detector types

" Locating and spacing detectors

" Performing installation tests and maintenance.

As illustrated in Table II, this report separately addresses each of these

activities for commercially available detector sensing units and, in so

doing, questions the adequacy of applicable design criteria, design

details, and qualification testing.

12
TABLE II

Relationship Between Design and Maintenance Activities

and Evaluation Categories

Design and Maintenance Activities

0 Establishing area detection

requirements

* Selecting specific detector

types

" Locating and spacing detectors

* Performing installation tests

and maintenance.

AdequacIy?

DISCUSSION

Task 2 Evaluation

Categories

* Design Criteria

" Design Details

" Qualification

Testing

III.

Before proceeding with the Task 2 evaluation,

identify those detectors most suitable for review.

was decided that the following five major types of

detectors should be chosen:

it was necessary to

For this purpose, it

commercially available

" Area heat detectors

" Continuous line heat detectors

e Ionization type products of combustion detectors

* Photoelectric smoke detectors

Ultraviolet/infrared flame detectors

Although other types of detectors are being developed, none of the

new-concept detectors, as explained in Reference 1, has been proven in

situations outside of a laboratory environment. In contrast, each of the

commercial, detectors listed above has been demonstrated to be effective

13
when installed and maintained in a manner consistent with its governing

qualification tests.

A. Establishing Area Detection Requirements

The first decision that must be reached regarding fire detection is

whether or not automatic detection is required for a particular power

plant area. To make this decision from a plant safety viewpoint, a

careful assessment of automatic detection must be made on the basis of

many factors, including:

" Importance of the area to overall plant safety

" Susceptibility of the area to surrounding fire hazards

e Degree of fire hazard within the area

e Potential of fire spreading to other areas

e Type of available fire suppression (e.g., manual or

automatic; inert gas or water)

* Cost of added detection capability

* Normal occupancy of the area

Unfortunately, it is not always possible to assess all of these factors

objectively for each area of a nuclear power plant, and, because of this,

detection requirements generally have been designated on the basis of an

area's safety importance, regardless of the actual fire risk associated

with the area. One possible exception to this practice occurs in those

instances where detection requirements are dictated by the operational

needs of an associated fire suppression sysEem. Tnis latter detection

case is being evaluated separately, in conjunction with another Sandia

study addressing suppression system operations.

1. Design Criteria for Establishing Area Detection Requirements

Many factors influence how much added safety automatic detection can

provide, including the reliability of the detection system, the method

used for fire extinguishment, and the importance of the protected area to

14
overall plant safety. Because of these factors, it is. difficult to assess

quantitatively what positive benefits are derived from having versus not

having automatic fire detection in a particular nuclear power plant area

without studying the interrelationships among all affected plant safely

systems and their associated fire suppression and fire containment

systems. Because such a systems study lies beyond the scope of this

report, area fire detection can best be evaluated here on the intuitive

basis that the sooner a fire is discovered the better are the chances of

limiting the fire damage. On this basis, current nuclear power plant area

detection requirements were reviewed.

Table III summarizes the area detection design criteria currently

available innuclear regulatory and insurance agency documents, and

although other information sources soon may be available, such as those

being developed by the National Fire Protection Association and the

American National Standards Institute, drafts of these new documents

provide little guidance beyond that shown in Table III. From Table III,

it can be seen that each document reviewed provides a unique listing of

plant areas requiring automatic fire detection. In some instances,

differences between the lists can be explained in terms of each document's

charter (i.e., public safety versus property safety), while in other cases

the basis for differences is not entirely clear. For example:

(a) The terminology applied to various plant areas is not uniform.

For instance, the remote shutdown rooms mentioned in Draft

Regulatory Guide 1.120 may be equivalent to the auxiliary panel

rooms in the NEL-PIA Guide, or the emergency/standby cooling

equipment referred to in the International Guidelines may be

comparable to the safety-related pump rooms in Draft Regulatory

Guide 1.120. Interpretation of terminology is left to the user

of the guides.

(b) There appears to be no consistent use of detectors as a function

of potential fire hazard. Some areas, such as the diesel or

cable spreading rooms, represent a significant fire potential

and should have detectors, while other areas with little or no

15
fire loading, such as many primary containment areas or nuclear

fuel storage areas, may need no automatic fire detection.

TABLE III

Area Detection Guidelines

Draft

Regulatory Guide International NEL-PIA

1.120, Rev. 1, Guidelines, Guide,

Draft 2, (Ref. 2) (Ref. 3) (Ref. 4)

Areas that Contain

or Threaten SafetyRelated Equipment x

Nonsafety-Related

Turbine Areas x

Control Room x x x

Switchgear Rooms x x x

Decontamination

Areas x x x

Emergency Battery/

Diesel Areas x x x

Cable Spreading

Room Area x x

Computer Room x x

Remote Shutdown

Rooms x x

Instrument Rooms x x

Relay Rooms x x

Primary Containment

Area x

Hazards Within

Primary Containment x

Control Room

Cabinets/Consoles x

16
TABLE III (cont)

Dr a ft

Regulatory Guide International NEL-PIA

1.120, Rev. 1, Guidelines, Guide,

Draft 2, (Ref. 2) (Ref. 3) (Ref. 4)

Control Room Inlet

Air Ducts x

Cable Spreading

Room Trays x

Safety-Related Pump

Rooms x

New Fuel Area x

Spent Fuel Area x

Cable Culverts/

Shafts x

Feed Water Pumps x

Power & Control for

Primary Pumps x

Filter Equipment x

Emergenc y/Standby

Cooling Equipment x

Air Handling System

Rooms x

Motor Control Centers x

Auxiliary Panel Rooms x

The seriousness of the above inconsistencies is minimized if it is

recognized that detectors are intended to provide improved safety through

early fire warning. Accordingly, it is reasonable for automatic detection

to serve all plant areas which contain or present potential fire exposure

to nuclear safety-related equipment, irrespective of the in situ fire

hazard that may exist.' This is especially true for those areas which are

normally unoccupied. In this regard, Draft Regulatory Guide 1.120

provides the best design criteria currently available for establishing

17
safety area detection requirements, when supplemented by the other two

documents for nonsafety plant areas.

2. Design Details and Qualification Tests for Establishing Area

Detection Requirements

In the information sources reviewed for this study, there is

virtually no guidance addressing either the design details or qualification tests governing area detection requirements. Except in those instances where the use of certain gaseous suppression techniques call for

automatic detection, even the National Fire Protection Association (NFPA)

codes applying to detectors and nuclear power plant fire protection5 6 are

silent with regard to area detection requirements. Because of this lack

of information, several problems arise regarding the design criteria

discussed in the previous section. Specifically, the following is noted.

(a) The requirement of Draft Regulatory Guide 1.120 to install

detectors in "all areas that present potential fire exposure

to safety-related equipment" causes a problem defining which

areas actually pose a threat to a given safety area. Areas

either immediately adjacent to or separated from a safety area

may or may not present a potential fire exposure, depending on

the level of fire hazard and the adequacy of existing barriers

and suppression systems. An assessment of these factors requires a detailed definition of what constitutes a potential

fire exposure. Without such a definition and a design technique

for determining potential fire exposure, it is difficult to

establish what level of detection coverage actually meets the

design criterion in Draft Regulatory Guide 1.120.

(b) The requirement in Draft Regulatory Guide 1.120 to install

automatic detection inside control room cabinets and along trays

in the cable spreading room lacks confirmatory testing. Because

of this, it has not been proven whether any added benefits are

derived from these special detection measures, although it

can be reasoned that a detector located close to a fire may

prove more effective. Without testing to demonstrate the

18
superior effectiveness of cabinet and tray detectors over area

detectors, it is difficult to justify, in all cases, the cost

and complexity associated with their use. This is especially

true when it is recognized that current qualification testing of

line detectors uses a ceiling configuration, not a cable tray

installation.

B. Selecting Specific Detector Types

Once area detection requirements have been established, it is

necessary to determine what type of detector or combination of detectors

is most suited to the fire hazards found in each area. As explained

earlier, five major types of commercially available detectors have been

considered here because of their proven effectiveness when properly

installed and maintained. The following sections examine how well existing sources guide in the selection of each detector type and what additional guidance is needed to help designers make an informed detector

choice.

