NIST Technical Note 1461

Full-Scale Flammability Measures for

Electronic Equipment

Matthew Bundy

Thomas Ohlemiller

 
NIST Technical Note 1461

Full-Scale Flammability Measures for

Electronic Equipment

Matthew Bundy

Thomas Ohlemiller

Fire Research Division

Building and Fire Research Laboratory

Gaithersburg, MD

August 2004

U.S. Department of Commerce

Donald L. Evans, Secretary

Technology Administration

Phillip J. Bond, Under Secretary for Technology

National Institute of Standards and Technology

Arden L. Bement, Jr., Director

 
Certain commercial entities, equipment, or materials may be identified in this 

document in order to describe an experimental procedure or concept adequately. Such

identification is not intended to imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor is it intended to imply that the 

entities, materials, or equipment are necessarily the best available for the purpose.

National Institute of Standards and Technology Technical Note 1461

Natl. Inst. Stand. Technol. Tech. Note 1461, 46 pages (August 2004)

CODEN: NTNOEF

 

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Executive Summary 

An experimental study of the bench-scale fire performance of eighteen different

commercial polymeric materials was previously conducted by the National Institute of Standards 

and Technology. The results of that study described the ignition resistance, self-extinguishing 

behavior, heat release rate (HRR), and combustion product yields of these materials using three 

standard bench-scale fire tests. The current report details the second of a two part study in which 

the relationship between bench-scale and full-scale fire performance was examined. Five of the 

eighteen materials characterized in the bench-scale study were examined here in the form of 19”

computer monitor housings. The ignition resistance, fire growth rate and threat to surrounding

objects were characterized using several ignition methods. While the objects studied here were 

computer monitor enclosures and keyboards, the qualitative conclusions should apply to other 

electronic equipment that could be similarly ignited, such as printers or other peripherals, as well 

as TV sets, that are enclosed in similar housings. 

Four of the monitor enclosures were molded using UL94 V-class (V-0, V-1, V-2) 

plastics; these did not yield sustained ignition when exposed to a small open flame ignition 

source (a 38 W needle flame, height=20 mm). The one UL94 HB rated monitor enclosure was 

easily ignited using the needle flame and resulted in a peak HRR of (200 ± 25) kW. The threat 

of fire spread to surrounding objects (i.e., the farthest distance at which piloted ignition could 

occur) was determined using the measured radiant heat flux distribution near the fires. The 

ignition threat distance for this fire was found to be (58 ± 15) cm for piloted ignition of a stack of 

paper and (112 ± 28) cm for ignition of insulated cotton fabric. A UL94 HB rated polystyrene 

keyboard was also tested using a small open flame ignition source resulting in a measured peak 

HRR of (23 ± 3) kW. 

The fire resulting from ignition of a keyboard was used as a more severe ignition source 

for the monitor housings. The specimen using a V-2 class polypropylene material clearly posed 

the most significant fire hazard of the V-class specimens in this scenario. The peak HRR and 

ignition threat distances for this monitor were almost identical to the HB monitor exposed to the 

smaller ignition source, but due to the low viscosity of the V-2 monitor the polymer melt pool 

had greater potential for transport away from the original specimen footprint. Only one of the

monitor specimens, the V-0 ABS (brominated FR), did not result in significant fire propagation 

away from the keyboard. 

A radiant heat panel was used as a well controlled heat flux source to simulate an existing

burning item that threatened to ignite the computer monitor. A 21 kW/m2

 heat flux was imposed 

by the panel on the side area of the monitor where a localized open flame was also applied. This

combination resulted in ignition and significant flame spread for each of the monitor specimens. 

The relative performance of the specimens in this test series was consistent with that in the

keyboard fire ignition tests. These tests demonstrated that even highly flame retarded materials 

can contribute to the HRR of an existing fire. 

A main objective of this study was to assess the accuracy of the bench scale tests in

predicting full scale fire performance. For the materials considered here the UL94 test 

accurately predicted the self extinguishing behavior of the full-scale specimens exposed to the 

needle flame ignition source, but provided limited information on the response to the two larger 

ignition sources. A reasonable qualitative correlation was observed between the Cone

Calorimeter results and full-scale peak HRR for the radiant panel ignition tests, but the 

relationship between the Cone test results and the response of the full-scale specimen to the 

needle flame ignition source was less obvious. 

 
Previous bench scale testing demonstrated little correlation between UL94 and Cone

Calorimeter performance. This was partly attributed to the sample orientation in the standard

Cone tests, which do not capture the vertical flame spread and melting observed in the UL94 test 

and in many real fire scenarios. For these reasons additional Cone testing was performed in 

which the sample configuration was modified to capture the dynamics of a developing melt/drip 

pool fire. The results of the melt/drip Cone Calorimeter were able to show both the self 

extinguishing response of the full scale specimens to the needle flame ignition method and the 

qualitative fire growth when exposed to a larger ignition source. The melt/drip Cone test 

correlates rather loosely with full scale tests, however, and there is a continuing need for a better 

bench-scale test. As a result, a full-scale test remains the only certain way to obtain a definitive 

measure of fire hazard. 

A secondary objective of this study was to provide empirical evidence that could be used 

to support a standard setting the maximum allowable peak HRR for electronic equipment 

assemblies. The 200 kW fire resulting from the needle flame ignition of the HB monitor 

specimen would be a serious fire hazard in any home or office. The 23 kW fire resulting from

the ignition of a keyboard would be a threat to any item in close contact (such as a monitors used 

in this study), and was shown to have an ignition threat radius of up to 27 cm for an item such as

an upholstered office chair. A peak HRR of less than 10 kW would reduce the radiant ignition 

threat radius to less than 12 cm. 

 ii
Acknowledgements 

The authors would like to thank Scott Dillon and Ken Steckler from the ATF Fire

Research Laboratory for their assistance in performing the full-scale experiments. Randy 

Shields was instrumental in setting up and helping to carry out the Cone Calorimeter melt/drip

fire tests. 

Special thanks are given to the following companies for their generous donation of 

materials and resources to this project: The Dow Chemical Company, Albemarle Corp., Polyone

Corp., Cheil Industries, and Underwriters Laboratories Inc. 

The following individuals are acknowledged for their participation: Sanghyun Hong, 

Alex Morgan, Tony Kingsbury, Susan Landry, Douglas Wetzig, Robert Backstrom, David

Edenburn, Robert Grifffin, Gordon Nelson, Edward Watt, Michael Smith, Richard Harris, 

Takashi Kashiwagi, Jeffrey Gilman and Richard Lyon. 

 iii
Table of Contents 

Executive Summary......................................................................................................... iv 

Acknowledgements ..........................................................................................................iii 

Introduction....................................................................................................................... 1 

Background ....................................................................................................................... 1 

Description of Full-Scale Calorimeter ............................................................................ 3 

Description of Full-Scale Experiments............................................................................ 7 

Full Scale Resins ............................................................................................................. 7 

Full Scale Test Specimens............................................................................................... 7 

Ignition Methods.............................................................................................................. 8 

Small local ignition source........................................................................................... 8 

Large ignition source (radiant heat panel).................................................................. 9 

Large ignition source (polystyrene keyboard)........................................................... 11 

Experimental Setup........................................................................................................ 12 

Results.............................................................................................................................. 15 

Needle Flame Ignition Results ...................................................................................... 15 

Keyboard Fire Ignition Results...................................................................................... 17 

Radiant Heat Panel Ignition Results.............................................................................. 21 

Threat of Ignition of Other Objects............................................................................... 25 

Modified Cone Calorimeter Tests................................................................................. 37 

Bench-Scale and Full-Scale Comparison...................................................................... 42 

Conclusions...................................................................................................................... 44 

References........................................................................................................................ 45 

 iv
Introduction 

This report describes an experimental investigation by NIST to study the fire hazard of 

electronic equipment having thermoplastic enclosures. This work was part of the project titled 

“Flammability Measures for Electronic Equipment” which was supported under the NIST 

“Reduced Risk of Flashover” program. It was one of several related projects aimed at studying 

fire growth and spread on real materials. 

Consumer electronics are ubiquitous in today’s society. The fact that fires originating 

from consumer electronic equipment represent less than one percent of all residential fires in the

United States is largely credited to the use of flame retardant plastics. Although fires originating 

within these items are rare, the hazard presented when exposed to a small external ignition 

source (such as a candle) is not well known. Even when the equipment is not the first item 

involved in a fire its contribution to the total fire load and impact on flashover of a room can be 

significant. Both of these issues are important due to an increasing number of both candles and 

electronics in the home. It should also be noted that in recent years the number of electronic 

fires has increased in many European countries following a reduction in the use of some flame

retardant compounds due to environmental concerns [1]. It is anticipated that this trend could 

follow in the United States. 

The objective of this work is to relate the full-scale flammability and fire hazard of

consumer electronics assemblies having enclosures made from different resin formulations to 

bench-scale fire performance of these resins. A research consortium was established between 

NIST, UL, Dow, Polyone, Albemarle and Samsung Cheil to conduct this research. Eighteen 

commercial resins were evaluated using three different standard bench-scale flammability tests.

Based on the bench-scale test results, five of these resins were molded into 19” computer 

monitor housings and examined in full-scale fire tests that measured the overall heat release rate 

(HRR) and the heat flux threat to the surroundings. The selection of these materials was based 

on HRR, UL94 performance and physical burning behavior such as melting and charring. The 

results are compared and contrasted to bench-scale results from a previous study [2] to infer 

useful guidelines. 

There is a current international effort (IEC TC108) to develop a hazard based standard for

electronic equipment. This report aims to provide useful data to help determine standard 

requirements. 

Background 

A number of previous studies have examined the fire performance of electronic 

equipment. A comprehensive study was sponsored by the Society of the Plastic Industry (SPI) in 

1981 [3] that rated the relative performance of 5 flame retarded plastic materials (UL94 V-0 and 

V-1) using 10 different bench-scale fire tests and compared the ranked performance to the fire 

performance of model electronic enclosures exposed to a 3 kW propane sand burner. The results 

showed reasonable qualitative agreement between the overall bench-scale and full-scale 

performance. 

The Flame Retardant Chemical Association (FRCA) sponsored a study by the National 

Bureau of Standards (NBS) in 1988 [4] that showed a significant reduction in the fire hazard of 

TV cabinets using flame retardant materials. 

Several reports [5,6,7,8] by the Swedish National Testing and Research Institute (SP) and 

the National Association of Fire Marshals (NASFM) compared the fire growth of off the shelf 

printers, computer monitors and CPU’s to the UL94 ranking of the enclosure material and 

 1
concluded that enclosures using HB rated plastics are vulnerable to ignition by a small flame and 

can lead to flashover of a room. 

The fire growth from ignition of a European television using a 1 kW flame was reported

by the Technical Research Centre of Finland (VTT) [9] resulting in a peak HRR of over 250 kW. 

