Bench-Scale Flammability Measures 

for Electronic Equipment

Matthew Bundy

Thomas Ohlemiller

U.S. Department of Commerce

Technology Administration

National Institute of Standards and Technology

Gaithersburg, MD 20899

NISTIR 7031
 

NISTIR 7031

Bench-Scale Flammability Measures 

for Electronic Equipment

Matthew Bundy

Thomas Ohlemiller

U.S. Department of Commerce

Technology Administration

National Institute of Standards and Technology

Gaithersburg, MD 20899

July 16, 2003

U.S. DEPARTMENT OF COMMERCE

Donald L. Evans, Secretary

TECHNOLOGY ADMINISTRATION

Phillip J. Bond, Under Secretary of Commerce for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

Arden L. Bement, Jr., Director
1

BENCH-SCALE FLAMMABILITY MEASURES 

FOR ELECTRONIC EQUIPMENT 

Matthew Bundy and Thomas Ohlemiller 

National Institute of Standards and Technology, Gaithersburg, MD 

Abstract

 An experimental study of the bench-scale fire performance of 18 commercial 

polymeric materials was conducted by the National Institute of Standards and 

Technology. The performance of these materials was characterized using three standard 

flammability tests. The ignition resistance, self-extinguishing behavior, heat release rate, 

and combustion product yields for these burning materials were evaluated at two material 

thicknesses and are discussed in terms of fire safety. This report details the first of a two 

part study in which the relationship between bench-scale and full-scale fire performance 

will be examined. Several of the materials characterized in this report will be selected for 

use in the full-scale study. 

Introduction

 An experimental investigation is in progress at NIST to study the fire hazard of 

electronic equipment housed in thermoplastic enclosures. This work is part of the project 

titled “Flammability Measures for Electronic Equipment” which is funded by the NIST 

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

studying fire growth and spread on real materials. 

 Three standardized bench-scale flammability tests were used to characterize a set 

of commercially available resins. The bench scale flammability tests included the Cone 

Calorimeter test (ASTM E 1354), the UL94 vertical burn test, and the Glow Wire

Ignitability Temperature test (GWIT) (IEC 695-2-1/3). 

 The objectives of this report are to describe the bench scale tests performed, and 

to describe the results of the bench scale tests with statistical uncertainties. 

 The ultimate goal of this project is to determine the accuracy of bench scale 

material testing in predicting full-scale end product fire performance. One aspect of fire 

performance that will be addressed is the extent to which the specimen contributes to the 

propagation of fire from a candle flame to surrounding objects. Another aspect of fire 

performance that will be addressed is the response of a specimen to an existing fire. 

 

Experimental Materials

 The formulations used in this study were chosen based on industry use and flame 

retardant (FR) approach. Industry experts were consulted in choosing a set of 18 resins 

which included a variety of resin types, FR levels and FR approaches. Commercial resins 

were chosen instead of model formulations so that the effects of processing aids and other 

additives are included in the fire performance results. The compounded formulations 

were provided by four different resin manufacturers. The 18 different material 

identification labels used in this study are listed in Table 1. 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), Polypropylene (PP), 

Polyvinyl Chloride (PVC) and a PC/ABS blend. The flame retardant types include 
2

Bromine/Antimony (BFR), Phosphate (PFR), non-halogenated (NH) and no flame 

retardant (NFR). Material number 16 was not received from the supplier and was omitted 

from this study. 

Table1. List of materials used in bench-scale tests. 

1-PC-NH 7-ABS-BFR 13-PP-BFR 

2-HIPS-BFR 8-PC/ABS-PFR 14-PP-BFR 

3-HIPS-NFR 9-HIPS-BFR 15-PP-NH 

4-PC-NFR 10-PC-BFR 17-PVC-NFR 

5-PC-BFR 11-PP-BFR 18-HIPS-NH 

6-PC/ABS-NFR 12-PP-NH 19-ABS-NH 

Bench-Scale Tests

UL94 Vertical Burn Test 

 The UL94 horizontal and vertical burn tests are the U.S. industry standard 

flammability tests for selecting materials to be used as enclosures for electronic 

equipment. The UL94 vertical burn test was used for this study. This test is a measure of 

a specimen’s resistance to self-sustained ignition in an upward flame spread 

configuration. The test was designed to simulate a short duration ignition source such as 

an internal electric fault. The test is not designed to predict full scale fire performance. 

The test results reported here were obtained by Underwriters Laboratories at the 

Melville, NY facility. 

 The ignition source for this test consisted of a 50 W premixed methane-air flame 

produced by a standard laboratory Bunsen burner (ASTM D5025 Burner @ 105 ml / min. 

flow rate). The test flame was calibrated according to standard practice (ASTM 5207-

98). The test flame was entirely blue in color and approximately 20 mm in height. Prior 

to each test the specimen was mounted in a vertical position, 30 cm above a piece of 

loose cotton on the floor of the test chamber. 

 All UL94 test specimens were injection molded by the supplier. Each specimen 

had length of 125 ± 5 mm and width of 13 ± 0.5 mm. The thickness of each specimen 

was 1.6 ± 0.1 mm or 3.2 ± 0.1 mm. 

The flame was applied such that the top of the burner barrel was ~10 mm below 

the lower edge of the sample, as shown in figure 1. The test operator adjusted the 

position of the flame during the application such that the separation distance was 

maintained as the specimen receded and or deformed (some of the specimens used in this 

study tended to curl when heated by the 

flame). The burner was tilted at a 45 

degree angle when necessary to prevent 

dripping particles from entering the barrel 

of the burner. The flame was applied for 

10 seconds and removed from the 

specimen. The amount of time that the 

specimen continues to burn (visible 

flames) after the removal of the burner 

flame was recorded as the after-flame 

time, t1. If t1 was less than 30 seconds, the 

flame was immediately reapplied to the Figure 1. Standard 50 W UL94 test flame applied to 

specimen in vertical burn test. 
3

specimen for 10 seconds and removed. The second after-flame time was recorded as t2. 