1. Design Criteria for Selecting Specific Detector Types

None of the nuclear regulatory or insurance agency documents reviewed

for this study2 - 4 provides definitive design criteria for the selecting

detectors. In Draft Regulatory Guide 1.120 reference is made only to

continuous line heat detectors for cable trays, while the International

Guidelines state simply that, ". . . detectors should be selected

according to the operational and local requirements." Based on this lack

of guidance, more specific design criteria need to be defined. At a

minimum, detector selection criteria should acknowledge the influence of.

the following factors on detector choice.

(a) Combustion Products -- Detectors which prove to be sensitive to

combustion products from test materials (e.g., cellulosic and

liquid flammables) may be insensitive to the combustion products

produced by other materials commonly found in power plants

(e.g., cable insulation). To illustrate, ionization detectors

may not detect large smoke particles, which lack mobility in a

19
static electric field. Similarly, an infrared or ultraviolet

detector may not be able to detect flames through heavy smoke or

through combustion products that may screen the portion of light

spectrum to which the detector is sensitive.

(b) Fire Development -- Because some fires propagate rapidly (e.g.,

oil fires) while others start more slowly (e.g., cable fires),

it would be appropriate to select a detector whose response time

is consistent with the speed of anticipated fire development.

Also, the size to which a fire may be permitted to grow safely

in a particular plant area can influence the appropriateness of

a detector choice. A heat detector may be. the correct choice

for an oil fire but may be too slow to respond to a cable fire.

(c) Ventilation -- In rooms having large ventilation rates, combustion products and heat may be drawn from a room before reaching

the point of triggering heat, photoelectric, or ionization

detectors. To overcome this, line-of-sight area detectors which

do not depend on smoke concentrations for operation or continuous line local heat detectors which may be located closer to

the fire source should be considered. However, since ventilation rates are often a function of plant operating conditions,

outside temperatures, and ventilation system design, it is

difficult to predict how severely ventilation conditions can

degrade a particular detector's operation and under what circumstances line-of-sight or continuous line detectors would be

superior.

(d) Room Congestion -- In rooms containing large amounts of piping,

ductwork, cable trays, and equipment, certain detectors which

depend on line-of-sight "viewing" of a fire (e.g., infrared or

ultraviolet detectors) may be ineffective because a fire may be

blocked from the detector by room congestion.

20
(e) Room Geometry -- Rooms with high ceilings may render heat, photoelectric, and ionization detectors ineffective because the

buoyant effect of the rising combustion gases may be insufficient to overcome the ceiling height and may stratify the gases,

especially if ventilation rates are low. In this case, infrared

or ultraviolet detectors may be the best choice.

(f) Operational Activities -- If operational activities produce

signals to which a given detector is sensitive, false alarms may

result. For instance, an infrared or ultraviolet detector may

interpret welding activities as a fire or an ionization detector

may be unable to distinguish combustion products from an operating diesel from those of a fire.

(g) Maintenance Effect -- The sensitivity of some detectors may

degrade more dramatically with age than that of others. As a

result, frequent maintenance and testing may be required of

certain detectors in order to ensure satisfactory performance.

(h) Cost -- On a relative basis, the costs of detector elements can

be expressed approximately as follows:

i) Heat detectors $ x

ii) Ionization and $ 6x

photoelectric detectors

iii) Infrared detectors $ 6x

iv) Ultraviolet detectors $ 18x

The use of a large number of ultraviolet detectors in areas

where heat detectors are sufficient would be prodigal, unless

the broader area coverage gained through use of ultraviolet

detectors would significantly reduce the total number of

detectors required.

21
The importance of these factors in considering various power plant

detector applications is discussed in the next section.

2. Design Details for Selecting Specific Detector Types

Detailed guidance addressing the selection of detectors, based on the

criteria listed in the previous section, should be available. However, a

review of NFPA codes 5 6 revealed little information useful in determining

which detector types should be selected for specific plant locations.

Only general guidance describing the operating principles of detectors is

presented in the codes. As a result, the selection of a particular

detector must be made by a designer on the basis of operating principles,

rather than on a rigorous application of the criteria previously listed.

In an effort to define more clearly the types of detectors most

suited to different plant areas, a listing was developed of the plant

areas outlined in Table III vis a vis the physical characteristics of each

area as related to fire detector selection. Table IV shows the result of

this effort.

In developing Table IV, a number of judgments were made regarding the

relative importance of each area design characteristic and the relative

rating of conditions within each plant area. Figure 1 summarizes the

logic used in choosing a detector type for each area. From this logic

chart and Table IV, a number of observations can be made. First, in those

situations where either a fast or slow fire may develop, ionization and

photoelectric detectors were chosen over heat detectors because of the

delayed response time of heat detectors to slowly developing fires. Only

in diesel generator rooms, where diesel combustion products may set off

photoelectric or ionization detectors, does the selection of a heat

actuated detector appear suitable. Second, it should be recognized that

the permissible size of a fire from the standpoint of its effect on plant

safety should be considered in the selection of a detection system, in

addition to the anticipated speed of fire development. Because of the

difficulty in defining what constitutes a maximum acceptable fire size,

this factor has been excluded from Figure 1. Third, it may not be

22
possible to quantify what constitutes "significant background radiation,"

a "corrosive atmosphere," a "cable tray concentration," or a "congested

room." Therefore these factors have been only qualitatively considered.

Fourth, in those instances where more than one detector choice is given,

no effort has been made to define where ionization, photoelectric, or line

detectors may be superior. This is because many poorly defined and

misunderstood factors can influence the particular choice. For instance,

as concluded in an earlier Sandia Laboratories fire protection study,

relative detector reliability is understood only in a qualitative manner;

none of the additional literature reviewed for this current report has

revealed any new data to modify this conclusion. In addition to the

reliability factor, other studies 1 6 have concluded that:

(a) the sensitivity of photocells used in detectors may 'drift'

with aging, and

(b) at 'small' distances from a fire, ion chamber detectors are.

more sensitive than photoelectric devices, while at 'large'

distances the situation is reversed.

These examples of subtle differences among detectors demonstrate the

difficulty in developing Table IV and Figure 1 much beyond the point shown

in this report, and, as will be seen inf the next section, detector qualification test procedures fall short of answering many of the more important

questions influencing detector selection.

3. Qualification Tests for Selecting Specific Detector Types

The qualification test standards currently being used by Underwriters

Laboratories (UL) for nonresidential detector applications are:

UL 167 - 'Smoke Detectors, Combustion Products Type'

UL 168 - 'Smoke Detectors, Photoelectric Type'

UL 521 - 'Fire Detection Thermostats'

23
TAIILE IV

Physical Characteristics of Selected Safety-Related Plant Areas

as Related to Detector Selection

Plant Areas

Control Room

Cable Spreading

Room

Switchgear Rooms

Decontamination

Areas

Batery Rooms

Diesel Rooms

Computer Rooms

Safety Pump

Rooms

Nuclear Fuel

Areas

Primary

Co•,•air. eat

Relay Rooms

Remote

Shutdown Rooms

Instrument Rooms

Other =ectrical

Equipment Areas

Predominant

Combustibles

Cable Insulation

Cable Insulation

Cable Insulation

Plastic.i. Cloth,

-Cable Insulation

Hydrogen Gas

Cable Insulation

Lube Oil

Diesel Fuel Oil

Cable Insulation

Plastics, Paper

Cable Insulation

Cable Insulation

Lube Oil

Plastics

Cable Tnsulation

Cable Insulation

Lube Oil

Cable insulation

Cable 1nsulation

Cable Insulation

Cable Insulation

Anticipated (a) Room Congestion (b) Room (d)

Fire Development 'for Detection Ceiling Height

Slow

Slow

Initially Fast -

High Voltage Short

Slow - Propagation

Fast or Slow

Explosive or Slow

Fast or Slow

Fast or Slow

Fast or Slow

Fast or Slow

Fast or Slow

Slow

Slow

Slow

Slow

Low

High

Low

Variable (c)

Low

Low

Low

Low

Variable

Medium

High

Medium

iHigh

Variable

Low

Low

Medium

Variable (W)