A study funded by the European Flame Retardants Association (EFRA) examined the fire 

safety of TV sets and computer monitors sold in Europe, the United States and Japan [10] and 

demonstrated the reduced fire safety level of products sold in Europe. 

A 1998 report [11] by the U.S. Consumer Product Safety Commission (CPSC) compared 

the UL94 performance of materials sampled from off the shelf electrical appliance enclosures

and UL746C end product fire test results. Appliances using HB rated materials were reported to 

provide inadequate fire safety when exposed to both internal and external ignition sources. 

In 2000 Safety Engineering Laboratories (SEL) prepared a report for the Consumer 

Electronics Association (CEA) [12] that described fire testing of 15 TV sets with UL94 V-0 

plastics enclosures and one UL94 HB enclosure TV set. The conclusion was that TV sets sold in

the US have adequate fire safety levels due to the required used of V-0 materials. 

The contribution of a computer terminal to the fire development in an office workstation

was considered as part of a NIST/GSA study [13]. Cone calorimeter data were used in a model

to predict the fire growth. The fire hazard of the computer was not the focus of this study. 

A statistical risk analysis for fires involving electrical appliance enclosures was 

performed in 2002 [14]. The author states that, based on the statistical evidence in the US, fires 

involving electronic equipment enclosures are relatively low (compared to other equipment) and 

do not warrant any urgent change in current standards and regulations in the United States. 

The flammability of fire retarded (FR) styrene resins was studied in the context of 

monitor and TV housings [15]. UL94, Cone Calorimeter and limited oxygen index (LOI) benchscale data were compared to the qualitative burning of the housings when exposed to three

different ignition n sources. The results showed that the UL94 and Cone data were good 

indicators of full-scale behavior and the V-0 and V-1 resins resisted sustained ignition in all the 

tests, while the HB and V-2 resins exhibited significant fire spread. 

 

 2
Description of Full-Scale Calorimeter 

All full scale tests were performed using the 3 m square exhaust hood located at the 

Alcohol Tobacco and Firearms (ATF) Fire Research Laboratory in Beltsville, Maryland. This 

facility was designed to accommodate sustained fires with a net heat release rate (HRR) of up to 

1MW. A schematic of the exhaust flow configuration is shown in Figure 1. The exhaust mass 

flow rate was set to 2 kg/s (≈3600 SCFM) for these tests to provide optimal resolution for fires 

less than 400 kW in size. An active control damper was used to maintain a constant mass flow 

rate. The exhaust flow rate was measured using a bi-directional probe and 2 thermocouples. An 

orifice plate located just downstream of the duct inlet was used to insure adequate mixing and 

flow uniformity. A perforated tube was used to sample the gas across the exhaust duct. A

paramagnetic gas analyzer was used to determine the composition of oxygen in the exhaust flow. 

The carbon dioxide and carbon monoxide compositions were measured using an infrared 

absorption analyzer. The exhaust sample gas stream was dried and filtered before entering the

analyzers. A pollution control smoke abatement system was used to clean the exhaust gases

before they entered the atmosphere. 

Heat release rate measurements were based on the well established oxygen consumption 

principle [16,17]. This principle states that for a wide range of materials (13.1 ± 0.35) kJ of

energy is released for each gram of oxygen consumed by combustion. The energy contribution

due to the formation of CO was also taken into account for these measurements. For calibration 

tests using natural gas a more specific value of 12.55 kJ/g was used for the heat of combustion 

per mass of O2. The exact form of the equations used for calculating the heat release rate can be

found in reference [18]. 

The heat release and exhaust flow measurements were calibrated using the natural gas 

sand burner shown in Figure 2. The calibration burner consisted of a 23 cm square steel box 

filled with course gravel and a 5 cm layer of sand. The results from 7 different calibration tests 

over a three week period, during which all fire tests were conducted, are shown in Figure 3. 

Each of the data points in this figure represents an 8.5 min average during a period of steady heat 

release rate from the burner. The HRR plot for an individual calibration is given in Figure 4. The

burner heat release rate was calculated using the following equation: q . 

The volumetric flow rate, V , was measured using a dry test meter. The relative standard 

uncertainty of the proving volume time was less than ± 1 %. The net heat of combustion of the

natural gas, = (48.4 ± 0.3) MJ/kg, was determined using the average fuel composition 

from a series of gas chromatograph reports attained from the local utility company during the 3

week test period. Methane was the main component with a volume fraction of (94.94 ± 0.59) %. 

The natural gas density,

l

burner = NGVNG ∆Hc,NG & & ρ

NG

&

l ∆Hc,NG

ρ NG , was calculated using the ideal gas law with measured temperature

and pressure and using a molecular weight of 17.05 g/mol from the gas composition. A 

propagation of uncertainty analysis of the calibration gas burner data at 255 kW resulted in a 

combined expanded relative uncertainty (95 % confidence level) of 2.5 % for the burner heat 

release rate. 

The exhaust flow rate can be a large component of the total uncertainty in the HRR 

measurement due to a non-uniform duct velocity profile and a 5 % relative accuracy of the bidirectional probe constant [19]. The slope of the linear regression analysis of the calibration data 

in Figure 3 was found to be 0.9409 ± 0.003. It was assumed that the difference between the 

 3
burner output and HRR measurement could be attributed to the exhaust flow measurement. A 

correction factor was applied to the volumetric flow rate to account for the position of the 

velocity probe in the non-uniform flow field. 

To verify the bi-directional probe measurement the exhaust mass flow rate was 

independently measured using the tracer gas dilution method (ASTM E2029-99) [20]. The CO2

produced by the natural gas calibration burner was used as the tracer gas for this analysis. The 

carbon mass fraction in the natural gas was calculated from the gas composition data as 0.7562. 

All of the carbon in the exhaust was assumed to be in the form of CO2 (negligible amounts of CO 

were measured). The exhaust mass flow rate, , was calculated using the following

relationship, where Y

me &

CO2,e is the mass fraction of CO2 in the exhaust, YCO2,a is the ambient CO2

mass fraction and m& CO2,i is the mass flow rate of CO2 produced by the combustion of natural gas. 

( )

( ) CO i

CO e CO a

CO e

e m

Y Y

Y

m 2,

2, 2,

2, 1 & & −

− =

The results of the CO2 tracing analysis on 18 sets of calibration data (each 8.5 min of 

steady time averaged values) gave an exhaust mass flow rate of (1.97 ± 0.075) kg/s. This was 

consistent with the exhaust mass flow rate measurement of (2.00 ± 0.088) kg/s using the velocity 

probe and correction factor on the same data set. The uncertainty values given in this report are 

the standard deviation based on repeat measurement unless otherwise noted. 

The delay and response times of the calorimeter were characterized using the method 

described in reference [21]. The delay time was defined as the period from a 3 oC change in the

exhaust temperature signal to a 0.05 % change in the O2 signal and a 0.02 % change in the CO2

signal. The O2 signal had a delay time of (12.6 ± 0.7) s and the CO2 delay time was 

(12.9 ± 0.7) s, which was dominated by the flow time in the gas sampling line. Since the data 

sample rate was 2 s for the tests described here, the delay time was rounded to 12 s in the HRR 

calculation. The response time was defined as the period of 10 % to 90 % change in the 

measured signal. The gas analyzer response times were measured as 7 s and 11 s for O2 and 

CO2, respectively. 

There was a significant amount of noise from the gas analyzer and bi-directional probe 

signals that propagated into the HRR measurement. Although some of this noise represents real 

turbulence in the exhaust duct, it does not represent real fluctuations in the fire. Filtering this

noise is important for reporting a meaningful peak value of heat release rate. For this reason

many testing and research laboratories use some type of smoothing when processing HRR data. 

The amount of smoothing required is not unique because it depends on both the transient nature 

of the measured fire and the inherent physical smoothing of the system (e.g. analyzer response 

time and diffusion in sampling line). For the test results reported here a ± 10 s moving average 

was applied to the oxygen analyzer and bi-directional probe pressure transducer signals. This 

significantly reduced the amount of noise while preserving the important features of the HRR 

curve. The effect of this smoothing on the heat release rate measurement using the calibration

burner is shown in Figure 4.

 4
3.0 m x 3.0 m square hood

0.655 m I.D. exhaust duct

2.1 m

4.15 m

floor

0.365 m I.D. orifice plate

Gas sampling tube

Bi-directional probe

& thermocouples 

10.0 m

Ceiling

Mezzanine

Main Exhaust Flow

Flow control damper Instrumentation 

Room

0.67 m

4.1 m 4.4 m

2.9 m

Figure 1. Schematic drawing of exhaust hood and instrumentation.

Figure 2. Natural gas calibration burner (HRR ≈ 275 kW)

 5
y = 0.9409x

R2

 = 0.9981

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300 350

Measured HRR (kW) from Oxygen Calorimetry

Natural Gas Calibration Burner H

R

R (k

W)

Figure 3. Summary of calorimeter calibration results using natural gas burner.

0 5 10 15 20 25 30 35 40 -50

0

50

100

150

200

250

300

350

400

Time (min)

HRR(kW)

Figure 4. HRR data from natural gas calibration burner. Solid line represents ±10 s moving 

average.

 6
Description of Full-Scale Experiments 

Full Scale Resins

The 18 formulations used in the bench-scale phase of this study [2] were chosen based on 

extent of industry use and on diversity of flame retardant (FR) approach. The 5 materials used in 

the full scale tests reported here were selected to represent a wide range of fire performance in 

the bench scale tests. A list of materials used in these tests and a summary of results from 3 

bench-scale tests (3.2 mm thick samples) are given in Table 1. The resin identification labels in

Table 1 are consistent with the previous study. The format of the label is: number - resin type – 

FR type. The resin types include Acrylonitrile Butadiene Styrene (ABS), High Impact 

Polystyrene (HIPS), Polycarbonate (PC) and Polypropylene (PP). The flame retardant types 

include Bromine/Antimony (BFR), non-halogenated (NH) and no flame retardant (NFR). The 

cone calorimeter results shown are for an incident heat flux of 50 kW/m2

. The UL94 Vertical 

Burn Test and Glow Wire Ignitability Test (GWIT) are described in detail in reference [2]. The 

full scale specimen mass listed in Table 1 is the combined mass of the front and rear pieces of 

the pre-assembled monitor enclosure. 

Table 1. Summary of bench-scale performance for materials used in full-scale tests, and initial 

mass of combustible material on full scale specimens. 