If the after-flame time (t1 or t2) reached 35 seconds, the flaming specimen was manually 

extinguished. If the specimen continued to smolder after it self-extinguished, the 

afterglow time was recorded as t3. The afterglow time was zero for all of the tests 

reported here. Additional footnotes were used to denote whether or not dripping material 

was observed, and if dripping material ignited the cotton indicator. The standard UL test 

data sheet includes a record of specimen thickness, width and color. The specimen 

weight before and after the test and the measured burn length were also recorded for 

these tests. The burn length was defined as the difference between the original specimen 

length and post-burn undamaged specimen length. 

To attain a UL94 classification each test was repeated five times, per thickness, 

per conditioning set. The two different sample conditioning requirement sets are defined 

as follows. The “normally conditioned” set of specimens was conditioned at 23 ± 2 °C 

and 50 ± 5 % relative humidity for at least 48 hours. The “thermally conditioned” set of 

specimens was conditioned at 70 ± 1 °C for 168 hours, and then placed in a desiccator 

with less than 20 % relative humidity for a minimum of 4 hours. The high temperature 

conditioning is intended to simulate the effects of material aging over the normal lifetime 

of the material. 

 The criteria for V-rated classification are listed below. In addition to the 

requirements listed below, the specimen should not burn up to the holding clamp for a V0, V-1 or V-2 classification. If the specimen does not satisfy these criteria, it will be 

described as V-fail or V-not. Although the horizontal burn test was not performed in this 

study, it can be assumed that the V-not specimens are classified as HB based on product 

information from the manufacturers. 

V-0 classification: 

a) The after-flame time, t1 or t2, for each individual specimen is less than 10 seconds. 

b) The total after-flame time for any condition set (t1 + t2 for the 5 specimens) is less than 

50 seconds. 

c) The cotton indicator is not ignited by flaming particles or drops. 

V-1 classification:

a) The after-flame time, t1 or t2, for each individual specimen is less than 30 seconds. 

b) The total after-flame time for any condition set (t1 + t2 for the 5 specimens) is less than 

250 seconds. 

c) The cotton indicator is not ignited by flaming particles or drops 

V-2 classification: 

a) The after-flame time, t1 or t2, for each individual specimen is less than 30 seconds. 

b) The total after-flame time for any condition set (t1 + t2 for the 5 specimens) is less than 

250 seconds. 

c) The cotton indicator is ignited by flaming particles or drops. 

Cone Calorimeter Test 

 Heat release rate per unit area, mass loss, and smoke yield measurements for each 

of the 18 materials were performed using the Cone Calorimeter at NIST. The total heat 

release rate of a fire is important because it defines its size and potential hazard. Heat 

release rate per unit area, as measured in the Cone Calorimeter, has been used 

successfully for some situations to predict full scale fire growth and behavior. 
4

Heat release calculations were 

based on the oxygen consumption 

principle which states that for complete 

combustion of a wide range of fuels, 13.1 

(± 5 %) kJ of energy is produced for every 

1 gram of oxygen consumed by the fire. 

This calculation required the measurement 

of oxygen concentration and mass flow 

rate in the exhaust duct. The oxygen was 

measured using a paramagnetic analyzer 

and the exhaust mass flow rate was 

calculated based on measurements from a 

thermocouple and the pressure differential 

across an orifice plate located downstream of the gas sampling ring and exhaust blower. 

The specimen mass loss rate was calculated at each time scan using a five point 

numerical differentiation of the load cell output. Additional measurements of carbon 

dioxide, carbon monoxide and smoke in the exhaust duct were performed. These 

measurements were used in calculating combustion product yields, but not in the heat 

release rate calculation. 

The cone specimens were 10 ± 0.1 cm in diameter and 1.6 ± 0.1 mm or 3.2 ± 0.1 

mm in thickness. All of the specimens were conditioned at 50 ± 5 % relative humidity 

and 23 ± 3 °C for a minimum of 48 hours. The cone heater was positioned 25 mm above 

the horizontal specimens. The cone heater temperature was adjusted to impose the 

required heat flux at the surface of the specimen. The heat flux calibration was 

performed using a water cooled Schmidt-Boelter type flux meter with an accuracy of ± 3 

%. The specimens were placed in a round aluminum foil pan with a lip of 5 mm above 

the top surface of the sample. The samples were then placed on a low density ceramic 

wool lined sample pan and mounted on the load cell in the test chamber as shown in 

Figure 2. A cone radiation shutter was used to shield the specimen from heat prior to the 

start of the test. A standard calibration burner (as specified in ASTM E1354) was used to 

calibrate the heat release rate measurements on each test day using research grade 

methane (99.5% purity). The description of the apparatus and procedures are in 

accordance with ASTM E1354 -02d with the exception of using round instead of square 

specimens. 

Glow Wire Ignition Temperature Test 

Glow Wire Ignition Temperature tests (in accordance with UL 746A) were 

performed at Underwriters Laboratories in Melville, NY for 16 of the 18 materials 

described previously. The test sample size and shape were the same as described for the 

Cone Calorimeter tests. The specimens were conditioned at 23 ± 2 °C and 50 ± 5 % 

relative humidity for at least 40 hours. 

 The “glow wire” ignition source was a 4 mm diameter chrome-nickel alloy coil 

imbedded with a type-K thermocouple. The temperature of the wire, as measured by the 

thermocouple, was controlled by adjusting the voltage applied across the length of the 

wire. The specimen was mounted to a carriage in the vertical position. A pulley and 

counterweight were used to bring the specimen into contact with the glow wire, such that 

Figure 2. Cone Calorimeter test at 50 kW/m2 .
5

the contact force was 1 ± 0.2 N, for a duration of 30 ± 1 s. For each of the specimens 

considered here the glow wire tip penetrated through the material surface to a depth of 7 

mm (through the back side of the specimen). The temperature was set to the desired 

value, in increments of 25 °C, and maintained within 2 °C for 60 s prior to contact with 

the specimen. 