Low

High

Low

Variable

High

Variable

Medium

Variable

Medium

Variable

Other Factors

False Ceilings

Continuously Marned

Nune

Htigh Temperature

Potential

Transient Fire

Loads. Background

Radiation

Corrosive

Atmosphere

Diesel Combustion

Products

False Ceilings &

False Floors

None

Transient Fire

Loads. Background

Rtdiation

Background

Radiation

None

None

Suitable Detector Choice

Ionization or Photoelectric

Ionization or Photoelectric

or Line Type

Ionization or Photoelectric

Photoelectric

Photoelectric (plus hydrogen

sensor or ventilation)

Heat - Rate of Rise or

Ultraviolet or Infrared

Ionization or Photoelectric

Ionization or Photoelectric

Photoelectric

Photoelectric

Ionization or Photoelectric

Ionization or Photoelectric

Ionization or Photoelectric

Ionization or Photoelectric

None

None

(a) Based on cable burning tests performed at Sandia Laboratories (References 7 and 8) cable fires, involving IEEZ - 383 approved cables. develop slowly.

in the time span of mirnute&. In this table, fires, such as oil which can fully develop in time spans of seconds, were rated as "fast".

(b) The influence of room congestion on detector selection is a factor only in those cases where line-of-sight detectors are satisfactory from the standpoint

of all other characteristics being considered.

(cW "Var-table" refers to those situations in which there are either transient fire conditions within an area or significant variations of physical characteristics

between different power pLnts.

(dW The terms low, medium, an d high ceilings were arbitrarily chosen as rooms having real or false ceilings: low, less than 10 feet high; medium, 10 to 30

feet high; high, greater th.n 30 feet high.
tit

Figure 1. Flow Chart for Detector Selection

25
In addition to these standards, another standard, UL 268-"Smoke

Detectors for Fire Protective Signaling Systems," is being developed to

combine UL Standards 167 and 168. A review of a proposed version of UL

268 has revealed, however, that many of the deficiencies to .be discussed

later, which are inherent in UL 167 and 168 for nuclear power plant fire

detection, still exist in the new standard, although some improvements

have been attempted by utilizing several air flow rates in one test

Sequence and by subjecting detectors to a smoldering fire condition in

another test. Unfortunately, the varied air flows in UL 268 are used only

in a test for checking false alarming and sensitivity to gray smoke produced by a cotton wick, while the smoldering fire test uses smoke from

wood heated on a hotplate. Neither of these conditions is typical of

nuclear power plant combustibles.

In terms of the detectors considered in this study, no published UL

standard covers ultraviolet or infrared detectors, while UL 167, UL 168,

and UL 521 address ionization, photoelectric, and area and line heat

detectors. Each of these test standards contains a wide range of construction and performance tests to establish detector sensitivity, reliability,

safety, and overall quality; once a detector has passed all applicable UL

tests, it then may be marketed as a "UL Listed" detector.

Because UL listed detectors are installed in a variety of industrial

locations, UL test procedures are generic in nature and may not be applicable to some nuclear power plant situations. Examples of this include

the following:

(a) UL Standard 167 for ionization detectors subiects the detectors

to combustion products from paper, polystyrene, gasoline, wood,

and cotton, while UL 168 for photoelectric detectors uses paper,

polystyrene, gasoline, wood, punk, and kerosene. Neither of

these standards tests detectors with cable insulations, lube

oils, diesel oils, or plastics commonly found in nuclear plants.

(b) None of the UL standards for smoke or heat detectors permits an

evaluation of detector response times as a function of smoke and

26
heat release rates. This is because the UL tests subject different detector types to different combustibles. In addition to

paper, gasoline, wood, and polystyrene tests, which are common

to UL 167 and 168, other tests involving cotton in UL 167, punk

and kerosene in UL 168, and alcohol in UL 521 are also performed. No correlation is made among these latter tests and a

cable insulation test.

(c) From the standpoint of detector location and spacing, discussed

more thoroughly in Section III.C of this report, none of the UL

detector tests measures the effect of area ventilation rates on

detector performance under fire conditions. Only in the UL 167

cotton test for ionization detectors and the UL 168 punk and

kerosene tests for photoelectric detectors has there been an

attempt to determine the influence of smoke movement on detector

sensitivity. Unfortunately, these tests are conducted in a

smoke chamber apparatus, not in a room, and the smoke velocities

used in these tests are only 30 to 35 feet per minute (1.6 to

1.9 m/sec)--well below ventilation velocities found in some

13

power plant areas.

(d) For testing detectors in a room environment, all of the UL standards use rooms having a smooth ceiling, with no physical

obstructions between the fire source and detectors, and with air

movement not exceeding 10 feet per minute (0.5 m/sec). As a

result, the influence of room congestion typically found in

power plants is not measured.

(e) UL standards 167 and 168 call for test rooms approximately 12

feet (3.65 m) high, while UL 521 specifies a 15-foot (4.57 m)

ceiling. Without testing each type of detector at several

higher ceiling heights, it is difficult to assess how well a UL

listed detector will perform in high bay areas of a power plant.

(f) From the standpoint of operational and maintenance considerations, the UL detector st-andards are basically complete. Each

27
standard calls for corrosion tests, humidity tests, and vibration tests. In addition, other tests applying only to ionization and photoelectric detectors, include static discharge,

paint loading, and dust accumulation tests. For a nuclear

plant, only the effects of radiation, diesel combustion products, different corrosive atmospheres, and other interferences

are needed to supplement the UL tests.

Based on the above comments, it is apparent that without some additional qualification testing, the indiscriminate installation of UL listed

detectors may not, in itself, assure satisfactory detector performance.

Because of this uncertainty, at least one other detector study has recommended a new qualification test method.1 7 This new procedure calls for

all types of detectors to be tested using the same set of conditions. As

proposed, the testing would include fifteen different tests made up of

three fire sizes for each of five combustibles. To represent a broad

spectrum of fire types and detector sensitivities, the fire test combustibles would include a flaming cellulosic, a smoldering cellulosic, a

flaming plastic, a smoky oil, and a nonsmoky alcohol, while each of the

three fire sizes would be about twice the size of the next smaller fire

with the smallest fire for each combustible being selected to assess a

detector's maximum sensitivity. Unfortunately, even this new method is

susceptible to some of the shortcomings of current procedures, including

the use of ceiling heights, ventilation conditions, and some combustibles

not common to nuclear power plants.

C. Locating and Spacing Detectors

Once plant areas requiring fire detection have been established, and

appropriate detector types chosen, it is necessary to locate and space the

detectors in a manner consistent with (1) the environment in which the

detector must function and (2) the qualification standard to which the

detector was tested. The following sections examine how well existing

information sources guide the locating and spacing of detectors and what

additional guidance is needed to help designers.

28
1. Design Criteria for Locating and Spacing Detectors

None of the nuclear regulatory or insurance agency documents reviewed

for this study 2 - 4 provides definitive design criteria for locating and

spacing detectors. Only through reference to NFPA 72 E, "Standard for

Automatic Fire Detectors"' 5 does Draft Regulatory Guide 1.120 acknowledge

the influence of location and spacing on detector performance. As a

result of this lack of guidance, more specific design criteria need to be

defined to take into account the factors listed below, some of which have

been assessed in terms of their influence on detector selection (Section

Iii. .B).

(a) Ventilation -- Bulk air flow through a room or local air flow in

the vicinity of ventilation ductwork can dilute combustion products or prevent the products from reaching a detector. Proper

detector positioning must balance the effects of bulk air flow

through a room against dilution near return air duct openings.

(b) Ceiling Height -- Stratification of combustion products below

the ceiling can delay the response of a heat or smoke detector

until a fire has grown to dangerous proportions. Before a detector can be effectively installed, the anticipated stratification

in a room must be determined as a function of the floor-toceiling combustion product buoyancy gradient under various

permissible fire sizes, room ventilation rates, and outside

temperature conditions.

(c) Ceiling Construction -- Solid ceiling joists and beams or sloped

ceilings can cause stagnant air pockets which prevent combustion

products from spreading uniformly. Under these conditions,

combustion products may need to spill over from one stagnant

zone to another before detection can be accomplished, thereby

delaying detector response.