Resin 

Identification 

Cone peak 

HRR (kW/m2

) 

@50 kW/m2

UL94 

Classification 

GWIT (o

C) / 

GWFT (o

C) 

Full-Scale 

Enclosure 

Mass (g) 

 3-HIPS-NFR 1307 HB 750 / 725 2335 

13-PP-BFR 1916 V-2 800 / 960 1999 

18-HIPS-NH 398 V-1 NT 2453

1-PC-NH 586 V-0 825 / 960 2839 

7-ABS-BFR 409 V-0 750 / 960 2683 

Full Scale Test Specimens

As shown in Figure 5, two piece 19” CRT computer monitor housings were molded from 

the materials listed in Table 1. The average specimen wall thickness was (3.0 ± 0.25) mm. The 

fire characterization was performed using both real and simulated internal components. The 

simulated internal frame consisted of 1.6 mm steel sheet metal formed roughly into the shape of 

the real components. Draped over the frame was a sheet of aluminum foil that served to increase 

the lateral cross section of the sheet metal frame. The frame also served to partially support the 

plastic enclosure during the fire test and shield interior surfaces from radiation. The frame was 

thus intended to achieve the same qualitative effects that real monitor components have on a fire.

The real internal components consisted of a cathode ray tube (CRT) and other various electronic 

components (see right side of Figure 5), some of which were combustible. The 22 cm x 29 cm

opening at the base of the enclosure was covered with 1.6 mm sheet metal. The specimen was 

placed on a brick such that the mid-length side lower edge was (8 ± 1) cm from the table surface. 

 7
The table surface, on which much of the burning occurred, was 12.7 mm thick Marinite I1

, a 

calcium silicate board. 

Figure 5. Photograph of 19” computer monitor test specimen. A 19” CRT is shown on the right 

side mounted to the front bezel.

Ignition Methods

Small local ignition source 

A small local ignition source representing a typical 

candle sized flame was used for these tests. A 0.5 mm I.D. 

needle flame burner was used to produce an n-butane flame 

with a height of (20 ± 1) mm, shown in Figure 6. The fuel 

mass flow rate was measured as (0.84 ± 0.02) mg/s and the net 

heat release rate of this flame was calculated as (37.5 ± 2) W. 

An effective net heat of combustion value of 44.7 kJ/g was 

used for n-butane fuel. 

The needle flame burner was mounted to a flexible arm 

to allow the position and orientation of the test flame to be 

easily adjusted. The flame was applied mid-length along the

side of the specimen, (3 ± 1) cm above the lower edge (shown 

in ). This emphasized both the potential for upward 

flame spread and for the development of an interactive melt 

pool fire on the table surface. 

Figure 7

The initial flame application was for a period of 20 s. 

If the burning specimen extinguished within 60 s, the flame was immediately re-applied for 60 s. 

The 60 s application was repeated 3 times for a total flame application time of 200 s. In the case 

Figure 6. 20 mm 

needle flame ignition 

 1

 Certain commercial products are identified in this paper in order to specify the experimental procedure adequately. 

Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards 

and Technology, not is it intended to imply that the materials or equipment identified are necessarily the best 

available for this purpose. 

 8
that a hole was formed in the specimen, the test flame was moved laterally to remain in contact 

with the enclosure (chasing the receding material). 

This ignition method was designed to provide information on the fire performance of the

equipment when exposed to a localized short duration ignition source, and also the possibility of 

a much longer duration ignition source such as an unattended candle. 

 

Figure 7. Needle flame ignition of 19" monitor specimen. 

Large ignition source (radiant heat panel)

The response of the specimens to a larger ignition source was simulated using a 48 cm x 

33 cm natural gas radiant heat panel. This was intended to represent a situation where the

monitor was not the first item involved in a fire. The panel was supplied with 224 L/min of

compressed air and 22.4 L/min of natural gas with a net heat of combustion of 48.4 MJ/kg. The 

centerline heat flux was 21 kW/m2

 at a location of 15 cm from the surface of the panel. Heat flux

measurements were made using a total heat flux gauge (Medtherm Model 20679, SchmidtBoelter type, 6 mm diameter sensor face, 13 mm diameter body) mounted to a linear translation 

stage. 

The horizontal and vertical heat flux distributions from the panel are shown in

and . The origin of the coordinates in this figure is the midpoint on the front surface of

the panel and the z direction is normal to the front surface. A removable copper plate shutter 

was used to protect the specimen from the heat flux panel prior to the start of the test. The shutter 

was water cooled and painted black to minimize the tendency of the gas-fired panel to increase in 

temperature when shielded. A 1.6 mm I.D. open tube burner was used to produce the 10 cm nbutane pilot flame. The fuel flow rate was (4.0 ± 0.08) mg/s and the net heat release rate was 

(178 ± 5) W. This pilot was normally applied in a location similar to that of the needle flame. In 

some test it was held in contact with melted material that had fallen to the table top. An image of 

the radiant panel ignition configuration is shown in Figure 10. 

Figure 8

Figure 9

 

 9
0

5

10

15

20

-40 -30 -20 -10 0 10 20 30 40

Horzontal Position from centerline, x (cm)

Total Heat Flux (kW/m2

)

z=20 cm

z=15 cm

width of panel

Figure 8. Heat flux profiles across radiant heat panel at two locations and vertically centered

(y=0).

0

5

10

15

20

25

-10 -5 0 5 10 15 20 25 30 35

Vertical position from centerline, y (cm)

Total Heat Flux (kW/m2

)

z=15 cm, x=0 cm

Top of panel

Figure 9. Vertical heat flux profile 15 cm normal to panel and horizontally centered.

 10
Figure 10. Image showing the relative position of the radiant heat panel, specimen and 10 cm

pilot flame. 

Large ignition source (polystyrene keyboard)

A generic non-FR polystyrene keyboard was used as a secondary ignition source for the 

monitor specimens in some tests. The total weight of the keyboard was (580 ± 5) g. The

keyboard was placed under the front bezel of the monitor, Figure 11, and ignited using the 

20 mm needle flame described previously. The needle flame was applied for 20 s to the side of

the F9 key. Tests were also conducted using only the keyboard to determine its contribution to 

the heat release rate. 

Figure 11. Keyboard ignition using 20 mm needle flame.

 11
Experimental Setup

All experiments were performed directly below the 3m x 3m exhaust hood described 

previously. A schematic drawing of the needle flame ignition test setup is shown to scale in 

. The keyboard was present only for the specimens that did not sustain ignition using 

only the 20 mm needle flame. The test configuration for the radiant panel ignition tests is shown 

in Figure 13. A photograph of the hardware configuration during a test is shown in Figure 14. 

Figure 12

A 12.7 mm thick calcium silicate board (Marinite I) was used as the surface for the tests.

This material was chosen because of its thermal properties and resistance to fire. A new test

surface was used for each test. 

An array of four total heat flux gauges (Medtherm Model 20679, Schmidt-Boelter type, 6 

mm diameter sensor face, 13 mm diameter body) was placed in a position to view one side of the 

burning object (monitor or keyboard). The goal of the array was to obtain data on the 

distribution of radiative heat flux versus distance along a line perpendicular to the object surface 

being viewed. This information is used below to infer the maximum distance at which different 

materials could be ignited as a result of radiative heating from the object fire. 

The four gauges were arranged as follows. The front and rear gauge were on the same

horizontal axis, both facing along this axis, and separated by 25 cm to 30 cm. The remaining 

two gauges were on a single vertical axis, both facing in the same direction as the first two, i.e.,

toward the side of the burning object. That vertical axis was displaced 5 cm from the horizontal

axis of the first two gauges. The two gauges on this vertical axis were separated vertically by a

distance of 15.3 cm, symmetrically above and below the horizontal axis of the first two gauges. 

This vertical axis was approximately midway along the horizontal axis between the first two 

gauges. This arrangement ultimately supplies three measures of the heat flux versus

perpendicular distance away from the viewed surface of the burning object. In addition, since

this distribution depends also on the height at which it is measured, the two vertical gauges

provide a first order correction for this effect. A side view of the heat flux gauge array is shown 

in Figure 15. 

Since the gauges (and their physical supports) had a finite size and could be within the 

field of view of those behind them, corrections had to be made to their readings for this

shadowing, using a procedure described later. 

For the isolated keyboard fires, the flux gauge array was centered mid-length along the 

keyboard, facing the front of the keyboard. For the monitor fires in which either a small flame or

a burning keyboard was the igniter, the flux array faced one side of the monitor at its mid-length 

(and approximately, at mid-height). For the monitor fires in which one side was exposed to a 

radiant panel, the flux array faced the rear end of the monitor and was laterally centered on it. In

all cases the horizontal axis of the flux array was 15.3 cm above the Marinite surface on which 

the burning test object was supported. The gauges were cooled with 21 o

C water which was the 

same temperature at which they had been calibrated. 

Data were sampled at 2 s intervals on 21 channels using a 12 bit data logger. All signals 

were recorded for a period of 4 min before ignition and after extinguishment of the specimens. 

The ambient temperature, pressure and relative humidity were recorded during each test. An 

event marker channel was used to record the time of any significant event during the test. Video 

cameras were used to record all tests from two different view angles.

 12
74 cm

Steel Table

Marinite I (61 cm x 81 cm)

Needle flame ignition point

Keyboard

Two piece monitor enclosure

Floor

Load cell

Simulated internal frame

HF gauges 1&2

HF gauge 3

HF gauge 4

Figure 12. Side view schematic drawing of experimental setup for needle flame ignition and 

keyboard fire ignition tests.

15 cm

Radiant heat panel

Heat flux 

gauge array

Simulated internal frame Monitor enclosure

Removable water cooled shutter

Marinite board

10 cm pilot flame location

Figure 13. Top view schematic drawing of experimental setup using radiant heat panel.

 13
Figure 14. 3-HIPS-NFR monitor test #4, simulated internal components. HRR=155 kW,

7.5 min after ignition with needle flame.

Figure 15. Side view of heat flux gauge array during monitor test # 12a. 

 14
Results 

Needle Flame Ignition Results

The results of the needle flame ignition tests are summarized in Table 2. All of the tests 

were performed in random order (grouped by ignition method) with at least one replicate 

measurement per condition. The peak heat flux and flux gauge distance from the specimen are 

given for the gauge furthest from the test specimen. The heat flux values in this table are not 

corrected for shadowing. A detailed analysis of the heat flux data is given in a later section. 