The Glow Wire Ignitability Temperature (GWIT) - in accordance with IEC 

695-2-1/3, is defined as the temperature (in degrees C), which is 25 °C hotter than the 

maximum temperature of the tip of the glow-wire which does not cause ignition of the 

material during three subsequent tests. Ignition is defined as the appearance of flames on 

the surface of the specimen for at least 5 s. 

The Glow Wire Flammability Temperature (GWFT) - in accordance with IEC 

695-2-1/2, is defined as the highest temperature (in degrees C) at which, during three 

subsequent tests, flaming or glowing of the test specimen extinguish within 30 seconds 

after removal of the glow-wire without ignition of the indicator by burning drops of 

material. 

The maximum glow wire temperature (GWT) is 960 °C. The initial temperature 

of the glow wire was set to 750 °C for each set of tests. The following two examples 

demonstrate the search routine used to determine the test results for a particular material. 

The after-flame time is defined as the time to self-extinguishment after the 30 s glow wire 

application. Note that in the second example the material self-extinguished at a GWT of 

750 °C, however to establish the GWFT the test was conducted at the maximum 

temperature of 960 °C. Between 5 and 12 specimens were required for each set of tests. 

Example of sequence of glow wire temperatures (GWT) for two typical tests: 

______________________________________________________________________ 

GWT (°C) ignition After-flame time (s)

750 no -- 

800 yes 30+ 

775 no -- 

775 no -- 

775 no -- → result: GWIT=800 °C, GWFT=775 °C

 

________________________________________________________________________

750 yes 4 

700 yes 7 

650 no -- 

675 yes 5 

650 no -- 

650 no -- 

650 no -- → result: GWIT=675 °C

960 yes 8 

960 yes 2 

960 yes 6 → result: GWFT=960°C 

________________________________________________________________________
6

Results and Discussion

UL94 vertical flame test 

The UL94 testing was performed by one UL technician over a period of several 

months. In order to obtain a representation of the measurement reproducibility associated 

with this test the specimen order was randomized. A summary of the UL94 results is 

listed in table 2. The results summarized in table 2 represent a total of almost 3 hours of 

total flame application and after-flame burn time for all of the 350 specimens combined. 

The flame classification was based on the test results of 10 specimens (5 

specimens per conditioning set). For 15 of the 18 materials tested, the flame 

classification did not change as the specimen thickness increased from 1.6 mm to 3.2 

mm, however the average after-flame time was consistently less for the thicker 

specimens. For all of the materials considered here, the classification can be determined 

from the maximum after-flame time, and the footnotes. The footnotes apply to each test 

specimen; therefore multiple footnotes are listed for some materials where the behavior 

varied within the set of 10 specimens. 

The effect of sample conditioning on the total after-flame time is shown in table 

2; see total flame times for the two conditioning sets. Although the flammability of 

several of these materials was affected by conditioning, these results do not show any 

significant general trends and no classification was affected by conditioning. This was 

not unexpected, since the effects of thermal aging and water absorption can have 

competing effects on flammability which can vary with resin type and FR type. 

The mean after-flame times and burn lengths for each material and thickness are 

listed in table 2 and shown with standard uncertainty bars in figures 2 and 3. The 

uncertainties listed are based on the standard deviation of the ten total measurements for 

each specimen. These results indicate that a large range of self-extinguishing behavior 

was observed for these materials. Note that increased sample thickness usually shortened 

the mean after-flame time and changed the V-rating of some resins. The UL94 test is 

thickness sensitive since the 10 s flame exposure time leaves a non-uniform temperature 

profile in the sample depth. Thicker samples then pose more of a heat sink to the nascent 

flames, making then less likely to self-sustain. 

The materials that were classified V-2 ignited the cotton indicator for at least one 

of the specimens tested. The behavior of the flaming particles from the specimen varied 

for different materials. Some V-2 specimens (such as 11-PP-BFR) had low viscosity 

flaming drips that fell at fairly regular intervals. Some other V-2 specimens (such as 4-

PC-NFR) had a highly viscous drip of flaming material break off and immediately 

extinguish the flame. The later of the two behaviors was less repeatable; however, in 

both cases the melt/drip event had an apparent impact on the extinguishment of the 

specimen. 
7

Table 2. Summary of Results from UL94 Testing. Sample Identification Color Thickness(mm) Flame Classification Max. after-flame time (s) Total t1+t2 (s) 48h-23C Total t1+t2 (s) 168h-70C 