(d) Room Congestion -- Ductwork, piping, and cable trays can deflect

combustion products away from a detector, especially if

29
ventilation conditions for detection are already unfavorable.

Significant congestion may dictate the installation of detectors

away from the ceiling and closer to those fire hazards requiring

maximum protection.

(e) Zoning -- To minimize the possibility of unintentionally actuating an automatic suppression system, some form of detection

zoning, requiring the operation of more than one detector before

automatic suppression starts, may be useful. The type and

degree of zoning selected, however, should consider the benefits

of reduced false alarms versus the risk of delayed detection

system response under actual fire conditions.

The importance each of the above factors plays in power plant applications and the level of design guidance available for each factor are

discussed in the next section.

2. Design Details for Locating and Spacing Detectors

A detector can function properly only if the fire properties to which

it is sensitive (e.g., heat, smoke, flame, or combustion products) are

able to reach the detector. This has been recognized for many years and

much of the design guidance developed for detectors in NFPA Standard 72E5

has addressed location and spacing. Unfortunately, little of the available design guidance goes beyond a qualitative assessment of the criteria

listed in Section III.C.I. Even in those instances where quantitative

direction is given, there appears to be a lack of supporting experience or

test data.

Table V compares the design guidance in NFPA 72E with criteria governing the location and spacing of detectors. A review of Table V shows a

number of design uncertainties applying to each locating and spacing

design criterion. The significance of these uncertainties is discussed

more thoroughly in the following paragraphs.

30
TABLE V •

Comparison of Detector Location and Spacing Criteria with Governing

Design Guidance Quoted from NFPA 72E

AREA HEAT DETECTORS

Des•en Criteria

(a) Ventilation

NFPA 72E

Design Guidance

NFPA 72E

Paragraph

Reference Comments

None None Guidance needed

(b) Ceiling Height Generally, height is the most important

single dimension where ceiling heights

exceed 16 feet.

As smoke and heat rise from a fire. they

tend to spread in the general form of an

inverted cone. As the ceiling height increases, a larger size fire is required

to actuate the same detector in the same

time. In view of this, it is mandatory

that the designer of a fire detection system

calling for heat detectors consider the size of

the fire, and rate of heat release, which may

be permitted to develop before detection is

ultimately obtained.

The most sensitive detectors should be

employed which are suitable for the

maximum ambient temperature at heights

above 30 feet.

Spot-type heat detectors shall be located

upon the ceiling not less than 6 inches

from the side wall, or on the side walls

between 6 inches and 12 inches from the

ceiling.

Spacing

Irregular Areas. For irregular shaped

areas the spacing between detectors may

be greater than the listed spacing, provided the maximum spacing from a detector

to the furthest point of a side wall or

corner within its zone of protection is

not, greater than 0.7 times the listed spacing.

Open Joist Construction. The spacing of

spot-type heat detectors installed on a

joisted ceiling shall not exceed 50 percent of

their listed spacing when measured at right

angles to the solid joists.

B-1. 2 thru

B-1. 5

I. Ventilation interaction ignored

ii. Manner of considering fire size and

rate of heat release unclear

lL The basis for 16 feet (4.9 m) and

30 feet (9. 1 rr,) is undocumented and

apparently unrelated to the UL test

heights of 12 feet (3. 6 m) for smoke

detectors and 15 feet (4.5 m) for heat

detectors (See Section III. B. 3)

(c) Ceiling

Construction

3-4.1, 3-5 I. S-uitability of 6 and 12 inch (0.15 and

0.3 m) distances not confirmed by UL

tests

ii. The 50% of listed detector spacing for

partitions near smooth ceilings or open

joist ceilings is not confirmed by UL

detector tests

III. A beam depth of 4 inches (0.1 m) for

a "smooth" ceiling may be excessive

(Reference 14)

iv. The guidance for sloped ceilings Is not

confirmed by UL detector tests 167.

168. or 521

W..

H
TABLE V (cont)

DeEign Crit*eria

NFPA 72E

Design Guidance

Beam Construction. It shall be treated as a

smooth ceiling if the beams project no more

than 4 inches below the ceiling. If the beams

prcject more than 4 inches below the ceiling,

detectors shall be located at no more than

two-thirds the spacing schedule in the

direction at right angles to the direction of

beam travel. If the beams project more

than 18 inches below the ceiling, each bay

formed by the beams shall be treated as a

separate area.

Sloped Ceilings. A row of detectors

shE.ll first be spaced and located at or within

three feet of the peak of the ceiling. The

number and spacing of additional detectors,

if any, shall be based on the horizontal

projection of the ceiling in accordance with

the type of ceiling construction.

NFPA 72E

Paragraph

Reference Comments

(d) Room Congestion

(e) Zordng (for

mlnmrnlzing

false alarms)

None

None

None

None

Guidance needed

Guidance needed

CO.XTN-%OQtS LINE REAT DETECTORS

(a) Ventilation

(b) Ceiling Height

None None

i.ne-type heat detectors shall be

located upon the ceiling or on the side

walls not more than 20 inches from

the ceiling

Also, ceiling height design guidance

for area heat detectors applies

3-4.2

Guidance needed; normal ventilation

could affect line detectors by interfering

with heat buildup along a ceiling

1. Line detector applications other

than on or near a ceiling are

ignored (e. g.. along cable trays)

ii. The 20-inch (0. 5 m) limit Is not

confirmed by UL test standard 521

Iii. Other comments for area heat

detectors apply

Guidance unnecessary for line detector

applications except on or near ceilings.

B-i. 2 thru

B-1. 5

Cc) Ceiling

Construction

None o None
TABLE V (cort)

CONTINUOUS LINE HEAT DETECTORS

NFPA 72E

Design Guidance

NFPA 72E

Paragraph

Des=. Criteria Reference

Md) Room Congestion

(e) Zodr.4g (for

r.inL-nizing

faise alarms)

None

None

None

None

Comments

Guidance needed; high temperature spots

resulting from normal operation of congested

equipment could actuate a local line detector

Guidance needed

IONIZATION AND PHOTOELECTRIC DETECTORS

(a) Ventilation

(b) Ceiling Height

(c) Ceiling

Const ruction

Spacing of smoke detectors shall

result from an evaluation based

upon engineering judgment

supplemented, if feasible, by field

tests. Ceiling shape and surfaces,

ceiling height, configuration of

contents. burning characteristics of

the stored combustibles, and

ver.:ila*ion are some of the parameters

that shall be considered.

Stratification occurs when the temperature of the smoke particles as generated.

usually from a smolddring or small fire,

reach the temperature of the surrounding

air. Since it has lost the thermal lift,

the smoke stops rising and stratifies.

For proper protection for buildings with

high ceilings, detectors shall be installed

alternately at two levels; one half at ceiling

level, and the other half at least three feet

below the ceiling.

Joisted Ceilings. Ceiling obstructions

8 inches or less in depth shall be considered equivalent to a smooth ceiling in

view of the "spill over" efrect of smoke.

Slope Ceilings (Peaked or Shed-Type).

A row of detectors shall first be spaced

and located within 3 feet of the peak measured

horizontally. The number and spacing of

additional detectors, if any, shall be based on

the horizontal projection of the ceiling.

4-4.1

4-4.5.1.

4-4.5.2

4-4.3,

4-4.4v

4-4.6

Guidance inadequate

i. Stratification from hot air heating systems

has been ignored

ii. The term "high ceilings" is not defined

quantitatively

ill. The effectiveness of two level detectors

separated by three feet (0. 9 m) is

questionable for all "high ceilings" found

in power plants

1. None of the distances for ceiling construction

or detector location are confirmed suitably by

UL tests

ii. The recommendations of manufacturers for

smooth ceilings are not independently tested

for validity by an impartial testing laboratory
TABLE V (cat)

Des!en Cr:teria

NFPA 72E

Design Guidance

Beam Construction. Beams 8 inches or less

in depth can be considered equivalent to a

smooth ceiling in view of the "spill over" effect

of smoke. In beam construction over 8 inches

in depth, movement of heated air and smoke

may be slowed by the pocket or bay formed by

the beams. In this case, spacing shall be

reduced. If the beams exceed 18 inches in

depth and are more than 8 feet on centers.

each bay shall be treated as a separate area

requiring at least one detector.