Table 2. Summary of results from needle flame ignition tests on 19” monitors

Specimen ID 

test 

# CRT

Peak HRR 

(kW)

Total 

Mass 

Loss (g) 

Peak Heat 

Flux 

(kW/m2

) 

Flux Gauge 

Distance 

(cm) 

1-PC-NH 7 no ---- ---- ---- ----

1-PC-NH 8 no ---- ---- ---- ----

3-HIPS-NFR 1 no 208 2401 27.4 40.1

3-HIPS-NFR 4 no 200 2478 27.7 41.3

3-HIPS-NFR 26 yes 144 3309 8.3 50.3

7-ABS-BFR 6 no ---- ---- ---- ----

7-ABS-BFR 11 no ---- ---- ---- ----

13-PP-BFR 5 no ---- ---- ---- ----

13-PP-BFR 12 no ---- ---- ---- ----

18-HIPS-NH 2 no ---- ---- ---- ----

18-HIPS-NH 10 no ---- ---- ---- ----

None of the 4 flame retarded materials produced a measurable fire when exposed to the 

20 mm needle flame. The monitor enclosure molded using the non flame retardant material, 3-

HIPS-NFR, was easily ignited during the initial 20 s application of the flame and produced a fire 

that consumed the entire monitor housing. The HRR curves for these specimens are shown in

. The initial test flame was applied at 4 min into the data file for all tests described in

this report. The fire growth and peak HRR on the monitors with the simulated internal frame 

(test #1 and #4) were very reproducible. For each of the specimens the fire grew slowly during 

the first 3 min then rapidly accelerated to its peak value during the next 3 min. The presence of 

the CRT decreased the fire growth rate and lowered the peak HRR by approximately 30 %. An 

image of the burning specimen near the peak HRR (test #26 in Table 2) is shown in Figure 17. 

Figure 16

The total mass loss measurement in this series of test was compromised by several 

factors. The Marinite I sheet below the specimen contained roughly 3 % water weight (150 g) 

that partially vaporized during the test. In addition, some of the glass from the CRT was ejected

from the monitor during the test. For these reasons it was not possible to distinguish the mass 

loss due to the burning plastic from the overall mass loss. The initial weight of the monitor 

enclosures for tests 1, 4 and 26 was (2335 ± 5) g. 

 15
The combined expanded relative uncertainty (95 % confidence level) of the peak heat 

release rate measurement was ±12 %. The dominant components of this uncertainty were the 

exhaust mass flow rate and the fuel heat of combustion per gram of O2. 

0 5 10 15 20 25 30 35 0

50

100

150

200

250

Time (min)

HRR(

k

W)

monitor 1

monitor 4

monitor 26 1 

4 

26 

t

ign

 = 4 min

Figure 16. Heat release rate curves for needle flame ignition of 19” monitors. Ignition flame 

applied to specimen at t = 4 min.

Figure 17. Image of monitor test #26, 3-HIPS-NFR, near peak heat release rate. Array of heat 

flux gauges is shown on right side of image. 

 16
Keyboard Fire Ignition Results

The results of the keyboard fire ignition of the monitor specimens are summarized in

Table 3. The keyboard ignition tests were performed following the needle flame ignition method 

for the four flame retarded (FR) specimens that did not ignite and had only local fire damage to 

the enclosure. For example test #7a was performed after test #7 from Table 2. Varying degrees 

of fire spread from the keyboard to the monitor enclosure were observed for the tests in this 

configuration. 

Three tests were conducted to determine the contribution of a stand-alone keyboard to the 

HRR. The results of 3 replicate measurements are shown in . The average peak HRR 

was 22.7 kW. The time from ignition to peak heat release rate for the stand-alone keyboards was

approximately 10 min. When the keyboard burned, its resin did not flow outward more than 

1 cm to 2 cm. Thus, when used as an ignition source, it was essentially stationary. Portions of 

the monitor (the front bezel) immediately above it were partially immersed in its flames. More 

remote portions of the monitor saw only limited radiation from the keyboard fire plume. 

Figure 18

The HRR data for the 1-PC-NH (UL94 V-0) specimens are shown in . In test

#7a the fire spread to the front part of the monitor housing during the first 10 min and then the 

rear part of the monitor fell away from the keyboard and self-extinguished. A thin steel bar 

restraint was added for test #8a to prevent the enclosure from falling away from the ignition

source. The fire spread to the entire enclosure during test #8a and produced a peak HRR of 

120 kW. The same configuration was repeated for test #31 but resulted in a peak HRR of only 

55 kW. The fire growth and spread on this material was less reproducible than the other 

materials considered in this study. 

Figure 19

The 7-ABS-BFR (UL94 V-0) specimens, Figure 20, had the best fire performance in this

configuration. Only the enclosure material directly in contact with the fire from the burning 

keyboard was ignited. The contribution of the enclosure to the peak HRR was between 10 kW 

and 20 kW and the rear half of the enclosure was not involved in the fire. The CRT was not a 

significant factor in the fire performance of this specimen. 

Of the FR specimens 13-PP-BFR was the most vulnerable to the keyboard fire ignition. 

Once ignited the fire quickly grew into a large pool fire that covered the entire surface area of the 

Marinite. The edge of the Marinite board was protected with aluminum foil to contain the melt 

pool, however a small amount of burning plastic spilled over the edge. Each of the housings

made from 13-PP-BRF produced a fire greater than 180 kW in size (see Figure 21). 

The response of material 18-HIPS-NH to the keyboard fire ignition method is shown in 

. Although the fire was slow to develop it eventually spread to the rear part of the

enclosure and consumed most of the mass of the enclosure. As with the other specimens the

presence of the real CRT delayed the fire growth and lowered the peak HRR. 

Figure 22

 17
Table 3. Summary of results from keyboard fire ignition of 19” computer monitors.

Specimen ID 

test 

# CRT

Peak 

HRR 

(kW)

Total 

Mass 

Loss (g) 

Peak Heat 

Flux 

(kW/m2

) 

Flux Gauge 

Distance 

(cm) 

PS-keyboard 9 ---- 22.5 470 3.1 40.1

PS-keyboard 24 ---- 22.6 456 3.3 43.3

PS-keyboard 29 ---- 23 ---- 3.4 43.3

1-PC-NH 7a No 46 768 4.7 42.6

1-PC-NH 8a No 120 2048 12.5 42.6

1-PC-NH 28 yes 55 ---- 2.3 50.7

1-PC-NH 31 No 55 1626 5.5 47.7

7-ABS-BFR 6a No 44 797 3.0 43.4

7-ABS-BFR 11a No 31 831 1.7 43.2

7-ABS-BFR 27 Yes 35 830 1.7 50.2

13-PP-BFR 5a No 205 2469 24.5 42.0

13-PP-BFR 12a No 199 2545 24.0 43.7

13-PP-BFR 30 Yes 180 3303 11.2 57.5

18-HIPS-NH 2a No 115 1483 11.4 40.1

18-HIPS-NH 10a No 89 1607 10.8 41.7

18-HIPS-NH 25 Yes 73 ---- 4.6 48.3

0 5 10 15 20 25 30 35 0

5

10

15

20

25

30

35

Time (min)

HRR(kW)

keyboard 9

keyboard 24

keyboard 29

Figure 18 Heat release rate curves from stand-alone polystyrene keyboards ignited at t=4 min 

using 20 mm needle flame.

 18
0 10 20 30 40 50 0

20

40

60

80

100

120

140

Time (min)

HRR(

k

W)

monitor 7a

monitor 8a

monitor 28

monitor 31 8a

31 

28 

7a 

Figure 19. Heat release rate data for keyboard fire ignition of 1-PC-NH (UL94 V-0) monitors. 

Real CRT was used in monitor 28.

0 5 10 15 20 25 30 35 0

10

20

30

40

50

60

Time (min)

HRR(k

W)

monitor 6a

monitor 11a

monitor 27

6a 

27 

11a 

Figure 20. Heat release rate data for keyboard fire ignition of 7-ABS-BFR (UL94 V-0) 

monitors. Real CRT was used in monitor 27.

 19
0 10 20 30 40 50 60 0

50

100

150

200

250

Time (min)

HRR (

k

W)

monior 5a

monior 12a

monior 30

5a 12a 

30

Figure 21. Heat release rate data for keyboard fire ignition of 13-PP-BFR (UL94 V-2) monitors. 

Real CRT was used in monitor 30.

0 10 20 30 40 50 0

20

40

60

80

100

120

Time (min)

HRR (kW)

monitor 2a

monitor 10a

monitor 25

2a 

10a 

25 

Figure 22. Heat release rate data for keyboard fire ignition of 18-HIPS-NH (UL94 V-1) 

monitors. Real CRT was used in monitor 25.

 20
Radiant Heat Panel Ignition Results

The results of the radiant heat panel ignition of the monitor specimens are summarized in 

Table 4. All of these tests were performed using the specimens with simulated internal

components. The radiant panel was positioned so that a 21 kW/m2

 total heat flux was imposed at 

the point on the side of the specimen where the local ignition source was applied. As in the 

previous tests a barrier of foil was applied to the edge of the edge of the tests surface to prevent 

material from dripping onto the floor and damaging the load cell and instrument wires. Two 

3.2 mm thick steel bars were positioned in front of the heat panel to prevent the enclosure from

tipping over and contacting the face of the panel. The uncorrected peak heat flux data given in

Table 4 include approximately 1 kW of radiation from the heat panel. 

Specimen 1-PC-NH was easily ignited with this method and the fire quickly consumed

the entire specimen and grew to exceed 100 kW in size. As shown in the time from

ignition to peak HRR was about 4 min. As expected, the non-FR HIPS specimen, shown in 

, ignited and quickly developed into a large pool fire in less than 5 min. 

Figure 23

Figure 24

The 7-ABS-BFR specimen did not ignite during the first two attempts (test #13 and #15). 

All of the material on the side of the enclosure melted away from the 10 cm pilot flame before it

could ignite. During the third attempt, test #23, the pilot flame was lowered to remain in contact 

with the developing melt pool on the surface of the Marinite. The enclosure ignited and slowly 

spread to the far side of the specimen. The HRR, Figure 25, had a peak of 25 kW nearly 15 min 

after the initial flame application. Similar behavior was observed for the 13-PP-BFR specimens,

except that the result was a larger fire. Only after applying the pilot flame to the melt pool for 

approximately 5 min did the fire begin to propagate to the other sides of the enclosure. Once 

ignited however the fire grew very quickly and had a similar growth rate and peak HRR 

(Figure 26) to the keyboard fire ignition method of the same material. 

The heat release rates of the 18-HIPS-NH (UL94 V-1) specimens ignited using the 

radiant panel and pilot flame are shown in Figure 27. The enclosure side that was exposed to the 

radiant heat flux of 21 kW/m2

 was ignited within the first minute and the fire spread to the far

sides of the enclosure within 10 min. The average peak heat release rate, 91 kW, was 

substantially lower than the HIPS resin with no flame retardant. 

 21
Table 4. Summary of results from radiant heat panel ignition tests of 19” computer monitors. 

Specimen ID test # CRT 

Peak 

HRR 

(kW)

Total 

Mass 

Loss (g) 

Peak Heat 

Flux 

(kW/m2

) 

Flux Gauge 

Distance 

(cm) 

1-PC-NH 18 no 124 1504 11.0 45.6

1-PC-NH 20 no 117 1441 11.1 44.3

3-HIPS-NFR 14 no 240 2475 16.9 45.9

3-HIPS-NFR 19 no 190 2413 14.1 45.5

7-ABS-BFR 13 no ---- 24 1.0 46.4

7-ABS-BFR 15 no ---- 23 1.0 46.4

7-ABS-BFR 23 no 25 765 3.9 45.8

13-PP-BFR 17 no 193 1776 11.1 45.6

13-PP-BFR 22 no 167 1849 11.4 46.7

18-HIPS-NH 16 no 88 1267 7.0 45.5

18-HIPS-NH 21 no 94 1329 6.7 46.8

0 5 10 15 20 25 0

50

100

150

Time (min)

HRR (

k

W)

monitor 18

monitor 20

18

20

Figure 23. Heat release rate data for radiant heat panel ignition of 1-PC-NH (UL94 V-0) 

monitors.

