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NBSIR 80-1992 mar is isbo

il Development of Flammability

I

Criteria for Transformer Dielectric

I Fluids

I Richard G. Gann

fj'

R Center for Fire Research

R National Engineering Laboratory

R National Bureau of Standards

« U S. Department of Commerce

Washington, D.C. 20234

iLWc

Final Report

February 1980

Issued March 1980

Prepared for: U.S. Department of Energy

Electric Energy Systems Division

Power Delivery Branch

Washington, D.C. 20545

NBSIR 80-1992

DEVELOPMENT OF FLAMMABILITY

CRITERIA FOR TRANSFORMER DIELECTRIC

FLUIDS

Richard G. Gann

Center for Fire Research

National Engineering Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, D.C. 20234

Final Report

February 1980

Issued March 1980

Prepared for: U.S. Department of Energy

Electric Energy Systems Division

Power Delivery Branch

Washington, D.C. 20545

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

TABLE OF CONTENTS

Page

LIST OF TABLES

LIST OF FIGURES

Abstract 1

1. INTRODUCTION 1

1.1 Background 1

1.2 Magnitude of the Problem 4

1.3 Objectives of This Effort 5

2. THE CURRENT STANDARD 6

3. THE SLOW LEAK SCENARIO 7

3.1 Description of Hazard 7 3.2 Characteristics of Pool Fires 8

3.2.1 Ignition 8

3.2.2 Flame Spread Over the Pool Surface 9

3.2.3 Ignition of Surrounding Fuels 10

3.2.4 Dependence of Pool Burning Rate on Prevailing Atmospheric Conditions 11

3.3 Pool Fire Performance Tests 12

3.3.1 The Factory Mutual Approval Scheme 12

3.3.2 Rate of Heat Release Determinations 14

3.4 Aging of Fluids 15

4. THE VIOLENT RUPTURE SCENARIO 17

4.1 Description of Hazard 17

4.2 Applicability of Standard Test Methods 18

4.3 Explosion Tests 18

4.4 Model for the Ignition of Remote Fuels

by Flaming Droplets 19

5. EVALUATING ALTERNATIVE FIRE SAFETY STRATEGIES 23

6. RECOMMENDATIONS FOR FURTHER WORK 26

6.1 Assessment of the Current Status 26

6.2 Needed Test Development 26

6.2.1 Fluid Ignitability 27

6.2.2 Radiant Ignition of Surrounding Materials 28

6.2.3 Contact Ignition of Surrounding Materials 28

6.2.4 Damage to the Building 29

6.3 Epilogue 29

iii
TABLE OF CONTENTS (continued)

Page

7. ACKNOWLEDGMENTS 30

8. REFERENCES 31

APPENDIX A. COMPARISON OF RADIATION CHARACTERISTICS OF

SILICONE AND HYDROCARBON FLUID POOL FIRES A-1

APPENDIX B. A RECENT CASE OF PCB LEAKAGE AND POLLUTION

from The Washington Post , September 29, 1979 B-1

iv
LIST OF TABLES

Table Page

1. Expected annual national losses 34

2. Cost plus loss per transformer over transformer lifetime . 35

A-1. Long-wavelength pass filters A-5

LIST OF FIGURES

Figure Page

1. Temperature profiles of solid-liquid system at droplet

impact (t=0) and at some later time (t=t') 36

A-1. Apparatus schematic A-6

A-2(a). Photomultiplier response data from pump oil fire A-7

A-2(b). Photomultiplier response data from silicone fluid fire . . A-8

A-2(c). Photomultiplier response data from tungsten bulb A-9

A-3(a) . Spectral data from pump oil fires (intensity in

arbitrary units) A-10

A-3(b). Spectral data from silicone fluid fires (intensity in

arbitrary units) A-11

A-3(c). Spectral data from tungsten bulb fires (intensity in

arbitrary units) A-12

V
'1

1
DEVELOPMENT OF FLAMMABILITY CRITERIA

FOR TRANSFORMER DIELECTRIC FLUIDS

Richard G. Gann

Abstract

With the recent ban on the use of polychlorinated

biphenyls, it has become necessary to examine the fire

safety requirements for electrical insulating fluids.

The hazards are delineated and the magnitude of the

transformer fire problem assessed. The current fire

code and standard test methods are shown to be

inadequate. Approaches to fluid fire performance

testing are presented, as is a basis for evaluating

the economic Impact of alternative fire safety

strategies. The report concludes with recommendations

for further work.

Key words: Fire; fluids; pool fires; transformers.

1. INTRODUCTION

1.1 Background

The routine availability of electrical power has become an essential

facet of our life style. With the exception of an occasional shock or blown fuse, we assume total safety and reliability of the power transmission network. However, this has only evolved because each element

in the system has bee'a itself engineered to be safe and reliable. We

have responded to changes in technology in the past and maintained or Improved the system. Rubber cable insulation has given way to polyvinyl

chloride, circuit breakers are replacing fuses, and grounded outlets are becoming commonplace.

1
Due to certain recent events, we now need to reexamine one of the

basic elements—the transformer. These devices convert an available

input voltage to that needed by the device at hand. There are millions

of indoor transformers in use, ranging from the small step-up transformers

in televisions to the large step-down power transformers in apartment

complexes and shopping centers.

Inside a transformer case are two coils of wire, each consisting

of a number of turns wound on a single iron core. The coils are insulated from each other and from the core. Each turn is insulated

from its neighbor as well. The power is transformed and transmitted

as the current flow in the incoming, or primary, coil induces a current

flow in the outgoing, or secondary, coil.

Ideally, the ratio of the number of turns in the two coils is also

the ratio of the primary to secondary voltage. In practice, the power

output of a transformer is somewhat less than the power input due to

impedance heat losses in the windings and the core. While the efficiency

of large transformers approaches unity, even a small heat loss poses a cooling problem. Thus an insulating, or dielectric, medium is required

to also transfer heat from the source to the case. From there, energy

is radiated and convected to the surroundings.

For many transformers, liquids of appropriate dielectric strength

and viscosity are being used to meet the insulation and heat transfer

objectives. The fluids have had admirable in-service histories.

Nevertheless, they pose a potential hazard in that under sufficiently

strenuous conditions, virtually all liquids will burn. Transformer

fires fall into two classes, those resulting from slow fluid leaks

and those resulting in violent rupture of the transformer case. The

former are far more prevalent; the latter are potentially more hazardous.

Nonetheless, fires of either origin can ruin the transformer, delay the

return of electrical service, damage the room or building, and injure

or kill occupants or firefighters. Thus, a third constraint is placed

2
on the transformer, and specifically the fluid—it must operate within

an acceptable degree of fire risk.

Heretofore, two classes of fluids, mineral oils and polychlorinated

biphenyls, have found wide usage. The former are the more prevalent.

These petroleum distillate fractions are relatively inexpensive and meet

conventional electrical and environmental requirements, at least to the

extent the latter have been formulated. Since they are deemed to present

an unacceptable flammability hazard, their use is constrained by the

National Electrical Code [1]^ to outdoor transformers or indoor units

enclosed in a fire resistant vault. By contrast, the polychlorinated

biphenyls, also referred to as PCBs or askarels, not only have excellent

electrical properties, but have also been considered nonflammable. Thus

they represent the dielectric of choice in a large number of indoor

uses where their high cost is more than offset by the savings in the

cost of supplemental fire protection. However, over the past decade,

evidence has accumulated that these compounds present a significant

biological hazard. They are thus considered unacceptable for manufacture

and use.

Industry has not been idle during this dilemma. A variety of

candidate substitute fluids have been developed to "replace" the PCBs.

These fall into three classes: high performance hydrocarbons, polydimethylsiloxane (silicone), and chlorinated aromatics. However, no operational fire safety criteria had been developed. As a result, we

are now faced with a desire to use a substitute fluid for askarels

without having a basis to determine acceptability.

lumbers in brackets refer to the literature references listed at the

end of this report.

3
1.2 Magnitude of the Problem

Our prime source of fire data is the National Fire Incident

Reporting System (NFIRS) which is operated by the U.S. Fire Administration [2]. In a survey of their data for 1976, 1977 and early 1978,

including nearly one million fires in the data base and eight states

reporting, 209 cases involved indoor transformers. Four of these fires

resulted in an Injury, none in any deaths. A more recent sampling of

1978 fires revealed that in a data base of about 230,000 fires, only seven began with indoor transformers. There were no injuries or deaths.

The maximum reported damage in these seven fires was $2000.

