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NBSIR 85-3274

An Exploration of Combustion

Limitations and Alternatives to the

NBS Toxicity Test Method

Reference

NBS

PUBLICATIONS

Barbara C. Levin, Vytenis Babrauskas, Emil Braun,

Joshua Gurman, and Maya Paabo

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

November 1985

^ i part by:

100 Consumer Product Safety Commission

. U56 MD 20207

85-3274

1985

national bureau

OF STANDARDS

ilBRARY

NBSIR 85-3274

AN EXPLORATION OF COMBUSTION

LIMITATIONS AND ALTERNATIVES TO THE

NBS TOXICITY TEST METHOD

Barbara C. Levin, Vytenis Babrauskas, Emil Braun,

Joshua Gurman, and Maya Paabo

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

November 1985

Sponsored in part by:

The U.S. Consumer Product Safety Commission

Bethesda, MD 20207

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director

Table of Contents

Page

List of Figures v

List of Tables vii

Abstract 1

1. INTRODUCTION 1

2. CHARACTERISTICS OF THE "IDEAL" COMBUSTION AND EXPOSURE SYSTEM 5

3. ALTERNATIVE COMBUSTORS 7

4. EVALUATION OF LIMITATIONS 11

4.1 Amount of material to be tested 11

4.1.1 Experiments in the cup furnace 11

4.1.2 Experiments in the cone radiant heater 12

4.1.3 Conclusions on amount of material to be tested .... 13

4.2 Means of continuous mass monitoring 13

4.2.1 Experiments in the cup furnace 13

4.2.2 Experiments in the cone radiant heater 15

4.2.3 Conclusions on means of continuous mass monitoring . . 16

4.3 Specimen orientation effects 16

4.3.1 Experiments in the cup furnace 16

4.3.2 Experiments in the cone radiant heater 17

4.3.3 Conclusions on specimen orientation effects 18

4.4 Non-uniform specimens 19

4.4.1 Experiments in the cup furnace 19

4.4.2 Experiments in the cone radiant heater 20

4.4.3 Conclusions on non-uniform specimens 21

4.5 Thermal exposure conditions 22

4.5.1 Experiments in the cup furnace 22

4.5.2 Experiments in the cone radiant heater 23

4.5.3 Conclusions on thermal exposure conditions 24

4.6 Oxygen limitations 25

4.6.1 Experiments in the cup furnace 25

4.6.2 Experiments in the cone radiant heater 27

4.6.3 Conclusions on oxygen limitations 28

4.7 Other constraints of the cone radiant heater apparatus 28

5. RECOMMENDATIONS 30

5.1 Modifications to the NBS toxicity test using a cup furnace ... 30

5.2 Increased emphasis on achieving fullscale/bench-scale correlation 31

6. ACKNOWLEDGEMENTS 33

7. REFERENCES 34

iii
Table of Contents (continued)

Appendix A. Criteria Developed by Anderson et al., [2] for a Satisfactory Fire Toxicity Test Method

Appendix B. Design Features of the Cone Radiant Heater Apparatus

Appendix C. Operational Description of the Cone Radiant

Heater Toxicity Apparatus

Appendix D. Toxicity of the Combustion Products from a Flexible

Polyurethane Foam and a Polyester Fabric Evaluated

Separately and Together by the NBS Toxicity Test Method

iv
List of Figures

Page

Figure 1. Cup Furnace 41

Figure 2. Design of the Weyerhaeuser radiant heat toxicity

test apparatus 42

Figure 3. The cone radiant heater in vertical and horizontal modes . . 43

Figure 4. Cone radiant heater in combination with animal

exposure chamber 44

Figure 5. Carbon monoxide generation from materials decomposed in the

non-flaming mode at various mass loadings 45

Figure 6. Rate of carbon monoxide generation during decomposition

of flexible polyurethane foams and polyester ......... 46

Figure 7. Hydrogen cyanide generation from nitrogen-containing

materials decomposed in the non-flaming mode at various

mass loadings 47

Figure 8. Rate of CO and C0 2 generation from Douglas fir decomposed in

the flaming mode 48

Figure 9. Load cell attached to cup furnace 49

Figure 10. Weight loss of flexible polyurethane foam decomposed at

375 °C in the cup furnace 50

Figure 11. Aerator inside quartz beaker that fits into cup furnace. ... 51

Figure 12. Generation of CO from the flaming combustion of flexible

polyurethane foam in the presence of various air flow rates

through the cup furnace 52

Figure 13. Generation of C0 2 from the flaming combustion of flexible

polyurethane foam in the presence of various air flow

rates through the cup furnace 53

v
List of Figures (continued)

Page

Figure 14. Generation of CO from the non- flaming thermal decomposition of

flexible polyurethane foam in the presence of various air

flow rates through the cup furnace 54

Figure 15. Generation of C0 2 from the non-flaming thermal decomposition

flexible polyurethane foam in the presence of various air

flow rates through the cup furnace 55

vi
List of Tables

Page

Table 1. Effect of Orientatin of Flexible Polyurethane Foam With and

Without Fabric Cover on the Generation of CO and C0 2 in the

Cone Calorimeter Tests 36

Table 2. Toxicity Results for Flexible Polyurethane #13 Using the Cone

Radiant Heater 37

Table 3. Toxicity Results for the Polyester Fabric Using the Cone

Radiant Heater 38

Table 4. Toxicity Results for Flexible Polyurethane #13 plus Polyester

Using the Cone Radiant Heater 39

Table 5. Toxicity of Modacrylic Decomposed at Different Temperatures . . 40

vii
_
AN EXPLORATION OF COMBUSTION LIMITATIONS AND ALTERNATIVES TO THE

NBS TOXICITY TEST METHOD

Barbara C. Levin, Vytenis Babrauskas, Emil Braun,

Joshua Gurman'*, and Maya Paabo

Abstract

Some limitations and potential limitations of the NBS toxicity screening

test method had been identified in earlier work. These limitations have now

been explored in greater detail. Also investigated was an alternative combustion system, consisting of a radiant cone heater, identical to the one in the

recently developed Cone Calorimeter, an enclosed combustion chamber, and a slightly revised variant of the animal chamber. The new animal chamber was so constructed that, prior to the insertion of the animals, it could be evacuated

and then back-filled with a desired sampling of the combustion products. The

radiant combustion system showed a different mix of capabilities and limitations compared to the cup furnace combustor in the existing test method. In

the present project, the more detailed assessment of the cup furnace operation

leads to the recommendation that there is no single, universally preferable

combustion environment, but that the cup furnace is adequate for the intended

purpose of providing toxicity screening.

Key words: combustion products; combustion toxicity; NBS toxicity test

method; plastics combustion; radiant combustion.

1. INTRODUCTION

The NBS Toxicity Test Method [1] is a bench-scale bioassay test method

which was developed as a screening tool to identify materials which may produce

unusual or extremely toxic combustion products. The detailed behavior of any

material so identified could then be explored by other, more detailed investigations. Work with the NBS test method has shown that most materials behave

Research Associate, American Iron and Steel Institute

1
relatively similarly, but that a few, unusual materials exist with

substantially different toxicity behavior [1].

The current test method comprises a cup furnace for heating and combusting material specimens connected to a 200 2, animal exposure chamber where six

rats are exposed to the products generated. The cup furnace used as the

combustion system consists of a removable quartz beaker surrounded by a heating

element which is encased in insulation (Figure 1). The advantages of this type

of combustion furnace were considered to be: (1) a low amount of heat is

generated in the animal exposure chamber, compared to other alternative

furnaces considered for use in this apparatus; (2) the autoignition temperatures of materials are easily determined and are reproducible; (3) thermal

decomposition conditions, both flaming and non-flaming, and experimental

results are reproducible; and (4) the quartz beaker is easily removable, easy

to clean, and easy to replace, allowing the use of multiple beakers so that

experiments can be run without stopping to cool or clean the beaker. In this

system, the total mass loss of material during an exposure is determined by

weighing the beaker and material before and after the test.

The NBS test method was evaluated by Anderson et al. [2], who prepared a

report for the State of New York in which they examined the currently available

test methods for evaluating the toxic potency of smoke. For this report, they

selected a set of criteria which they considered minimal technical standards

for such a test method and then proceeded to review 14 published methods using

these criteria (Appendix A). Only two methods (NBS and University of Pittsburgh) were found to comply with all these criteria. In addition to meeting

2
these basic standards, they noted that both these methods were designed as

screening tools and had good publicly-available data bases. These two methods

were then intensively studied under a number of diverse circumstances and for a

variety of commercially available materials. After performing over 600

separate experiments, Anderson et al. found that "both test methods are

scientifically sound". "The reproducibility is good between laboratories and

the test results can be replicated." The two test methods were "in substantial

agreement on the ranking and potency of smoke released by non-char-forming

materials." "Char-forming materials showed substantial differences but

generally appeared more toxic in the NBS test." Therefore, it can be considered that the NBS test method has been examined and validated by an outside

study, found to be of sound design and, if in error, on the more conservative

and safe side.

The documentation of the test method [1], published in 1982, stated that

there were a number of issues, which were seen as limitations and which

deserved further exploration. These items, which centered around the combustion system, were listed as follows:

(1) the size of the quartz beaker which fits into the furnace limits

the quantity of low density materials that can be tested,

(2) no means are provided for continuously measuring the mass loss of

material during the experiment,

(3) the effect of sample orientation cannot be assessed.

3
(A) assemblages of non-uniform structure cannot be evaluated, and

(5) the thermal exposure conditions employed do not represent all

possible fire conditions.

To this list, in subsequent discussions, was added one more concern:

(6) the sample exposure conditions may represent a substantially

oxygen- limited exposure.

Since 1982, considerably more experience has been gained with the test

method during normal testing, special tests have been made to determine the

effects of some of the variables listed above, and an alternative combustion

system coupled to a new, although similar, animal exposure box was built and

placed into use. Thus, we intend in this report to (1) investigate the actual

performance of the cup furnace combustion system for its intended purpose, (2)

consider the advantages and disadvantages of the alternative combustion

system, (3) review the expected properties of an "ideal" combustion system, and

(A) make recommendations on whether changes are needed to the cup furnace test

apparatus. The additional materials assayed in these studies were selected

as severe tests of the devices, as well as for their similarity to commercial

products used for upholstered furniture, a major presence in fatal fires.

A
2. CHARACTERISTICS OF THE "IDEAL" COMBUSTION AND EXPOSURE SYSTEM

There are a number of standard technical traits which a good combustor

and the animal exposure system should possess, i.e., ruggedness, good reproducibility, safety in operation, etc. Beyond these, however, there are a number

of characteristics which should be considered for a combustor in a biotest

procedure and for the means that combustion products are delivered to the

animals. Some of these characteristics were considered by the National Academy

of Sciences and by Huggett [3,4]. Many of these were explored in the original

report [1], In our work, further issues have also emerged as important, and we

believe they should be explicitly considered as well.

Square-wave exposure to the animals

This is desirable because Haber's rule (which postulates that the

product of exposure time and concentration is a constant which is

characteristic of a toxicant) cannot be a priori assumed to be

obeyed for a given gas or a combination of gases.