 22
0 5 10 15 20 25 0

50

100

150

200

250

Time (min)

HRR (

k

W)

monitor 14

monitor 19 14 

19

Figure 24. Heat release rate data for radiant heat panel ignition of 3-HIPS-NFR (UL94 HB) 

monitors.

0 5 10 15 20 25 0

5

10

15

20

25

30

35

40

45

50

Time (min)

HRR (

k

W)

monitor 13

monitor 15

monitor 23

Figure 25. Heat release rate data for radiant heat panel ignition of 7-ABS-BFR (UL94 V-0) 

monitors.

 23
0 5 10 15 20 25 30 35 0

20

40

60

80

100

120

140

160

180

200

Time (min)

HRR (

k

W)

monitor 17

monitor 22 17 

22 

Figure 26. Heat release rate data for radiant heat panel ignition of 13-PP-BFR (UL94 V-2) 

monitors. 

0 5 10 15 20 25 30 0

10

20

30

40

50

60

70

80

90

100

Time (min)

HRR (

k

W)

monitor 16

monitor 21

16 21

Figure 27. Heat release rate data for radiant heat panel ignition of 18-HIPS-NH (UL94 V-1) 

monitors. 

 24
Threat of Ignition of Other Objects

Any fire poses an ignition threat to objects in its surroundings. Such ignition could occur 

by one of several modes. Each has a differing direction or extent of reach beyond the boundaries 

of the burning object. 

Direct flame contact with the surface of another object 

The greatest reach by this mode is typically upward due to the buoyancy of the flames but 

fire plumes can be diverted laterally by interaction with object surfaces or by air movement in

the surrounding space. In the present tests, for the largest fires, lateral flame extent occasionally

reached about 15 cm from the original sides of the monitor surface, mainly as a result of

deflection of lower flames by a surface that was skewed temporarily in the process of collapsing

downward. The upward reach of the flame tips was, for the highest HRR cases, as much as 

1.5 m above the table surface on which the sample rested. Due to dilution, the mean gas

temperature at flame tip height (≈ 500 oC) is not much higher than that required to ignite many 

materials but, in combination with the radiation from the plume (see below), the ignition reach

above the fire is likely to be significantly greater than the flame tip height (this does not seem to 

have been investigated in the literature and was not a focus here). 

Movement of flaming material

For the thermoplastic-based electronic equipment enclosures that are the focus here, the 

main moving material hazard is lateral and downward flow of flaming molten resin. Here it has 

the potential to carry flames from desk top level to the floor. The principal threat of flaming 

melt material reaching the floor is associated with melts having low viscosity. The main resin 

posing this threat here was 13-PP-BFR. Flaming melt material reached the floor with some other 

resins but this was mainly a result of the small size of the table being used to support the 

sample2

. It is worth noting that a very low viscosity resin might also extend the lateral flame 

reach on something like a desk surface if a flaming flow continues to move outward3

. For some

burning materials or objects, another mode of flaming material movement could be floating

shreds or “brands” carried upward from the fire by buoyant flow and dropped virtually 

anywhere. No significant examples of this behavior were observed here. 

Remote ignition by radiation 

A sooty fire plume is a strong radiator. The intensity of this radiation drops off with 

distance from the fire in accord with the view factor a target point has with respect to the fire 

plume. The lateral reach of this radiation (at a threatening intensity) can be substantially greater 

than that of the flames themselves. For electronic equipment this implies a significant threat to

other objects that may be used in conjunction with it, e.g. other objects on a desk top. 

Assessment of this threat was the reason for including the heat flux gauge array in these tests and

 2

 Flaming material occasionally fell over the edge of the table while a monitor was in the process of collapse. This 

could happen in the real world if a monitor was near the edge of a desk. 3

 This sort of outward flow is inhibited by heat loss to the surface on which it is occurring and will usually stop 

unless a large fire plume is countering the heat loss to the surface. 

 25
is the main focus of this section. The rationale of how these results are interpreted is discussed

below. 

Radiative ignition has some unique characteristics. The principal characteristic that is 

relevant here is the fact that radiation heats a surface directly and not the surrounding gases.

Then, as a material begins to gasify as a result of this heating, the fuel gases generated move into 

a cooler gas phase which tends to inhibit their ignition. If a pilot heat source is available nearby,

the gases may readily ignite; if not, ignition might be postponed until substantially higher heat 

fluxes impinge on the area. 

Another relevant feature of radiative ignition is that below some flux level 

(corresponding to some distance away from the radiating fire plume), the surface of the heated

object will not get hot enough to be ignitable even if a pilot flame is present. The distance 

beyond which this is true defines the “threat radius” of the fire. It is this distance which we 

would like to quantify for the monitor fires; it will be shown to depend on both the fire intensity

and its time-wise variation. 

The problem addressed here is similar to that which is one focus of NFPA 555 (Guide on 

Methods for Evaluating Potential for Room Flashover). There the possibility of radiative 

ignition is assessed using a simplified geometry for the fire plume. Here, instead of making this 

assumption, we are measuring the radiant heat flux and then estimating the consequences for 

specific surrogate materials (described below). 

In assessing the maximum radiative ignition distance (or “reach”) of the monitor 

enclosures in these tests, we report the distances inferred on the basis of piloted ignition (i.e.,

based on the assumption that a “pilot” heat source is available to ignite gases being generated). 

This is the worst case assumption and is thus conservative. Real world cases may match this 

worst case in certain circumstances. If the closest part of an ignition target is just beyond the 

maximum piloted ignition distance for a given fire then it can be safely assumed that no part of it 

will ignite. On the other hand, if a target object extends from well inside the maximum ignition 

distance of the main fire to somewhere beyond it, the closest part of the object could ignite (due 

to the higher fluxes closer in) and then almost immediately induce (pilot) ignition out to the 

maximum ignition distance4

 (and subsequently beyond in a more finite spread rate process). 

Similarly, other lesser objects of similar ignitability laying in the space between the target object 

of interest and the main fire could form a chain of pilot flames toward that target. The point here

is that the maximum piloted ignition distance is that radius out to which all of a given material is 

ready to ignite, given any pathway for a suitable gas phase “spark” to reach it and thus it is a real

measure of threat radius around a fire. 

Different target objects have differing ignitability as a result of their specific chemical

and physical properties. It is not possible to make predictions for all objects which may 

plausibly be near an electronic equipment fire. Instead, surrogate materials are used in a manner 

like that of reference [22]. Here we consider two materials which are surrogates for common 

objects of interest in the vicinity of a desktop computer. The first is a stack of paper.

Specifically, the surrogate material is a 2.54 cm thick unbound pile of copier paper. This is a 

surrogate for books, magazines, manuals or printer paper that could be on a desk top. The 

 4

 Essentially, ignition will spread outward as fast as the surface reaches its ignition temperature. This is at least as 

fast as radiation from the burning object can heat successive radii on the target surface. The spread will be 

accelerated by the added radiation coming from the spreading fire front. When the spreading flame front reaches the

maximum reach of piloted ignition, it slows to a normal opposed flow flame spread process. 

 26
second is a medium weight cotton fabric which is a surrogate for a drape or for the seatback of 

an upholstered desk chair. The fabric is 100 % cotton and weighs 0.41 kg/m2

 (12 oz/yd2). 

The piloted ignition behavior of these materials was measured in a Cone Calorimeter 

[22,23]over a flux range from 70 kW/m2

 down to the minimum flux for ignition5. The results, 

taken from the two references, are shown in and . The Cone ignition process

is purely radiative in nature and includes a spark igniter as the pilot. Note, however, that the heat

flux there is constant in time (at each intensity level). In the monitor fires, the heat flux that 

would impinge on a target object rises and falls as the monitor fire builds and recedes. This has 

an effect on the viability of ignition and thus the Cone data cannot be used directly. Instead, it 

forms the basis for inferring the effective ignition properties of the surrogate material. A simple 

thermal ignition model is used to find effective property values which closely reproduce the 

measured ignition behavior from the Cone. These properties are the ignition temperature and the 

apparent thermal inertia (product of density (ρ), heat capacity (c) and thermal conductivity (k)). 

Actually, two versions of this model are needed since one material, the fabric, is thermally thin 

and the other is thermally thick. The models, which are based on the conventional concept of an 

ignition temperature and which are non-linear due to the inclusion of re-radiation from the heated 

material surface(s), are described in reference [22]. Both require numerical solution. In

and , the model fits are shown along with the experimental data; the effective 

ignition property values are shown in the figures. 

Figure 28

Figure

28

Figure 29

Figure 29

Given these effective ignitability properties and the measured heat flux versus time from

the monitor fire tests, this information can be used in the model(s) to predict the farthest distance

from the fire at which ignition of the surrogate materials can just occur. Since the number of 

heat flux gauges was quite limited, only some portion of the flux versus distance profile was 

measured in each test; thus it is necessary to extrapolate/interpolate the measured values. 

Before the raw heat flux data could be used (or extrapolated), it was necessary to correct

the raw reading for the fact that the field of view of the gauge may have been partially blocked. 

For the most part, this blockage was due to the supports of gauges which were closer to the fire 

being viewed but even the front gauge had some blockage due to a rod used to prevent the 

monitor from tipping over (off the support table) as it began to collapse. 

In general, the percent blockage of the field of view of one gauge by one or more gauges

in front of it depends on the size of the fire the gauge views. Thus it was necessary to take 

photos of the fires, from behind the flux gauge array, at their peak and use these along with 

measurements of the gauge and gauge supports as seen by each gauge. The actual blocked area 

was projected forward onto the fire whose area (in the plane of the near face of the burning 

object, using known spacings) was estimated from the photos. The correction was then made 

assuming that the blocked area of the fire was as radiant as all other areas of the fire. (In fact all 

areas of these fires are assumed equally radiant.) Strictly speaking, such corrections are timedependent since the fire size is time-dependent but it was not practical to account for this effect. 

The fire size varied on the same time scale as the flux peak being recorded so some shadowing 

corrections are underestimated meaning that the effective peaks are slightly broader (i.e., longer 

in time) than the values used below. Since the shadow corrections were generally in the 5 % to

10 % range, this is not a serious source of error. 