The difference between the two data sets is due to the small number

of Incidents. Generally injuries and deaths in this type of fire correlate with the fire spreading beyond the room of origin. Once a fire

spreads outside the room, it is unimportant how it started. Thus it

is fair to use the number of transformer fires that spread beyond the

room of origin, the total number of fires that did so, and the total

number of resulting injuries and deaths to estimate a total annual

transformer fire picture for the nation. With this approach, and using

the 1976-78 NFIRS data, we calculate there are about 6000 Indoor transformer fires per year, resulting in about 300 injuries and seven deaths,

as well as 40 million dollars of damage. These are extrapolated figures,

and it should especially be noted that n^ fire deaths appear in the raw

data.

To help put this in perspective, we experience some three million

reported fires per year (30 million unreported) , and the average death

rate is about three per thousand fires [3]. The numbers here are 6000

fires and about one death per thousand fires. Clearly product quality

and current codes and practices have resulted in a quite low fire-loss

profile. The question we now address is: With askarels removed, can

a (similarly) reasonable degree of fire safety be achieved with

replacement fluids?

4
1.3 Objectives of This Effort

In 1975, the Energy Research and Development Administration (ERDA)

requested the National Bureau of Standards to appraise the existing

flammability test methodology relevant to transformer fluids standards

and to elucidate the test-related research and development need to

evaluate new fluids. The final report on that project [4] noted that

while there were several standard flammability tests for fluids, they

are not sufficient to evaluate in-use performance. It was thus

recommended that research be directed at developing flammability

performance criteria. The authors also recommended the development

of tests that would be a realistic indicator of fire hazard.

Following that report, ERDA (now DOE) then requested the NBS

Center for Fire Research to proceed toward a comprehensive evaluation of

recommendations for test procedures for transformer fluid flammability.

During this project, we have performed in-house research, funded extramural research, and worked with other active committees and organizations.

Specific areas of effort have included:

1. Accumulation and evaluation of fire incidence data.

2. Detailing of the fire scenarios and the resulting fire hazard.

3. Development of performance tests for the slow leak scenario.

4. Establishment of the radiation characteristics of fires of

different fluids.

5. Development of test concepts for future study of the violent

rupture scenario.

6. Model for ignition of other materials by flaming fluid droplets

(violent rupture scenario)

.

7. Formalism for evaluating the relative merits of various fire

protection alternatives.

8. Development of an approach for evaluating the effect of

electrical aging on fluid flammability.

5
The remainder of this report is a description of the current

status of fluid flammability evaluation and test methods with details

of the NBS-CFR effort. Much supplementary background material is con- tained in a prior report [4] which should be considered prerequisite

reading. In addressing the problem, we have confined ourselves to

Indoor transformers. In the conclusion are recommendations for extension

of the current work and identification of further needs.

2. THE CURRENT STANDARD

The National Electrical Code [1] is the reference used by local

officials as a basis for approval of a transformer installation. This

is a frequently changing document, with further revisions under consideration now. Regarding Indoor, liquid-filled transformers, the most recent

(1978) version reads as follows:

"450-23. High Fire Point Liquid- Insulated Transformers. Transformers insulated with a nonpropagating liquid approved for the purpose,

having a fire point not less than 300°C, shall be permitted to be

installed indoors or outdoors. Such transformers Installed indoors and

rated over 35,000 volts shall be Installed in a vault.

For the purposes of this article, a nonpropagating liquid shall be one which, when subjected to a source of ignition^ may burn but the

flame will not spread from the source of Ignition.

450-24. Askarel-Insulated Transformers Installed Indoors. Askarelinsulated transformers Installed indoors and rated over 25 kVA shall be

furnished with a pressure-relief vent. When Installed in a poorly

ventilated place, they shall be furnished with a means for absorbing

any gases generated by arcing inside the case, or the pressure-relief

vent shall be connected to a chimney or flue that will carry such gases

outside the building. Askarel- insulated transformers rated over 35,000

volts shall be installed in a vault.

450-25. Oil-Insulated Transformers Installed Indoors. Oil-insulated

transformers Installed indoors shall be installed in a vault constructed

as specified in Part C of this article.

6
Exception No. 2: Where the voltage does not exceed 600, a vault

shall not be required if suitable arrangements are made to prevent a transformer oil fire from igniting other materials; and the total

capacity in one location does not exceed 10 kVA in a section of the

building classified as combustible, or 75 kVA where the surrounding

structure is classified as fire-resistant construction."

From the viewpoint of the consumer this is a simple procedure

to follow. Either the fluid supplier certifies certain properties

and test results or the transformer must be contained in a vault. A

typical vault with 3-hour fire resistance is of 6-inch thick reinforced

concrete. It is thus expensive, bulky and heavy. It is certain to

force design perturbations in a new construction and be most difficult

to incorporate when retrofitting transformers.

To be excepted from vault containment, the transformer must be

under 35 kV and filled with one of the pending PCB substitutes. This

in itself poses two problems. The first is that no test method or geometry is defined to establish the fluid as non propagating. Pool

tests of one geometry will give different results from another geometry.

All are likely to differ from a spray test. "Non propagating" is too

absolute a term; virtually all fluids can be made to undergo flame

spread under sufficiently severe conditions. The second difficulty is

the phrase "approved for the purpose." There is no definition of the

source(s) of authoritative approval. Thus, from the viewpoint of the

supplier’s liability, this is an untenable situation. To alleviate

this, we must define the fire hazards, quantify the risks, devise

appropriate test methods, verify their applicability, and identify

and obtain recognition from an appropriate organization.

3. THE SLOW LEAK SCENARIO

3.1 Description of Hazard

The sequence of events below generally results from external damage

to the transformer case. This may be due to a flaw in manufacture.

7
rough handling, perforation by a fork-lift truck, etc. The dielectric

fluid drains from the case, forming a puddle on the floor. Escaped

fluid can then be Ignited by a remote source as the fluid flows to it, or contained fluid can be ignited by the now overheated transformer

core. The result is a flaming pool of liquid which may or may not be

physically bounded. For reasons which will become obvious soon, we

will deal with bounded pools in this section and the unbounded case

in section 4. Even when the fluid itself is confined, the radiation

from the flames can pyrolyze and ignite remote fuel, while the radiative

and convective heat weakens the structural strength of the room or building. Thus, the fire phenomena of concern are Ignitability , flame

spread across the pool surface, and heat release rate,

3.2 Characteristics of Pool Fires

More than one hundred papers have been published on the burning

behavior of bounded liquids, i.e., pool fires. Beginning in the

post-World War II era, the modern effort continues with the classic,

comprehensive study of Blinov and Khudiakov [5] and a fine review paper

by Hall [6],

3.2.1 Ignition

The minimum temperature at which a fuel bursts into flames depends

on whether the stimulus is merely thermal or also includes a discrete

free radical source such as a flame, arc or spark. In the former case,

this is referred to as the autoignition temperature. In the latter, the

pertinent temperatures are the flash point, at which the first flames

appear, and the fire point, a slightly higher temperature at which the

flames are sustained. The lowest of the three is the flash point, the

temperature at which the lean flammability limit is reached in the vapor

above the liquid. The fire point is slightly higher since the flames must

feed back enough energy to the liquid surface to vaporize more fuel and

maintain at least a lean limit mixture in the vapor phase. The

8
autoignition temperature is much higher. Since no pilot is present

with a source of free radicals, the gases must be hot enough for

thermal breakdown of the fuel to free radicals to occur or for the

rate of fuel-oxygen reaction to be fast enough for oxidative pyrolysis

of the fuel.

The standard test methods to determine these temperatures are described in the previous NBS report. (No new tests have appeared

in the interim.) Small cups of fuel are used in a nominally isothermal

apparatus. An actual fuel spill is far from this. Most likely the

initial pool temperature will approach ambient. Since the fluid has

a finite thermal conductivity and a significant viscosity, an Ignition

source applied at one end of the pool may raise the temperature locally.

Heat losses to the rest of the pool and to the floor could well balance

the heat input at a temperature below the fire point, thus preventing

a sustained ignition. Clearly, then, it is not sufficient to know the

fire point of the fluid; one must also know its thermal properties and

those of the surroundings. To be sure, a fire point of 1000°C could

be required and would undoubtedly reduce the pool fire damages to

nearly zero. However, this criterion would not be met by any currently

known fluid of appropriate electrical properties. The current 300°C

minimum fire point required by the National Electrical Code is a compromise value, imposing a burden on the ignition source to

substantially heat the fluid yet keeping within the constraints of

industrial capability, fluid cost, and transformer compatibility. The

value is not unreasonable from a safety record viewpoint. However, it

still remains for us to ascertain the necessity of so high a value.