NFPA 72E

Paragraph

Reference Comments

(d) Room Congestiom

(e) Zoning (for

mini-izlng

false alarms)

None None

4-5.1

Guidance needed

The selection and installation of smoke Guidance needed

detectors shall take into consideration

both the design characteristics of the

detector and the areas into which the

detectors will be installed so as to prevent

false operation or nonoperation after

installation. Some of the considerations

are as follows:

1. Smoke detectors having a fixed temperature element as part of the unit shall

be selected in accordance with the maximum ceiling temperature that can be

expected in service.

2. The installation shall take into

consideration the maximrnum ambient

smoke density resulting from manufacturing

prccesses or other sources.

3. Since the projected beam-type unit will

operate when the light-path to the receiver

is interrupted or obscured; the light-path

shall be kept clear of opaque obstacles at

all times.
TABLE V (cOMt)

NFPA 72E

Design Guidance

NFPA 72E

Paragraph

Design Criteria Reference

ULTRAVIOLET IUIFRARED DETECTORS

(a) Ventilation None None

Comments

Guidance may be needed; normal

ventilation rates could affect flame

detector operation by allowing a

buildup of combustion products which

could screen the detector from the fire

source

There is no standard UL test for flame

detectors which establishes listed or

approved maximum spacings and installation heights

(b) Ceiling Height Except as otherwise permitted, flame detectors shall not be spaced beyond their

listed or approved maximums. Closer

spacing shall be utilized where the

structural and other characteristics of the

protected hazard would otherwise impair

the effectiveness of the detection.

5-4.1

(c) Ceiling

Construction

(d) Room Congestion

None None

5-4.2,

5-4.3,

5-5.1,

5-5.2

Specific guidance unnecessary; guidelines

for room congestion should be applicable

to ceiling construction considerations

Guidance appears adequate if coupled with

a standard qualification testing program

Flame detectors shall be so designed and

installed that their field of vision will be

sufficient to assure detection of a specified

area of fire.

Where conveyance of materials on chutes or

belts, or in ducts or tubes, or otherwise, to or

past if detector is involved, spacing considerations will not govern, but strategic

placement of detectors is required to ensure

adequate detection.

Since flame detectors are essentially line-ofsight devices, special care shall be taken in

applying them to assure that their ability to

respond to the required area of fire in the zone

which is to be protected will not be unduly compromised by the presence of intervening

structural members or o.her opaque objects

or materials.

The overall situation shall be reviewed

frequently to assure that changes in structural

or usage conditions that could interfere with

fire detection capabilities are remedied

promptly.

LI) (e) Zoning (for minimizing

false alarms)

None None Guidance needed
Ventilation -- In a power plant, air flow rates through portions of a

ventilated room can exceed 100 feet per minute (5.5 m/sec), while rates in

the vicinity of supply and return duct openings can reach 1,000 feet per

minute (55.0 m/sec). 1 3 These flow rates are well above boththe 30-35

feet per minute.(1.6 to 1.9 m/sec) test velocity currently used in detection sensitivity tests and the 10 feet per minute (0.5 m/sec) limiting

velocity specified for detector fire tests, 9 10 and a designer has no

means of analytically assessing the effects of these higher rates on

detector performance. As a further complication, it has been found that

some detectors can alarm under high velocity conditions but not under low

velocity conditions.16 The effects of both high and low air flow rates

are not completely understood. Since either of these conditions could

occur in a particular detctor installation, it is likely that testing

under ventilation conditions found outside of a detector's installed

environment will be inconclusive.

Ceiling Height and Ceiling Construction -- Ceiling heights in a power

plant can vary from 10 feet (3 m) in a pump room to 25 feet (7.6 m) in a

diesel generator room, 60 feet (18.2 m) in the turbine building, and 150

feet (45 m) in the reactor containment building; ceiling construction is

also variable. Yet, Underwriters Laboratories tests smoke and heat

detectors in a smooth-ceiling room at heights of 12 feet (3.6 m) and 15

feet (4.5 m). These disparities between testing conditions and actual

application may be significant, as indicated by research performed by R.

L. Alpert.14 Alpert identifies a strong correlation among ceiling height,

fire size, and detector sensitivity, as illustrated by the following

excerpts:

the maximum heat or mass transfer rates, and hence

minimum response times, will be attained for detectors located

a radial distance from the fire axis less than about 18 percent of total ceiling height and a vertical distance below the

ceiling of from 1 percent to 3 percent of total ceiling height

For optimum response time, fire detectors should be

spaced at intervals of 1/4 of the ceiling height. Spacings

smaller than this value will yield no significant improvement

in detector response time.

36
Although these conclusions are tempered by a number of restrictions (e.g.,

ceiling obstructions being less than 2 percent of the ceiling height and

the ceiling height being less than 2 to 4 times the room's wall-to-wall

horizontal separation), they point out the need to test detectors at

ceiling heights more closely approximating actual conditions. According

to Alpert, there exists a maximum ceiling height beyond which a fire of

given intensity cannot be detected. For example, heat detectors, rated at

135°F(57°C), located on a 20-foot by 20-foot (6 m x 6 m) square spacing

and mounted 35 feet (10.6 m) above burning fuel, will respond only to a

fire intensity greater than 100,000 BTU/minute (1.76 x i06 J/sec). In a

similar manner, Alpert argues that combustion product detectors will sense

a fire only if the interrelationship of fire intensity, ceiling height,

detector spacing, and detector sensitivity are properly considered.

Unfortunately, Alpert provides little quantitative information from which

to predict combustion product detector performance, especially in those

situations where room ventilation rates and floor-to-ceiling temperature

gradients can significantly interfere with the smoke flow patterns induced

by a fire.

Other research has demonstrated similar problems resulting from high

ceilings, particularly with smoldering fires. 1 8 The National Bureau of

Standards has found that in the early stages of smoldering fires in rooms

having ceiling heights greater than 8 feet (2.4 m) (15 feet [4.6 m] and 29

feet [8.8 m] being tested), smoke stopped short of the ceiling and spread

horizontally. Such behavior is not conducive to early fire detection.

Room Congestion -- As pointed out in Section III.B.2, it is difficult

to determine at what point room congestion constitutes a detection

problem. Although in most nuclear power plants auxiliary equipment and

cable spreading areas appear more congested than the switchgear or diesel

rooms, there exists no proven methodology for assessing what level of

congestion actually reduces the effectiveness of a particular detector or

what sensitivity and spacing adjustments can be made to overcome congestion detriments. This lack of guidance is not surprising when one considers the variety of room arrangements, ventilation rates, combustible

37
materials, burn rates, and room geometries that would need to be correlated with levels of room congestion.

Zoning -- Current detector zoning techniques for minimizing the incidence of false alarms or false actuation of extinguishing systems typically require two or more adjacent detectors to sense a fire and alarm. Although this approach successfully reduces false alarms, it can also reduce

the overall effectiveness of a detection system to below the level at

which the individual detectors originally were tested. For two detectors

to respond in the same manner as one detector, adjustments must be made

in the spacing, sensitivity, and reliability of the two-detector scheme.

Designers currently have no guidance for making these adjustments.

3. Qualification Tests for Locating and Spacing Detectors

The following paragraphs, quoted from the Underwriters Laboratories

Fire Protection Equipment List, 2 0 describe the locating and spacing conditions under which detectors are qualified, together with UL recommuendations for adapting test results to actual installation conditions.

(a) Area and Continuous Line Heat Detectors

The spacings specified are for flat, smooth ceiling construction of ordinary height, generally regarded as the

most favorable condition for distribution of heated air

currents resulting from a fire. Under other forms of

ceiling construction reduced spacing of thermostats may

be required. The fire tests conducted to determine the

suitability of the thermostat spacings are conducted in

a 60 by 60 ft room having a 15 ft 9 in.* high smooth ceiling and minimum air movement. The test fire (denatured

alcohol) is located approximately 3 ft above the floor

and of a magnitude so that sprinkler operation is obtained

in approximately two minutes.