Mean total after-flame time (t1+t2 ) (s) Mean Burn Length (mm) Footnotes 

1-PC-NH white 1.6 V-2 18 73 63 13.6 ± 5.1 44 ± 10 2,4 

2-HIPS-BFR black 1.6 V-0 3 4 5 0.9 ± 1.0 38 ± 13 2 

3-HIPS-NFR white 1.6 V-not 35 157 175 33.2 ± 5.4 125 ± 3 4 

4-PC-NFR clear 1.6 V-2 14 54 85 13.9 ± 6.2 30 ± 5 4 

5-PC-BFR tan 1.6 V-0 3 6 4 1 ± 1.1 35 ± 6 2 

6-PC/ABS-NFR black 1.6 V-not 35 175 175 35 ± 0.0 104 ± 16 4 

7-ABS-BFR white 1.6 V0 3 6 1 0.7 ± 1.1 44 ± 11 2 

8-PC/ABS-PFR white 1.6 V-2 15 50 30 8 ± 4.6 60 ± 8 2,4 

9-HIPS-BFR white 1.6 V-2 11 59 52 11.1 ± 6.6 43 ± 13 3,4 

10-PC-BFR black 1.6 V-0 5 21 10 3.1 ± 1.9 21 ± 6 2,3 

11-PP-BFR white 1.6 V-2 0 0 0 0 ± 0.0 19 ± 7 3,4 

12-PP-NH white 1.6 V-not** 31 59 58 11.7 ± 7.6 34 ± 21 2,3,4 

13-PP-BFR white 1.6 V-2 4 13 20 3.3 ± 1.7 24 ± 8 4 

14-PP-BFR white 1.6 V-2 16 5 32 3.7 ± 4.9 23 ± 10 4 

15-PP-NH white 1.6 V-0 5 8 7 1.5 ± 1.6 25 ± 13 2,3 

17-PVC-NFR black 1.6 V-0 4 12 12 2.4 ± 1.2 26 ± 9 2 

18-HIPS-NH black 1.6 V-1 27 106 117 22.3 ± 7.7 59 ± 13 2 

19-ABS-NH black 1.6 V-not** 35 148 79 22.7 ± 10.2 68 ± 7 2 

1-PC-NH white 3.2 V-0 2 6 4 1 ± 0.8 19 ± 4 2 

2-HIPS-BFR black 3.2 V-0 2 2 1 0.3 ± 0.7 12 ± 3 2 

3-HIPS-NFR white 3.2 V-not 35 175 171 34.6 ± 1.3 52 ± 9 4 

4-PC-NFR clear 3.2 V-2 15 30 59 8.9 ± 4.1 14 ± 3 4 

5-PC-BFR tan 3.2 V-0 2 2 4 0.6 ± 0.8 14 ± 2 2 

6-PC/ABS-NFR black 3.2 V-not 35 175 175 35 ± 0.0 45 ± 13 4 

7-ABS-BFR white 3.2 V-0 0 0 0 0 ± 0.0 17 ± 4 2 

8-PC/ABS-PFR white 3.2 ------ 

9-HIPS-BFR white 3.2 V-2 11 26 37 6.3 ± 3.8 21 ± 8 2,4 

10-PC-BFR black 3.2 V-0 2 8 7 1.5 ± 0.5 14 ± 6 2 

11-PP-BFR white 3.2 V-2 0 0 0 0 ± 0.0 14 ± 8 3,4 

12-PP-NH white 3.2 V-0 3 1 3 0.4 ± 1.0 9 ± 5 2 

13-PP-BFR white 3.2 V-2 22 52 29 8.1 ± 6.9 19 ± 4 3,4 

14-PP-BFR white 3.2 V-2 7 18 11 2.9 ± 2.2 19 ± 4 4 

15-PP-NH white 3.2 V-0 0 0 0 0 ± 0.0 9 ± 3 2 

17-PVC-NFR black 3.2 V-0 2 6 3 0.9 ± 0.9 17 ± 4 2 

18-HIPS-NH black 3.2 V-1 27 100 98 19.8 ± 9.1 23 ± 7 2 

19-ABS-NH black 3.2 V-1 20 57 63 12 ± 6.6 32 ± 5 2 

** Only 1 of the ten specimens failed V-classification 

footnotes:

(2) Specimen did not drip 

(3) Specimen dripped particles which did not ignite cotton 

(4) Specimen dripped particles which ignited cotton 
8

0

5

10

15

20

25

30

35

40

45

7-ABS-BFR

2-HIPS-BFR

5-PC-BFR

15-PP-NH

17-PVC-NFR

10-PC-BFR

18-HIPS-NH

11-PP-BFR13-PP-BFR14-PP-BFR

8-PC/ABS-PFR

9-HIPS-BFR

1-PC-NH

4-PC-NFR

12-PP-NH

19-ABS-NH

3-HIPS-NFR

6-PC/ABS-NFR

Mean after-flame time, t1+ t2, (s)

V-0

V-1

V-2

V-not

Figure 3. UL94 mean after-flame times for 1.6 mm specimens. 

0

5

10

15

20

25

30

35

40

7-ABS-BFR

15-PP-NH

2-HIPS-BFR

12-PP-NH

5-PC-BFR

17-PVC-NFR

1-PC-NH

10-PC-BFR

19-ABS-NH

18-HIPS-NH

11-PP-BFR14-PP-BFR

9-HIPS-BFR

13-PP-BFR

4-PC-NFR

3-HIPS-NFR

6-PC/ABS-NFR

Mean after-flame time, t1+ t2, (s)

V-0

V-1

V-2

V-not

Figure 4. UL94 mean after-flame times for 3.2 mm specimens. 
9

Cone Calorimeter 

The results from Cone Calorimeter measurements for material 3-HIPS-NFR at a 

cone heat flux level of 50 kW/m2 are shown in figures 5 and 6. These data were acquired 

at 3 second intervals, with time zero equal to the opening of the cone shutter. The heat 

release rate and mass loss rate profiles shown in figure 5 are represented per unit surface 

area of the specimen, As=0.00785 m2

. The smoke extinction coefficient, k (1/m), was 

calculated by measuring the transmission of visible light in the exhaust duct, k = ln(I / Io) 

/L. The CO and CO2 yields shown in figure 6 represent the mass of combustion product 

species per unit mass of fuel consumed. 

