-pHrposes and- is no4 to. be-fett

I AY1 ©IS A L BURfO R

1 iAy r? iz* 1 <S> ’A ARDS REPO&l

NBS 421.02- PROJECT

11-4212427 March 16, 1966

421.02-

11-4215627

F10S REPORT

9067

SMOKE PRODUCED BY BURNING

AIRCRAFT FINISH MATERIALS

by

D. Gross, T. G. Lee and J. J. Loftus

for

Federal Aviation Agency

Washington, D, C.

IMPORTANT NOTICE

NATIONAL BUREAU OF STA

intended for use within the G

to additional evaluation and re listing of this Report, either in the Office of the Director, Nat however, by the Government r to reproduce additional copies

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015.

ogress accounting documents

Tally published it is subjected

^production, or open-literature on is obtained in writing from

inch permission is not needed,

repared if that agency wishes

SMOKE PRODUCED BY BURNING AIRCRAFT

FINISH MATERIALS

By

Do Gross, T. G. Lee and J. J. Loftus

ABSTRACT

Smoke -measurements and an indication of the concentrations of some toxic decomposition products resulting from open flaming and

smouldering combustion of 15 aircraft finish materials are reported.

Charts and tables are included to facilitate estimating approximate

smoke and gas concentrations which might exist in aircraft during

an assumed fire exposure„

SMOKE PRODUCED BY BURNING AIRCRAFT

FINISH. MATERIALS

By

Do Gross, To G. Lee and J. J. Loftus

1 . Mater i al

s

A total of 15 materials were hand-delivered by FAA personnel

on 9 and 17 February. All materials were stored in a specimen

conditioning laboratory at 73°F and 50 percent relative humidity

for at least one week prior to test. The materials are listed in

Table I.

2 . Test Metho d

Smoke measurements and indications of toxic gas concentrations

were made in an enclosed smoke chamber similar to that described in

NBS Report No. 8947. Tests were performed under both flaming and

non-flaming (smoldering) exposure. The former test involved irradiating

the normally exposed surface of the specimen (2-9/16 in. square) with

2.5 watts/cm- and the application of a small pilot flame to induce

open flaming. The latter test involved the same radiant exposure

without the pilot flame. The smoke level was determined by measuring

the progressive attenuation of a light beam passed through the smoke

aerosol. Indications of the toxic gas concentration were obtained by

drawing a sample of the gas mixture in the test chamber through com- mercial colorimetric gas detector tubes and reporting results on the

basis of the manufacturers calibrations for the selected gases. In some instances an attempt was made to extend the range of these indicators by drawing less than the recommended gas volume through them

and reporting results on the assumption of linearity of indicated

concentrations with sample volume used.

3 . Smoke Measuremen t

Smoke is reported in terms of a specimen property, specific

optical density, a dimensionless attenuation coefficient which re- lates the quantity of smoke accumulated from a specimen of given

thickness, in terms of photometric obscuration.

Optical density is defined as D-log-^Q (where T = percent

light transmission), and is the single most characteristic measure

of the obscuring quality of a smoke. If the smoke is produced from

a surface of area A and collected in a closed chamber of volume V,

the optical density of the generated smoke should be directly proportional to A and inversely proportional to V. Optical density

is also proportional to the optical path length L, so that it is

appropriate to write

1

D s is termed the specific optical

the optical density measured over unit

chamber of unit volume produced from a area. Thus,

D

s V , 100

AL

lo§

10 T

density, and represents

path length within a specimen of unit surface

For the test chamber, V = 18 ft?, A = 0.0456 ft^, and L = 3 ft.

Ideally, the change in D g with time during the smoke accumulation

process will depend only upon the thickness of the specimen, its

chemical and physical properties, and the exposure conditions.

However, there are definite limitations to the use of specific

optical density for extrapolation and comparison with other box

volumes, specimen areas and photometric systems, and for extension

to human visibility. The degree to which such extensions are valid

depend upon a number of major assumptions: the smoke generated is

uniformly distributed, and is independent of the amount of excess

air available and of any specimen edge effects; coagulation and

deposition of smoke is similar regardless of the specimen size,

or the size and shape of the chamber; for any given smoke the

optical density is linearly related to concentration; and human

and photometric vision through light-scattering smoke aerosols,

expressed in terms of optical density, are similar.

4 . Toxi c Gas Measuremen t

Several times during each smoke test, a measured volume of

gas was drawn through one of several commercial gas detector tubes,

using a small syringe or bellows pump. Concentration was indicated

by a color change for carbon monoxide (M-S-A Carbon Monoxide Tester)

,

and by the length of color stain along pre-cal ibrated detector tubes

for all other gases (Draeger Multi-Gas Detector). The gas detector

tube was inserted into the smoke chamber from the top, and was situated approximately 20 inches above the specimen.