*It should be noted that a discrepancy exists between the 15 foot-9-

inch (4.8 m) test ceiling height quoted for photoelectric and ionization

detectorg Td the 12-foot (3.6 m) height called for in UL Standards 167

and 168.

38
S.. The placement and spacing of thermostatic devices

should be based on consideration of the ceiling construction, ceiling height, room or space areas, space subdivisions, the normal room temperature, possible exposure of

the devices to abnormal heat such as may be produced by

manufacturing processes or equipment, and to draft conditions likely to be encountered at the time of a fire.

Authorities having jurisdiction should be consulted in all

cases before installation.

(b) Ionization Detectors

Spacings - Although no specific spacings are being allocated

to these detectors, the test fire spacings of 30 ft may be

used, if practicable, only as a GUIDE or starting point in

a detector installation layout. IMPORTANT: THE TEST FIRES

CONDUCTED BY THE LABORATORIES ARE BASED ON ONLY ONE SET OF

CONDITIONS, NAMELY A 15 FT 9 IN. HIGH SMOOTH CEILING, NO

AIR MOVEMENT, AND NO PHYSICAL OBSTRUCTIONS BETWEEN THE FIRE

SOURCE AND DETECTOR. It should be realized that these are

fairly ideal conditions for a symmetrical detector layout.

For conditions other than above it is mandatory that

engineering judgment be applied regarding detector location and spacing. In all likelihood closer spacings and

irregular distribution would be required for those installations containin- high stockpiles, higher than 16 ft high

ceilings, small bays and other ceiling obstructions, and

particularly in areas where there is rapid air movement

from air conditioning and ventilating systems. The air

current patterns should be checked by test smoke or light

tissue paper to determine proper location of detectors.

(c) Photoelectric Detectors

Guidance similar to that provided for ionization detectors

appears to apply to photoelectric detectors, even though the UL

listing does not restate the information.

(d) Ultraviolet/Infrared Detectors

The location of flame detectors should be based on an

engineering survey of the conditions to be anticipated in

service and the principle of operation. Detectors should be

installed only after a thorough study has been made of the

area or premises to be protected (whether in planning or construction state) and of the life and property values involved.

Prior to engineering a layout of an installation, a copy of

the manufacturer's technical bulletin should be obtained and

reviewed to determine recommended detector locations.

39
Consideration should be given to all features which could

have a bearing on the location and sensitivity of the detectors, including such pertinent factors as coverage in partitioned sections, ceiling heights, overlapping of areas of cone

coverage to provide maximum protection. Test flames should

be employed to check proper detector location.

It is apparent from the above statements that the ideal conditions of

detector test are recognized, but the guidance provided for adapting

qualified detectors to nontest conditions is vague, with considerable

reliance placedupon "engineering judgment" and installation testing.

D. Performing Installation Tests and Maintenance

Because detector installations seldom resemble the controlled conditions of a qualification test and because environmental conditions can degrade the original performance of some detectors, in-place testing should

be performed following installation and at regular intervals throughout a

detector's design life. These activities are of major importance in confirming the adequacy and continued reliability *of a detection system,

especially in light of the marginal design information and qualification

testing alluded to in earlier sections of this report. The following

sections examine how well existing information sources guide the installa-

*tion testing and maintenance of detectors and what additional guidance is

needed to help design and operations personnel perform these activities.

1. Design Criteria for Performing Installation Tests and Maintenance

The quality assurance section of Draft Regulatory Guide 1.120 provides the following limited criterion for performing fire protection

system testi.ng:

A test should be established and implemented to ensure that

testing is performed. and verified by inspection and audit to

demonstrate conformance with design and system readiness

requirements.

To supplement this criterion, the Standard Technical Specifications,

issued by the NRC for nuclear power plant fire protection, states that:

40
Each fire detection instrument shall be demonstrated operable

by performance of the manufacturer's recommended tests at

least once per 6 months.

In addition to these NRC documents, other sources of criteria include the

International Guidelines for Fire Protection3 and a Nuclear Energy

Liability-Property Insurance Association bulletin. 1 5 These sources simply

state that:

The protective measures against the fire hazards should be

periodically checked for their efficiency.

and

Detectors should be properly maintained by qualified persons

in accordance with manufacturer's recomnendations. As a

minimum, annual cleaning, sensitivity adjustment, and

operational testing should be performed.

From the above statements, it is clear that the testing and maintenance criteria available in regulatory and insurance documents can

easily be expanded into a more definitive list of criteria. Such a list,

presented below, was gleaned from a number of sources, including the NFPA

Standard on Automatic Fire Detectors 5 and the Underwriters Laboratories

Fire Protection Equipment List and associated standards. 9 -11 20

(a) Installation Test Criteria

* A visual inspection of all detectors should be made to

ensure that detectors are installed according to design

specifications.

" Each detector should be checked to confirm proper wiring

and power connections.

* The stability of the detection system should be monitored

for several weeks prior to activation of the central fire

alarm system to identify potential sources of false alarms,

such as background radiation or combustion products.

41
* The response of the detection systems should be confirmed

using a test fire under environmental conditions anticipated to occur normally in the area being protected. The

test fire should produce the type and degree of flame,

heat, smoke,. and combustion products characteristic of combustibles found in the protected area. The environmental

test conditions should be representative of the temperatures and ventilation rates expected normally to occur.

(b) Maintenance Criteria

* Detectors should be periodically tested in place to

confirm continued satisfactory operation.

* Detectors should be periodically cleaned to remove

accumulated dust and dirt. The frequency of cleaning

will depend on the type of detector involved and the prevailing environmental conditions.

* Following periodic testing or cleaning, detectors should

be restored to service promptly.

It is apparent that a designer needs additional guidance before even

these abbreviated testing and maintenance requirements can be implemented.

This additional guidance, which is needed to define maintenance intervals,

inspection techniques, required training, and calibration standards, traditionally has come from either detector manufacturers or what is termed in

fire protection literature as "the authority having jurisdiction." The

next section of this report addresses the adequacy of the traditional

testing and maintenance design details available with respect to nuclear

power plant applications.

2. Design Details for Performing Installation Tests and Maintenance

Performing installation tests and maintenance in accordance with the

recommendations of a detector manufacturer has both advantages and

42
disadvantages for a nuclear power plant. Table VI lists some of the more

important concerns in this regard.

It can be seen from Table VI that, although detector manufacturers

have the potential for providing the most comprehensive guidance for

testing and maintaining detector systems, there is little commercial

incentive for a manufacturer to research the special problems of nuclear

power plant fire detection. Based on this, it is questionable whether the

testing and maintenance programs recommended by manufacturers are entirely

suitable for power plant applications. Furthermore, since design

guidelines such as NFPA Standard 72E, 5 defer much of their authority to

"manufacturer's recommendations," there is no standard to which a designer

can turn for either absolute or relative evaluation of the performance of

an installed detection system. Such a standard appears to be needed for

nuclear power plant detection systems.

3. Qualification Tests for Performing Installation Tests and Maintenance

At present, there are no uniformly applied qualification tests for

confirming the in-place response characteristics and maintenance requirements of detectors. Although UL standards subject detectors to a variety

of corrosion, vibration, humidity, temperature, and dust accumulation

conditions, the UL test results are judged as either pass or not pass,

with no extension of the qualification tests to developing in-service

maintenance procedures or test intervals. In addition, no part of the UL

standards identifies what minimum installation tests a UL-listed detector

should undergo to confirm performance after installation. Such installation tests should be conducted, although the development and implementationof the tests-may be beyond the purview of Underwriters Laboratories

and may need to be the subject of a future independent research effort.

In the interim, however, it is important to identify what course of action

should be followed to assure dependable detector operation in a nuclear

power plant. The conclusions and recommendations sections of this report

which follow attempt to identify and justify a proper course of action.

43
TABLE VI

Advantages and Disadvantages of Performing Detector Testing and

Maintenance According to Manufacturer's Recommendations

Advantages

41. Manufacturers are most familiar with the

capabilities of their detectors and can best

recognize the most stringent conditions under

which they should be tested and maintained.