 5

 The ignition results for paper were obtained on a horizontal stack. We apply them here unchanged for paper

oriented vertically which receives the higher radiative flux in the situation under consideration. This could be a

vertical surface on the same objects for which this material is a surrogate. 

 27
Generally (though not in all cases) the higher of the two vertically arrayed gauges read a 

higher peak flux. This indicates that the horizontal axis on which the front and back gauges were 

placed was not at the height of maximum outward reach of the flux distribution. To help

compensate for this, the front and back gauge readings were corrected up to the level of the 

higher vertical gauge. Note that this is a correction in the right direction but it is not necessarily

complete, i.e., the maximum outward reach of the flux distribution is almost certainly greater 

than that calculated in this manner. On the other hand these height corrections were typically of 

the order of 5 %, so, once again, this should not be a serious source of error. 

The net result was a three point estimate of the flux distribution along a line 

perpendicular to the face of the burning object. Figure 30 shows an example of this corrected

flux distribution, in this case for 3-HIPS-NFR, which had one of the most outward reaching flux 

distributions. Note that the peak flux at the farthest gauge location was approximately 30 kW/m2 

. It will be shown below that the surrogate materials being examined here are capable of igniting 

at substantially lower heat fluxes than this. Thus, in this case, to find the maximum outward 

reach of ignition of such materials, it was necessary to extrapolate the flux distribution shown in

. In other cases, it was necessary to interpolate between pairs of points of the flux 

distribution. 

Figure 30

Figure 30

Also shown in Figure 30 are the data for the time width of the transient fluxes seen by the 

three gauges as the fire grew and then subsided. The time width is that at 50 % of the peak 

value. Because the flux data have substantial variability (due to the turbulent nature of the fire 

plume), it is simpler to approximate the transient nature of the flux by using a Gaussian time 

dependence. The Gaussian is specified to match the peak flux and its time width at 50 % of the 

peak. Since the three measures of peak width were generally quite comparable, the average of 

the three was used in the ignition model calculations 

The simplest interpolation or extrapolation of the flux peak data in is a straight

line that includes two of the measured points; extrapolation with a fitted polynomial could be 

seriously misleading. A more physically-based method uses the concept of radiative view factor. 

In the latter approach, the fire plume is broken, for convenience, into two rectangular segments, 

one above and one below the front flux gauge height. The view factor for this pair, as seen along 

a line through the front and rear flux gauges, is constructed with the usual assumption that both

areas are uniform, diffuse radiators [24]. The view factor, plus the effective radiating 

temperature of the fire plume, sets the predicted variation and absolute level of flux versus

distance along the line. Since this construction is to be used to interpolate or extrapolate the 

local flux gauge measurements, its prediction of the flux variation with distance from the near 

side of the burning object is force-fitted through the linear average flux at a point midway 

between the two gauges nearest the distance of interest (usually the outer two flux gauges). The 

force-fitting to match this midpoint is achieved by varying the effective radiator temperature. 

shows an example of the result. Note that the line calculated from the view factor does 

not go through any of the measured peak flux values at the three gauge distances from the side of 

the monitor. This is presumably a result of non-uniform radiation from the fire plume plus 

various approximations such as those mentioned above. In spite of this, the concave upward 

curvature of the line is more correct than the zero curvature of the straight line approximation. 

We use both to estimate the maximum outward reach of piloted ignition for the two surrogate 

materials described above. In cases where the estimated maximum reach is well beyond the 

outermost flux gauge (see below), the view factor based extrapolation is expected to be more 

accurate. However, given the low slope of the flux vs. distance curves in such cases, the 

Figure 31

 28
absolute accuracy of that result is probably no better than ± 25 %. It is substantially better 

(± 5% to 10 %) for cases which involve an estimated reach which falls between or very near the 

gauges. 

The line shown in relates flux and distance. When the ignition model yields a

result for the lowest flux at which a given surrogate material will just ignite, the line shows the 

maximum distance at which this can occur. The uncertainties just noted apply to this result. 

Figure 31

The cotton fabric, as noted above, is a surrogate for such items as drapes or the seat back 

of an upholstered desk chair. These two target objects could have significantly differing heat 

loss conditions on the back surface of the fabric, affecting their ignitability. Thus the upholstery 

application would typically involve polyurethane foam behind the fabric, making heat losses

there minimal. A drape, depending on its exact physical configuration (folded vs. flat) could 

have heat losses on the back of the fabric that are as much as those on the front or nearly as little 

as those for the upholstery application. Thus the results were computed for the two extremes; 

adiabatic back surface or equal back and front surface heat losses (re-radiation plus convection). 

The ignition behavior of the paper surrogate was computed with the thermally thick model using 

a 2.5 cm depth. This is thick enough that the back surface condition is irrelevant on the time 

scale required for ignition. 

Table 5 shows the computed maximum piloted ignition reach values for the cotton fabric 

and the paper. This was done only for a select set of fire tests since it is quite labor intensive.

Most of the cases reported there are for the monitor enclosures containing the pseudo-CRT

interior; the main goal is a comparison of the differing resins, plus some guidance regarding 

“acceptable” fire sizes. For both surrogate materials, reach values for both linear and view 

factor-based extrapolation/interpolation of the flux vs distance curves are reported. Again note 

that the view factor-based values are expected to be more accurate in cases involving 

extrapolation beyond the outermost flux gauge (i.e., cases in Table 5 where the reported value is 

greater than about 0.4 m to 0.43 m). 

There are several observations to be made regarding the results in Table 5. First, for the 

monitor fires, the nature of the resin made a substantial difference in maximum ignition reach.

The reported numbers show about a factor two variation. However, the best-behaved case was 

for 7-ABS-BFR for which ignition reach values could not be directly calculated (indicated by 

N.A. in Table 5). The reason for this was that the fire stopped before it propagated as far along 

the side as the flux gauge array and the peak flux values recorded even for the front flux gauge,

were less than 4 kW/m2

. Even the most ignitable surrogate case (cotton fabric with adiabatic

rear surface) required a minimum peak flux of about 8 kW/m2

 to ignite. Extrapolation of the 

available flux data imply that this would not be reached even at the monitor surface, at least in 

the vertical plane of the flux gauges. Closer to the front end of the monitor where the keyboard 

fire was forcing some burning, the ignition reach was probably finite but it was probably also 

dominated by the keyboard fire. The ignition reach for a keyboard alone is shown in Table 5 but 

this value is for gauges that view the keyboard from its front; the reach values for a side view are 

expected to be less since the radiative view factor there is less. Thus it would appear that the 

most effective resin can virtually eliminate the radiative ignition reach from a monitor fire by

essentially squelching that fire. 

Next, note the substantial differences in ignition reach for the two surrogate materials as 

well as the dependence of ignition reach on rear surface boundary conditions for the cotton

fabric. This emphasizes that the (piloted) ignition process is governed by the simple issue of 

getting (and retaining) enough energy in the surface of a material for it to generate an ignitable 

 29
gas mixture (here taken as equivalent to achieving an ignition temperature). The ignition reach 

for a layer of paper is less because that layer is a conductive heat sink pulling heat away from the

paper surface. Similarly, the cotton fabric can, in some configurations, lose a substantial portion 

of the incoming radiant heat through its rear surface; this also makes it require a higher radiant 

flux to achieve an ignitable condition and this in turn is achieved only closer to the monitor fire. 

Another factor at work in the differing material responses was the ratio of the heat flux 

peak width to the response time for heating of the sample surface. The cotton fabric was

thermally thin and sufficiently low in thermal mass to essentially follow the time-varying radiant 

flux from the monitor fire. As a result, it could ignite at fluxes as low as 8 kW/m2 which, as

implies, requires a few hundred seconds to achieve. The paper stack, with its in-depth 

conduction, has a much longer thermal response time; to compensate it required substantially 

higher minimum peak heat fluxes (typically at least 15 kW/m2

) to reach its ignition temperature6. 

Had any of these fires been shorter in duration, the minimum heat flux would have gone up and 

thus the maximum ignition reach would have decreased. 

Figure 28

The worst case situation (maximum ignition reach) is for the cotton fabric with no rear 

surface heat losses. Recall that this can be a surrogate for a folded drape or the back of an 

upholstered desk chair. The worst fires here threaten to ignite such objects from as much as 1 m

away, the more moderate fires from more than half a meter. It is not possible to make a

statement about how many secondary fires this situation would induce in the real world. One 

can only infer that the probability of a secondary fire is roughly proportional to the area 

encompassed by the ignition reach and thus to the square of the ignition reach value. Since this 

type of fire growth process is self-bootstrapping (the combined fires from primary and secondary 

objects threaten to ignite tertiary objects, etc.), it clearly is desirable to minimize the ignition

reach of the primary fire. 

The best measure of the size of a fire is its heat release rate. Typically some fraction of

the total heat being released is given off as radiation from the plume; that fraction varies with the

sooting tendency of the material burning. Thus for a simple fire geometry like a pool fire the 

radiant flux to the surroundings, for a given material, will be proportional to heat release rate. 

The fire geometries here are not simple due to the complex shape of the monitor enclosures and

especially due to the presence inside these enclosures of opaque, non-flammable materials. 

These materials effectively break the fire plume into segments and can prevent radiation from 

some segments from going in some directions. One result could be that the heat flux gauge array 

sees little of the radiation being given off by major segments of the fire. This could disrupt the 

relation between fire size and heat release rate even if the monitor enclosures were all made of

the same material. This disruption is less if the fire plume is so sooty that the radiation 

essentially all comes from those portions of the plume closest to the gauge array. All of the fire 

plumes here did appear to be very soot laden. 

Figure 32 and show the measured relation between peak heat release rate and 

maximum piloted ignition reach (for the cotton fabric with no rear surface heat losses and for 

paper, respectively). Note that one of the points on each plot is for a keyboard alone; the 

remaining points are for the monitor shells with the pseudo-CRT interiors. Note also that the 

lowest point on each plot is for the ABS-BFR monitor enclosure where, as was noted above,

specific information on ignition reach was not obtained, only a clear indication that the numbers 

were near zero. For the purposes of this plot these points have been assigned values of 0.05 m

Figure 33

 6

 Figure 29 indicates that if the heat flux was constant, as it is in the Cone calorimeter, the paper would ignite at 

fluxes as low as 11 to 12 kW/m2. 

 30
for the drape and 0.02 m for the paper as estimates of reach values that could pertain closer to 

that limited portion of the assembly that did burn. Clearly the fitted lines are not particularly

sensitive to these values, as long as they are near zero. 

While the relationship between maximum piloted ignition reach and peak heat release 

rate is not precise, for the reasons indicated above, it is sufficient to suggest that for a reasonable 

assurance that secondary ignitions will be unlikely, it is necessary to stay very near the lower left 

corner of the plots. Even a heat release rate peak of about 20 kW (here seen for the keyboard 

alone) can potentially ignite the back of an upholstered desk chair or a drape nearly 0.3 m away. 