A summary of the Cone results at an external heat flux of 50 kW/m2 is listed in 

table 3a. Each of the values in Table 3a represents an average of three replicate 

measurements. The type A standard uncertainty listed for each of the values represents 

the statistical measurement repeatability. In addition, the type B uncertainties are given 

for the peak heat release rates. These values were calculated using the results of a 

ASTM/ISO study that described the lab to lab reproducibility of the peak heat release rate 

as, 141 max R = 60.4 + 0. q&′′ , using a linear regression model and results from a set of interlaboratory trials. For three of the materials considered here the peak heat release rate was 

greater than 1500 kW/m2 (or ~12 kW). The flame height above this heat release rate 

level can exceed the height of the exhaust hood and the accuracy of these measurements 

is not well characterized. For these 3 materials the total time above this threshold was 

less than 20% of the total test time. It should be noted that these results represent a 

forced flaming scenario and are not representative of heat release for a material in a freeburning scenario. The UL94 test is more akin to a single item free burning scenario. 

The values in table 3b represent the products of combustion per mass of specimen 

consumed. The mean effective heat of combustion is defined as the total heat release 

divided by the total specimen mass. To compare the amount of smoke generated by 

different burning materials it is useful to define an average specific extinction area, σf = 

k V / mf, where k is the average extinction coefficient, V is the total exhaust volume and 

mf is the total mass loss of the specimen. A specific extinction area can also be defined 

in terms of the mass of the smoke particulate, σs. It has been observed (Mulholland and 

Croarkin, 2000) that for a wide range of materials, within a 95% confidence level, σs = 

8.7 ± 1.1 m2

/g. Therefore, the smoke yield can be determined by, Ys = σf / σs. 

A comparison of peak heat release rate, at 50 kW/m2

 irradiance, and UL94 mean 

after-flame time is shown graphically for all 18 materials in figure 7. It is evident from 

this plot that a strong correlation between these two measurements does not exist. Several 

V2 rated materials exhibited a very large heat release rate (HRRpeak,50 > 1500 kW/m2

) and 

a short after-flame time in the UL94 test (t1+t2,max < 10 s). This suggests that mass loss in 

the UL94 vertical flame test due to melting can be an important mechanism for flame 

extinguishment (and it has no counterpart in a horizontal Cone test). Conversely several 

materials with relatively low heat release rate (HRRpeak,50 < 500 kW/m2

) performed 

poorly in the UL94 test (t1+t2,max > 30 s). 

Additional Cone measurements were performed at heat flux levels of 30, 50 and 

90 kW/m2

 using the 3.2 mm thick specimens. The results of these tests for all 18 

materials are summarized in table 4. Each of these values represents a single 

measurement. Note that, because the heat release rate dependence on heat flux differs 
10

among the resins, the relative rankings of the resins by heat release rate can change with 

flux level. 

A steady state energy balance at the surface of the fuel can be used to predict the 

functional relationship between external heat flux, qext &′′ , and heat release rate, HRR, of the 

material. In the following equation q flame &′′ is the surface heat flux from the flame, qrad &′′ is 

the net radiative heat flux at the surface, mf & ′′ is the fuel mass loss rate, Lg is the heat of 

gasification and ∆hc.eff is the effective heat of combustion. 

qnet qext q flame qrad mf Lg &′′ = &′′ + &′′ − &′′ = &′′ ⋅ , HRR mf ∆hc.eff = & ′′ ⋅ 

0

. . q HRR

L

h

L

h q HRR ext

g

c eff

g

c eff net ⋅ ′′ +

∆ = ∆ ⋅ ′′ = & & (1) 

Although several simplifying assumptions were made in this analysis, the result 

can be used as a first order predictor of heat release rate as the external heat flux goes to 

zero. The unforced peak heat release rate, HRR0, for each material is plotted in figure 8, 

and grouped by UL94 classification. 

Note that many of these resins may not burn at all as the external heat flux is 

reduced to small values. HRR0 is the intercept of a plot made in accord with eqn. (1). 

HRR0 contains the difference between the flame heat flux and the surface re-radiation 

and, as such, can be viewed as a measure of the net driving force that the flame provides. 

Figure 8 suggests that HRR0 may correlate somewhat better with UL94 rating than does 

peak HRR at one specific flux (i.e. 50 kW/m2

). 

The error bars in figure 8 represent the standard error associated with the three 

point linear regression analysis of the data. There are several possible reasons why a 

linear relationship between qext &′′ and HRR may not be observed, including measurement 

uncertainty and unsteady burning. In addition, the assumption of a constant q flame &′′ and 

∆hc,eff may not be valid. 

An unsteady heat transfer analysis of thermally thick fuels heated by a constant 

surface heat flux yields the following well-known relationship between ignition delay 

time, tign, and incident heat flux, qext &′′ . Tign is the surface ignition temperature, Ta is the 

ambient temperature (and initial fuel temperature), and kρc is a term which contains 

material properties of the solid fuel and is sometimes called the “thermal inertia” or 

“thermal response parameter”. The minimum heat flux for ignition is qcritical &′′ .

2

4 



 





′′ − ′′

− =

ext critical

ign a

ign q q

k c T T

t & &

ρ

π

 (2) 

The main assumption in this expression is that the material is thermally thick. By 

definition, thermally thick means the heat transfer to the solid is independent of sample 

thickness and thermally thin means that the temperature is uniform within the solid. 

Most of the specimens considered here are somewhere in between these two limiting 

cases. Equation (2) can be rewritten to show a linear relationship between ign 1 and t

qext &′′ . A three point linear regression analysis was used to predict the external heat flux for 

sustained ignition at an arbitrary fixed time of 300 s. The results of this analysis are 
11

given in table 4 and plotted in figure 9 with uncertainty bars representing the combined 

standard uncertainty based on a propagation of error analysis. Of all the materials 

considered here the 4 polycarbonate resins had the highest ignition resistance as defined 

in this manner. Specimen 12-PP-NH exhibited the shortest ignition delay time at 30 

kW/m2

. The calculated heat flux of 1.2 kW/m2 for ignition at 300 s is not physically 

realistic for this material, possibly because the assumption of infinite thickness may break 

down at very low external heat flux levels. 
12

-

200

400

600

800

1,000

1,200

1,400

- 50 100 150 200 250

Time (s)

Heat Release Rate (kW/m^2)

-

10

20

30

40

50

60

Mass Loss (g/s m^2), Smoke Ext. Coeff. (1/m)

Heat Release Rate

Mass Loss Rate

Smoke Extinction

Coefficient

Figure 5. Cone Calorimeter measurements for material 3-HIPS-NFR, 3.2 mm thickness. 