2. Manufacturers can readily modify their test

and maintenance conditions to more appropriately cover the requirements of a particular

customer, including changes to reflect room

geometry, ventilation conditions, and combustible material present.

3. Manufacturers are willing to assist a customer

in testing and correcting a poorly functioning

detector system.

4. Manufacturers often have broad experience

in the areas of residential and commercial

fire detector applications. This experience

can benefit a test and maintenance program,

especially in solving problems involving

ceiling obstructions, fast ventilation rates,

and a typical combustion materials.

Disadvantages

1. Manufacturers have a vested interest in ensuring

customer satisfaction by demonstrating that a

detector is sensitive enough to detect fire but

stable enough to preclude false alarms. This

may lead to test and maintenance conditions

favoring detector operation but misrepresenting

actual fire and environmental conditions.

2. Testing and maintenance procedures are often

proprietary in nature and, as such, vary from

one manufacturer to the next. Because of this,

there is no uniformity between the procedures

used and no independent verification, similar

to UL testing, of the validity of each procedure.

3. In the interest of satisfying a customer and

"solving" a detector response problem, a

manufacturer may find it necessary to reposition

and adjust installed detectors, possibly at the

expense of overall detection system performance.

4. Because of the relatively small nuclear power

plant fire detection market, detector manufacturers have concentrated efforts in commerical

and residential areas. This means that many

available detectors have been designed to perform

best under conditions not often found in a power

plant (e. g., low ventilation rates, low ceiling

heights, smooth ceilings, and cellulosic

combustibles).
IV. CONCLUSIONS

This report examined the adequacy of fire detection in the context of

nuclear power plant safety. Topics considered were (1) establishing area

detection requirements, (2) selecting specific detector types, (3)

locating and spacing detectors, and (4) performing installation tests and

maintenance. As discussed in Section III of this report, each of these

activities lacks the technical bases needed for accomplishing a thorough

and quantitative detection system design. The basis for this conclusion

is summarized for each activity in the following paragraphs.

Establishment of Area Detection Requirements

e Current insurance and regulatory agency criteria are inconsistent and often conflict by referring to various plant

areas by different names and by requiring different levels of

detection coverage for the same plant areas.

Selecting Specific Detector Types

* Although it is possible to make gross judgments in choosing

a particular detector type, such as an area heat detector in

preference to a smoke detector, it is difficult to make more

subtle selections among similar detector types, such as ionization versus photoelectric detectors. Furthermore, since different detector types are tested under different conditions,

it is doubtful whether any predictable correlation of detector

performance can be made for candidate detectors. This is

because there are conditions under which detectors now are not

fully tested.

Locating and Spacing Detectors

e Locating and spacing cannot be accomplished in an analytical

manner based on present testing methods. Instead, engineering judgment and vendor recommendations must bridge the gap

between test conditions and installed conditions. Unfortunately, judgment and recommendations can vary widely,

45
depending on the skill of the individual providing the

guidance.

Performing Installation Tests and Maintenance

S There is no uniformly applied set of installation tests and

maintenance procedures at this time. Only the recommendations

of detector manufacturers are available to a designer. Since

detector manufacturers often have diversified interests, only

a fraction of which may involve nuclear power plant fire protection, there has been little incentive for a manufacturer to

develop installation test and maintenance procedures primarily

geared to the nuclear power plant market.

From this summary, it is apparent that present fire detection operating principles and qualification tests do not permit the prediction of

detector response characteristics. Further, it is doubtful whether any

theory can be developed and proven in the near future to describe the

complicated interaction of each physical parameter affecting detector

operation. Therefore, it appears that the best approach to solving the

uncertainties of nuclear power plant fire detection is through in-place

testing of detectors under environmental conditions anticipated to occur

normally in each area being protected. This conclusion is consistent

with: (a) the test results and recommendations of a full-scale test program performed by the Coast Guard in a 100,000 cubic foot ship machinery

space1 9 and (b) the current approach being followed by the largest

detector manufacturer in Europe (Cerberus of Switzerland).

Through in-place testing, during both initial installation and subsequent maintenance intervals, satisfactory detector performance can be

assured for the variety of conditions found in power plants. As a further

benefit, an in-place testing program can be developed and used in power

plants without affecting any of the existing qualification test procedures

and installation instructions developed and applied by Underwriters

Laboratories and others for primarily commercial and residential

applications.

46
On the basis of these conclusions, the final section of this report

recommends a number of steps that may be taken to improve the guidelines

now available to designers of nuclear power plant fire detection systems.

V. RECOMMENDATIONS

The recommendations listed here have been developed to address some

of the more important detection system design problems identified throughout this report. A few of the recommendations cited involve administrative action, while others require further research and testing. In some

instances, the recommendations suggest that no action be taken, because of

the limited benefits that could be derived from further work in certain

areas. It should be recognized that the objective of each recommendation

is to achieve a level of detection system reliability which warrants the

added cost and complication associated with detector installation.

A. Establishing Area Detection Requirements

1. The terminology used to describe plant areas requiring detection needs to be made more uniform or at least be descriptive

enough to eliminate the need for interpretation on the part of

the designer.

2. Plant areas requiring detection need to be determined on the

basis of each area's safety importance and the incremental

contribution to overall plant safety afforded by a fire detection system. This determination can best be made by comparing

the effectiveness of added detection with the safety benefits of

other fire protective measures and with the safety importance of

the area being protected. Such a comparison should be part of a

fire hazards analysis conducted for each area in question.

47
3. The cost effectiveness of using detectors inside cabinets and

along cable trays needs to be confirmed by testing. It may be

that such added detection is unjustified.

B. Selecting Specific Detector Types

1. Guidance is needed to make designers aware of the factors

influencing detector selection (discussed in Section III.B.l).

These factors are combustion products, fire development (both

speed and permissible size), ventilation, room congestion, room

geometry, operational activities, maintenance effects, and cost.

2. Guidance is needed to identify suitable detector choices and the

basis for these choices for those plant areas requiring detec:-

tion. Information provided in Table IV and Figure 1 of this

report can serve as a starting point for this guidance.

3. In those cases where it is difficult to choose among several

detector types (e.g., choosing among photoelectric, ionization,

and line detectors in Table IV, Section III.B.2), some form of

uniform comparative testing needs to be done using combustibles

and conditions found in nuclear power plants. As a first step,

such testing should focus on determining the performance of

various detector types, under some fixed set of environmental

conditions, when subjected to combustion products from power

plant materials. Subsequent comparative testing should consider

as many of the additional factors cited in recommendation B.1 as

possible.

4. It appears that no effort needs to be directed toward developing

more sophisticated detectors or modifying existing commercially

available detectors, because there is a sufficient variety on the

market to meet the design requirements of the nuclear industry.

Accordingly, the guidance and testing referred to in recommendations B.2 and B.3 may be limited to commonly available detectors.

48
C. Locating and Spacing Detectors

1. Because of the difficulty in characterizing the numerous room

configurations and environmental conditions affecting detector

performance, it appears that no effort should be made to develop

quantitative detector location and spacing guidelines beyond

those already available or being developed by the NFPA and the

National Bureau of Standards. Instead, regulatory documents may

limit guidance'to making designers aware of (a) the qualitative

aspects of fire detection, as affected by the factors listed in

recommendation B.1, and (b) the importance of in-place testing.

2. It appears that no effort should be directed toward modifying

guidance on detector locating and spacing currently provided in

the commercial and residential design information developed by

independent testing laboratories and fire protection associations. Any major modification of these existing guidelines could

only be justified through an extensive detector test program

using the range of conditions expected in nuclear power plants.

Such an effort would be costly and would not negate the need for

the confirmatory in-place testing recommended in C.1 and D.I.

D. Performing Installation Tests and Maintenance

1. A detector installation test procedure needs to be developed

which is based on confirmatory research, and is representative of

the combustibles, environmental conditions, and detector types

(i.e., area, cabinet, and cable tray fire detectors) found in

nuclear plants. This test procedure should: (a) address the

factors listed in recommendation B.1, (b) provide reproducible

test results, and (c) present a minimum disruption to normal

plant operations.

