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4
SMOKE TOXICITY TESTING
INTRODUCTION
This report is primarily concerned with toxic hazards associated with fires.
However, the overall fire hazard (i.e., fatalities resulting from the inability of potential
victims to escape from a fire) should actually be considered in terms of three major factors:
(1) obscuration of vision, (2) heat, and (3) toxicity. The limits of human tenability for each
of these factors have been reasonably well defined; whichever of the three factors first
precludes escape sets the critical tenability limit for that fire scenario. Experience has
shown that individual tenability limits are often reached in the order stated above (i.e.,
obscuration of vision and incapacitation due to heat generally occur before the tenability
limit for inhalation of toxic gases is reached). This is especially the case with rapidly
developing, flaming fires. In terms of lethality, however, about 70 percent of fire fatalities
result from smoke inhalation (Hardwood and Hall, 1989~.
Smoke most often Is defined as the airborne solid particulates and liquid aerosols and
fire gases evolved when a material undergoes pyrolysis or combustion (ASTM, 1982; see also
Appendix B of this report). The fire gases have received the most attention, while
knowledge of the effects of inhaling particulates and aerosols from smoke is still quite
limited.
Although a wide variety of combustion products may be generated (Tables 4-1 and-
4-2), the toxicants are usually separated into three classes based on type of effect:
asphyxiants; irritants, which may be sensory or pulmonary; and to~cicants exhibiting other or
unusual toxic effects.
Asphyxiants can cause central nervous system depression, with loss of consciousness
followed by death. The effects of asphyxiant-producing toxicants depend on the
25
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26
TABI E 4-1. Toxicological effects of combustion products from polymers.
TOXICANT | SOURCES | TOXICOLOGICAL
EFFECTS
_ ~
Hydrogen cyanide (HCN) | From combustion of wool | A rapidly fatal asphyxiant |
silk, polyacrylonitrile9 nylon' poison.
polyurethane and paper.
Nitrogen dioxide (NO,) adduced in small quantities | Strong pulmonary irritant
other oxides of nitrogen from fabrics and in larger capable of causing immediate
quantities from cellulose death as well as delayed
nitrate and celluloid. injury.
Ammonia (OHS) | Produced in combustion of | Pungent unbearable odor; |
wood, silk, nylon and irritant to eyes and nose.
melamine; concentrations
generally low in ordinary
building fires.
Hydrogen chloride (MCI) ~ From combustion of ~ Respiratory irritant; potential
polyvinyl chloride) (PVC) toxicity of HC1 coated on
and some fire-retardant particulate may be greater
treated materials. than that for an equivalent
amount of gaseous HCI.
,
Carbon monoxide (CO) ~ From combustion of carbon- ~ Absorbed via the lungs into |i
containing polymers. the bloodstream and
CO2/CO ratio dependent on combining with hemoglobin
oxygen supply. to the exclusion of oxygen
resulting in arterial hypoxia.
Other halogen acid gases l From combustion of | aspiratory irritants.
(HF and HBr) fluorinated resins or films
and some fire-retardant
l materials containing bromine.
Sulfur dioxide (SO2) From materials containing A strong irritant intolerable
sulfur. well below lethal
l concentrations.
.
Isocyanates From urethane polymers; Potent respiratory irritants;
pyrolysis products such as believed the major irritants
toluene-2 4-diisocyanate in smoke of isocyanate-based
(TDI) have been reported in urethanes.
small-scale laboratory studies;
their significance in actual
fires is undefined.
Acrolein From pyrolysis of polyotefins Potent respiratory irritant
and cellulosics at lower
| temperatures (-400°C). l l
Source: Adapted from Terrill et al. 1978.
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27
TABLE 4-2. Volatile products from the pyrolysis of
poly(m-phenyleneisophthalamide) fabric..
,
. ~
COMPOUND
QUANTITYb-
1 ' - 11
Carbon monoxide 32.
Methane
2.9
Carbon dioxide 56.
Nitrous oxide
Ethylene
Acetylene
Ethane
Cyanogen
Propane
Hydrogen cyanide
Water
Acetonitrile
Acetone
Propenenitrile
Acetic Acid
3-Butenenitrile
Benzene
Butenenitrile
Dio~cane
Toluene
Chlorobenzene
Xylene
Phenol
Benzonitrile
Toluonitrile
Dicyanobenzene
TOTAL
0.01
0.027
0.003
0.014
0.001
0.014
0.44
0.27
0.020
0.029
0.43
0.17
7.1
0.020
0.037
1.9
0.033
0.13
0.10
13.6
1.2
1.1
170.55
Pyrolyzed in nitrogen at 550°C.
b Milligrams of compound produced per gram of
polymer as measured by analytical techniques.
Source: Adapted from Einhorn et al., 1974.
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28
accumulated doses (i.e. both the concentration and the duration of exposure). The severity
of the effects increases with increasing doses. Although many asphyxiants may be produced
by combustion of materials, only carbon monoxide (CO) and hydrogen cyanide (HCN) have
been measured in sufficient concentrations in smoke to cause significant acute toxic effects.