Cone heater flux = 50 kW/m2

. 

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 20 40 60 80 100 120 140 160

Time (s)

CO2 Yeild (g/g)

0

0.05

0.1

0.15

0.2

0.25

0.3

CO Yeild (g/g)

Y_CO2

Y_CO

Figure 6. Cone Calorimeter measurements for material 3-HIPS-NFR, 3.2 mm thickness. 

Cone heater flux = 50 kW/m2

.
13

Table 3a. Summary of results from Cone Calorimeter tests at 50kW/m2 flux level. 

Sample Identificationcolor Thickness (mm) Peak Heat Release Rate (kW/m2) 

Std. Uncertainty (type A) Std. Uncertainty (type B) Total Heat Release (MJ/m2

)

Std. Uncertainty (type A) Time to Ignition(s) Std. Uncertainty (type A) Time to Peak HRR (s) Std. Uncertainty (type A) 

1-PC-NH white 1.6 829 17 177 38.8 1.0 46 2.5 70 0 

2-HIPS-BFR black 1.6 318 41 105 23.8 0.4 33 8.8 90 10 

3-HIPS-NFR white 1.6 723 15 162 59.5 0.7 30 8.2 103 10 

4-PC-NFR clear 1.6 885 33 185 37.5 0.9 77 4.8 96 2 

5-PC-BFR tan 1.6 378 21 114 35.2 1.6 51 11.5 79 13 

6-PC/ABS-NFR black 1.6 543 34 137 44.4 1.7 34 3.0 67 5 

7-ABS-BFR white 1.6 312 6 104 21.0 1.2 42 7.4 80 11 

8-PC/ABS-PFR white 1.6 388 47 115 35.0 2.3 45 1.0 88 5 

9-HIPS-BFR white 1.6 502 94 131 33.8 1.0 41 10.3 97 3 

10-PC-BFR black 1.6 280 20 100 45.9 1.5 39 2.8 185 21 

11-PP-BFR++ white 1.6 1833 142 319 60.3 3.5 37 1.3 87 3 

12-PP-NH white 1.6 320 25 105 67.0 11.4 16 1.9 85 3 

13-PP-BFR++ white 1.6 1663 219 295 73.5 5.6 33 1.8 91 10 

14-PP-BFR++ white 1.6 2190 430 369 69.8 3.6 34 2.8 79 3 

15-PP-NH white 1.6 583 40 143 28.9 1.2 32 0.9 63 6 

17-PVC-NFR black 1.6 206 19 89 31.2 1.0 28 0.1 36 3 

18-HIPS-NH black 1.6 313 24 105 42.2 0.3 34 4.0 83 9 

19-ABS-NH black 1.6 282 11 100 37.6 0.8 28 1.0 78 7 

1-PC-NH white 3.2 586 43 143 82.3 2.7 63 7.9 133 52 

2-HIPS-BFR black 3.2 428 58 121 42.2 2.1 33 0.9 85 3 

3-HIPS-NFR white 3.2 1307 17 245 122.3 1.5 40 6.8 113 3 

4-PC-NFR clear 3.2 628 53 149 72.8 2.7 101 7.2 145 3 

5-PC-BFR tan 3.2 350 41 110 73.4 3.2 62 1.5 109 8 

6-PC/ABS-NFR black 3.2 741 38 165 87.5 3.3 42 2.7 81 3 

7-ABS-BFR white 3.2 409 22 118 40.4 0.9 42 4.5 115 29 

8-PC/ABS-PFR white 3.2 524 86 134 69.4 2.4 52 2.1 96 2 

9-HIPS-BFR white 3.2 985 124 199 62.0 2.2 46 5.1 127 14 

10-PC-BFR black 3.2 301 17 103 77.5 4.8 47 4.7 368 15 

11-PP-BFR++ white 3.2 2255 252 378 121.6 0.3 47 6.5 147 12 

12-PP-NH white 3.2 364 17 112 125.1 2.2 19 2.1 261 15 

13-PP-BFR++ white 3.2 1916 178 331 129.9 3.6 38 3.7 138 11 

14-PP-BFR++ white 3.2 2209 403 372 130.4 15.8 33 1.5 128 12 

15-PP-NH white 3.2 422 12 120 60.0 1.2 43 0.5 69 3 

17-PVC-NFR black 3.2 223 12 92 48.8 2.3 25 1.9 35 6 

18-HIPS-NH black 3.2 398 13 117 67.5 1.1 30 0.6 87 10 

19-ABS-NH black 3.2 328 18 107 67.7 1.4 33 3.2 49 4 ++ HRRpeak > 12 kW (1540 kW/m2

), above calibrated range of calorimeter. 
14

Table 3b. Summary of results from Cone Calorimeter tests at 50kW/m2 flux level 

Sample Identification

color Thickness (mm) Mean Effective Heat of Combustion (kJ/g) Std. Uncertainty (type A) Mean Specific Extinction Area (m2/kg) 

Std. Uncertainty (type A)

Mean CO2 Yield (g/g) 

Std. Uncertainty (type A) Mean CO yield (g/g) Std. Uncertainty (type A) 