° Apparatus suitability for a fixed-time exposure

It has become accepted in the community to do toxicity screening

for fixed exposure time, generally 30 minutes. Thus, combined

with the previous characteristic, it is considered desirable to be

able to provide a square-wave exposure for a prescribed (i.e., not

dependent on what is being tested) time, most preferably 30

5
minutes. In cases where shorter duration testing may be desired,

an apparatus capable of a 30 minute exposure will also be adequate.

o Minimum loss of gases and particulates

It is generally agreed that toxicity can be caused by particulates and liquid aerosols, not solely by vapors. Some of these

aerosols will be lost if they are condensable at a temperature

higher than the prevailing animal chamber temperature. It is

logically impossible to test for these species without simultaneously subjecting the animals to some heat stress. Particulates

will also be lost to some extent because of sedimentation and wall

losses. This should be kept to a minimum. Also to be minimized

are losses of small, polar molecules (e.g., HC£), which can be

readily adsorbed onto certain wall materials.

Representation of full-scale conditions

Although desirable, this is extremely difficult to determine for

two reasons: (1) there are negligibly few full-scale measurements

of fire toxicity to animals; and (2) there are very few studies of

flow, distribution, and losses of fire gases and aerosols under

full-scale conditions.

6
Our discussions below will thus attempt to address the issues raised not

only by the initial concerns, but also take into account these additional

characteristics considered desirable.

3. ALTERNATIVE COMBUSTORS

Some of the questions raised can be seen to be difficult to answer

without substantially modifying the existing test apparatus. Given that

realization, the chosen approach was to use a different apparatus, one whose

strong points would be precisely in those areas where limitations were seen

with the existing apparatus (which will be here referred to as the cup furnace

apparatus). The performance from that system could then be compared to the

results obtainable with the cup furnace to see if and where improvements might

actually be needed.

Initially, the possibility of using the Weyerhaeuser radiant heating

system [5,6] was considered for use as such an alternate apparatus. This

scheme involves replacing the cup furnace with a radiant heater which is placed

below the animal chamber floor. As shown in Figure 2, the radiant energy is

supplied by two tungsten-filament quartz lamps located below the exposure

chamber and is focused on the sample. The sample is suspended on a balance

pan attached to a load cell which monitors mass loss. The whole system

is enclosed in a Vycor glass enclosure. NBS staff ran some tests with this

system in 1980. The advantages of this apparatus, relative to the cup furnace,

were seen to be: (1) it can accommodate larger samples, (2) composite materials can be placed in the sample holder such that the side normally exposed to

7
the radiant heat of a fire is exposed to the heat flux of the lamps, and (3)

the system continuously measures the mass loss of the material during the

thermal degradation.

This system also has some relative limitations:

1. The position of the quartz lamps results in a higher average temperature in the animal exposure chamber. (Testing for combustion product

toxicity is predicated to only exposing animals to toxic stress, and

not to heat stress. Elevated chamber temperatures are undesirable and

may lead to erroneous data and conclusions.)

2. The weighing assembly has a lack of precision at low mass, and it is

important to distinguish those materials which are toxic in small

quantities

.

3. To vary the mass loadings, it is necessary to vary proportionately the

specimen area, drastically reducing the area for high toxicity specimens

Thus, edge burning and rear surface losses are highly variable and it is

not possible to represent the burning on a per-unit-face-area basis.

4. The local oxygen concentration in the combustion system is not monitored

and probably drops rapidly in this closed combustion system.

5. There is no means of evaluating sample orientation (vertical vs. horizon

tal) effects on toxicity.

8
6. Soot deposits on the glass barrier between the heater and the specimen,

with a consequent change in actual irradiance during test, and with the

practical difficulty of requiring disassembly, cleaning, and reassembly

prior to the next test.

From these experiences, we concluded that some of the shortcomings were

operational and could possibly be minimized with sufficiently innovative

design. However, one of them--the size reduction requirement- -was fundamental

enough to negate most of the benefits of radiant heating. Thus, we did not

pursue use of the Weyerhaeuser device.

Another system of substantial promise is the German DIN test [7]. In

this test a long, narrow specimen, sufficient to produce enough pyrolysate for

a full 30 minute exposure is located horizontally inside a quartz tube. The

tube is placed on a lathe bed and surrounded by a travelling tube furnace,

propelled by the lathe drive. This system has the strong advantage that enough

material can be generated to have a true dynamic, or flow-through test. The

limitations, however, were seen to be several:

1. The DIN apparatus is dimensioned only for very narrow, non-composite materials, scarcely wider than wires. Even in this small

scale, it is a very expensive apparatus. The cost of scaling up to

a size sufficient that a composite specimen of adequate width might

be burnt was considered prohibitive.

9
2. The scheme is not well suited to represent the total process of

combustion. That is, it cannot be readily made to gather products

from the burning of the top layers at the start of test, the middle

layers later, and the bottom layers at the end. This issue does

not arise if one is testing homogeneous, single-step kinetics

substances, but in the case of composites it is a major limitation.

3. The apparatus involves a quartz glass tube between the heater and

the specimen, with consequent problems of soot deposition.

4. Adequate mass loss measurements do not appear to be possible with

this geometry.

Based on these observations, the travelling furnace type test geometry was

also not pursued.

We then considered the fact that the ideal heater, from the point of view

of efficiency and uniformity, is a conical heater. Of all the possible heater

types known to us, this delivers the highest fraction of its input power to

the specimen, with the highest surface radiant flux uniformity. We had used

such an arrangement in developing the Cone Calorimeter [8], and achieved

good results. With the addition of an animal exposure capability to the Cone

Calorimeter, it was considered that the system could meet the requirements set

forth for a good combustor, which would not have the limitations outlined

for the cup furnace method. The details of design of the new features of the

cone radiant heater (as distinct from the Cone Calorimeter, which is the

10
similar, existing device without bioassay capabilities) are shown in Figures 3

and A and described in Appendix B. The operation of this alternate test system

is described in Appendix C.

A. EVALUATION OF LIMITATIONS

A.l Amount of material to be tested

A. 1.1 Experiments in the cup furnace

Most of the initial data prior to the 1982 report had been obtained with

a 300 mil beaker. Since that report, all work has been done with the 1000 m2,

beaker. The materials for which beaker capacity is in question are, specifically, foam plastics, which are the lightest density materials that have had

their fire performance data evaluated. With the 1000 m2, beaker, we have been

able to test mass loadings of polyurethane foams of 8 g [9]; this amount of

material decomposed in a 200 2 chamber equates to a concentration of A0 mg/ 2.

In some cases, the materials have been found to have LC 50 values greater than

A0 mg/2. Values of LC S0 greater than this number would generally be classified

as representing materials of low toxicity potential. Since the whole development focus of the test method has been to characterize materials and products

likely to be identified as fire concerns, further precision is not needed for

an item which proves to be less toxic than the majority of investigated

materials

.

11
4.1.2 Experiments in the cone radiant heater

The maximum concentrations (equivalent numerically to mass loadings) that

can be introduced with the cone radiant heater can be computed as follows.

The specimen maximum size is 0.1 x 0.1 x 0.05 m, giving a volume of 0.0005 m

3

.

For a specimen density of p (kg/m 3 ), the specimen mass is 0.0005p. The animal

chamber volume is 200 2,. Let the maximum fraction of combustion or pyrolysate

product conveyable from the combustion chamber to the animal chamber be 3-

This maximum value of 3 is realized at minimum combustion chamber air supply

and exhaust rates. Then the maximum loading achievable in the animal exposure

chamber is represented by 2.5p3 (mg/ 2.). Tests conducted with minimum practical maintainable air flow rates (approximately 25 2,/min) going through the

combustion chamber suggest that 3

~ 0.6. Rigid plastics can have a density on

the order of 10 3 kg/m 3

; for them, a large concentration can be generated.

Flexible foams, on the other hand, may have a p « 16 kg/m 3. This then will

result in a maximum measurable LC 50 of 24 mg/2,. This is acceptable since it is

similar to the LC 50 determined for flexible polyurethane foam in the cup

furnace [1,9). A special operational uncertainty arises in the cone radiant

heater method because of the large volume of the combustion chamber, compared

to the small air flow rates that are necessary when burning lightweight

materials. At the start of the test the combustion chamber represents a large

reservoir which the combustion products must gradually fill, before an

equilibrium concentration is established. (This limitation does not arise in

the Cone Calorimeter, since there the air flow rates are large and the

equilibration time is very fast.) If the burn time is not long, then the

12
initial products are somewhat more dilute than calculated on the basis of a

steady flow concentration.

A. 1.3 Conclusions on amount of material to be tested

On this particular point, the cup furnace method and the cone radiant

heater alternative are adequate, and are about equal in performance. Materials of very low toxicity cannot be quantified in either system, but since the

purpose of the screening method is to identify materials of high toxicity, this

is not considered a real limitation. Furthermore, consideration of more novel,

yet practical achievable systems suggests that it would be very difficult to

make an improvement here.

4.2 Means of continuous mass monitoring

4.2.1 Experiments in the cup furnace

The normal procedure with the cup furnace has been to obtain the tare

mass of the beaker, the initial mass of the specimen, and the final mass of

beaker and residue. This is sufficient data to determine the specimen mass

lost. The only additional purpose for which a time-dependent mass loss record

might be necessary is to assure that the sample combustion time is short

compared to the exposure time and, thus, that a square-wave exposure has been

achieved. Decomposing materials within 25°C of their autoignition temperatures in the cup furnace system presupposes the maximum pyrolysis rate and that

the animals will be exposed to all of the fire gases for close to 30 minutes.

13
In principle, it might be possible to envision some material which decomposes

at a rapid rate only during the last few minutes of the 30 minutes of heating,

but, in practice, such materials are usually not found.

That such a problem does not exist can be shown without a real-time mass

measurement capability, by deducing the time-behavior of the burning process by

using combustion product (CO, C0 2 , and HCN) generation data. Figures 5-8 show

these results from a diverse group of materials that we have tested. Under

flaming conditions, the generation rates of CO and C0 2 indicate that for

all of the tested materials the effective burning is completed in 2 to 10

minutes (Figures 6 and 8). This constitutes a reasonable conformance to the

desire that the gas generation period be much shorter than the 30 minute total

exposure time and that a square-wave exposure is approximated. Under nonflaming conditions (with the exceptions of Douglas fir, red oak and polyester)

most of the effective thermal degradation, as indicated by the generation of CO

and HCN, is also completed within 10 minutes (Figures 5 to 7).

The error resulting from an imperfect square-wave exposure can be bounded

for those materials where Haber's rule is obeyed. In that case, the error is

simply the difference between the actual area under the concentration-time

curve, and the area of the circumscribed bounding rectangle. Figures 5 through

8 clearly show these differences to be less than a factor of two. It must be

emphasized that it cannot be presumed that the test material being screened

obeys Haber's rule, and thus that, in general, no a posteriori correction could

be made to the results to adjust for non-square-wave exposure by the use of

load cell data.