2. A detector maintenance procedure needs to be developed. This

procedure could identify the maintenance details and maintenance

intervals required for each type of detector installed in power

plants as a function of enviromental conditions found in various

49
plant areas. The establishment of maintenance intervals could be

accomplished on. the basis of analysis or testing which demon-

.strates a detector's reliability and which corresponds to the

minimum acceptable reliability of a detection system.

It is apparent that the greatest benefit to nuclear fire protection

can be derived from accomplishing recommendations A.2, B.3, D.1, and D.2.

Through the enactment of these and the other recommendations, nuclear

power plant detection systems can be selected, installed, tested, and

maintained in a manner which assures reliable operation.

50
VI. REFERENCES

1. Report on Task I, Fire Protection System Study, SAND76-0630, Sandia

Laboratories, Albuquerque, New Mexico, February 1977.

2. Fire Protection Guidelines for Nuclear Power Plants, Revision 1,

Draft, U. S. Nuclear Regulatory Commission Regulatory Guide 1.120,

November 1977.

3. International Guidelines for the Fire Protection of Nuclear Power

Plants, 1974 Edition, 2nd reprint, Published on behalf of the

National Nuclear Risks Insurance Pools and Associations.

4. Basic Fire Protection for Nuclear Power Plants, Nuclear Energy

Liability-Property Insurance Association (NEL-PIA) - Mutual Atomic

Energy Reinsurance Pool (MAEPA), April 1976.

5. Standard on Automatic Fire Detectors, NFPA 72E, 1974.

6. Standard on Recommended Fire Protection Practice for Nuclear

Reactors, NFPA 802, 1974.

7. Cable Tray Fire Tests, SAND77-1125C, Sandia Laboratories,

Albuquerque, New Mexico, July 1977.

8. A Preliminary Report on Fire Protection Research Program (July 6,

1977 Test), SAND77-1424, Sandia Laboratories, Albuquerque, New

Mexico, October 1977.

9. Smoke Detectors, Combustion Products Type for Fire Protective

Signaling Systems, Underwriters Laboratories Standard UL 167,

November 1974.

10. Smoke Detectors, Photoelectric Type for Fire Protective Signaling

Systems, Underwriters Laboratories Standard UL 168, January 1976.

11. Fire Detection Thermostats, Underwriters Laboratories Standard UL

521, April 1974.

12. Single and Multiple Station Smoke Detectors, (Residential

Applications), Underwriters Laboratories Standard UL 217, January

1976.

13. Carrier System Design Manual, Part 2, Chapter 3, Carrier Air

Conditioning Company, Syracuse, New York.

14. Alpert, R. L., "Calculation of Response Time of Ceiling-Mounted Fire

Detectors," Fire Technology, Vol. 8, No. 3, (pp. 181-195), August

1972.

51
15. Bulletin to Agents and Brokers and Architect/Engineers, NEL-PIA's

Recommendations for Cable Systems at Nuclear Power Stations, Nuclear

Energy Liability-Property Insurance Association (NEL-PIA) - Mutual

Atomic Energy Reinsurance Pool (MAERP), April 1976.

16. Fire Detection: The State-Of-The-Art, NBS Technical Note 839, U. S.

Department of Commerce, National Bureau of Standards, Washington,

D. C., June 1974.

17. A New Test Method for Automatic Fire Detection Devices, NBSIR 76-

1172, U. S. Department of Commerce, National Bureau of Standards,

Washington, D. C., December 1976.

18. Environments of Fire Detectors - Phase 1: Effect of Fire Size,

Ceiling Height, and Material, Volume I Measurements, NBS-GCR-77-86,

U. S. Department of Commerce, National Bureau of Standards,

Washington, D. C.', May 1977.

19. Machinery Space Fire Detecting Tests - Phases I and II, United States

Coast Guard Office of Research and Development, Shipboard Fire and

Safety Testing Facility, Test Advisory Group Report, U. S. Coast

Guard Headquarters, Washington, D. C., August 1971.

20. Fire Protection Equipment List, (p. 124), Underwriters Laboratories,

January 1976.

52
APPENDIX A

Confusion Over Class A System Designations

The requirements in Draft Regulatory Guide 1.1201 for designing detection systems in accordance with the Class A system requirements specified

in NFPA 72D "Standard for the Installation, Maintenance and Use of

Proprietory Protective Signaling Systems" can be misinterpreted. As

explained in Articles 110 and 130 of NFPA 72D, a Class A design provides

emergency operation for fire 'alarms, waterflow alarms, and guard tour

signals, in the event of a single break or ground fault of the "signaling

line circuit" or of any devices connected to it. NFPA 72D defines a

"signaling line circuit" as a circuit connecting transmitters or control

units to the central supervising station over which fire alarm, waterflow,

guard tour or supervisory signals are transmitted. According to NFPA 72D,

circuits of lesser importanc' connecting individual detectors to control

units are not part of the "signaling line circuit," and, therefore,

apparently need not meet Class A criteria. Although it is correct to

"electrically supervise" individual detector circuits in accordance with

Article 240 of NFPA 72D so that the occurrence of a break or ground fault

will cause a trouble signal, a requirement that these less important circuits be operable under faulted conditions (Class A) goes beyond the

intent of NFPA 72D. Because some licensing confusion regarding this issue

has arisen, Regulatory Guide 1.120 should state more clearly the scope of

Class A design to be used in nuclear power plants.

1 Fire Protection Guidelines for Nuclear Power Plants, Rev. 1, USNRC,

November 1977

53-54

APPENDIX B

Abbreviated Description of Commercially Available Detectors

a. Heat Detectors (area and line type)

1. Types

a) Bimetallic strip thermostats (Figure B-i)

b) Snap-action disc thermostats

c) Thermostatic cables (Figures B-2 and B-3)

d) Fusible link and quartzoid bulbs

2. Uses

a) Area protection

b) Spot detection

c) Initiation of extinguishing devices

b. Photoelectric Detectors

1. Types

a) Beam (Figure B-4)

b) Spot

1. Obscuration

2. Light scattering

c) Sampling

1. Obscuration

2. Light scattering

2. Uses

a) Air conditioning

b) Vaults

c) File rooms

d) Computer centers

e) Warehouses

systems

55
c. Ionization Detectors

I. Types

a) Ionization (Figures B-5 and B-6)

b) Resistanance grid

c) Combination ionization/resistance grid

2. Uses-similar to photoelectric detectors

d. Flame Detectors (Figure B-7)

1. Types

a) Ultraviolet

b) Infrared

2. Uses

a) Any industrial or warehousing operations

b) Spot protection

c) Control of fixed extinguishing systems

d) Explosion suppression

THERVIOSTAT - FIXED TEMPERATURE

BIM'IETALLIC TYPE

Figure B-i

56
Thermostatic Cables

APPROXIMATELY

1 18' DIAMETER

HEAT SENSITIVE

MATERIAL

I OUTER

COVERING

PROTECTIVE

TAPE

Figure B-2

- -. ~ _ __ zZ~~J

- ~/r~- -~

* r ~. ________-

% - 4.--

- - - *YA

WIRE LINE TYPE DETECTOR

Figure B-3

SMOKE DETECTOR - PROJECTED BEAM TYPE

TO

POWER

SUPPLY LL-0 TO BALANCED -0 BRIDGE TYPE

CIRCUIT

LIGHT

SOURCE

PHOTOCELL

Figure B-4

57
Ii

-Battery

- (D.C. Power Sourc

Positive

+ Electrode (p1)

Alpha'

• Positive .iti e + ,-.'', -, ~ Particles

,~= d--.-.n

Negative " A

Ion

T..,mt-trnr.. (P2))Negative

Galvanometer.

Ionization Chamber Principle

Figure B-5

L

DUAL CHAMBER IONIZATION DETECT.OR

A-Alpha sourte; An-anode; B-detector base; G-gas

discharge Tube; J-locking shell; K-cathode; L-locking

screw; N-neon lamp; 0--outer chamber; P-control pin;

S-starter electrode; V-0 ring; W-inner chamber electrode;

X-inner chamber.

Figure B-6

58
FR!4VEWCY

D/sc//4/IAMT/oNUG/ITYUS~srlvs

EC: esWr

-C0L0 CAh7X7Z4X

Figure B-7

59
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