3.2.2 Flame Spread Over the Pool Surface

The magnitude of the heat release rate and the longevity of the fire

itself will be in large part determined by the rate at which the flames

engulf the entire fuel surface. In assessing this process, much the same points are involved as in the previous section. Once the initial.

9
localized flame Is established, both subsurface convection [7] and flame

plume radiation [8] heat the adjacent fluid. When the surface temperature

reaches the fire point for a given incremental area, the vapor above it

is ignited by the adjacent flame and the plume expands to cover this new

area as well. This will continue until the full surface is involved or (rarely) until some location is reached where the heat losses to the

surroundings exceed the incident energy. The rate of flame spread will

depend on fluid properties (thermal conductivity, viscosity), flame

characteristics (height, breadth, opacity), pool container properties

(surface area, aspect ratio, container thermal conductivity), pool

properties (pool depth, lip height above fluid), and surroundings

(degree and geometry of confinement, thermal conduction losses and

radiative reinforcement)

.

At present there is no standard test method for flame spread over

liquids. Even if there were, with this complexity of variables, its

applicability to any given situation would be fortuitous. Fortunately,

for the fluids currently involved here and the geometries under consideration (see section 3.3), the flame spread time to cover the entire fuel

surface is well under the total burning time even for fairly shallow pools

(~5 cm). Thus, in this scenario, the rate of flame spread upon sustained

ignition is a secondary issue.

3.2.3 Ignition of Surrounding Fuels

The mechanism here is similar to that involved in flame spread,

except that it is now the lean limit of the vapors from the remote fuel

which must be reached. Unless the fuel is directly over the pool,

energy transfer is purely radiative in nature. A limited amount of

work has been directed at determining minimum irradiances for ignition

of materials. For instance, canvas ignites at about 2.1 W/cm^, pine at

3.3 W/cm^, black rubber at 6.2 W/cm^, all for 3-minute exposures [9].

Knowing this, we also need to obtain the incident radiance from the

pool fire plume. Such measurements are dependent on the opacity and

10
temperature of the flames, their spatial extent and the view factor

from the remote fuel. Pioneering studies underway at the Factory

Mutual Research Corporation [8] are beginning to yield such information.

However, at this date we are unable to quantify this hazard.

An Implicit assumption here is that the effective flame radiation

is alike for all fuels, i.e., it is continuum, gray-body emission with

little contribution from discrete bands [8]

.

This is reasonable since,

in this configuration, much soot is generated, and the hot soot dominates

the emitted energy. However, while these flames appear to be orange on

a black soot background, the flames from silicone fluids appear more

yellow and the "soot" white. Different radiant spectra could lead to

different absorptlvities by remote fuels. We therefore investigated

the applicability of the gray—body assumption for a typical silicone

fluid and found that the emission spectrum and temperature are similar

to those for hydrocarbons. Details of this study are presented in

appendix A.

3.2.4 Dependence of Pool Burning Rate on Prevailing Atmospheric Conditions

For the large, turbulent fires of concern here, breezes affect the

burning rate and thus the heat release rate [5]. Even drafts as small

as 0.5 m/s Increase the oxygen availability, increasing the otherwise

diffusion-limited transport to the flame front. This increases the

completeness of reaction, and thus the flame temperature. Since the

flame radiation is proportional to the fourth power of the temperature

[10], more energy is incident on the fuel surface, increasing the

evaporation rate. This increase in burning rate is tempered somewhat

by the fact that as the air velocity increases, the flames are displaced

from the fuel pool, which reduces the radiative feedback. Eventually,

this leads to the flames being blown off the pool and being extinguished.

For hydrocarbon fuels this occurs at relatively high air velocities

which are not likely to be encountered around indoor transformers [11].

11
Moreover, for pool diameters of the order of one meter or larger, there

is evidence that the natural turbulent entrainment of oxygen reduces

the importance of even strong wind effects to less than 20 percent [12]

A second necessary consideration is vitiation or oxygen depletion

of the incoming air supply. A one square meter pool fire can theoretically consume all the oxygen in about one cubic meter of air in one second. Thus the pool can be its own vitiation source, certainly

so in small rooms. Under reduced oxygen concentrations, the burning

rate is also reduced, and at some level the fire is extinguished. For

small, diffusion-controlled fires of hydrocarbons where heat losses to

the pan are important, this occurs at 15-16 percent oxygen [13]. For

large, turbulent fires, limits closer to 10 percent have been observed

[14].

3.3 Pool Fire Performance Tests

It is abundantly clear from the earlier discussion that the

available standard tests which might be used to assess fluid flammability cannot represent the actual situation. Realizing this, the

involved community has continued to address the problem and is arriving

at credible, if partial, solutions.

3.3.1 The Factory Mutual Approval Scheme

During the past several years, the Factory Mutual Research

Corporation (FMRC) , with the assistance of industry and government, has

constructed a philosophy for hazard reduction, performed experimental

and theoretical research, and now has issued a test sequence for recognition of less flammable transformer fluids [15]. The demands placed

on the fluid are intended to reduce the likelihood of structural damage

to the roof of a noncombustible building with noncombustible occupancy.

Situations in which either the building or the fluid fail to qualify

must be dealt with by a selection of containment or suppression devices

12
The first requirement is that the fluid have a fire point of at

least 300°C, consistent with the current National Elecrical Code. This

temperature is sufficiently high to afford resistance to small ignition

sources, such as matches, but is still low enough to be met by the several

classes of commercial fluids discussed earlier. There appears to be no technical basis for selecting this particular value.

Next, the transformer must be located within a dam that is at least

four times the area of the transformer tank and is deep enough to contain

all the fluid in the event of a spill. Should the fluid be ignited, and

it is assumed that it will be and become fully involved in flames, this

insures that the flames will not spread along the floor. It assures a fixed flame geometry.

This leads to the third requirement—a maximum allowable rate of

convective heat release. In a nonflammable building with nonflammable

contents, the risk of extensive fire loss is mainly to the structure

itself. If the celling over the fire is overheated, collapse of the

roof could ensue. Plume theory was used to develop curves which provide

a maximum allowable heat release rate for a given ceiling height,

ceiling material and pool area. The accuracy of these curves has

been experimentally verified [16] . The heat release rates are to be

measured by FMRC using a procedure described below. This approval

scheme is already active.

With the assumptions involved and the limited applicability, this

is indeed a conservative approach. However, it is the first of its

kind to combine performance tests with theoretically-derived,

operationally-verified performance limits and apply them to the

reduction of fire risk. Hopefully it will serve as a model for future

test development.

13
3.3.2 Rate of Heat Release Determinations

The FMRC approach to measuring convective heat release rates is

to burn large pans of the fluid in a building of very high ceiling

and measure the temperature rise of an array of thermocouples suspended

above the plume [17]. A radiative component is also determined, using a single radiometer, for fluid use in outdoor transformers located near

a vulnerable wall. The pan was selected to be 1.73 m in diameter

and 7.6 cm deep. As Hottel noted [18], for fires above one meter in

diameter, the mass burning rate per unit surface area is independent of

that surface area. Thus the one measurement should be characteristic

of the fluid for the range of dike areas expected. The fluid is

Ignited by an outer, concentric, ring-shaped pan which is filled with

_n-heptane floating on water. The heat release measurements are taken

after the entire surface of the candidate fluid has ignited and the

ignition trough has burned out.

Tests have been run with samples of most commercial candidate

fluids [17]. The hydrocarbon fuels all had similar convective and

radiative heat release rates of approximately 700 kW per square meter

of pan area and 400 kW/m^, respectively. The silicone fluid values

were about 50 kW/m^ and 30 kW/m^, and were less precisely determined

since the fluid crusts during burning and this gives non-steady values.

The RTE Corporation also ran a series of 12 tests. They used a similar pan, but ignited the fluid with a propane burner. A conceptually

similar, but dimensionally different thermocouple array was used for the

convective measurements. A different radiometer and view factor was

used. As of this date, only a preliminary report [19] has been issued.

It presents the results for one hydrocarbon test and one silicone test.

The hydrocarbon fluid convective and radiative components were 400 kW/m^

and 330 kW/m^, respectively. The silicone fluid values were 150 kW/m^

and 340 kW/m^.