14
Nonetheless, to more fully address the issue of availability of this

diagnostic tool, we have installed a load cell in a modified version of the cup

furnace (Figure 9). The load cell has a tare capacity of 3500 g, a weighing

capacity of 500 g, and a resolution of ±0.01 g. Figure 10 shows an extremecase result for a flexible polyurethane foam specimen at 25 °C below its

autoignition temperature which unpredictably ignited approximately 5 minutes

after the start of the test. In experiments where animals are exposed,

the results from such a test would be discarded, since in flaming tests,

according to the current test protocol [1], the material must ignite within 10

seconds, and in non-flaming tests, the material should not ignite at all.

Nonetheless, the results show that close to 90% of the material was consumed

at 6 minutes after the start of the test, and, thus, that a reasonable approximation to a square wave exposure holds.

4.2.2 Experiments in the cone radiant heater

The cone radiant heater is equipped with a load cell, whose output is

regularly recorded during a test (Figure 3). Mass loss rate data are very

important in the normal use of the Cone Calorimeter for obtaining effective

heats of combustion, and also for quantification of the release rates of gas

and smoke on a per-mass basis. In the operating procedure described in

Appendix C, we have found it convenient to use the load cell for determining

the mass loss rate over a given period. Since, unlike with the cup furnace,

in the cone radiant heater method the combustion products of the complete

15
specimen degradation period are not necessarily introduced into the animal

exposure chamber, the specimen load cell is a very convenient feature.

A. 2. 3 Conclusions on means of continuous mass monitoring

For the cone radiant heater apparatus, the adopted operating procedures

serve to assure that a square-wave exposure is being generated. The load cell

is useful in that apparatus, nonetheless, for easy determination of the

fraction of the specimen pyrolysate which is being introduced into the animal

exposure chamber. In the cup furnace apparatus, while it has been demonstrated

that a load cell can be successfully implemented, it is not proposed to modify

the screening test procedures to add this measurement for the following

reasons: (1) the data generated cannot be quantitatively used in assisting

the process of screening materials; (2) its use would increase the screening

test complexity and cost; and (3) the maximum errors are estimated to be less

than a factor of two, which is considered within the validity bounds of the

toxicity screening test.

4.3 Specimen orientation effects

4.3.1 Experiments in the cup furnace

Specimen orientation effects are considered important when the modeling

of surfaces exposed to fire is done, i.e., in radiant heating environments.

In the cup furnace a small mass of specimen is used, not intended to represent

the same surface boundary conditions as in actual fires. Thus, it was not

16
appropriate to vary specimen orientation in the cup furnace apparatus. It was

possible, nonetheless, to make appropriate experiments in the cone radiant

heater, as shown below, which characterize the magnitude of this effect.

4.3.2 Experiments in the cone radiant heater

A detailed investigation was made in the cone radiant heater geometry to

assess the effects of material orientation on the generation of the toxic gases

CO and C0 2

. (Specifically, since only gas generation data were needed, the

experiments were done in the Cone Calorimeter). As an example of a typical

end use item, a flexible polyurethane foam, with a density of 21.8 kg/m 3

, was

used. Table 1 shows the results for both this foam alone and as a composite

with a cotton fabric covering. The fabric weight was 0.61 kg/m 2

. In only one

case (non-flaming, no fabric) was there a significant difference in the

generation of CO between horizontal and vertical specimen orientation. In that

one case, about a 3:1 ratio for CO was observed. This difference could be due

to specimen variations, since only small samples were tested, and it is wellknown that for some polyurethane foam manufacturing processes substantial

variations may occur over the width of a full-scale specimen. Also, the number

of specimens tested was small, i.e., 3 for the vertical orientation and 4 for

the horizontal orientation. (The data from two of the non-flaming horizontal

tests had discarded since flaming occurred. This also happpens occasionally in

the standard cup furnace test method. Some materials show sufficient intrinsic

variability that in a given test which is at 25 °C below the autoignition

temperature and is intended to represent non-flaming conditions, flaming can

erupt, in which case these data are to be discarded.)

17
Additional corroborative data had been gathered earlier with the Cone

Calorimeter. For instance, the original report [8] illustrates the rates of

heat release for polymethylmethacrylate (PMMA) and red oak. The rates of heat

release for PMMA are typically 10% lower in the vertical orientation as

compared to the horizontal; for red oak, the comparable figure is 30%.

Neither of these would be significant in the context of fire toxicity

screening. The difference in ignition times is, again, slight, being longer in

the vertical orientation by about one standard deviation. In general, observations of combustion in the Cone Calorimeter point out that there are often

slight, but statistically significant differences in ignition times for

different orientations; some marginally igniting specimens may ignite in one

orientation but not the other; melting/dripping specimens can show anomalous

behavior in the vertical orientation; and most specimens show slightly higher

rates of heat release in the horizontal orientation. Taken together, these

general observations, combined with the specific tests conducted above, suggest

that the effects of orientation are minor. There is one caveat to this,

namely, that radiant testing in the vertical orientation should not be conducted on specimens prone to melt and drip.

4.3.3 Conclusions on specimen orientation effects

Based on the work with the Cone Calorimeter, it is concluded that

specimen orientation effects are small, and that it is sufficient to conduct

toxicity screening test using any one orientation of specimen.

18
A. 4 Non-uniform specimens

It is undoubtedly important to be able to evaluate non-uniform (i.e.,

composite or laminated) specimens, and thus it may be desirable, but not

necessarily mandatory to test non-uniform specimens. A lot has to do with the

scale of the non-uniformity. A specimen whose only non-uniformity is that it

consists of two different bonded layers of fabrics or films could obviously be

readily tested. Contrariwise, a wall construction system which is non-uniform

on a 16 inch modularity (as has been common for innovative housing) could not

be tested by a truly representative specimen in any bench-scale test.

A. 4.1 Experiments in the cup furnace

In the cup furnace, we have studied a flexible polyurethane foam and a

polyester fabric, two common components of commercially available upholstered

chairs. The fabric and foam were heated individually and then together; in

the latter case, the fabric was dropped into the cup followed by the foam.

These experiments indicated that; (1) Both materials contributed to the

toxicity of the combined materials, (2) The gases generated from the mixture in

the non- flaming mode could be predicted from a summation of the gases produced

by the separate materials, and (3) The amounts of CO and HCN generated by the

mixture in the flaming mode were greater than the sum of the concentrations

from the individual materials. The results of these experiments were sent to

the CPSC in September, 1984 and have been presented at the Eighth Joint

Meeting of the U.S. -Japan Panel on Fire Research and Safety in Tsukuba, Japan

in May, 1985 [10] and at the First International Meeting on Fire Science

19
Safety, National Bureau of Standards, Gaithersburg, MD in October, 1985. A

copy of the presented paper containing the detailed results is included as

Appendix D.

4. A. 2 Experiments in the cone radiant heater

One of the primary design considerations with the Cone Calorimeter was

the capability to test non-uniform materials under conditions typifying end

use. A large number of furniture composites, wall material composites, and

composite reinforced plastics have so far been satisfactorily tested in the

Cone Calorimeter [11]. This capability is clearly an operational advantage of

the cone radiant heater over the cup furnace.

Difficulties, however, were encountered in the determination of LC 50

values when the above flexible polyurethane foam and polyester fabric were

tested singly in the cone under conditions designed to generate the maximum

combustion products, i.e., low air flow rates, flux levels close to the

materials' autoignition energy levels, maximum amounts of materials, etc. No

animal deaths were observed following exposures to either the flaming (F) or

non-flaming (NF) combustion products from either materials. The estimated LC 50

values for the polyurethane would be >20 mg/ 2., NF and >25 mg/ 2,, F (Table 2).

For the polyester, the estimated values would be >5 mg/2., NF and >52 mg/2,, F

(Table 3). (No animals were exposed to the non-flaming polyester since the

concentrations were so low.) However, when the composite, consisting of the

fabric covered foam, was decomposed, some animal deaths occurred (Table 4). In

these experiments, the results were similar to those of the cup furnace in that

20
post-exposure deaths occurred in the non-flaming mode and with- in exposure

deaths occurred in the flaming mode. Estimated LC 50 values ('vlO mg/2,, NF and

between 34 and 48 mg/ 2,, F) were not greatly different from those achieved with

the cup (48 mg/ 2,, NF and 39 mg/ 2,, F) (See Appendix D).

4.4.3 Conclusions on non-uniform specimens

Satisfactory toxicity screening results can be achieved with the use of

the cup furnace method. Composites for which it is known that the surface

materials do not offer a substantial fire barrier protection to the underneath

layers can be tested simply as an agglomeration, instead of a layered composite. (At the other extreme, interstitial materials which are very adequately

protected from fire involvement by the surface layer may not need to be tested

at all.) There is an intermediate regime, where the surface layers act to slow

down, but not to wholly eliminate, the burning of the underneath layers. If a

detailed characterization of such construction is required, it is possible, in

principle, to determine in the Cone Calorimeter the relative involvement of the

layers, and then to conduct several cup furnace tests using individual materials or agglomerations.

We do not believe that the present state of the art of fire hazard

modeling warrants such detailed testing plans. That is, the prediction

of actual fire involvement in a system where composite materials are involved

has not been systematically undertaken. Thus, while it is possible to use the

toxicity screening test to evaluate the individual layers and any desired

21
agglomerations (to test for synergisms or antagonisms), it is not at all

evident that there would be an application for the data so obtained.

From this, we conclude that the cup furnace method is adequate for

testing practical materials, that limitations on testing of non-uniform

assemblies can be addressed using a supplementary technique for screening

composites, if and when such testing becomes a necessity, but that substantial

progress will have to be made with fire hazard modeling before such experimental capabilities will be required.

4.5 Thermal exposure conditions

4.5.1 Experiments in the cup furnace

There can be a very large number of thermal exposure conditions possible

in real fires, depending on the fire scenario, article type, location, etc. A

screening test cannot possibly take into account this multiplicity of environments. What can be done, however, is to select a set of conditions which

tend towards a worst case characterization. The results of NBS work, the

findings from the laboratories that participated in the interlaboratory

evaluation of the toxicity test method [12], and the literature all indicate

that the most toxic conditions are probably generated at temperatures close to

each material's autoignition point. In the non-flaming mode, as the temperature rises and approaches the autoignition temperature, more and more of the

material is degraded and more toxic products are produced. And, of course, in

the flaming mode, the higher the temperature, the more complete the combustion,

22
the ultimate results of which is the production of only carbon dioxide and

water. Thus, in the cup furnace, each material is tested at 25 °C above and

below that material's autoignition point, i.e., a flaming and non-flaming

exposure. The autoignition temperature in this test is defined as the lowest

furnace temperature which causes a material sample to ignite spontaneously

within 30 minutes. That such an approach is reasonable has been demonstrated

in the original report [1J. For example, a modacrylic material was decomposed

at different temperatures in both the flaming and non-flaming mode (Table 5).

The results clearly showed that as the temperature increases in the non-flaming

mode, the LC 50 decreases, i.e., less material is needed to cause the animals to

die. A systematic study on this point with a large number of varied materials

has not been done, however, a large number of investigators have studied

temperature effects [11]; in most cases, their observations were consonant

with our approach to minimize the flaming condition temperatures and maximize

the non-flaming temperatures.

4.5.2 Experiments in the cone radiant heater

From several points of view, the cone heater arrangement is extremely

versatile: heating fluxes of zero to 110 kW/m 2 can be imposed; air flow rates

from negligible to 50 l/s can be set; and combustion air supply 0 2 /N 2 ratios

can be varied across the whole range from pure oxygen to pure nitrogen.