1-PC-NH white 1.6 23.6 0.6 1072.0 64.6 2.19 0.08 0.06 0.003 

2-HIPS-BFR black 1.6 12.3 0.2 2624.0 210.5 0.59 0.03 0.15 0.008 

3-HIPS-NFR white 1.6 33.9 0.6 1578.2 123.4 2.63 0.08 0.07 0.001 

4-PC-NFR clear 1.6 24.0 0.7 1043.0 86.2 2.28 0.08 0.06 0.003 

5-PC-BFR tan 1.6 22.3 2.2 1416.0 146.8 1.88 0.12 0.08 0.001 

6-PC/ABS-NFR black 1.6 29.7 4.9 1385.8 247.6 2.24 0.08 0.05 0.005 

7-ABS-BFR white 1.6 13.9 4.2 2924.5 850.2 0.50 0.10 0.13 0.008 

8-PC/ABS-PFR white 1.6 20.6 1.4 1433.2 108.7 1.75 0.07 0.09 0.003 

9-HIPS-BFR white 1.6 16.4 1.8 2518.7 342.5 0.93 0.09 0.13 0.015 

10-PC-BFR black 1.6 21.2 1.0 1103.4 128.8 1.88 0.10 0.06 0.004 

11-PP-BFR white 1.6 41.0 3.0 1027.4 148.5 2.30 0.06 0.15 0.012 

12-PP-NH white 1.6 41.7 7.2 716.0 30.8 2.63 0.10 0.05 0.011 

13-PP-BFR white 1.6 65.3 11.4 1195.2 233.9 2.98 0.12 0.09 0.006 

14-PP-BFR white 1.6 43.1 1.2 833.8 5.3 2.80 0.16 0.12 0.008 

15-PP-NH white 1.6 15.3 0.1 1396.9 47.4 0.62 0.02 0.15 0.005 

17-PVC-NFR black 1.6 13.1 0.3 960.3 13.0 0.84 0.07 0.07 0.002 

18-HIPS-NH black 1.6 22.3 0.3 1715.6 205.3 1.55 0.03 0.10 0.002 

19-ABS-NH black 1.6 21.0 0.4 1931.1 75.5 1.37 0.05 0.13 0.000 

1-PC-NH white 3.2 24.0 0.9 1100.4 146.2 2.21 0.07 0.06 0.002 

2-HIPS-BFR black 3.2 11.4 0.6 2434.1 139.5 0.56 0.02 0.13 0.007 

3-HIPS-NFR white 3.2 36.3 1.0 1408.7 70.3 2.94 0.07 0.08 0.001 

4-PC-NFR clear 3.2 22.4 0.9 1049.5 94.5 2.08 0.08 0.05 0.003 

5-PC-BFR tan 3.2 21.9 1.0 1217.0 66.0 2.00 0.10 0.07 0.005 

6-PC/ABS-NFR black 3.2 27.2 0.7 1163.5 94.8 2.22 0.13 0.05 0.004 

7-ABS-BFR white 3.2 11.2 0.3 2415.5 141.7 0.53 0.03 0.13 0.005 

8-PC/ABS-PFR white 3.2 21.7 0.6 1484.6 127.8 1.87 0.05 0.09 0.003 

9-HIPS-BFR white 3.2 18.6 1.1 2036.9 202.0 1.03 0.02 0.14 0.006 

10-PC-BFR black 3.2 22.6 1.3 1005.9 132.8 2.05 0.10 0.06 0.003 

11-PP-BFR white 3.2 38.1 1.2 998.9 31.4 2.20 0.10 0.16 0.011 

12-PP-NH white 3.2 40.0 0.9 653.9 40.8 2.82 0.08 0.05 0.008 

13-PP-BFR white 3.2 47.7 6.4 857.8 85.5 2.99 0.19 0.08 0.004 

14-PP-BFR white 3.2 43.6 4.4 886.3 93.7 2.67 0.07 0.13 0.009 

15-PP-NH white 3.2 16.6 0.3 1625.1 84.0 0.66 0.02 0.15 0.002 

17-PVC-NFR black 3.2 14.0 0.6 974.3 49.8 0.92 0.03 0.08 0.010 

18-HIPS-NH black 3.2 21.5 0.5 1821.3 86.7 1.47 0.04 0.10 0.001 

19-ABS-NH black 3.2 22.2 0.3 1965.4 45.3 1.46 0.03 0.13 0.003 
15

0

500

1000

1500

2000

2500

3000

0 5 10 15 20 25 30 35 40 45

UL94 Average After-Flame Time, t1+t2 (s)

Cone Calorimeter Peak HRR (kW/m2

)

V-0, thk=1.6 mm

V-1, thk=1.6 mm

V-2, thk=1.6 mm

V-fail, thk=1.6 mm

V-0, thk=3.2 mm

V-1, thk=3.2 mm

V-2, thk=3.2 mm

V-fail, thk=3.2 mm

Figure 7. Comparison of peak heat release rate at 50 kW/m2 irradiance and UL94 afterflame time. 

Table 4. Summary of results from Cone Calorimeter, 3.2 mm thick specimens. 

Sample 

Identification

Peak Heat Release 

Rate (kW/m2

) 

60 s Average Heat 

Release Rate 

(kW/m2

)

Time To 

Sustained 

Ignition (s) 

Heat Flux for 

300 s 

Sustained 

Ignition 

(kW/m2

) 