14
Under contract from Dow-Corning, the Southwest Research Institute

(SwRI) burned pool fires of high performance hydrocarbon and silicone

fluids [20]. These were similar to those burned in the other two sets

of tests. Pan sizes differed somewhat from the prior studies, and a propane burner was the ignition source. The total hydrocarbon heat

release rates were about 1200 kW/m^; the silicone was about 150 kW/m^.

Although multiple tests were run by both FMRC and SwRI, no indicator of reproducibility was provided in either report. Clearly,

secondary changes in ignition and measurement techniques have a sizable

effect on the reported heat release rates, indicating a need for

standardization, if not refinement, of the procedures. Factory Mutual

has since performed more tests and is establishing such limits of

uncertainty [16]

.

3.4 Aging of Fluids

In the preceding discussion, it has been tacitly assumed that the

appropriate fluid to be studied, and eventually tested, is the fresh

fluid. Since transformers have lifetimes of decades, some consideration

must be given to the likelihood that the fluid will undergo some partial

metamorphosis during this period. Changes in chemical structure could

lead to variations in the fluid's flammable limits and thus its fire

point.

The thermal degradation of gaseous organic molecules is well-studied

[21] and in the high pressure limit is similar to the degradation of

liquids [22]. The process is, in its early stages, unimolecular , and

the buildup of decay products is linear with time. The reaction rate

rises exponentially with increasing temperature. Thus laboratory

scaling of these processes to shorter lifetimes is a relatively easy

process. The complexities of the transformer interior negate such a simple approach. While the fluid temperature may reach 150°C near the

core, it may be nearly 100°C lower near the case. In addition, the

15
fluid is perturbed by intentional additives, such as antioxidants, and

unintentional components, such as extracts from paper insulation or metal atoms from the case and colls. Their effects on the fluid decay

rate are neither kinetically simple nor spatially uniform. This is an area that needs attention.

In this section, the major topic of concern is electrical aging.

During its lifetime, a fluid is subjected to strong electrical fields

and perhaps partial discharges. As these occur, there are formed low

molecular weight gases, which may dissolve in the fluid or occupy the

ullage above, lower molecular weight fluid components, and higher

molecular weight fluid components. Since we are concerned with the

ignitability of the fluid, it is the former two sets of products that

matter. The lower molecular weight fluid molecules volatilize at lower

temperatures. By Raoult's Law, an increase in their concentration in

the liquid will produce a richer vapor above, thus lowering the fire

point. The electrical generation of gaseous products produces the same

result. A lower fire point increases the likelihood of ignition by

smaller pilot sources.

We are performing preliminary experiments to establish the means

for evaluating the enhanced flammability of electrically degraded fluids.

Our approach is to measure the change in vapor pressure of a fluid induced

by the electrical stress. Full details will appear in a later report.

A conceptual description follows.

The insulating fluids under investigation were found to contain

dissolved air. Thus the fluid was gently heated, pumped to a stable

vapor pressure, about 10 m torr (1.3 pa), and the vapor pressure measured

as a function of temperature. The sample was then transferred to a “150 cm^ high voltage cell and subjected to a voltage of 25 kV for six

hours. The vapor above the fluid was then collected and analyzed with

a mass spectrometer by direct injection. Following removal of this

vapor, the vapor pressure of the fluid was again measured.

16
Three experiments with silicone fluid resulted in vapors consisting

of water, nitrogen and oxygen. These were probably the result of further

outgassing. In one case, several electrical breakdowns occurred and some hydrogen was produced. This is consistent with a prior study on arc-decomposed fluids [23]

.

A mineral oil sample also experienced

arcing with the resulting generation of hydrogen. The comparative vapor

pressure measurements are still in progress.

4. THE VIOLENT RUPTURE SCENARIO

4.1 Description of Hazard

In this type of transformer failure, the potential for damage is

far greater than that discussed earlier. Here, a typical fault often

begins as turn-to-turn current leakage, gradually involving more turns

and progressing to coil-to-coil or coil-to-ground discharge [24]

.

This

suddenly releases a large pulse of energy, generally in about one ac cycle. This in turn thermally expands the fluid, forcing it against

the case, which yields. Upon contact with the air, the now hot com- bustible gases dissolved in the fluid or in the ullage autoignite

and then ignite the escaping fluid. A violent emission of liquid blobs

ranging in size from microns to centimeters in diameter occurs. Depending on the fluid and conditions, all or some of the droplets may

be flaming. Thus they may ignite other fuels by aerial impact. In

addition, upon settling to the ground they may form ignited pools which

may flow to other fuels or may cause structural damage as noted in

section 3.

We have assumed that we are not in a position to reduce the

frequency of electrical transformer failures. Thus the discussion that

follows deals only with ameliorating the impact of such explosions.

17
4.2 Applicability of Standard Test Methods

Because of the highly specialized nature and lack of detailed study

of this type of event, and the track record of askarels, no test methods

have been developed specifically for it. The standard ignition temperature measurements do not apply since the arc energy is so large. In

addition, combustible gases from arc-decayed fluid and paper insulation

provide an Intense piloted ignition. The fluid is blown out in a pulse,

not with a sustained backing pressure, so steady state spray ignition

tests are difficult to relate. In a nutshell, there is no premise for

assessing the fire safety of a fluid in this mode. There is no voluntary

standards committee work in this area at present.

4.3 Explosion Tests

If one has available a source of high current (> 5000 amperes) at

high voltage (> 5000 volts) , it is possible to simulate the sudden

electrical failure of a transformer. Such high power laboratories are few in number and expensive to operate. Nonetheless, both General

Electric and RTE have performed tests of this type [25]. Faults were

induced in containers of potential and current dielectric fluids. The

outcomes were filmed, yielding mainly qualitative data. Mineral oil

produced a huge, black and orange fireball. Silicone fluids generally

produced large white clouds with far less extensive flames. The high

performance hydrocarbons similarly outperformed the mineral oil.

Surprisingly, a PCB explosion yielded a large black cloud with some orange flames. Thus, even the "nonflammable" fluid could be ignited.

These pioneering tests, as crude as they were, have provided a "feel"

for further studies. However, because of the perceived cost-benefit

ratio, an extensive research program was not pursued.

Recently, the National Electrical Manufacturers Association (NEMA)

proposed and was awarded a contract to study explosions in a less

expensive, more controllable manner. Using a model by Barkan [22],

18
black powder charges would be designed to simulate the rate of energy

release from electrical failures. Various-sized transformer cases and

complete transformers are to be exploded, and the reproducibility

determined. The result will be an assessment of whether this approach

can be used in further studies of this scenario. In addition, several

combustible materials, such as fiberboard, polystyrene, and plywood, will

be placed at discrete locations about the explosion site. Their ignitability by ejected fluid will be determined visually, and the results

used to test the model described in the next section of this report.

The project has begun, and completion is scheduled for early 1980.

4.4 Model for the Ignition of Remote Fuels by Flaming Droplets

In the event of a violent transformer explosion, the major fire

hazard results from secondary ignition by ejected, flaming fluid. The

burning globules impact some combustible material, locally heat it above

its fire point, and ignite it. This hazard is clearly reduced if the

fluid droplets lose too much heat to the contacted surface and are themselves extinguished. This would result in the need for the target

material to be raised to its (much higher) autoignition temperature for

flaming to ensue. Our purpose, then, is to identify the ignitiondetermining fluid and target material properties and ascertain whether

control of them is feasible.

The simplified physical model is as follows. A flaming liquid

droplet impinges on a horizontal surface, forming a thin, hot layer with

flames above it. Prior to impact, the liquid has reached a steady-state

temperature with endothermic evaporation balancing the radiant heating

from the flames. Upon Impact, the liquid is initially Isothermal at T^,

which is above the liquid’s fire point. Since the liquid is thin, it is

assumed to remain isothermal. However, the value of T will approach

1j the fire point as heat is removed by the solid. The solid surface

itself is non-porous, thermally thick, and initially at T^, the room

temperature. As time progresses, the temperature profile of the system

behaves as shown in figure 1.

19
The problem is one of one-dimensional heat transfer to a semi- inf inite

slab. We assume that heat is lost from the liquid only to the solid.

Within the solid, the spatial and temporal temperature profiles

are described by the Fourier equation [26]:

2 3T a T

with boundary conditions on the solid of T=T^ at t=o for all values of

X, T=Tj^ at x=o for all t will vary with time), and T=T^ at x = “

for all t. The solution for this is

T-T

o T-T

L o

( 1 )

where a is the thermal diffusivity of the solid. This expression

assumes T is a constant, whereas in this model, T will decrease from

J-i Li its initial value, T (0)

,

to the fire point of the fluid, T . At

L r r T , extinction occurs. The equation is valid when T

~ T , and

r r L r P

T-T generally will be much less than T-T for high fire point

L r r L O

fluids. Hence, we will assume the validity of the solution, subject

to later examination.