This threat is directional for this type of source fire but one cannot assume any specific spatial 

arrangement of combustibles in the real world. It would be safest to stay well below this level of 

peak heat release rate. If the goal is set that the radiative ignition reach not exceed the 15 cm

direct flame contact reach as some monitors collapsed, then Figure 32 suggests that the peak 

HRR be kept below approximately 10 kW. 

Note that the preceding results show that the peak HRR from an electronic enclosure 

depends on the size and intensity of the ignition source. Thus it is necessary to put the object in 

context, decide on plausible ignition sources, and test the object in full-scale to find its peak 

HRR. Only then can the ignition reach results presented here pertain to a specific monitor. If the

only plausible ignition source is match-sized, and the object is not used in proximity with nonFR peripherals, then all FR resins here would be adequate since none led to a significant fire. 

 31
Table 5 Maximum Piloted Ignition Distances for 0.41 kg/m2 (12 oz/yd2) Cotton Fabric As Drapery or as Seat Cu

(Calculated With and Without Rear Surface Heat Losses)

Resin/Test Condition 

Peak HRR 

(kW)

 (Rear Loss) 

Max. Ignition 

Distance (m) 

(VF Extrap.)7

 (Rear Loss) 

Max Ignition 

Distance (m) 

(Lin. Extrap.)8

 (No Rear Loss) 

Max. Ignition 

Distance (m) 

(VF Extrap.) 

3- HIPS-NFR Monitor9 / Small 

Flame Ignition / Side View 

200 0.71 0.57 1.12 

13-PP-BFR Monitor / Keyboard Ignition / Side View 

198 0.65 0.69 0.97 

18-HIPS-NH Monitor / Keyboard Ignition / Side View 

89 0.36 0.36 0.56 

7-ABS-BFR Monitor / Keyboard Ignition / Side View 

31 N. A. N. A. N. A. 

1-PC-NH Monitor / Keyboard Ignition / Side View 

120 0.36 0.38 0.58 

1-PC-NH Monitor / Radiant Panel Ignition / Rear View

124 0.36 0.35 0.51 

Isolated Keyboard / Small Flame Ignition / Front View 

22.5 0.12 0.11 0.27 

7 Results based on flux vs. distance using a view factor-based interpolation/extrapolation. 8 Results based on flux vs. distance using a linear interpolation/extrapolation of data from two nearest flux gauges. 9 All of the monitors here used the pseudo-CRT interior. 

 32
Table 5, Cont’d. Maximum Piloted Ignition Distances for Paper.

Resin/Test Condition Peak HRR (kW) 

Max. Ignition Distance (m) 

(VF Extrap.) 

Max. Ignition Di

(Lin. Extr

3- HIPS-NFR Monitor10 / Small 

Flame Ignition / Side View 

200 0.58 0.52

13-PP-BFR Monitor / Keyboard Ignition / Side View 

198 0.56 0.62

18-HIPS-NH Monitor / Keyboard Ignition / Side View 

89 0.29 0.28

7-ABS-BFR Monitor / Keyboard Ignition / Side View 

31 N. A. N. A. 

1-PC-NH Monitor / Keyboard Ignition / Side View 

120 0.31 0.30

1-PC-NH Monitor / Radiant Panel Ignition / Rear View

124 0.26 0.29

Isolated Keyboard / Small Flame Ignition / Front View 

22.5 0.08 0.06

10 All of the monitors here used the pseudo-CRT interior. 

 33
o

Figure 28. Comparison of Cone ignition data (triangles) and ignition model (black dots) using 

indicated values of ignition temperature and thermal inertia; cotton fabric.

o

o

o

2

Figure 29. Comparison of Cone ignition data (black dots) and ignition model prediction 

(triangles) using indicated properties; paper stack. 

 34
Figure 30. Peak heat flux and flux peak width vs. distance from side of monitor; 3-HIPS-NFR;

small flame ignition. 2 

Figure 31. Measured points on flux distribution and view-factor based extrapolation curve; 

1-PC-NH monitor; keyboard fire ignition.

 35
Figure 32. Experimental relation between maximum piloted ignition reach and peak HRR from

monitor fire; Cotton fabric as ignition target (with adiabatic rear surface); Reach data are those 

based on view factor extrapolation. 

Figure 33. Experimental relation between maximum piloted ignition reach and peak HRR from

monitor fire; Paper stack as ignition target; Reach distance based on view factor extrapolation. 

 36
Modified Cone Calorimeter Tests

A distinct shortcoming of the normal Cone Calorimeter tests as applied to thermoplastic 

materials is that none of the complications of polymer melt flow are captured. The horizontal 

sample may turn to a liquid but it stays in its holder and retains the same surface area. When a 

real thermoplastic object like a computer monitor enclosure is burned the vertical and horizontal 

sides flow downward onto some lower catch surface and may partially burn there. In the process 

there can be substantial changes in the surface area per unit mass of polymer and this, plus the 

possible heat-sinking effects of catch surfaces, can have a major effect on the overall burning 

rate11. There have been only a few studies of this process [25,26,27] and currently there is no

test method which predicts the impact of this sort of complexity on the heat release rate of a

thermoplastic object. 

An attempt was made in this study to develop a test which could include some of these 

complexities within the context of the Cone Calorimeter so that their impact on heat release rate

could be measured. Thus the sample was vertical and thin (3 mm) much like a section of the side

of a monitor enclosure. The sample was heated nearly uniformly on one face by radiation from 

the Cone and, at the same time, was locally heated by a small gas flame to produce localized

ignition. The sample was free to flow downward onto a catch surface just below the vertical 

sample holder where it could possibly burn interactively with the remains of the original sample 

in its holder12. Heat release rate was measured as a function of incident radiant heat flux in

separate tests. The Cone HRR is usually reported in units of kW per unit area of the sample. 

Since the burning area is not well defined for the melt-drip tests the HRR is given in absolute

units (kW). The analogy between this test set-up and the early stages of the monitor enclosure 

tests, especially with the radiant panel, should be apparent. It also has fundamental similarities 

to the keyboard ignition scenario. 

Figure 34 shows a photo of the sample and catch pan assembly. The resin sample,

compression molded into a sheet 102 mm wide by 127 mm tall by 3 mm thick, was held on three 

sides (vertical side and top but not on the bottom) in a steel frame holding only the outer 6 mm.

The catch surface was Marinite I, a calcium silicate board, 12.7 mm thick, 76 mm deep 

(perpendicular to the irradiated sample face) and 203 mm wide; it was 30 mm below the bottom

edge of the sample. It was contained in a stainless steel pan with enough of a lip to more than 

fully contain the original resin sample volume. A 3 mm OD stainless steel tube served as an 

igniter flame holder. It pointed at the sample surface at an angle 30o from the surface normal 

from a near point of 7 mm. Methane was fed to this tube at a controlled rate of approximately 

84 cm3

/s to give a flame height against the sample surface of approximately 50 mm. Note that 

the flame impinged on the sample surface at approximately 30 mm up from its base; only the 

front face was thus ignited initially. 

This assembly was placed 100 mm from the outer lip of the Cone heater, with the sample

center on the Cone axis. This is four times the usual sample distance in the Cone, made 

necessary by the depth of the catch pan and the need to keep its outer lip somewhat away from

the Cone heater. Flux distribution data in the literature [28] imply that, at this distance, the flux 

onto the sample face falls off at the lateral edges by only about 10 % relative to that on the

 11 The surface area/unit mass may decrease substantially if the thin sheet collapses downward into a thick heap as 

happens with high viscosity resins. For low viscosity resins which also continue to burn on the catch surface, 

outward flow may be able to ultimately produce an increase in surface area/unit mass. 12 This interactive process, in which the pool fire heats the object and thereby feeds itself, can lead to strong fire 

growth; see [24]. 

 37
center; vertically it may fall off a bit more near the top but the thickened convective boundary 

layer there compensates somewhat. 

Measurements were made of the radiant flux from the Cone heater onto the catch pan 

surface. The distribution was somewhat complex. The flux was higher along the central area of

the catch surface, being at a maximum in the central area nearest the Cone. The flux fell to half 

this maximum on the outer ends of the catch surface. The center of the catch surface had a flux

of 45 % to 46 % of that falling on the center of the sample face; the outer ends of the catch 

surface had a flux of about 25 % of that on the sample face. 

Even though the sample is physically thin, it is not thermally thin. Application of the 

analytical solution for an opaque solid slab (in this case, 3 mm of polypropylene) heated on one 

face by a constant radiant flux [29] indicates that a flux of 20 kW/m2

 can cause a front-to-back

temperature gradient of 150 oC. In-depth radiation absorption will ease this gradient but one 

expects the heated face of the sample to begin to soften and/or degrade first. 

A 30 s preheat was chosen to preclude appreciable distortion of the sample prior to

application of the igniter flame. No pre-heat was used in the full-scale tests. The test sequence

was as follows. The Cone was pre-heated to a steady temperature to give a desired radiant flux 

level. The sample assembly, with the sample face protected by an insulated shield, was placed 

into position in front of the Cone. At time zero the insulating shield was removed from the 

sample face. At 30 s the methane flame was ignited. The subsequent heat release rate from the 

sample was recorded. Its physical behavior was videotaped. The burning process was followed 

until it was nearly out. In successive tests the radiant flux was set to different levels; the range

covered was 0 kW/m2

 to 30 kW/m2. 

Figure 35 and show the flux-dependent peak HRR and the total heat evolved, 

respectively, for the five resins used also in the full-scale monitor tests. The first point that

emerges from the Figures is that the measured fire behavior is highly flux dependent and the 

relative behaviors of the resins in this test change with the flux. This is not surprising. It is not 

uncommon for flame-retarded materials to perform well in isolation and then begin to burn as 

external heat is added; the strength of burning at any given external flux depends both on the 

resin and the flame retardant. Here we have the added complication of melt flow; each resin can 

be expected to have differing temperature-dependent melt viscosities and, in fact, each had a 

unique, flux-dependent tendency to sag or flow under the influence of gravity. 

Figure 36

This heat flux dependent behavior means that the results in a full-scale test, where the

radiant flux seen by a resin is position and time-dependent, will be difficult to predict. Indeed 

these tests were run well before the full-scale tests and an attempt was made to use them to

predict even the qualitative outcome as to how far a fire would spread on a monitor enclosure 

(partly, fully, not at all). The tests correctly predicted that with no added radiation, only the nonFR monitor resin (3-HIPS-NFR) would burn and it would likely burn completely. This is a 

minimal accomplishment. Beyond the zero flux case the ambiguity clearly increases. This is 

especially true when one considers the radiant flux situation in the full scale tests. With either 

keyboard ignition or radiant panel ignition, the resin nearest the heat source sees the highest flux 

but the flux decreases as the resin fire begins to spread on the monitor surfaces (only one surface 

was close to the heat source). Figure 35 indicates that each resin has a complex response to the 

decreasing flux. Without a detailed model of fire spread, it is not possible to estimate what the 

net response of a resin will be in this gradient flux situation: continued fire spread or extinction 

at some critical distance from the source. This suggests that a more appropriate predictive test 

would be a modified LIFT test (ASTM 1321) in which polymer melt flow was factored in; this 

 38
test incorporates a radiant flux gradient and focuses on opposed flow fire spread which was at the 

heart of the full-scale fires. 