The details of thermal exposure conditions and their effects on sample

materials have been published for the Cone Calorimeter [8]; the thermal

exposure conditions applicable to the cone radiant heater are essentially

23
identical. Nonetheless, even in this highly flexible apparatus, certain scale

associated parameters cannot be independently adjusted. Specifically, a

radiant source exposure, over a small sample, still may fail to simulate fullscale phenomena such as turbulence (specifically, large-scale turbulent

structures), optically thick plumes or wall layers, and other actual

conditions. Thus, while any adequate test method should be capable of heating

the specimen to an agreed-upon level, the details of how that heating is

accomplished may never be fully under the experimenter's control.

4.5.3 Conclusions on thermal exposure conditions

In the context of a toxicity screening method, great flexibility in

varying combustion conditions over wide extremes is not a suitable objective.

Some day, fire hazard models may become available which treat finer details of

localized combustion phenomena. It is important to realize that, at the

moment, there is not even a model to determine what fraction of a building's

fire gases may be due to flaming versus non-flaming exposure condition elements .

For the present, the cup furnace, operating in the flaming and nonflaming modes, is clearly capable of identifying highly toxic materials. No

other method has detected any such materials that this method has missed.

Thus, we conclude that the cup furnace method successfully provides the

information which is required for toxicity screening purposes.

24
A. 6 Oxygen limitations

A. 6.1 Experiments in the cup furnace

The cup furnace geometry presents a very complex system from a fluid

mechanical point of view. Similar combustion systems studied in the past

which involved a partly enclosed volume communicating to the environment have

on occasion shown "gulping" instabilities and similar patterns. To our

knowledge there has not been a study, however, of a combustion geometry which

is sufficiently close to the present one, so that quantitative judgments could

be made. Indeed, the problem of studying the flows in detail is very difficult

and was not considered rewarding enough to make such a large effort.

Instead, we decided to determine the magnitude of the effect of varying

the available oxygen. For this investigation, an aerator was constructed

(Figure 11). It consisted of a 6 mm diameter glass tubing insert, lowered

down into the beaker to sit next to the beaker wall (clear spacing = 3 mm) and

to provide a flow of gas to the immediate vicinity of the specimen. This flow

was made approximately axisymmetric by providing the aerator with 29 holes,

each 1 mm in diameter, equi-spaced along the bottom perimeter. In principle,

the aerator could be used to deliver any desired choice of gas. We concluded

for these exploratory tests that recirculated chamber air was the best choice.

The use of pure oxygen or some other 0 2 /N 2 mixture would have been tantamount

to changing the overall animal chamber environment, and we would have lacked a

control.

25
A series of experiments was conducted under both flaming and non-flaming

combustion conditions to determine what effect, if any, ventilating the cup

furnace with this aerator would have on the overall composition of the thermal

degradation products as indicated by CO and C0 2 generation. A flexible

polyurethane foam (code PUF // 32) was thermally degraded at 375°C (non-flaming

conditions) and 450°C (flaming conditions) with ventilation flows through the

aerator of 250, 500, 2000, and 4000 md/min. At the highest flow rate in the

1000 mil cup furnace, the air volume in the cup would be exchanged every 15

seconds. During each 30 minute test, CO and C0 2 levels inside the chamber were

recorded every 15 seconds.

The CO and C0 2 levels produced under flaming and non- flaming conditions

were compared for the various air flow conditions (Figures 12-15). While

some differences in the concentrations or generation rates of CO and C0 2 under

the different ventilation conditions were observed, it was concluded that they

were not consistent enough to indicate a unique trend. Under the flaming

conditions, the absolute amounts of CO and C0 2 appear to be greater with the

aeration than with no aeration (Figures 12,13). However, this probably indicates only a slightly enhanced combustion rate and not a changed toxicity. A

more meaningful evaluation would be based on the C0/C0 2 ratio which is an

indication of both the completeness of combustion and of the total ultimate

proportioning of the products. Final, 30-minute C0/C0 2 ratios under the

different flow conditions were: naturally buoyant = 0.018; 250 md/min = 0.023;

500 md/min * 0.024; 2000 md/min 0.021; and 4000 md/min = 0.017. Based on

these C0/C0 2 ratios, the combustion completeness obtained under the naturally

buoyant condition is concluded to be as good as that for the aerated tests.

26
Under the non-flaming conditions, the average CO concentration was

somewhat greater without aeration than with aeration (Figure 14). However, the

ultimate CO levels reached in the tests with flow rates of 250 and 4000 m2,/min

were essentially identical to that obtained with no air flow. The C0 2 concentrations also similar to those obtained under the various air flow conditions

(Figure 11). The average C0/C0 2 ratios were: naturally buoyant conditions =

0.77; 250 mZ./min = 0.81; 500 m2,/min = 0.54; 2000 mi/min = 0.55; and 4000

mH/min = 0.66. These C0/C0 2 data indicate that ventilating the cup does not

necessarily reduce the CO generation tendencies under non-flaming conditions.

In fact, since the oxygen level in the total exposure system did not drop below

20% during these tests, it is unlikely that the cup was in a vitiated state. A

possible cause for the slightly different overall CO and C0 2 levels in the nonflaming aerated tests may be the shortened residence time volatilized components might spend in the heated zone. Thus, we conclude that even though some

slight differences were observed in the CO and C0 2 levels under the static and

aerated test conditions, these differences did not indicate a consistent trend.

4.6.2 Experiments in the cone radiant heater

There are no significant shortcomings to the apparatus in this area. In

normal operation free access to 21% oxygen supply air is available at all

times. If desired, up to 100% pure oxygen can be introduced as the combustion

air supply. While the apparatus provides for such a possible operation, we

have not operated under conditions of oxygen different from 21%. No specific

experiments were considered needed in this area.

27
4.6.3 Conclusions on oxygen limitations

Based on our aerator experiments, oxygen supply does not appear to be a

limitation in the normal operation of the cup furnace test method. Thus, it

is not recommended to require the normal use of the aerator, nor to make any

other changes for enhanced oxygen delivery.

4.7 Other constraints of the cone radiant heater apparatus

The following limitations, not present in the cup furnace apparatus, were

found for the cone heater apparatus:

° Transfer line clogging. The transfer line clogged badly due to

soot deposition. It was not considered desirable to filter or

otherwise eliminate the soot since this can have a potential effect

on the total effluent toxicity. The amount of deposition required

that the line be disassembled after every test, cleaned out, and

reassembled. It also meant that toxic products might not be

reaching the animals. This deposition might have been lessened by

heating the line, since a portion of such wall losses are due to

thermophoretic effects, which would be eliminated if the line

temperature were kept above the gas temperature. However, since

part of the line is located inside the combustion chamber, since a

28
control valve is involved, and since the animal chamber temperatures could be adversely affected, the design of a proper line

heater could be quite difficult and was not undertaken. The

decomposition of soot in the stack between the combustion chamber

and the sampling line also posed the problem of potential carryover of toxicants from one test to another, especially if the

testing mode changed from non-flaming to flaming.

a Difficulties in filling rate control. The filling rate was controlled by monitoring the differential pressure across a length of

transfer line, and using the manual control valve to maintain this

pressure at a level corresponding to a uniform filling rate. The

relationship between the pressure readings and the filling rate was

pre-determined from flow calibrations (see Appendix B). In some

cases, good control was difficult to achieve under all conditions,

i.e., both with the animal chamber evacuated and with the chamber

nearly back-filled. A mass flow controller was considered but was

not implemented because significant difficulties were expected from

sooting.

a Large reservoir volume in the combustion chamber. The Pyrexenclosed combustion chamber represents a substantial volume of

approximately 100 8, if the exhaust piping up the stack control

valve is included. The mixing and dilution of the combustion

products with this volume of initially ambient air is not a problem

if combustion rates and flow rates of the air are rapid. In the

29
case of low density foam, however, only a small amount of specimen

mass is available. Therefore, very small combustion chamber air

flow rates must be set. Under these conditions, there is a

substantial error in determining the concentration of combustion

products in the combustion chamber, and, consequently, in the

equivalent mass loading needed to calculate the LC 50 . Also, any

effects of secondary combustion from heater hot surfaces can

likewise be dependent on the combustion chamber air flow rate.

Test running time. It takes about 30 minutes to evacuate the

animal test chamber. Another half hour or more may be spent

disassembling and cleaning the transfer line. General calibration

and setup for the system is also substantially longer than for the

cup furnace. Consequently, there is at least a doubling of the

time required to conduct tests.

5. RECOMMENDATIONS

5.1 Modifications to the NBS toxicity test using a cup furnace

We recommend no changes to the NBS toxicity apparatus or procedures at

present. Our explorations based on a cone radiant heater alternative apparatus

confirmed some limitations of the cup furnace combustor, but also pointed out a

number of equally serious limitations in the alternative apparatus. With the

acceptance of a new methodology as proposed above, the bulk of the toxicity

testing effort will be shifted to the Cone Calorimeter heat release rate

30
apparatus, along with its necessary gas analysis instrumentation. The needs

for a final bioassay check can be adequately met by the cup furnace apparatus.

Since fire modeling needs will be primarily met by the results from the Cone

Calorimeter, it will not be necessary to seek the elusive goal of the "perfect"

bioassay tool. It will merely be necessary to be confident that the bioassay

tool used is the one best suited for the task. Based on our initial work [1],

the studies of the National Academy of Sciences [3], Anderson et al., [2] and

Huggett [A], and on our review of the world-wide study of combustion toxicity

test methods prepared by Kaplan et al.[17], we do not see any indications at

the present that there either is a significantly better tool than the cup

furnace, or that one could be feasibly and affordably developed.

5.2 Increased emphasis on achieving fullscale/bench-scale correlation

While great strides have been made over the last few years in quantifying

toxic agent effects, essentially no progress has been made on an issue which

is every bit as important- -the validation of bench-scale techniques against

full-scale measurements. Very few such attempts have even been made [13].

In every case, the test programs were very limited and the results subject to

enough uncertainty that it could not be fairly concluded that progress was

being made. This is not for the lack of good intentions, however. Full-scale

testing is at least one, and generally two, orders of magnitude more costly

than bench-scale work.

A second impediment to progress has been the lack of an integrated

measurement tool. Little progress was made in room fire testing as a science,

31
until it was realized that what had to be measured were not point measurements,

such as temperatures, but integrated measurements, especially the heat release

rate. Once this was realized, the Furniture Calorimeter and other full-scale

heat release rate measuring tools could be constructed, and rapid progress

resulted.

In toxicity evaluations, however, such an integrated measure is still

somewhat elusive. In a very simple approach, only the total mass outflow rate

for specific gases could be monitored. These could be measured in the exhaust

system where room and corridor flow products are collected. This may not be

adequate, since wall losses are involved, an issue which does not arise in

conjunction with measuring oxygen consumption to describe the heat release

rate. An even more serious complication is the modeling of local conditions.

For heat modeling, it is sufficient to know the heat release rates since models

exist for calculating the desired local variables (e.g., temperature) once

these rates and basic geometric properties are known. Toxic hazard modeling

requires not only all of the necessary heat modeling, but also modeling of

local mixing, diffusion, losses, and, potentially, reactions. This is a task,

some features of which are starting to be worked, but, which is, nonetheless,

unsolved and very difficult.