The next expression needed is for the energy loss rate per unit area transferred from the fluid to the solid, q" [26].

00

(T-T ) c p dx

o s s

( 2 )

where c^ and are the specific heat and density of the solid,

respectively.

20
Substituting equation (1) into (2),

7

(T -T ) L O

1-erf c p dx

s s (3)

Assuming the heat capacity and density of the solid change little as a function of temperature,

q" = -(T^-T^)

CO

0

l-erf

(A)

which integrates to:

-(T -T )c

L O S S (5)

Integrating with respect to time, and withdrawing the lost energy evenly

throughout the liquid (q" = dC p AT ) , we obtain an expression for the

1j 1j temperature decrease of the fluid:

AT

L

T -T

L o d

1/2

( 6 )

where the subscript L refers to the fluid and d is the thickness of

the fluid layer. We can rearrange this equation to get the contact

time in which the fluid temperature would be reduced from its starting

temperature to its fire point, AT .

2 (7)

21
Before proceeding further with this quite approximate model, it is

valuable to calculate a typical magnitude of a flame quenching time.

For silicone fluid, mineral oil and several high performance hydrocarbons, the specific heat is about 1.5 J/g-K and the specific gravity

is about 0.9 g/cm^. The thermal diffusivity is the thermal conductivity

(3 X 10 ^ J/s-cm-K for wood) divided by the product of the density

(0.8 g/cm^ for wood) and specific heat (2.4 J/g-K for wood). For the

moment, we will assume the liquid layer is about 0.3 cm thick. The

fluids of interest will have fire points in the range of 300°C, and T^

will generally be about 25°C. We will use a value of 50°C for 4T^^. For

wood, then, t is about one half of a second. This is far less than the

ignition time for the wood [27].

With this in mind, it is now important to ascertain whether there

are any critical fluid properties that can be used to evaluate this

ignition risk in realistic cases where far more fluid might land on the

solid and where large flames might cause radiative heating of the solid.

As already mentioned, the thermal properties of the wide range of

currently-known dielectric fluids do not vary much. Furthermore, the

liquid temperatures during flaming and the fire points are relatively

uniform. By contrast, fluid surface properties offer some hope. Fluids

that preferentially form small droplets upon expulsion have a lower

probability of delivering large quantities of fluid to any one surface.

Fluids that wet the impacted surface well will form thin, readily cooled

layers. These aspects need further investigation.

From this crude model, we can also begin to refine the coarse terms

"combustible" and "noncombustible" used in the National Electrical Code.

Some differentiation can be made on the basis of thermal properties. In

terms of this scenario, solids with higher values of heat capacity,

density and thermal conductivity will be less ignitable. In addition,

solids whose surfaces resist droplet adhesion or, at the other extreme,

promote good thermal contact will also perform favorably. This is also

a line of study which would be worth pursuing.

22
5. EVALUATING ALTERNATIVE FIRE SAFETY STRATEGIES

As with any issue concerning public safety, the dielectric fluid

flammability problem has two aspects. Heretofore, this report has

dealt with scientific characterization of the fire phenomena. In this

section, we address the equally important question of how to select

approaches to achieve a desired degree of fire safety.

There are inherent difficulties in regulating the safety level

of transformer installations. There is a lack of available, detailed

case data on past transformer fires. The fire ignition and spread

phenomena are only qualitatively understood. The pertinence of available

test methods is questionable. Experts disagree on technical issues and

may be biased by disciplinary or commercial interests, and above all

there are serious value judgments to be made regarding the degrees of

property loss, accidental injuries and deaths that are acceptable.

The methodology of decision analysis [28] provides a structuring of

this problem. By creating a formalism of non-exclusive alternatives,

we are able to reduce a complex problem to a series of specific issues.

Probabilistic methods can then be used to address the uncertainties.

Existing expertise can answer the purely technical aspects, and explicit

value judgments can be introduced to facilitate comparisons. In the

end, we have a dollar value for the costs and losses associated with each

possible regulatory decision. These can then be examined in view of the

degree and type of fire safety desired. This approach has recently been

successfully applied to the equally complex reduction of upholstered

furniture fire loss [24].

In the present study [30]

,

a decision tree was constructed to

estimate the losses from transformer fires in terms of property damage,

injuries and deaths. Branches on the tree included the probability of a fluid leak, probability of ensuing transformer failure, location of tank

rupture, fraction and volume of fluid emitted, likelihood of ignition.

23
degree of fire protective construction present, fuel load in the room,

and extent of fire spread. Using NFIRS data, average losses were

calculated for contemporary transformer failures under historicallyevolved regulations (defined as the "base case") . Since essentially

no PCB- filled transformers have caused fire damage and since relatively

few transformers were filled with other high performance fluids at the

time interval counted, it was assumed that all fires involved mineral

oil.

Seven intervention strategies were then evaluated by calculating

their cost of implementation and using the decision tree to estimate

their effectiveness:

1. Requirement of a periodic, in-use fluid testing program

consisting of acidity level, dielectric strength, interfacial

tension, color, and combustible gas analysis.

2. Requirement of a 300°C fire point.

3. Requirement of a "fire-proof" fluid, with a performancerelated standard yet to be developed.

4. Requirement that the transformer be contained in a room of

3-hour fire resistant construction.

5. Requirement that the transformer be contained in a room of

1-hour fire resistant construction.

6. Requirement of a dike around the transformer to contain any

spilled fluid and a metal sheet around the transformer to

eliminate spreading of sprayed fluid.

7. No protection at all.

24
These were then compared with each other and with the aforementioned

base case (which includes partial use of some of the above protection

measures). In doing so, dollar values were assigned to human losses.

Sensitivity analyses were performed to determine the dependence of the

outcome on the values of the various input parameters.

The expected annual losses after implementing any or none of these

strategies are listed in table 1. The cost-plus-loss figures over the

transformer lifetime are shown in table 2. Note that the effect of

each strategy on deaths, injuries, and property loss is calculated

independently, thus the fractional reductions in the three types of

losses are not necessarily equal. As one would have guessed, the data

show that safety costs money.

The concept of risk attitude now becomes pivotal. The regulator

must decide what the public will not tolerate and what costs are acceptable. This decision is inevitable. The Improvement lies in the existence of concrete data to base his judgment. For instance, if over one

thousand injuries and thirty deaths a year are considered small compared

to some other pressing demand on his resources, the "no protection"

alternative might be selected. If the regulator anticipates a public

outcry over even one fire death, there are three possible approaches,

and their relative merits can be considered.

It is important to note that the conclusions are based on the best

data available and consider only a few representative strategies. While

these cover the three basic approaches (inspection, fluid upgrading, and

physical barrier) , clearly further thought and commercial progress

should suggest further ideas. The model itself can also be made more

sophisticated as needed.

25
6. RECOMMENDATIONS FOR FURTHER WORK

6.1 Assessment of the Current Status

At this time, no new PCB-filled transformers are being supplied,

and there is mounting pressure to retrofill or replace the existing

units. The former alternative is problematic [31]; both alternatives

are costly. Nonetheless, existent PCB-filled units will disappear for

two reasons. First, many transformers eventually leak, and there will be

no PCBs to top them off. Second, the leaked fluid poses potential

health problems as noted in the recent case cited in appendix B. Both

the hazard and the outcry are intolerable.

The NFIRS data indicate that the current variety of transformer

installations and environments pose relatively little fire risk. It is

assumed that this record will be sustained. This will be complicated by

the fact that older buildings may not be able to support fire-resistant

enclosures, and the only currently-allowed exceptions are situations

approved by the Factory Mutual standard, i.e., noncombustible occupancy

in a noncombustible structure. New buildings will have to be designed

with the strength and space for vaults, an expensive consideration

beyond the cost of the vault itself.

At present, there is no pending relief, in the form of enlightened

recommended practices, from the expense or even impossibility of rigid

adherence to current standards.

6.2 Needed Test Development

There are three components necessary to advance the possibility of

lower cost fire safety. The first is to model the specific fire hazards

of the fluids and identify which fluid properties determine them. Our

current study has performed much of this. The second is to characterize

the surroundings in terms of their contribution to a fire initiated

26
by the transformer. After these, the third step is to use this knowledge

to create germane test methods to identify fluid and occupancy combinations that are compatible with the desired degree of fire safety. We

have learned enough to project what these might look like. In reading

the ensuing discussion, it should be remembered that it is still

necessary to identify parties or agencies that will endorse such tests

and concepts upon their development.