Indicator tubes were used to search for CO, HC1 , HCN, NC^, Cl^,

NH^ and COClg- Information regarding the measuring range, interfering

reactions, reuse, and the effects of temperature and relative humidity

were provided by the detector tube manufacturer. The upper and lower

limits of the measuring ranges for these tubes and some references

to the toxic hazard limits of these gases are summarized in Table II.

The toxic limits, which are included only as background information,

are not well defined, and will be discussed later.

No verification has been made by this laboratory of the manufacturers' claims for the accuracy of the indicators. Although not

recommended, a rough estimation was made of HC1 concentration above

the measuring range using a smaller volume than that prescribed and

multiplying the concentration accordingly.

2

5. Test Results

The test results given in Table I are based on the average

of duplicate tests (with few exceptions). Duplicate tests were

fairly reproducible in terms of both smoke buildup and indicated

gas concentration.

The smoke buildup curves for a typical flaming and a typical

smoldering test on each material are shown in Figures 1 through

15. In Table I are listed the specific optical density at a time of 2 minutes, and the peak specific optical density. For

Materials 10 and 11 under flaming exposure, peak specific optical

density values were not directly measurable since the very heavy

smoke concentrations exceeded the measuring capability of the

system.

Except for CO, HC1 and 1ICN, indicated gas concentration levels were generally below the M.A.C. values, so that interest was mainly

confined to these three gases. Although only a limited number of

gas measurements could be taken during each test, the peak indication

appeared to occur at approximately the same time as the peak smoke

level. It was noted, however, that the indicated 1IC1 concentration

dropped off rapidly after reaching a peak, whereas the CO and HCN

indications tended to maintain their peak indications for much longer

periods

6 . Discu s sion

Limitations were previously noted to the use of specific optical

density for extrapolation to other enclosure volumes and surface

areas. Within these limitations, the relationship between the

measured value of D and the geometrical factor for various

s LA

values of light transmission (or optical density) is shown in

Figure 16. The optical density level through which a lighted exit

sign may be seen can vary over wide limits depending on the general

illumination level, on the contrast threshold and the extent to

which the observer's eyes have been dark-adapted, as well as on

the irritating nature of the smoke. In Figure 16, five lines are shown for transmission values ranging from SO to 2.5 percent

(optical density 0.1 to 1.6) corresponding to the possible range

of visual limits.

If, as an example, it is assumed that a lighted exit sign can be seen when the transmission is down to 40% (optical density

0.4), and an aircraft cabin has a volume of 10,000 ft^ within

which smoke is uniformly dispersed, then Table III shows -the

estimated area A of material which may just begin to limit seeing

the exit sign at various distances L for several values of D s

. The choice of a critical specific optical density for each material

3

can presumably be based on a prescribed time period which is

sufficiently long to permit escape or defensive action. In

Table I are listed values of D s at a time of 2 minutes after

the start of thermal exposure (flaming or nonflaming) , and it

may be noted that these varied from 0 to 525 for the 15 materials

tested. The peak specific optical density values varied from

below 20 to over 530.

It has been assumed that the only smoke-producing material

involved was a single layer of the material tested. In the case

of the foam seat cushion (Material 15) , the specimen thickness

was only 1/2 inch, whereas the cushion was about 3 inches thick.

As noted previously, no verification was made by this laboratory of the manufacturers' claims for the accuracy of the colorimetric gas indicator tubes. The use of the recorded values as true concentration values with any high degree of confidence may

be limited by a number of factors, including the time and location

of sampling, the effects of relative humidity and elevated temperatures, the absorption of gas on the surfaces of the chamber and

on smoke particles, interpretation of the color change, and interfering reactions by other gases. The error in reading the color

stain length may be up to ±15 percent in some cases. No correction

was made for the temperature of the gas sample, the maximum value

of which was approximately 40°C for the smoldering tests and 50

to 85°C £or the flaming tests.

Even if the true gas concentrations were known, their use

in terms of toxicological limits, such as illustrated in Table II,

would still be open to some question. For example, there does not seem to be sufficient information available on the synergistic

(combined) effects of several toxic components. It may be noted

from the table that reference values of the toxic concentrations

lethal within a few minutes can vary from 20 to 400 times the

established M.A.C. values for the gases listed. Despite these

shortcomings, the colorimetric indicator tubes appear to serve

an immediate need, and it is useful to examine and interpret the

test results even if only in comparative terms.