Thus, it is recommended that greater effort be placed into modeling of

full-scale fire toxic hazard conditions, and that close coordination be kept

between the development of bench-scale tests and their validation in full

scale. This, especially, suggests that excessive fine-tuning of bench-scale

32
methods is not prudent, pending any needed redirection from full-scale findings.

6. ACKNOWLEDGEMENTS

Laura Baier, Trudi Holt, William H. Twilley, and Gerald King participated

in various phases of the experimental work. The contributions of J. Randall

Lawson at a critical point of the work were essential to its success. This

work was supported in part by the Consumer Product Safety Commission, Project

No. 753-1388 (CPSC Task Order No. 84-5) Dr. Rita Orzel, Project Officer.

33
7.

REFERENCES

1. Levin, B. C., Fowell, A. J. Birky, M. M. , Paabo, M. , Stolte, A., and

Malek, D. , Further Development of a Test Method for the Assessment of

the Acute Inhalation Toxicity of Combustion Products, NBSIR 82-2532.

[U.S.] Nat. Bur. Stand. (1982).

2. Anderson, R. C., Croce, P. A., and Sakura, J. D. , Study to Assess the

Feasibility of Incorporating Combustion Toxicity Requirements into

Building Material and Furnishing Codes of New York State. Final report

to the Dept, of State, Office of Fire Prevention and Control, Albany,

NY, from A.D. Little, Inc., Reference #88712, Vols. 1-3 (May 1983).

3. Committee on Fire Toxicology, Fire Toxicology: Methods for Evaluation of

Toxicity of Pyrolysis and Combustion Products (Report No. 2). Nat.

Acad. Sci., Washington (1977).

4. Huggett, C., Combustion Conditions and Exposure Conditions for Combustion Product Toxicity Testing, J. of Fire Sciences . 2, 328-347 (1984).

5. Alexeeff, G.V. , and Packham, S.C., Use of a Radiant Furnace Fire Model

to Evaluate Acute Toxicity of Smoke. J. of Fire Sciences . 2, 306-320

(1984).

6. Levin, B.C., The National Bureau of Standards Toxicity Test Method.

Fire Tech . 21, 134-145 (1985).

7. Kimmerle, G. , Aspects and Methodology for the Evaluation of Toxicological Parameters During Fire Exposure. JFF/Comb. Tox . 1_, 4-51 (1974).

8. Babrauskas, V., Development of the Cone Calorimeter - a Bench-scale

Heat Release Rate Apparatus Based on Oxygen Consumption, NBSIR 82-2611.

[U.S.J Nat. Bur. Stand. (1982).

9. Levin, B. C., Paabo, M. , Fultz, M. L. , Bailey, C., Yin, W. , and Harris,

S. E., An Acute Inhalation Toxicological Evaluation of Combustion

Products from Fire Retarded and Non-Fire Retarded Flexible Polyurethane

Foam and Polyester, NBSIR 83-2791. [U.S.] Nat. Bur. Stand. (1983).

10. Levin, B.C., Paabo, M. , Bailey, C.S., and Harris, S.E., Toxicity of the

Combustion Products from a Flexible Polyurethane Foam and a Polyester

Fabric Evaluated Separately and Together by the NBS Toxicity Test

Method, paper presented at UJNR meeting, Tsukuba, Japan (May 1985).

11. Babrauskas, V., Bench-scale Methods for Prediction of Full-scale Fire

Behavior of Furnishings and Wall Linings, Technical Report 84-10,

Society of Fire Protection Engineers, Boston (1984).

34
12. Levin, B.C, Paabo, M. , and Birky, M. , Interlaboratory Evaluation of the

1980 Version of the National Bureau of Standards Test Method for Assessing the Acute Inhalation Toxicity of Combustion Products, NBSIR 83-2678.

[U.S.] Nat. Bur. Stand. (1983).

13. Levin, B.C., A Summary of the NBS Literature Reviews on the Chemical

Nature and Toxicity of the Pyrolysis and Combustion Products from Seven

Plastics: Acrylonitrile-butadiene-styrenes (ABS), Nylons, Polyesters,

Polyethylenes, Polystyrenes, PVC, and Rigid Polyurethane Foams, NBSIR

85- [U.S.] Nat. Bur. Stand. (1985).

14. Levin, B.C., Paabo, M. , Bailey, C. , Harris, S.E., and Gurman, J.L.,

Toxicological Effects of the Interactions of Fire Gases and Their Use

in a Toxic Hazard Assessment Computer Model. The Toxicologist . 5, 127

(1985).

15. Hartzell, G.E., et al. , Analysis of Hazards to Life Safety in Fires: A

Comprehensive Multi-dimensional Research Program, SwRI Project Report

01-7606, Southwest Research Institute, San Antonio (1985).

16. Tsuchiya, Y., and Sumi, K. , Evaluation of the Toxicity of Combustion

Products, J. Fire and Flammability . 3, 46-50 (1972).

17. Kaplan, H.L., Grand, A.F., and Hartzell, G.E., Combustion Toxicology . Technomic Publishing, Lancaster PA (1983).

35
TABLE 1

Effect of Orientation of Flexible Polyurethane

Without a Fabric Cover on the Generation of

in the Cone Calorimeter Tests

Foam With and

CO and C0 2

Mode Cover Orientation

CO

(ppm)

CO 2 (ppm)

C0 2 /C0

ratio

flaming + horizontal 970 + 126 60400 + 1100 62 + vertical 1330 + 129 50900 + 4100 38

- horizontal 400 + 28 72900 + 3000 183

- vertical 400 + 34 77800 + 3600 230

Non-flaming + horizontal 2810 + 50 42700 + 9500 15 + vertical 2550 + 473 39500 + 11800 15

- horizontal 1210 + 104 56800 + 3600 47

- vertical 430 + 27 62300 + 7200 145

Values of CO and C0 2 are in ppm + standard deviations from 2-4 tests. These

values were computed on the basis of all the combustion products from an 8 g

specimen filling a 200 8, box.

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Toxicity

Results

for

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Polyurethane

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Polyester

Using

the

Cone

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Heater c

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TABLE 5

Toxicity of Modacrylic Decomposed at Different Temperatures [1]

lc 50

Temperature (.30 minutes + 14 days)

Mode (°c) (mg/ 8,)

Flaming 760 - 775 7.1 ( 6.4- 7 . 9

)

a

Non-flaming 710 - 720 7.8 ( 6.3- 9.7)

445 - 460 10.0 ( 6.9-14.4)

390 - 400 13.6 (10.7-17.3)

295 - 305 21.8 (18.4-25.8)

250 - 260 ^23.

8

b

( 17 .

0

c -28 .

3

d

) 200 >22.

6

e

a: 95% confidence limits

b: Approximate value determined from values in brackets

: 0/6 animals died at this mass loading/chamber volume

: 5/6 animals died at this mass loading/chamber volume

e: No animals died at this mass loading/chamber volume

40
1000

ml

QUARTZ

BEAKER

92

mm

0J).

15

cm

high

41

HEATING

ELEMENT

IN

BOTTOM
EXPOSURE

CHAMBER

42

Figure

2.

Design

of

the

Weyerhaeuser

radiant

heat

toxicity

test

apparatus
TOP

OF

FURNACE

OPEN

TO

ALLOW

GASES

TO

PASS

THROUGH

43

Figure

3.

The

cone

radiant

furnace

in

vertical

and

horizontal

inodes
To

axhaust

blower

j

!

44

Figure

4.

Cone

radiant

furnace

in

combination

with

animal

exposure

chamber.
6000

aasrsassisss

ilisliil

O

CO

in

OJ

o

OJ

8

in c

hJ

in

(uidd) 00 45

Figure

5.

Carbon

monoxide

generation

from

materials

decomposed

in

the

non-flaming

mode

at

various

mass

loadings.

ABS:

acrylonitrile—

butadiene—

styrene

,

DFIR.

Douglas

fir;

FPU:

flexible

polyurethane

foam;

MOD:

modacrylic;

PPS:

polyphenylsulfone

;

PSTY:

polystyrene;

PVC:

poly(vinyl

chloride);

PVCZ:

poly(vinyl

chloride)

with

zinc

f

errocyanide

;

REDO:

red

oak;

RPU:

rigid

polyurethane

[1]
CO

CppnO

C0

Cpprr °

Figure 6. Rate of carbon monoxide generation (ppm) during decomposition

of flexible polyurethane foams (Samples 11,12,13 and 14) and

polyester (Sample 15) at a concentration of 30 mg/1 [9]

46
250

r\

to©

-4-> D

C

E

v-/

IxJ z:H

CUKJd^ NOH

47

Figure

7.

Hydrogen

cyanide

generation

from

nitrogen-containing

materials

decomposed

in

the

non-flaming

mode

at

various

mass

loadings

(for

abbreviations,

see
o

UJ

5

K

<c

_0l * n*W)

NC«ivyiNaoHOO svo

48

Figure

8.

Rate

of

CO

and

CO^

generation

from

Douglas

fir

decomposed

in

the

flaming

mode.
Quartz baakar

Haating

alamants

Furnaca

Insulation

Thermocouple

wall

Aluminum

platform

Support rod

• Load call

Figure 9. Load cell attached to cup furnace

49
100.0 Isvr8o

in

COoo

COo

in

CVJ o

CVJ o

inoo

in

(%) 1W0I3M

50

Figure

10.

Weight

loss

of

flexible

polyurethane

foam

decomposed

at

375°C

in

the

cup

furnace
Figure 11. Aerator inside quartz beaker that fits into cup

furnace. Aeration holes are on bottom of ring.

51
(ludd) NOI1VU1N30NOO 03

52

Figure

12.

Generation

of

CO

from

the

flaming

combustion

of

flexible

polyurethane

foam

in

the

presence

of

various

air

flow

rates

through

the

cup

furnace.
60000

53

Figure

13.

Generation

of

C09

from

the

flaming

combustion

of

flexible

polyurethane

foam

in

the

presence

of

various

air

flow

rates

through

the

cup

furnace
6000

Ul

1

h-

(Ujdd) NOIlVdlNaONOO oo

54

Figure

14.

Generation

of

CO

from

the

non-flaming

thermal

decomposition

of

flexible

polyurethane

foam

in

the

presence

of

various

air

flow

rates

through

the

cup

furnace
5000

(uidd) NOI1VH1N30NOO zOO

55

Figure

15.

Generation

of

C0

o

from

the

non-flaming

thermal

decomposition

of

flexible

polyurethane

foam

in

the

presence

of

various

air

flow

rates

through

the

cup

furnace.

Appendix A. Criteria Developed by Anderson et al., [2] for a Satisfactory Fire Toxicity Test Method

Criterion 1 - temperature range or more than one fixed temperature will be used

for sample decomposition.

The reason for criterion one is that toxicity is clearly dependent on

temperature. The use of a single predetermined temperature will compare

materials under identical conditions but will not explore the range of behavior

of the material being studied. Since one aim of a toxicity study is to

determine the worst behavior of the material, the single fixed temperature is

not a successful approach.