6.2.1 Fluid Ignitability

Should the fluid escape from the transformer case and form a puddle,

there will be a minimum energy input rate if flames are to ensue. The

current assumption is that this will be available. Rather, for any

given installation, the surrounding energy sources and the ignition

potential of the transformer itself should be quantified. The fluid

should be physically bounded, as noted in the Factory Mutual scheme. A

heat balance model should be constructed involving the heat transfer

mode (radiative, convective or conductive) from the ignition source and

the heat dispersion capability of the fluid and its container. These

loss terms would rely mainly on the thermal properties of the fluid and

the container. The criterion for acceptability would be whether the

eventual maximum fluid temperature reached the fire point or autoignition temperature, the choice depending on the nature of the igniter at

hand. A fluid that can resist all available ignition sources should be

relatively fire-safe.

The test method for verification should involve a thermally thick

pool of the fluid, the depth being determined using such studies as reported in references [6] and [7]. The pool should be large enough to

simulate actual usage and to reduce the edge effects, which create

excessive heat loss. A diameter of one meter and a depth of ten

centimeters is a reasonable a priori estimate. Thermal sources would

be simulated by an immersed electrical coil, flaming sources by an impinging propane torch. Each fluid would be given a rating based on

27
the magnitude of ignition sources it could withstand. If the rating

level exceeds the ignition sources in a given usage, it would no longer

be necessary to require the building or surroundings to be noncombustible

under the slow leak scenario.

6.2.2 Radiant Ignition of Surrounding Materials

Should a fluid be found ignitable under the above criteria, it

still may be relatively safe. Since it is geometrically contained by a dam, its means of igniting further fuels is mainly radiative. The

radiation may arise from the fire plume itself or from the layer of hot

gases which would accumxilate in the upper portion of the room [32].

There are solid efforts to characterize the plume radiation [8] and the

radiative ignition of fuels [33]. There is already some data on the

minimxim irradiances or minimum time exposures for ignition of various

fuels [9,34]. More such data are sorely needed. Ideally, simple com- parison of the fire radiances with fuel susceptibilities would provide

an indicator of compatibility. For verification, at least a few fullscale room fire tests should be conducted.

Successful ignition resistance is the most convenient outcome for

establishing a degree of fire safety. Ignition delay times that are long compared to, perhaps, halon extinguisher or sprinkler activation

times could also be accommodated.

6.2.3 Contact Ignition of Surrounding Materials

In the event of already flaming fluid escaping from the case, we

need to know if surrounding materials can be ignited by impacting fluid

before the fluid extinguishes. This situation is most likely to occur under the violent rupture scenario. The model presented in section 4.4,

a first attempt at understanding this, will be tested in the current

NEMA project. Extension of the model, in directions indicated earlier,

and further experiments will probably be necessary. The important

28
characteristic is whether all the ejected fluid is flaming. If the

radius of the fireball from the explosion is significantly smaller than

the throw radius of the fluid or if the falling globules are no longer

flaming, the fluid possesses a reduced potential for further ignition.

One possible approach to a correlative laboratory test method

involves the currently-discarded spray test. As noted by Factory Mutual

[17b], all the current candidate fluids will ignite under certain spray

conditions. Some set of such conditions should be selected, and spray

fires established. Samples of various materials would then be introduced

into the spray at appropriate locations for appropriate time intervals.

Selection of values of these parameters would require some further

study. The fluids which failed to ignite all appropriate samples would

be designated acceptable for use under this scenario. Conversely,

materials which resisted ignition from a given fluid spray could be

designated "compatible" with that fluid. This would provide a basis for

defining an occupancy as "noncombustible".

6.2.4 Damage to the Building

Some aspects of this have been discussed above: the building's

exposed construction and interior finish materials would be treated the

same as its contents. If these materials are noncombustible, the Factory

Mutual scheme addresses the avoidance of structural damage. Thus this

consideration is moderately well in hand. The only further instance of

concern is when the building materials are not ignitable by the fluid,

yet are not steel or concrete. Extension of the Factory Mutual calculations to include structural loss of such materials, e.g., wood, would

complete the picture.

6.3 Epilogue

The most serious need is for more detail on any transformer- initiated

fires that do occur. This will ensure the thoroughness of the fire

29
safety analysis. While qualification of fluids for general usages could

be based on a general series of criteria, it would be operationally and

economically more feasible for the selected fluid to meet the specific

flammability constraints of its specific usage. Lest this be considered

as impractical, such a system is currently used for portable fire

extinguishers [35]. The formalism of decision analysis provides a means

for evaluating such an approach.

7 . ACKNOWLEDGMENTS

A project of this extent requires the contributions of many, both

as participants and consultants. In particular are three colleagues

from the Center for Fire Research: Dr. Gary Mallard, who devised the

quenching model described in section 4.4; Michael Manka, who performed

the fluid aging tests with the cooperation of Drs. Robert Hebner and

Edward Kelley of the NBS Center for Electronics and Electrical Engineering;

and Dr. Kermit Smyth, who performed the flame radiation measurements

described in appendix A. Dan Levinthal of Harvard University

performed the decision analysis in section 5, in consultation with

Dr. Fred Offensend of SRI International and Benjamin Buchbinder of the

Center for Fire Research.

Invaluable advice and reference materials were provided by

representatives of the Factory Mutual Research Corp., Dow-Coming Corp.,

Westinghouse Electric Corp., General Electric Co., RTE Corp., Doble

Engineering Co., the National Electrical Manufacturers Association, and

Versar, Inc. The IEEE S-32 Committee on Fluid Dielectrics served as a major resource.

The author thanks his Center for Fire Research colleagues,

Marva Brown for typing the manuscript, Alan Gomberg for accessing the

NFIRS data, and Dr. Clayton Huggett for his helpful advice, especially

in the early stages of the project.

30
8 . REFERENCES

[1] National Electrical Code, 1978 Edition, National Fire Protection

Association, Boston, Mass.

[2] National Fire Incident Reporting System, U.S. Fire Administration,

Washington, D.C.

[3] Fire in the United States, U.S. Fire Administration, Washington, D.C.

(1978).

[4] Miller, D. B. et al.. An appraisal of tests and standards for the

evaluation of electrical insulating fluids, Nat. Bur. Stand. (U.S.),

NBSIR 76-1054 (1976).

[5] Blinov, V. I. and Khudiakov, G. N. , Diffusion Burning of Liquids,

English translation. National Technical Information Service,

AD 296762, Springfield, Va. (1961).

[6] Hall, A. R. , Pool Burning, in C. F. H. Tipper, ed. , Oxidation and

Combustion Reviews, Vol. 6, Elsevier, New York (1973).

[7] Mackinven, R. , Hansen, J. G. and Glassman, I., Comb. Sci. and

Tech. 1, 293 (1970).

[8] de Ris, J. , 17th Symposium (International) on Combustion, p. 1003,

The Combustion Institute, Pittsburgh, Pa. (1979).

[9] Smith, W. K. , Ignition Chart for Fire Bomb Range Calorimeter Plates,

Technical Note 40604-10, Naval Weapons Center, China Lake (1968).

[10] Richards, J. A., Sears, F. W., Wehr, M. R. and Zemansky, M. W.

,

Modern University Physics, Addison-Wesley Co., Reading, Mass.

(1960)

.

[11] Hirst, R. and Sutton, D. , Comb, and Flame 319 (1961).

[12] Burgess, D. S., Strasser, A. and Grumer, J. , Fire Res. Abstr. and

Rev. 3 , 111 (1961).

[13] Nelson, G. L. and Webb, J. L. , J. Fire and Flam. 210 (1973).

[14] Gann, R. G. et al. , Comb. Sci. and Tech. 1^, 155 (1978).

[15] Approval Standard - Less Flammable Transformer Fluids, Factory

Mutual Research Corp., Norwood, Mass. (May 30, 1979).

[16] Hemstreet, R. , Factory Mutual Research Corp., private communication.

31
[17a] Factory Mutual Loss Prevention Data Sheet 5-45/14-85, Factory Mutual

Research Corp., Norwood, Mass. (1979).

[17b] Hemstreet, R. , Flammability Tests of Askarel Replacement Transformer

Fluids, Serial 1A7R3.RC, Factory Mutual Research Corp. (1978).