Irradiation (kW/m2) 30 50 90 30 50 90 30 50 90 

1-PC-NH 576 531 532 333 385 388 193 67 17 26.0 

2-HIPS-BFR 304 461 566 162 283 388 87 31 9 17.2 

3-HIPS-NFR 1108 1265 1623 739 734 1051 151 50 16 21.0 

4-PC-NFR 734 703 984 494 523 644 500 129 40 35.7 

5-PC-BFR 321 343 437 168 240 311 260 78 24 27.5 

6-PC/ABS-NFR 850 790 762 506 530 530 137 56 21 16.6 

7-ABS-BFR 459 395 515 221 268 411 126 50 17 17.4 

8-PC/ABS-PFR 428 567 611 212 322 361 154 53 23 16.1 

9-HIPS-BFR 930 760 827 349 376 562 136 44 17 17.0 

10-PC-BFR 225 214 258 10 124 219 461 72 16 32.9 

11-PP-BFR 1650 2090 2391 747 662 1136 221 62 20 25.0 

12-PP-NH 265 337 392 30 101 214 50 25 10 1.2 

13-PP-BFR 1689 2206 2529 382 727 1169 124 46 12 21.5 

14-PP-BFR 1677 2200 2581 348 219 1025 110 35 16 11.2 

15-PP-NH 380 487 530 256 361 371 140 48 19 16.6 

17-PVC-NFR 179 243 305 127 176 231 103 23 11 11.8 

18-HIPS-NH 391 445 639 284 378 463 98 30 9 18.3 

19-ABS-NH 290 293 454 188 243 319 99 36 11 17.4 
16

0

200

400

600

800

1000

1200

1400

1600

1800

1-PC-NH

2-HIPS-BFR

5-PC-BFR

7-ABS-BFR

8-PC/ABS-PFR

10-PC-BFR

12-PP-NH15-PP-NH

17-PVC-NFR

18-HIPS-NH

19-ABS-NH

4-PC-NFR

9-HIPS-BFR

11-PP-BFR13-PP-BFR14-PP-BFR

3-HIPS-NFR

6-PC/ABS-NFR

HRR0 (kW/m^2)

V-0 V-1

V-2

V-fail

Figure 8. Cone calorimeter unforced, zero flux, peak heat release rate from the intercept 

of the plot of peak HRR vs. incident flux (see equation 1). 

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

1-PC-NH

2-HIPS-BFR

5-PC-BFR

7-ABS-BFR

8-PC/ABS-PFR

10-PC-BFR

12-PP-NH15-PP-NH

17-PVC-NFR

18-HIPS-NH

19-ABS-NH

4-PC-NFR

9-HIPS-BFR

11-PP-BFR13-PP-BFR14-PP-BFR

3-HIPS-NFR

6-PC/ABS-NFR

External Heat Flux for 300 s Ignition (kW/m^2)

V-0 V-1

V-2

V-fail

 

Figure 9. Cone calorimeter critical external heat flux for sustained ignition at 300 

seconds. 
17

Glow Wire Ignition Temperature Test

Ignition resistance to a hot wire was characterized for 16 of the 18 materials in 

this study. The results of the glow wire ignition temperature (GWIT) tests and the glow 

wire flammability temperature (GWFT) tests are summarized in Table 5. There does not 

appear to be a consistent effect of thickness on the GWIT; values go both up and down 

with increased thickness depending on the resin. 

A GWFT of less than 960 o

C indicates the specimen did not self extinguish within 

30 seconds. Two of the 1.6 mm thick specimens, 4-PC-NFR and 9-HIPS-BFR, were 

classified as V-2 in the UL94 vertical flame test, and did not self-extinguish in this test. 

The self extinguishing nature of all the V-0 specimens was confirmed by the GWFT 

results. 

Figure 10 shows a comparison of GWIT and external heat flux for 300 s ignition 

for the 3.2 mm specimens. With the exception of two materials, (12-PP-NH and 17-

PVC-NFR), there is a reasonably good correlation between the ignition resistance 

measured using the cone and using the glow wire apparatus. 

Table 5. Summary of results from Glow Wire Ignition Temperature Testing. Sample Identification Color Glow Wire Ignition Temperature (°C) 1.6 mm Glow Wire Ignition Temperature (°C) 3.2 mm Glow Wire Flammability Temperature (°C) 1.6 mm Glow Wire Flammability Temperature (°C) 3.2 mm 

1-PC-NH white 800 825 960 960

2-HIPS-BFR black 650 675 960 960

3-HIPS-NFR white 700 750 675 725

4-PC-NFR clear 900 850 900 960

5-PC-BFR tan 900 825 960 960

6-PC/ABS-NFR black 800 725 775 700

7-ABS-BFR white 700 750 960 960

8-PC/ABS-PFR white 725 725 960 960

9-HIPS-BFR white 700 650 875 960

10-PC-BFR black 850 875 960 960

11-PP-BFR white 800 725 960 960

12-PP-NH white 700 750 960 960

13-PP-BFR white 800 800 960 960

14-PP-BFR white 700 650 960 960

15-PP-NH white 750 650 960 960

17-PVC-NFR black 875 900 960 960
18

0

5

10

15

20

25

30

35

40

600 650 700 750 800 850 900 950

GWIT (o

C)

External Heat Flux for 300 s Ignition (kW/m2)

Figure 10. Comparison of glow wire ignition temperature and Cone ignition heat flux 

for 16 of the materials at a thickness of 3.2mm. 

Conclusions

 The materials considered in this study exhibited a wide range of performance in 

three standard bench-scale flammability tests. The ignitability, upward flame spread 

resistance, heat release characteristics and product yields were characterized for these 

materials in several well-defined configurations. Although a detailed study of full-scale 

performance of these materials is not available at this time, it is likely that both UL94 

performance and the rate of heat release measurements are necessary to predict how these 

materials can be expected to react in a real fire hazard scenario. Each of these standard 

tests are fundamentally very different and therefore strong correlations between them 

were not expected; however some generalizations were observed. The unforced peak 

heat release rate, HRR0, was lower for V-0 and V-1 materials than that for HB and V-2 

materials (see figure 8). On average, materials that exhibited a longer ignition delay time 

(or higher critical heat flux for ignition) in the Cone Calorimeter had a higher glow wire 

ignition temperature (see figure 10). The effects of melting and material thickness on 

flammability performance in these tests were not consistent and these effects should be 

reconsidered when determining fire hazard.