Criterion 2 - The sample should be tested as a single piece unless in actual

use the product is used in multiple small pieces.

This is in response to observations that burning behavior of materials is

geometry dependent, and subdivided samples may not yield toxicity data consistent with single piece samples.

Criterion 3 - The combustible portion of the test sample must fully decompose

in the test process.
Appendix A, page 2

Criterion three provides for evaluation of the entire combustible portion of

the test product as opposed to the rapidly released toxicants.

Criterion 4 - Test animals must be exposed to the full range of decomposition

products

Criterion four follows directly from criterion three.

Criterion 5 - The exposure chamber must be adequate in size.

Criterion five requires that the oxygen and carbon dioxide in the test

chamber remain within physiological limits during control conditions.

Criterion 6 - Timed endpoints must be clearly determined.

Criterion six requires that if a time event is used as an endpoint it must

be possible to determine that endpoint accurately. The respiration of a rodent

is frequently very shallow and difficult to detect near the point of death. A

monitoring system for measuring heart or respiration rate would be a satisfactory alternative.

Criterion 7 - Physical contact between animals should be prevented during

exposure.
Appendix A, page 3

Criterion seven is directed toward avoiding uneven exposure conditions which

result when animals huddle together, breathing through each others fur during

the exposure period.

Appendix B. Design Features of the Cone Radiant Heater Apparatus

Size and scale

It was decided at the start that any major scaling-up of the apparatus, compared to the existing Cone Calorimeter, would not be economically

feasible, and any minor variations to the specimen size would not have a

practical effect. Thus, we were committed to a specimen face size of 100 mm by

100 mm. In the Cone Calorimeter [5], the specimen depth is not standardized

unless a specific application category is identified. It is considered

reasonable to test specimens from 6 mm to 50 mm deep. The lower limit arises

because of the desire not to be overwhelmed by the heat loss effects to the

backing substrate. The upper limit comes from the objective of maintaining

planar burning, which would not be viable if the ratio of width to depth

dropped below about 2:1.

Means of achieving a square-wave exposure

Plastic foam materials, when tested at the maximum size of 100 x 100 x

50 mm, can burn for as short a time as 3 minutes. Conversely, a slab of solid,

high density plastic may burn for a half hour or more. The fact that some test

materials can be consumed in as short a time as 3 minutes was seen to preclude

any straightforward type of "dynamic" or flow-through geometry, if Haber's Rule

is not to be unwittingly invoked. This is because the standard methodology for

toxicity testing requires that the animal be exposed for a fixed, specified
Appendix B, page 2

amount of time. If, however, the concentration during that period is not

nearly constant, it is not possible to conclude that the animals were exposed

to a given concentration for that fixed time. Instead, all that can be

concluded is that a concentration * time product was delivered. It was then

observed that a time scale mismatch could be accommodated if the combustion and

the animal exposure processes were separated. Thus, the following scheme was

evolved:

The animal chamber is built so that it can be evacuated.

After each test, the chamber is flushed out with clean air and

then evacuated to a low-grade vacuum.

The animal chamber is filled with combustion products from the

combustion chamber at a controlled rate. This rate can be so

chosen as to backfill the animal chamber with either a uniform

representation of the products of the complete burning

sequence, or, for longer burning specimens, only the initial

products, or only the late products, etc.

Once the animal chamber is backfilled to ambient pressure, the

animal ports can be opened, animals exposed, and the actual

animal testing started.
Appendix B, page 3

This operational description is highly simplified; details of

construction are illustrated in Figures 3 and A of main text; the operational

procedures are described in Appendix C.

Appendix C. Operational Description of the Cone Radiant

Heater Toxicity Apparatus

The Cone Radiant Heater Toxicity Test Apparatus is composed of two

independent enclosures that are connected by a 9 mm I.D. stainless steel pipe.

The pipe is connected to a ball valve which manually controls the gas flow rate

between the combustion chamber and exposure chamber. A differential pressure

transducer is connected to two points along a straight section of the tube to

allow for the actual measurement of flow rate.

The combustion system is a modified Cone Calorimeter. It includes a

cone heater, load cell, and Pyrex enclosure connected to a hood discharging to

an exhaust duct with a damper control installed. The volume of the combustion

chamber is estimated to be about 100 2.; if one includes the duct work up to the

damper control, the volume is estimated to be 175 2,. Sampling of the

combustion atmosphere is performed 30 cm upstream of the damper control.

Unlike with the Cone Calorimeter, where the normal combustion air comes from

the surrounding environment, flow through the combustion chamber in the present

apparatus is controlled by metering compressed gases into the bottom of the

combustion chamber. The gases flow from below the sample and cone support

structure up to the hood and out the exhaust duct. The duct continues beyond

the damper control to a blower system that is turned on to vent the various

enclosures as needed.

The animal exposure chamber is a 25 mm thick PMMA enclosure having a

volume of 200 2, and which is reinforced with steel supports. The enclosure is

fitted with provisions for the insertion of up to six animals in a head-only

exposure, and with a series of valves for gas inflow, outflow, and monitoring.
Appendix C, page 2

The valves connect the exposure chamber to either a vacuum pump, a series of

gas analyzers, and the combustion chamber. A thermocouple is installed through

one of the pipe fittings to allow for the measurement of exposure chamber

temperature. This is provided so that the animals would not be introduced into

the chamber if the temperature exceeds the maximum allowable value of 40 °C.

It is the intent of this design to expose the animals to fixed combustion

product concentrations previously piped in from the combustion chamber (i.e.,

square wave exposures).

Setup Procedure

Prior to beginning a test, the combustion and exposure chambers are

cleaned. It was found necessary to also clean the sampling pipe and control

valve connecting the two chambers after each test. Repeated use of the

uncleaned connecting hardware could result in clogging of components.

Because of the variability in sample thickness, the cone heater must be

adjusted to the proper height to insure that the upper sample surface is at the

proper distance from the cone heater. Power is applied to the cone heater

and the heater controller is set to maintain the cone heater at a constant

temperature. A water cooled heat flux meter is used to measure the actual

heat flux incident on the sample surface. When the cone heater is stabilized

at a desired energy level, the heat flux meter is removed.
Appendix C, page 3

While the cone heater is reaching equilibrium, the exposure chamber is

sealed at all openings. The ball control valve is shut, and the analyzer lines

and the animal ports are closed. The line to the vacuum pump is opened and the

pump is turned on. The exposure chamber is evacuated to approximately 3 kPa or

less of pressure.

The data acquisition system is turned on and the gas analyzers are calibrated with zero and span gases. Continuous gas analysis is performed for

three gases: CO, C0 2 , 0 2. The gas sampling line is equipped with a dead space

sampling loop that allows for intermittent gas sampling for gas chromatographic

analysis. For example, HCN would be sampled from the dead space sampling loop.

Preliminary Testing

The autoignition heat flux for a given sample is determined by exposing

a series of specimens to different incident heat flux levels and noting the

minimum heat flux necessary to cause a sample to self -ignite. In general, if a

specimen has not self-ignited within ten minutes, the incident heat flux level

needs to be increased. Actual testing is conducted with the incident heat flux

level set 1 to 2 kW/m2 below the autoignition heat flux. This results in a

non-flaming exposure. The same flux level is used for flaming exposures,

however, the decomposition products are induced into flaming by the use of an

AC electric spark discharge.
Appendix C, page 4

Sample Testing

Following the set-up procedure previously described, an airflow rate

through the combustion chamber is selected. It has been found that 25 2,/min

appears to be a usable value. The data acquisition system is initialized. The

sample is inserted into the combustion chamber and the data acquisition is

begun. With the damper control opened approximately 40%, the sample is

allowed to decompose. Depending on the combustion mode, flaming or non-flaming, sampling of the duct gases into the exposure chamber begins two to four

minutes after the start of the sample exposure.

The exposure chamber is filled at a rate that is less than the

combustion chamber airflow rate. This sampling rate is maintained throughout

the filling process by means of manual control, using the differential pressure

gage. This filling process is driven solely by pressure difference between the

evacuated animal chamber and the essentially neutral pressure combustion

chamber; thus, complete filling with combustion products would take an infinite

time. Instead, when the chamber is filled to a pressure of 95 kPa with

combustion products, the control valve is shut. The exposure chamber is then

filled to neutral pressure by introducing clean air from a supply tank. The

combustion chamber is cleared using the blower system with the damper control

completely opened.
Appendix C, page 5

With the exposure chamber at atmospheric pressure, the gas analyzers are

connected to the exposure chamber. Gases are drawn through the dead space

sampling loop unless a sample is to be taken for GC analysis. Switching the

the gas analyzers. After this, the animal chamber temperature is noted to

determine if it is below the maximum value permitted for the animals. It is

The animals are inserted and can be clearly observed throughout the

exposure time. Data is collected prior to and during the exposure.

Data Reduction

The mass loading (i.e., pyrolysate concentration) in the animal chamber,

in units of mg/2-, is computed as follows. The specimen mass loss rate,

dm(t)/dt (mg/s), during the period of combustion sampling is determined from

the load cell data. The air flow rate in the combustion chamber," V , is ai ir '

taken to be the value as metered in by the rotameters (2,/s). The concentration

in the combustion chamber outflow during the sampling period is given by

four-way valve creates the dead space volume without interrupting the flow to

possible to wait until the gases have sufficiently cooled before inserting the

animals

.

out

b
Appendix C, page 6

It is assumed that the animal exposure box is being filled at the same

concentration. The concentration in the animal exposure box is then

f(t)

c

V,

L

b

b

dt

Post Exposure

Following the preselected exposure time, the animals are withdrawn and

the exposure chamber is connected to the exhaust blower to clear remaining

decomposition products. Animals are treated as in the NBS Toxicity Test

Method

.
Appendix D

Toxicity of the Combustion Products From a Flexible

Polyurethane Foam and a Polyester Fabric Evaluated Separately

and Together by the NBS Toxicity Test Method^

Barbara C. Levin, Maya Paabo,

Cheryl S. Bailey, Steven E. Harris

Center for Fire Research

National Bureau of Standards

Gaithersburg, MD 20899

ABSTRACT

Representative specimens of two materials, a flexible polyurethane foam and a polyester, were thermally decomposed separately and together in order to compare

the toxicological effects of the combustion products from the combined materials

with those from the single homogeneous materials. Gas concentrations (CO, C0 2 , 0 2 and HCN), blood carboxyhemoglobin, and LC S0 values [the concentration of

material necessary to kill 50% of the test animals (Fischer 344 male rats) during

a 30 minute exposure and a 14 day post-exposure observation period] were determined for the separate and combined materials under both flaming and non-flaming

conditions. The results of the combined experiments indicated that under non- flaming conditions, both materials contributed in an additive manner to the

concentration of the combustion products. However, under flaming conditions,

the generation of HCN and CO is greater than that predicted from the addition of

the maximum amounts produced by the materials separately.