[18] Hottel, H. C., Fire Res. Abstr. and Rev. 41 (1959) and errata on final page of 1 , No. 2 (1959).

[19] Experimental Determination of Burning Characteristics of Transformer

Dielectric Fluids, RTE Corp. (1979).

[20] Kanakia, M. , Characterization of Transformer Fluid Pool Fires by

Heat Release Rate Calorimetry, Final Report SwRI Project

03-5344-001, Southwest Research Institute (1979).

[21] Benson, S. W., Thermochemical Kinetics, John Wiley & Sons, Inc.,

Somerset, N.J. (1968).

[22] Gardiner, W. C., Jr., Rates and Mechanisms of Chemical Reactions,

W. A. Benjamin Inc., New York (1969).

[23] Kuwahara, H. et al. , Study of Explosion and Fire Hazards of Silicone

Liquid Under Arc Conditions. Paper presented at the IEEE International Sjnnposium on Electrical Insulation, Montreal, 1976.

[24] Barkan, P. et al. , IEEE Transactions on Power Apparatus and Systems,

PAS-95, 37 (1976).

[25] The author thanks General Electric and RTE for copies of the movies

of these tests.

[26] Welty, J. R. , Wicks, C. E. and Wilson, R. E. , Fundamentals of

Momentum, Heat, and Mass Transfer, John Wiley & Sons, Inc.,

Somerset, N.J. (1976).

[27] Simms, D. L., Comb, and Flame 293 (1960).

[28] Raiffa, H. , Decision Analysis, Introductory Lectures on Choices

Under Uncertainty, Addlson-Wesley Co., Reading, Mass. (1968).

[29] Helzer, S. G. , Buchbinder, B. and Offensend, F., Decision analysis

of strategies for reducing upholstered furniture fire losses,

Nat. Bur. Stand. (U.S.), NBS Technical Note 1101 (1979).

[30] Levlnthal, D. , Applications of decision analysis to a regulatory

problem: Fire safety standards for liquid insulated transformers,

Nat. Bur. Stand. (U.S.), NBS-GCR-80-198

.

32
[31] Morgan, L. A. and Osthoff, R. C., Problems Associated With the

Retrofilling of Askarel Transformers. Paper presented at the

IEEE Winter Power Meeting, New York, 1977.

[32] Quintiere, J, , Growth of Fire in Building Compartments, in

A. Robertson, ed. , Fire Standards and Safety, STP-614, American

Society for Testing and Materials, Philadelphia, Pa. (1976).

[33] Kashiwagi, T. , Comb, and Flame 34, 231 (1979).

[34] Hallman, J. R. , Ignition Characteristics of Plastic and Rubber,

Ph.D Thesis, University of Oklahoma (1971).

[35] McKinnon, G. P. and Tower, K. , eds.. Fire Protection Handbook,

National Fire Protection Association, Boston, Mass. (1976).

33
Table 1. Expected annual national losses [30]

Strategy Property damage Injuries Dea ths

Base case $40. 6M 299 7

Fluid testing $26. 7M 197 4

High fire point $146. 4M 1040 33

"Fire proof" fluid $1.5M 10 0

3-hour vault $14. 7M 118 0

1-hour vault $15. IM 120 0

Dike and sheet $25. 9M 199 3

No protection $148. 2M 1053 34

34
Table

2.

Cost

plus

loss

per

transformer

over

transformer

lifetime

[30]

CO3

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a. 3 CN vr CN o c CO 3 OO vC os m 00 o f O rH CN CN CO rH CN f CO rH <j> o r a

M-lo 3 i jr 1 (U VJ i 3 3 rH O cn c c o o CO 1 rH 3 CO- 3 "3 > j

M-l 3 1i o 3 I H CN CN CO o rH rH CN X

<u Vi •CO- 3 3

rH3 c > •H i m KD in CC r- in

CO o c o o o 'o

rH rH rH rH rH rH rH r-J

4-i

X

X

X

XXX

X

X 3 cs c» o o CO X o o 3Q rH \0 o rH rH m O !

j- CO in -d- cn

m o o o o o o c 1 3 rH rH rH rH rH rH rH rH ' •H X X X X X X X X

Vi vO os CTi CN CN o CTi 3

tn lO cn rH rH CN CN CO rH * 3 1 M

>. 3

Vi 00 1 3 3 es o rH rH CN o m

CV £ fO CN rH rH rH rH CN “H O 3 </> rH rH

v< T3 : u cO o CN —H

rHm

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</> "3 I •H3 u I—j

r-* JH oc tH 3 d o “ U 3 O 1 •H cv lu rH rH 1-! 1 u o 3 3 iJ 3 3 3 o 3 3 a

>> 3 3 Vi Vi > > 3

oc 3 4J •H cv r* sLJ 3 3 V Vi 3 o

T3 3 3 2 V 1 3 3 •H u O o 3 r>. Vi 3 3 oC 1-1 r* v>

4-> 3 rH •H r- 1 1 1-1 o

CO CQ fc

— - CO i-H o z

35
Figure 1. Temperature profiles of solid-liquid system at droplet

impact (t=0) and at some later time (t=t')

36
APPENDIX A. COMPARISON OF RADIATION CHARACTERISTICS OF

SILICONE AND HYDROCARBON FLUID POOL FIRES

The purpose of this study was to resolve whether the emission

spectra from fires of different fuels (hydrocarbon vs silicone) are different. To investigate this possiblility we burned small pool fires

of typical hydrocarbon and silicone fluids and monitored their emission

spectra with identical equipment.

A.l Experimental Procedure

The hydrocarbon fluid used was NBS #10 pump oil, and the silicone

fluid was a commercial 50 cs sample. The pan employed for the pool fires

measured 15 cm x 13 cm x 2 cm. In this configuration there were two

problems which arose in measuring emission spectra: (1) The flames were

relatively small (15-25 cm in height) and somewhat turbulent. This led

to considerable flame flicker, so that any emission signal exhibited

large fluctuations at low frequency. (2) The amount of fuel burned was

small, with the result that reasonably steady flames were obtained for

only about 10 minutes. Thus, extensive signal averaging could not be

utilized to reduce the low-frequency noise arising from flame flicker.

These experimental limitations dictated the optical equipment

which could be used successfully. A careful monochromator scan of the

emission would require a more steady light source and longer times

than were available. Therefore, a simpler experimental setup was devised and is shown in fig. A-1. The emission was detected directly

with an RCA 4840 photomultiplier tube. This tube is very sensitive

at wavelengths down to the vacuum ultraviolet (~200 nm) and has good

response throughout the visible region (400-700 nm) . A series of

long-wavelength pass filters was used to isolate spectral regions

30 nm to 85 nm wide. Table A-1 presents the spectral characteristics

of the specific filters used in this investigation. To avoid the

photomultiplier tube "seeing" background and scattered light, a narrow

A-1
viewing angle was defined by using two irises and a length of

blackened pipe. This detection equipment was positioned to monitor

emission from an area approximately 5 cm above the pan in which the

pool fires were burned.

A data run proceeded as follows:

(1) The unfiltered light from the pool fire was allowed to irradiate

the photomultiplier tube.

(2) The first long-wavelength pass filter was then inserted (50%

transmission at 670 nm) , thus attenuating the light reaching the

photomultiplier tube.

(3) The filter was then removed, again allowing unfiltered light to

reach the photomultiplier tube.

(4) The second long-wavelength pass filter was next inserted (50%

transmission at 640 nm) , which attenuated the light somewhat less

than the first filter.

(5) The second filter was then removed, and this procedure was repeated

for the total of nine long-wavelength pass filters, listed in

Table A-1.

A. 2 Results and Data Analysis

The raw data obtained using the procedure outlined above are shown

in fig. A-2(a) for the hydrocarbon fluid and fig. A-2(b) for the silicone

fluid. At least five similar runs were made for each fluid. Fig. A-2(c)

presents the results of monitoring the emission from a lOOW tungsten

light bulb. This light source is much more stable than the pool fires,

and its emission spectrum is included to show the optical response of

the detection equipment.
The series of nine long-wavelength pass filters defines eight

spectral regions between successive filters. These spectral regions

are 30 nm to 85 nm in width. Thus, the net signal change between two

successive filters indicates the amount of light reaching the

photomultiplier tube in a specific spectral region. This net signal

change must then be normalized for the photomultiplier sensitivity and

the width of the spectral region. For example, consider filters #1 and

#2 in table A-1. The net signal change obtained using these two filters

is a measure of the light emitted in the 640-670 nm region. The raw

net signal change obtained from data such as those in figs. A-2 is then

normalized by the photomultiplier sensitivity at 644 nm (the mean

wavelength) and by the width of the spectral region (30 nm)

.