In each case (except Material 15), a single layer of the

material was subjected to the test exposure. It should be noted

that the weight of the specimens (see Table I) varied by a factor

of more than 8 and thus gas and smoke concentration would be

expected to vary over wide limits.

- 4 -

From Table I, it may be noted that the CO readings ranged

up to 600 ppm. Since a reading of 50 ppm was considered to be

the normal background level in the test cabinet, only readings

of 100 ppm and above should be considered significant. HCN

readings ranging up to 45 ppm were obtained. Here the normal

background level was approximately 1 ppm. The background level

of HC1 appeared to be less than 1 ppm or below the lower detectable limit of the tube. Because HC1 gas is very soluble in

water, the readings changed more rapidly, and were probably

greatly affected by high concentrations of moisture (and smoke)

Measurements indicated that the moisture content during these

tests was between 10 and 20 mg/liter. The manufacturer reports

that for moisture concentrations of 10 mg/liter the HC1 colorimetric tube reading is 25 percent low.

High HC1 concentrations were indicated for all vinyl (PVC)

and modified acrylic-containing materials tested. The readings

were generally higher under flaming compared to smoldering ex- posure conditions, presumably due to the higher temperatures

involved. The highest indicated HG1 concentrations were developed

by Material 12, which was reported to be acrylic-modified PVC

(this was also the heaviest material). Materials 9 and 13 also

produced high HC1 indications. Although the recommended upper

measuring range of the HC1 tube was only 30 ppm, very rough

estimates of higher concentrations were made by using a smaller

volume of gas and mul tipi ying . the indication accordingly. Therefore, the indicated values are of very limited accuracy.

The highest indicated HCN concentrations were obtained for

Materials 2 (modified acrylic) and 7 (acrylic with polyurethane

foam). With few exceptions the acrylonitrile-butadiene-styrene

(ABS) and wool-containing materials also gave significant indications of HCN. The peak indicated HCN concentrations were very

nearly the same under flaming and smoldering exposure.

An approximate relationship between the toxic gas concen- tration measured in the smoke chamber and the projected concen- tration within a much larger chamber, such as an aircraft cabin,

is given by

This simply scales concentration (C) in direct proportion to the

area A of specimen involved and in inverse proportion to the chamber

volume V. As an example, the gas concentration in a 10,000 ft^ cabin

is shown in Figure 17 for a series of lines corresponding to surface

areas of 10, 100 and 1,000 ft^.

5

7 . Summary

Laboratory measurements have been made of the concentrations

of combustion-generated smoke and indicated toxic gases for 15

aircraft interior finish materials. Both smoldering and active

flaming conditions were considered and it was found that significantly more smoke was produced for several materials in the absence

of open flaming.

The smoke concentrations are reported in terms of the optical

density, which is the single most characteristic measure of the

visual obscuring quality of a smoke. A very wide range of obscuration levels was measured. The general relationship between the

measured optical density and the level of smoke through which a lighted exit sign may be seen was discussed, and a method was suggested for extrapolating to other chamber volumes, specimen

areas and visual path lengths under ideal conditions.

Toxic gas concentrations, principally CO, HC1 and HON, were

indicated using commercial colorimetric gas detector tubes. No

verification was made by this laboratory of the manufacturers'

claims for the accuracy of the indicators. Considering our limited previous experience with such tubes, and the possible

interfering effects of a number of factors, measurements were considered only as "indicated concentrations". Despite these

limitations, the colorimetric' indicator tubes appear to serve

an immediate need, even if the test results are interpreted in

comparative terms only. For the materials tested, maximum con- centrations of 600 ppm CO, hundreds of ppm HC1 , and 45 ppm HCN

were indicated. Tne general relationship between the toxic gas

concentrations in the smoke chamber and the projected concentrations within a much larger chamber was presented in graphical

form to permit extrapolation to the volume of an airplane

cabin and the surface area of material involved.

6

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*

Multiply

by

6.6

in.

2

to

obtain

weight,

in

grams,

of

specimen

area

exposed

**

Indications

of

HCX

concentrations

greater

than

30

ppm

estimated

by

dilution

Table

II.

Measuring

Range

of

Colorimetric

Indicator

Tubes

and

Toxicological

Data

for

Selected

Gases

Gas

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Table III

Critical (Projected) Surface Area of Material

Burned in 10,000 ft^ Volume

Specific

Optical

Density D s

V/LA

(for OD = .4)

Light

Distance

L

Specimen

Area

A

10 25 3 ft 133 sq ft

10 25 10 40

10 25 30 13.3

10 25 100 4

50 125 3 26.7

50 125 10 8

50 125 30 2.67

50 125 100 0.8

100 250 3 13.3

100 250 10 4.0

100 250 30 13.3

100 250 100 0.4







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