Given the above discussion and the complexity of the behavior in and

, it is somewhat arbitrary to pick a flux for correlation purposes. Nevertheless a flux of 

22.5 kW/m2

 was chosen here to illustrate the extent of correlation between the Cone melt/drip

tests and the full-scale tests (in this case the tests with keyboard ignition). Figure 37 shows the

relation between the peak HRR in the full-scale tests and the peak HRR in the Cone scale tests at 

this radiant flux. The individual full-scale test results have been plotted against the average of 

the bench scale results (from two tests with each resin). While the slope of the line is

qualitatively correct, the scatter about the line is considerable. 

Figure 35 Figure 

36

Figure 34. Overall view of sample holder, local ignition source and catch pan.

 39
2

Figure 35. Peak heat release rate measured in Cone melt/drip experiments as a function of heat 

flux. 2 

2

Figure 36. Total heat release rate measured in Cone melt/drip experiments as a function of heat 

flux.

 40
y = 79.15x - 97.27

R2

 = 0.75

0

50

100

150

200

250

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Peak HRR at 22.5 kW/m2

 in Cone Melt Drip Test (kW)

Peak HR

R in Full Scale Tests with Keyboard Ignition (kW)

Figure 37. Correlation between peak HRR in Cone melt/drip experiments (at a flux of 

22.5 kW/m2

) and peak HRR in full-scale monitor tests with keyboard ignition. The open circles 

represent monitor tests using real CRT. 

 41
Bench-Scale and Full-Scale Comparison 

A summary of results from all of the bench-scale tests [2] and the full-scale monitor tests 

described in this report is shown in Table 6. The bench-scale test results are for 3.2 mm thick

samples. The full-scale peak HRR results in Table 6 represent the larger of the replicate 

measurements. Qualitatively, the UL94 vertical burn test and the melt/drip vertical Cone test at 

zero external heat flux gave the best indication of the full-scale monitor fire performance when 

exposed to the needle flame ignition source. All of the materials that self-extinguished in the 

UL94 test resisted sustained ignition in the full-scale monitor tests. 

Table 6. Comparison of Bench-Scale and Full-Scale test results. 

 

1-PC-NH 3-HIPS-NFR 7-ABS-BFR 13-PP-BFR 18-HIPS-NH 

UL94 Classification V-0 HB V-0 V-2 V-1

UL94 Mean after-flame 

time, t1+t2 (s) 1.0 34.6 0.0 8.1 19.8

Standard Cone Peak HRR 

@ 50 kW/m2

 (kW) 4.6 10.3 3.2 15.0 3.1

Cone Time to Ignition (s) 63 40 42 38 30

Glow Wire Ignition 

Temperature (o

C) 825 750 725 800 --

Melt/Drip Cone Peak HRR 

@ 0 kW/m2

 (kW) -- 5.2 -- -- --

Melt/Drip Cone Peak HRR 

@ 22.5 kW/m2

 (kW) 1.8 6.5 2.2 3.5 2.5

Full-Scale Peak HRR, 

needle flame ignition (kW) -- 208 -- -- --

Full-Scale Peak HRR, 

keyboard ignition (kW) 120 -- 44 205 115

Full-Scale Peak HRR, 

radiant panel ignition (kW) 124 240 25 193 94

The time to ignition in the Cone and the Glow Wire Ignition Temperature were the 

poorest indicators of full-scale fire performance in these tests. Although the presence of a flame 

retardant additive can cause a material to ignite faster and at a lower temperature, these factors 

did not help predict whether or not the flame would propagate once ignited. 

The peak HRR from the standard Cone Calorimeter test, ASTM E1354-99 [30], is often 

used to describe fire performance. The peak HRR from the Cone tests was not a good predictor 

of the full-scale response to the local ignition source in this study. A notable example of this is 

the polypropylene specimen (13-PP-BFR) that has a very high peak HRR in the Cone but did not 

ignite when exposed to the needle flame. In addition to examining the peak HRR, the peak HRR 

 42
extrapolated to zero heat flux (HRRo) and the Fire Growth Rate Index (FIGRA) were also

considered but did not show a large improvement in predicting the needle flame ignition fullscale response. 

The cone results compared more favorably with the full-scale monitor tests having a 

larger ignition source. The two specimens with the highest peak HRR in both the standard and 

melt/drip cone tests also produced the largest fires when exposed to the keyboard fire and radiant 

panel ignition sources. More research is needed to develop and interpret bench-scale tests 

capable of predicting full-scale performance. The most reliable existing measure is full-scale 

testing, assuming the appropriate ignition scenario can be identified. 

Difficulties of Correlating Bench-Scale and Full-Scale Fire Behaviors 

Bench-scale tests that predict full-scale fire behavior have been sought for decades in a 

variety of full-scale product contexts. Here it is worth considering in some detail the processes

occurring during the full-scale burning of an item such as a computer monitor so as to get a 

better feel for what one is asking the bench-scale test to predict. 

All of the resins considered here are thermoplastic. As a result they begin to melt and

flow downward as heat from nearby burning material reaches them. Since the typical resin

thickness is only a few millimeters, heat permeates the wall thickness in about a minute and 

those walls begin to collapse even before they begin to melt. By the time a spreading fire on a 

computer monitor housing is reaching its peak, the original geometry has been largely lost with

some melted resin material on the table support, some material draped and flowing over the inert 

components within the monitor and some material still recognizable as housing walls but 

displaced and re-oriented. Much of the exposed surface is burning. Due to the convoluted

burning surface geometry, various burning surfaces see a wide variety of radiant fluxes coming 

from the fire plume(s) and from other hot surfaces. This affects the heat release rate from each of 

these burning surfaces. In short, the peak heat release rate of this full-scale object is the sum of

the heat release from a complex distribution of burning melt surfaces (of unknown total area) 

seeing a full spectrum of heat fluxes and exposed to widely varying heat sinking effects from the 

materials on which they lay. In general, this distribution will depend on the location, size and 

intensity of the igniter, so it is not unique. 

A simple bench-scale test cannot capture all of this complexity. Extremes of behavior 

can, however, be captured. If the ignition source is small, a flame-retarded material may not 

even ignite. A test such as UL 94 easily picks up this behavior since it is, in this case, virtually a

full-scale replication of the localized ignition exposure. A material which is non flame-retarded 

can be expected to have a larger heat release rate than FR materials over much of the expected

heat flux range; then the Cone Calorimeter will tend to flag it as likely to give a high peak heat 

release rate in a full-scale test. Extremely low resin melt viscosity can lead to a large pool fire 

and a high peak heat release rate. A test that incorporates melt flow behavior may pick this up. 

All such tests may correctly sort out the resins that are very low in flammability from those that 

are very high in flammability. Most resins are more intermediate in character. A bench-scale

test that can correctly sort out the balance of resin characteristics that dictate the complete range 

of full-scale fire behavior is much more challenging. 

 43
Conclusions 

• Progressively larger and more intense ignition sources caused the burning of an 

increasing number of tested resins 

o The use of flame retardant materials (including non-halogenated) provided 

adequate protection against the needle flame that represented a “candle size” 

ignition source. The fire hazard from needle flame ignition of the enclosure 

having a non-flame-retarded material (3-HIPS-NFR) was significant and resulted

in the threat of fire spread to nearby objects. 

o The keyboard fire ignition source produced a significant fire hazard for all but one 

(7-ABS-BFR) of the monitor enclosures. 

o The radiant panel (heat flux=21 kW/m2) used to simulate an existing fire 

produced significant burning for all of the monitor specimens. 

• Several bench-scale flammability measures were assessed for ability to predict full-scale

monitor behavior with limited success. 

o The UL94 vertical burn test was a good indicator of the likelihood of the fullscale specimens to resist sustained ignition by a “candle size” flame. 

o The Cone Calorimeter test was a reasonable indictor of the response of the 

monitor specimens to ignition by a nearby burning object. 

o The Glow Wire Ignition Test was a poor indicator of the full-scale response to an 

open flame ignition source. 

o The modified Cone (melt/drip) test provided information on both self-extinction

and radiant forced burning of the materials. The predictive value of this test for

full scale peak HRR was only marginally better than the standard Cone test. 

o More research is needed to develop and interpret bench-scale tests capable of 

predicting full-scale performance. The best existing measure is full-scale testing

(if the ignition scenario is known). 

• Electronic enclosure fires pose a three-fold threat to surrounding objects 

o Direct contact with flames in the plume; flame height reached 1.5 m for some of 

the monitors in this study. 

o Flaming melt flow can reach the floor or spread on a desk surface. This threat is 

largest for low melt viscosity materials such as polypropylene. 

o Radiant ignition of remote objects 

 A 200 kW (peak HRR) fire produced a threat distance of 1.1 m for 

upholstery fabric 

 A (20 to 25) kW (peak HRR) fire produced a threat distance of 0.3 m for 

upholstery fabric 

 A peak HRR of less than 10 kW would likely produce a minimal radiant 

ignition threat to its surroundings, comparable to the threat of direct flame

contact. 

• Peripheral items (such as the keyboards in this study) are often made from non-FR 

materials and can serve as an ignition source for other items if ignited. 

 44
References

[1] M. De Poortere, C. Schonbach, and M. Simonson, The Fire Safety of TV Set Enclosure 

Materials, a Survey of European Statistics, Fire and Materials 24 (1), 53-60 (2000). 

[2] M. Bundy and T. J. Ohlemiller, Bench-Scale Flammability Measures for Electronic 

Equipment, NISTIR-7031 NIST, Gaithersburg, MD, (2003). 

[3] R. Bieniarz, Fire Experiments on Structural Foam Plastic Equipment Enclosures, File

C597 Underwriters Laboratories, (1981). 

[4] V. Babrauskas, R. G. Gann, R. H. Harris, and B. C. Levin, Fire Hazard Comparison of

Fire-Retarded and Non-Fire-Retarded Products, NBS-SP749 NBS, Gaithersburg, MD, 1-

86 (1988). 

[5] M. Simonson, Report for the Fire Testing of Computer Monitors, R31151 SP, (1999). 

[6] M. Simonson, Report for the Fire Testing of Deskjet Printers, P005848 SP, (2000). 

[7] M. Simonson, Report for the Fire Testing of One Printer and Two CPU's, P008664 SP, 

(2000). 

[8] D. Bliss and M. Simonson, Fire Performance of IT Equipment Studied in the Furniture 

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