The results of analysis of the data in figs. A-2 are presented in fig.

A-3(a) for the hydrocarbon fluid and fig. A-3(b) for the silicone fluid.

Each data point represents the emission in a spectral region defined by

two successive long-wavelength pass filters. Also indicated in figs. A-3

is the relative error in these determinations caused by the low-frequency

flame flicker. The relative error is largest at shorter wavelengths

where successive filters made little or no change in the detected light

for both fluids (i.e., the relative error is largest where the net

signal change is smallest)

.

Figs. A-2 and A-3 show immediately that there is little emission

below 500 nm from either the hydrocarbon or the silicone fluid. For

the hydrocarbon fluid it is difficult to measure net signal changes for

filters beyond #5 (50% transmission at 530 nm) . The data for the silicone

fluid are more noisy (fig. A-2(b)), with the result that no signal change

at all was reproducibly detected for filters #6, #7, #8, or #9.

Figs. A-3 also includes calculated gray-body (constant emissivity)

spectral distribution curves. The temperatures chosen for comparison

with the filter data were obtained from one-line, optical pyrometer

measurements. A number of pyrometer measurements were made, giving
1370 + 30K for the hydrocarbon fluid and 1470 + 50K for the silicone

fluid. The data from the long-wavelength pass filter results and from

the pyrometer measurements are consistent within the error limits of

the filter data. These error limits are sufficiently large that the

filter data are compatible with gray-body spectral distribution curves spanning several hundred degrees. However, the same determinations

made for the emission from the tungsten light bulb result in more

narrow error estimates, and show that the pyrometer temperature value

of 1790K is significantly lower than the results from the filter data

(fig. A-3(c)).

A. 3 Conclusions

(1) The spectral distribution of the emission from typical hydrocarbon

and silicone fluids is similar, in that there is little emission

from either fluid below 500 nm relative to the emission at longer

wavelengths

.

The spectral distribution of the emission from these fluids is

consistent with that expected for gray-body soot radiating at

temperatures determined from pyrometer measurements. These

temperatures are similar for the two fluids.

( 2 )
Table

A-1.

Long-wavelength

pass

filters

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1

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00 O'. o^

I

I

I

t

I

oc vj C a>

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O) *H m m tn ct O ' > M-l m <r -a- i SJ s m m <r -a- CO '

fl

1 o /H H S

CO o

CO 1 •H I S

— o o o o o m m o o ) X 4-1 '3' o^ c^ LO r*- —— * oc sC O m m < cn n i 5 c 1 <u ) 4J pH j (U 1 5<S O

> 1 <3 1 m 1

i

<r O' CO m m m i vC m O^- IT* m

* 1 1 m 1 1 CN CN CM :3 r •> O ' f f * cC ac oc CC X i

S-i a •U s ‘ a> •H •H •H w

4-1 2 G c 0 C i rH $-1 M u U < 1-t Q Q o u o U O 0 ' C.5 o a VI v: c/: ^ !

>«—

S

-N y—

V

y—

V

y—S ; r—i CM CO -3- m sC X V'

y S—

N— >- V—/

A5
A

Figure

A-1.

Apparatus

schematic
Photomultiplier response data from pump oil fire

(Numbers of inserted filters are indicated.)

A7

Figure A-2(a)

.
Figure A-2(b). Photomultiplier response data from silicone fluid fire

(Numbers of inserted filters are indicated.)

A8
Figure A-2(c). Photomultiplier response data from tungsten bulb

(Numbers of inserted filters are indicated.)
Figure A-3(a). Spectral data from pump oil fires (intensity in arbitrary units)

The curve represents the blackbody emission at the optical

pyrometer temperature.

A- 10
WAVELENGTH (mn|

Figure A-3(b). Spectral data from silicone fluid fires (intensity in arbitrary units)

The curve represents the blackbody emission at the optical

pyrometer temperature.

A- 11
350 400 450 500 550 600 650

WAVELENGTH (nmj

Figure A-3(c). Spectral data from tungsten bulb fires (intensity in arbitrary units)

The curve represents the blackbody emission at the optical

pyrometer temperature.

A- 12
APPENDIX B. A RECENT CASE OF PCB LEAKAGE AND POLLUTION

from The Washington Post , September 29, 1979

Pollutant PCB Discovered

In Food Products '^By Chance^ j By Joanne Omang

Washington Post Stall Writer The spread of the chemical pollu- tant PCB to human and animal food

in 17 states was spotted “just by

chan.'e” and could have gone unnoticed under current government

procedures, a Department of Agricul- ture official said yesterday. Assistant Secretary Carol Tucker Foreman told a House hearing that bureaucratic routine and slipups ac- counted for the six-week delay be- tween the taking of a food sample

that proved to be PCB-loaded and the day that the Food and Drug Administration was notified of the contamination. But “even under the best of cir- cumstances” it would have taken

three to four weeks, she said. The FDA is still tracking down ship- ments nationwide of cake mixes, waffle mixes and other products made

with eggs that might have contained PCB from a Montana animal feed

plant, according to acting FDA commissioner Sherwin Gardner, He said he was “reasonably certain” that none had escaped the FDA net but would

not know for sure imtil all the reports are in and cerified in another 30 days.

PCB is polychlorinated biphenyl, a

possibly cancer-causing chemical that has been linked to skin and liver dis- ease, bone problems and other ail- ments. Banned in 1977, it previously was used as a lubricant and hightemperature coolant and ^ntinues to

exist in older electrical transformers and industrial machinery.

It was such a transformer,

apparently damaged by some kind of farm machinery or loading vehicle as

it sat in a machine storage shed, that le^ed about 200 gallons of oil con- taining PCB at the Pierce Packing Co.

of Billin gs, Mont., according; to the FDA.

The oil went into a drainage system

that was routinely cleansed of fats for

inclusion in animal feed. Foreman

told the hearing that 399,000 pounds

of affected poultry and 16,000 pounds

of fresh pork have been located and

held off the market. The FUA and

USDA have also tracked the chemical

to 73,000 pounds of egg products, about 32,000 pounds of which have been withheld. The rest is being

-traced. The Agriculture Department monitoring system spot checks animal car- casses and ia designed to catch trends over a year-long period. Foreman said. “It was just by chance that we picked

up this single incident relatively

quickly,” she added. “It Is also possi- ble that a single incident of this size could go entirely undetected.” She said there are 120 million head

6f Uvestock and 3.5 billion poultry

marketed each year. “The cost of test- ing all of them for [dangerous chemical] residues would be about $100 bil- lion,” she continued. Further, she said there are some dangerous chemicals,

like the cancer-causing nitrofuranes,

for which no residue-detecting test exists. The PCB in this incident was found

first in a chicken taken routinely

from a processing plant in Provo,

Utah, on July 6, Foreman related. But

the USDA veterinarian who would

have mailed the sample to he tested was on vacation and his replacement

did not know a sample was waiting, so the mailing was delayed foria week. On Aug. 3, the USDA inspection of- fice in Alameda, Calif., was told the sample contained PCB, but waited until receiving written confirmation Aug. 8 before notifying the Utah of- fice. That office traced the hen to the Pierce plant by the 10th but did not

notify the FDA until Aug. 16, six weelm from the day the sample was

taken. “We shoxild have far more sensitivity,” Foreman said. “There should have been earlier and more compelling notification.” She said corrective measures are being taken at the De- partment of Agriculture, but warned,

“We have to realize that as long as we

use chemicals in agriculture . . , acci- dents will occur.” Idaho Gov. John V. Evans objected

in his testimony to “lapses . . . slip- shod procedures . . . inexcusable de- lays” in government agency perform- ance in the case. He recommended im- proved communication, technical and

laboratory facilities and called for some sort of indemnification program

for citizens damaged by future pollu- tion problems. “We’ve got to eliminate PCBs completely,” he said. But the subcommittee chairman. Rep. Bob Eckhardt (DTex.), said that would be “a massive and extremely difficult, costly thing.”

An Environmental Defense Fund wit- ness, Jacqueline Warren, told the hearing there are still 275 million gal- lons, of PCB oils in transformers in

use.‘Rep. Andrew Maguire (D-N.J.) asked whether it would be possible to ban PCB at least in the nation’s 125,-

(XM) food processing plants. Foreman

and Gardner said they thought that would be “feasible.”

B-1
NBS-114A (REV. 0-76)

USCOMM-DC