INTRODUCTION

In the industrialized world, the United States is second only to Canada in

the number of fire deaths per capita [1]. The fire scenario which produces

the most fire deaths in the U.S. begins with an inadvertently dropped cigarette

in an upholstered piece of furniture. Since the majority of commercially

available upholstered furniture today contains some formulation of flexible

polyurethane foam as a filling material and a covering fabric which is either a cellulosic or a thermoplastic such as polyester, these two materials were chosen

for this study. Many small-scale laboratory studies have examined the toxicity

of the combustion products from flexible polyurethane foams [2] or polyesters

[3]. There have also been numerous large-scale room burns of chairs, multiple

materials, or composite materials which included these materials. Alarie et al.

compared the toxicity of individual materials (determined in small-scale tests)

with the toxicity of multiple combined materials (determined in large-scale chair

burns) [4], However, the objective of their study was to compare the toxicity of

the major components of the chairs (flexible polyurethane foam, polyester, and

^This paper is a contribution of the National Bureau of Standards and not

subject to copyright
Appendix D, page 2

cotton fiber) with their individual toxicity in small-scale tests. They did not

study the toxicity of the combined components in the small-scale tests.

This study was designed to examine and to compare the toxicological effects

from the combustion products of a flexible polyurethane foam and a polyester

fabric in order to determine the contribution of the combustion products from

each material to the overall toxicity of the mixture. Two separate aspects of

this problem were considered: (1) Would the toxicity be affected merely because

the increased mass of the combined materials increase the concentrations of the

pyrolysis or combustion products or does some unexpected toxicological interaction occur? (2) Would the types or yields of toxicants be affected?

MATERIALS AND METHODS

The materials studied, polyester fabric and a flexible polyurethane foam, were

generically classified, i.e., the specific chemical formulations were unknown.

Both the polyester upholstery fabric (100% polyester, scoured and dyed dark blue)

and the flexible polyurethane foam were obtained from the Consumer Product Safety

Commission, Washington, DC 20207. The results of a previous toxicological study

on this polyurethane foam, designated CPSC // 1 3 , have been published [5].

The acute inhalation toxicity of the combustion products from these materials

was evaluated according to the NBS Toxicity Test Method [6]. Each material

was examined at 25°C above and below its autoignition temperature (Tables 1 & 2).

In addition, polyester was tested at the non-flaming temperature of the polyurethane foam (375°C), and the flexible polyurethane foam was examined at the

flaming temperature of the polyester (525°C). Combinations of the two materials

were thermally decomposed in the cup furnace at a non-flaming temperature of

375°C (which was the highest possible non-flaming temperature, since the polyurethane foam would flame at higher temperatures) and a flaming temperature of 525°C

(the temperature at which both the polyurethane and polyester would undergo

flaming combustion, if tested separately). In all cases, the amount of material

consumed was determined by weighing the residue.

Carbon monoxide (CO) and carbon dioxide (C0 2

) were measured continuously by non- dispersive infrared spectroscopy. Oxygen concentrations were measured con- tinuously by a galvanic cell or a paramagnetic analyzer. The HCN generated from

the polyurethane foam was sampled with a gas-tight syringe approximately every

three minutes and analyzed with a gas chromatograph equipped with a thermionic

detector [7].

Fischer 344 male rats, weighing 200-300 grams, were obtained from the Harlan

Sprague-Dawley Company (Walkersville, Maryland) or Taconic Farms (Germantown, New

York) and were allowed to acclimate to our laboratory conditions for 10 days

prior to experimentation. Animal care and maintenance were performed in

accordance with the procedures outlined in the National Institutes of Health's

"Guide for the Care and Use of Laboratory Animals" [8].

Six animals were exposed in the head-only mode in each experiment. Exposures

were for 30 minutes, during which blood for carboxyhemoglobin (COHb) analysis was taken at 0 time, approximately 15 minutes and just before the end of the experiment from cannulated animals (one or two animals per exposure were surgically

prepared with a femoral arterial cannulae 24 hours before experiments [9]). The

number of animals that died at each mass loading of material was plotted to

produce a concentration-response curve from which an LC 50 value was calculated

[10]. The LC 50 , in this case, is defined as the mass loading of material per
Appendix D, page 3

unit chamber volume (mg/2.) which caused 50% of the animals to die during the 30

minute exposure plus the 1A day post-exposure observation period. (Animals that

were still losing weight on day 1A were kept until they died or recovered as indicated by three days of successive weight gain. All deaths were included in

the LC 50 calculation. Surviving cannulated animals were sacrificed following the

test and only counted in the determination of the LC 50 if they died during the

exposure.) If no deaths occurred at the highest concentration tested, the LC 50

is listed as greater than that concentration.

RESULTS AND DISCUSSION

Flexible Polyurethane Foam

The chemical and toxicological data obtained from the flexible polyurethane

foam thermally decomposed under non-flaming (375°C) and flaming (A25°C and 525°C)

conditions are presented in table 1. Similar to other non-fire retarded flexible

polyurethane foams tested in this laboratory, no animal deaths occurred during

the 30 minute exposures to concentrations up to AO mg/ 2. regardless of the mode of

decomposition [5,6]. Post-exposure deaths only occurred following the non- flaming experiments. The LC S0 value for the non-flaming mode was 37.0 mg/ 2, with

95% confidence limits of 29.8-A6.0 mg/2,, whereas, the LC 50 value for the flaming

mode was greater than AO mg/2., i.e., no animal deaths were noted from any of the

concentrations tested up to AO rag/ 2.

Recent results [11] from this laboratory on the toxicity of CO, C0 2 and HCN alone

and in various combinations have shown that the 30 minute LC 50 for CO in air was

A600 ppm. No animals died below A100 ppm or post-exposure. The 30 minute LC 50

for C0 2 in air was greater than 18% (1% = 10,000 ppm). However, when CO and C0 2 were combined, the presence of 5% C0 2 increased the toxicity of CO such that

animals died from 30 minute exposures to 2500 ppm. Some of these deaths were within 2A hours. The combination of CO and HCN (30 minute HCN LC 50 = 160 ppm)

showed the following additive effect:

[col [HCN]

LC.„ CO LC,„ HCN

5U dU

> 1, the animals died.

When this formula equalled less than 1, the animals lived. Again deaths were

observed up to 2A hours post-exposure.

Comparison of the gas concentrations generated from the polyurethane experiments

to the pure gas experiments quoted above showed that lethal amounts were not

produced in any of the tests (Table 1). Therefore, the deaths, which occurred as late as 1A days in the non-flaming mode, were due to other toxic combustion

products or undetermined factor(s).

Polyester

All the chemical and toxicological data collected from the thermal degradation of

polyester are shown in table 2. In the non-flaming mode at A75°C, the LC S0 value

of the polyester was 39.0 mg/ 2, with 95% confidence limits of 38. A - 39.5 mg/ 2.. Animal deaths were noted both during and following the 30 minute exposures. At

375°C, however, no animal deaths were observed up to concentrations of 50 mg/2..

However, it is important to note that at the lower temperature (375°C), only 22-

55% of the original sample was consumed; whereas, at A75°C, approximately 85% of

the sample was consumed. Based upon a comparison of the toxicological effects at

the actual masses consumed at A75°C, deaths would not be expected at the masses

consumed at the lower temperature.
Table

Appendix D, page 4

U) * S*- + -a

fn

i

HJTJ

•s

S « ill

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Appendix T), page 6

Examination and comparison of the gas concentrations that were generated during

these non-flaming experiments with our pure and combined gas toxicity experiments

discussed above indicate that the average CO levels are 37-80% lower than that

necessary to cause death by CO alone. In many experiments, the CO levels did

not plateau but continued to rise throughout the exposures reaching a maximum at

30 minutes. This maximum value, however, was still lower than the 30 minute LC S0

value for CO in air (4600 ppm) (Table 2). The average C0 2 present is about 10%

of that necessary to increase the susceptibility of the rats to lower levels of

CO. However, the maximum COHb levels at the end of these 30 minute lethal

exposures are relatively high, 75-83%. These results indicate that CO, although

low, is contributing to the within-exposure deaths, but other toxic or irritant

gas(es) are also acting in conjunction with or to potentiate the effects of the

CO. The cause of the late post-exposure deaths are unexplained.

In the flaming mode, the LC 50 value for the polyester was 37.5 mg/ 2. with 95%

confidence levels of 35.3 - 39.8 mg/2 (Table 2). In the lethal experiments, the

COHb levels ranged from 83-85% and the rats died within exposure or shortly

thereafter. These factors would implicate CO as the main toxicant. However, the

average CO is approximately 50-65% of the lethal concentration determined for CO

alone. Even considering the effect of C0 2 on CO, the average values of CO and

C0 2 from flaming polyester are still too low to account for the deaths that

occurred during these 30 minute exposures. Only if one considers the maximum CO

levels along with the C0 2 concentrations would the deaths be predictable.

Combined Flexible Polyurethane Foam and Polyester

Non- flaming experiments . The thermal decomposition of both flexible polyurethane

foam and polyester in the non-flaming mode was studied at 375°C whi:h was 25°C

below the autoignition temperatures of the polyurethane. In these experiments,

the polyester fabric was folded and dropped into the cup furnace immediately

preceding the polyurethane foam. Upon heating, the samples collapsed in less

than one minute and formed a black ball in approximately two minutes.

Since the polyester, by itself, was not toxic at 375°C^ even at the highest

loading tested (50 mg/ 2), a sublethal amount of polyester (20 mg/ 2) was chosen to

test whether this addition would increase the toxicity (lethality) of the

polyurethane foam in the combination experiments. If the polyester component has

no effect at this temperatures, then the addition of 20 mg/ 2. of polyester to the

LC 50 value of the polyurethane would increase the LC 50 value of the mixture by

20 mg/2; that is, the LC 50 value of the polyurethane, 37 mg/2, would increase to

approximately 57 mg/ 2. The results, however, showed that the LC 50 value of the

combined materials only increased to 47.5 mg/ 2, an indication that the polyester

was not inert but contributed to the toxicity by about 10 mg/ 2 (Table 3). The

total amount of polyurethane in the combined LC 50 is only 27.5 mg/ 2, which is

outside the 95% confidence limits of the LC 50 for polyurethane alone.

Since a significant proportion of the polyester is not decomposed at 375°C,

these data were also analyzed on the basis of mass consumed/ chamber volume.

The experiments on the polyester alone at 375°C showed that when 3.88 grams (20

mg/2) were loaded into the cup furnace, 78% remained as residue and only 4.3 mg/

2

^This lower toxicity is probably due to the large fraction (more than 45% of

the initial mass loading) of the polyester which is not consumed at the lower

temperature.
Appendix D, page 7

were actually consumed. Using the same null hypothesis as before, that is,

the polyester at this temperature has no effect on the combined toxicity, then

one would expect the LC 50 of the polyurethane (31.9 mg/ 2, consumed weight) should

increase by 4.3 mg/2, producing a combined LC 50 of 36.2 mg/ 2. However, the LC 50 of

the combination is only 26.2 mg/ 2,, consumed weight, indicating that the polyester

increases the toxicity by about 10 mg/2,; this is the same value calculated when

the mass loaded, rather than mass consumed, was considered.

In these non-flaming experiments in which 20 mg/ 2. of polyester were added to

different loadings of flexible polyurethane foam, all deaths occurred during

the post-exposure period. These results are more characteristic of the polyurethane experiments, decomposed by itself, and different from those seen with the

polyester alone. The concentrations of measured gases (CO, C0 2 , HCN) were not

responsible for the post-exposure deaths that occurred.

The average concentration of the primary gases (CO, C0 2 , HCN) generated from the

thermal decomposition of the mixture of the materials appear to be approximately

equal to the sum of the average concentrations generated from the individual

materials under non-flaming conditions (Table 4 and Figure 1). Therefore, if the

concentrations of the primary gases from the thermal decomposition of the

individual components are known, then a reasonable prediction of the gas con- centrations from the mixture decomposed under the same conditions can be made.

Flaming experiments . The experiments in which the flexible polyurethane foam and

polyester were combined and tested in the flaming mode were conducted at 525°C

(25°C above the autoignition temperature of the polyester) to ensure that both

materials would flame. In these experiments, the mass concentration of polyurethane was kept constant at 20 mg/ 2, and only that of the polyester was varied

(Table 3). The reason for this approach was to see if a non-lethal amount of the

less toxic material (in this case, the polyurethane foam) would increase the

toxicity of the polyester whose LC S0 could be measured. The polyurethane foam

when tested by itself in the flaming mode at 425°C had produced no deaths either

during or post-exposure at concentrations up to 40 mg/ 2,, whereas, the polyester

fabric when decomposed by itself in the flaming mode at 525°C had produced both

within and post-exposure deaths. The LC 50 value for the flaming polyester fabric

by itself was 37.5 mg/ 2.. Therefore, if the polyurethane was toxicologically

inert, the addition of 20 mg/ 2. of polyurethane should have raised the LC S0 value

to 57.5 mg/ 2.. In actuality, the 30 minute and 14 day LC 50 value calculated for

the combined exposures was 39.0 mg/ 2. with 95% confidence limits of 36.0 - 42.2

mg/ 2,. These results, showing that the LC S0 value for the combined materials was

lower than expected by almost the exact amount of polyurethane added to the

system, are an indication that the polyurethane and the polyester are both

contributing in an additive manner to the toxicity. In other words, the combination of 19 mg/ 2 of polyester and 20 mg/ 2 of polyurethane produced the LC 50 ; whereas, 20 mg/ 2 of the polyurethane foam decomposed by itself in the flaming

mode produced no deaths (Table 1) and the polyester decomposed by itself did not

produce any deaths below a concentration of 35 mg/ 2 (Table 2). Thus individual

sublethal concentrations of this polyurethane foam and polyester fabric are adding up to a concentration which is lethal.

Examination of the average gas concentrations of CO, C0 2 , and HCN which were

generated during these exposures and comparison of these gas values with our pure gas toxicological studies shows that the concentrations of these gases were sufficient to account for the deaths that occurred. Table 3 also shows HCN

levels higher than those seen in the flaming exposures of polyurethane alone at

525°C which, in turn, were greater than at 425°C (Table 1). Figure 2 shows the
Table

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Appendix D, page 9

generation of HCN from 20 mg/ 2 of the flexible polyurethane when decomposed alone

or combined with the polyester under various flaming conditions. Polyurethane

decomposed alone at 425°C produced an average HCN concentration of 19 ppm;

whereas, at 525°C, it produced an average of 37 ppm in one experiment and 51 ppm

in another. The flaming decomposition of various amounts of polyester with 20

mg/ 2. of polyurethane at 525°C produced greater concentrations of HCN than in any

of the experiments on the polyurethane alone (Tables 1,3 and Fig. 2). This

result was unexpected since polyester contains no nitrogen and should not

contribute to the HCN generation. Figure 2 also shows that the HCN generation

over time from 20 mg/ 2. of flaming polyurethane foam alone tends to plateau during

the 30 minute test, whereas, in the combination studies of this polyurethane

(20 mg/ 2) and polyester, the HCN continues to increase throughout the experiments. The reason for this increased level of HCN is unexplained at this

time

.

Table 4

Gas Concentrations from the Thermal decomposition of

Mode Temp

.

(°C)

Polyurethane Foam and Polyester Alone and in Combination

Hass Loaded Average Gas Concentration*

Material Chamber Volume

(ma/O

CO

(ppm)

C0 3 (ppm) HCN

(ppm)

Flaming 525 Polyurethane 202 510 (+ 120) 14900 (+ 4200) 44 (+ 47)

Polyester 30 2220 25200 —

Total 2730 40100 44

Polyurethane 20 3070 34700 59 + + Polyester 30

Non- 375 Polyurethane 30 700 2690 4 Flaaing

Polyester 2Q3 50 600 —

Total 750 3290 4

Polyurethane 20 850 3400 5 + + Polyester 30

1 Average gas concentration:

integrated area under instrument response curve for 30 ainutes ppa- tin

30 ainutes

2 Results are average + range of two analytical experiaents

3 Analytical experiment (no animals

)

30 ain
Appendix D, page 10

In the flaming mode, the concentrations of CO from combined materials was also

greater than the sum of the CO concentrations from the individual materials

(Figure 3). This was more apparent from the graphic representation of the actual

generation of CO than from the tabular depiction of the average concentrations

(Table 4).

CONCLUSIONS

Individual Materials

• The decomposition products of the flexible polyurethane foam produced no deaths during exposure and only caused post-exposure deaths in the non- flaming mode.

• The polyester when decomposed 25°C above or below its autoignition temperature caused deaths both during and following exposures.

• Comparison of the CO, C0 2 , and HCN concentrations generated from the

individual materials with pure gas toxicity experiments (performed with

single and multiple gases) indicated:

1. the deaths from flexible polyurethane could not be explained by the

concentrations of these gases,

2. non-flaming polyester produced relatively high COHb (75-83%) levels,

but lower than lethal average or maximum CO concentrations. Even

when CO was considered with C0 2 (which potentiates the toxicity of

CO), the combination was not sufficient to account for the deaths,

and

3. the deaths from exposures to flaming polyester products were probably

due to CO since COHb values were 83-85%. In this case, the maximum

(not the average) concentrations of CO plus C0 2 were sufficient to

predict the deaths.

Combined Materials

• Depending on the amount thermally decomposed, both materials contributed

to the combined toxicity. In the flaming mode, the contribution was

additive.

• Similar to the polyurethane results, the non-flaming combined experiments

only produced post-exposure deaths which were not attributable to the

generated CO, C0 2 , and HCN concentrations.

• The deaths observed from the flaming combined experiments were explainable

based on the concentrations of CO, C0 2 , and HCN.

• Comparison of the gas concentrations from the combined materials to those

from the individual materials indicated:

1. The non-flaming generation of CO, C0 2 , and HCN appear to be approximately equal to the sum of the concentrations from the single

materials.
Appendix D, page 11

2.

The flaming generations of CO and HCN were greater than the sum of

those from the single materials.

ACKNOWLEDGEMENTS

This work was supported in part by the Consumer Product Safety Commission,

Washington, DC, Dr. Rita Orzel, Project Officer. The conclusions are those of

the authors and not the Consumer Product Safety Commission.

REFERENCES

1. Fire in the United States , Second Edition, Federal Emergency

Management Agency, FEMA-22, July, 1982.

2. "Literature Review of the Combustion Toxicity of Flexible Polyurethane

Foam," Status Report on Fire Combustion Toxicity, TAB-B. Consumer

Product Safety Commission, Washington, DC 20207, May 31, 1984, 103 p.

3. Braun, E. and Levin, B.C.: "Polyesters: A Review of the Literature on

Products of Combustion and Toxicity," Nat. Bur. Stand. (U.S.) Gaithersburg,

MD, NBSIR 85-3139, June 1985.

4. Alarie, Y., Stock, M.F., Matijak-Schaper , M., and Birky, M.M.:

"Toxicity of Smoke During Chair Smoldering Tests and Small Scale Tests

Using the Same Materials," Fund. & Appl. Tox. 3:619-626, 1983.

5. Levin, B.C., Paabo, M., Fultz, M.L., Bailey, C., Yin, W. , and Harris,

S.E.: "An Acute Inhalation Toxicological Evaluation of Combustion

Products from Fire Retarded and Non-Fire Retarded Flexible

Polyurethane Foam and Polyester," Nat. Bur. Stand. (U.S.) Gaithersburg, MD,

NBSIR 83-2791, November, 1983.

6. Levin, B.C., Fowell, A.J., Birky, M.M., Paabo, M. , Stolte, A., and

Malek, D. : "Further Development of a Test Method for the Assessment of

the Acute Inhalation Toxicity of Combustion Products," Nat. Bur.

Stand. (U.S.) Gaithersburg, MD, NBSIR 82-2532, June 1982.

7. Paabo, M. , Birky, M.M. , and Womble, S.E.: "Analysis of Hydrogen Cyanide

in Fire Environments," J. Comb. Tox. 6:99-108, 1979.

8. Committee on Care and Use of Laboratory Animals: "Guide for the Care

and Use of Laboratory Animals," DHEW publication No. (NIH) 78-23.

U.S. Dept, of HEW, Public Health Service, National Institutes of

Health, 1978.

9. Packham, S.C., Frens, D.B., McCandless, J.B., Patajan, J.H., and

Birky, M.M.: "A Chronic Intra-arterial Cannula and Rapid Technique for

Carboxyhemoglobin Determination," J. Comb. Tox. 3:471-478, 1976.

10.

Litchfield, J.T., Jr., and Wilcoxon, F.: "A Simplified Method of

Evaluating Dose-effect Experiments," J. Pharmacol, and Exp. Therapeut.

96:99-113, 1949.

Levin, B.C., Paabo, M., Gurman, J.L., Harris, S.E., and Bailey, C.S.:

"Toxicological Effects of the Interactions of Fire Gases and Their Use in a Hazard Assessment Computer Model," The Toxicologist , 5:127, 1985.

11 .
Appendix D, page 12 c

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NBS*1 14A (REV. 2-8C) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions

)

1. PUBLICATION OR

REPORT NO.

NBSIR 85-3274

2. Performing Organ. Report No. 3. Publication Date November 1985

4. TITLE AND SUBTITLE

An Exploration of Combustion Limitations and Alternatives to the NBS

Toxicity Test Method.

5. authoR(S) Barbara C. Levin, Vytenis Babrauskas, Emil Braun, Joshua Gurman and

Maya Paabo

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

10.

SUPPLEMENTARY NOTES

J Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bl iography or literature survey, mention it here)

Some limitations and potential limitations of the NBS toxicity screening

test method had been identified in earlier work. These limitations have now

been explored in greater detail. Also investigated was an alternative combustion system, consisting of a radiant cone heater, identical to the one in the

recently developed Cone Calorimeter, an enclosed combustion chamber, and a slightly revised variant of the animal chamber. The new animal chamber was so constructed that, prior to the insertion of the animals, it could be evacuated

and then back-filled with a desired sampling of the combustion products. The

radiant combustion system showed a different mix of capabilities and limitations compared to the cup furnace combustor in the existing test method. In

the present project, the more detailed assessment of the cup furnace operation

leads to the recommendation that there is no single, universally preferable

combustion environment, but that the cup furnace is adequate for the intended

purpose of providing toxicity screening.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Combustion products; combustion toxicity; NBS toxicity test method; plastics;

radiant combustion

13. AVAILABILITY

[xj Unlimited

f | For Official Distribution. Do Not Release to NTIS

H Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

|~xl Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

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