An atmosphere deficient in oxygen, caused by its consumption in a fire, is also considered
an asphyxiating condition.
Irritant effects, produced in essentially all fire atmospheres, are normally considered
by combustion toxicologists as being of two types: (~) sensory irritation,, or the illicitation
of pain in the eyes and upper respiratory tract, and (2) pulmonary irritation, which may not
cause a sensation of pain but does cause tissue damage in the lungs, leading to edema and a
decrease in functional ventilation. Most irritants produce signs and symptoms characteristic
of both sensory and pulmonary irritation.
Eye irritation, an immediate effect that depends only on the concentration of an
irritant, may be underestimated in its ability to impair a person's escape from a fire. Nerve
endings in the cornea are stimulated, which causes pain, defied blinking, and tearing.
Severe irritation may lead to subsequent eye damage. Victims may shut their eyes, which
can partially alleviate these effects but may also impair their escape.
Airborne irritants enter the upper respiratory tract, where nerve receptors are
stimulated, with burning sensations in the nose, mouth, and throat, along with the secretion
of mucus. Sensory effects are related primarily to the concentration of the irritant and do
not normally increase in severity as exposure time increases.
Following signs of initial sensory irritance, significant amounts of inhaled irritants
may be quickly taken into the lungs, with symptoms of pulmonary or lung irritation being
exhibited. Lung irritation often is characterized by coughing, bronchoconstriction, and
increased pulmonary flow resistance. Tissue inflammation and damage, pulmonary edema,
and subsequent death often follow exposure to high concentrations, usually after 6 to 48 h.
Exposure to pulmonary irritants also appears to increase susceptibility to bacterial infection.
Unlike sensory irritation, the effects of pulmonary irritation are related both to the
concentration of the irritant and to the duration of the exposure.
None of the smoke toxic potency tests to be described explicitly measures either
sensory or pulmonary irritation. A standard test does exist for sensory irritation (ASTM,
1984) based on respiratory rate depression in mice; however, its relevance to incapacitation
of humans expose to a fire atmosphere has been questioned (Potts and Lederer, 19781. In
the absence of a test of demonstrated validity, mass loss tenability limits have been proposed
for materials known to produce irritants in a fire (Purser, 1988~. This approach is described
under Human Incapacitation Movie! in Chapter 5.
The third general class of fire toxicants, those exhibiting either unusual toxic effects
or unusual toxic potency, has few documented examples. One involved the formation of a
neurotoxin from the thermal decomposition of a non-commercial rigid polyurethane foam
(Voorhees et al., 1975), while another was the unusual toxic potency exhibited by
polytetrafluoroethylene in certain laboratory tests. The latter case would now appear to be
largely an artifact of the test method (Baker and Kaiser, 1991~.
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29
BASIC PRINCIPLES OF SMOKE TOXICITY TESTING
Under the assumption that the toxicity of smoke produced from the burning of
materials could well be as complex as its chemical composition literally hundreds of
constituents may be present early efforts in the 1970s were directed toward the
development of laboratory tests for the smoke toxicity of materials. It was believed that
only ~ bioassay (i.e.' an animal exposure procedure), would be a reliable wav of evaluating
the combined effects of gases found in smoke.
,, ~
The various smoke toxicity tests have been extensively reviewed elsewhere (Kaplan et
al., 1983), and, except for those having significant utilization today, a comprehensive review
will not be repeated here. It is, however, of relevance to acknowledge that two key issues
are common to smoke toxicity tests.
1. A relatively small laboratory combustion device (generally termed the "fire models)
may or may not produce a fire effluent/combustion atmosphere that has the same
composition as an uncontrolled fire.
2. Toxicity data obtained from the exposure of laboratory animals (usually rodents)
may or may not be extrapolated both qualitatively and quantitatively to humans.
The first issue addresses the relevance of the laboratory combustion device; the second, that
of the biological model.
The Laboratory Combustion Device
In an effort to clarify the issues and bring a more systematic and scientific approach
to the problem, the International Organization for Standardization (ISO)/Technical
Committee 92/Subcommittee 3 (Toxic Hazards in Fire) established working groups to
address separate aspects of the toxicity testing of fire effluents. (Technical reports are still
in various stages of development, with only one having been issued by ISO as TR 9122-1,
Toxicity Testing of Fire Effluents Part 1: General.. ~
The first major contribution of an ISO working group was to set forth a systematic
classification of the types and stages of fires to be considered, along with the relevant
characteristics of each. This Is shown in Table 4-3.
The ISO group identified certain criteria for evaluating laboratory combustion devices
used in the testing of materiab for smoke toxicity. Particularly significant was the criterion
for relevance to uncontrolled! fires; the most impor~t considerations were identified as
ventilation (oxygen availability), CO2 (carbon dioxide)/CO ratios, temperature "~/or heat
nux, and residence times of fire effluents in the high-temperature zone. Realizing that no
one laboratory combustion device (fire moclel) can replicate or simulate all the features of
all fires, the ISO committee recommended that the selection of an appropriate fire mode}
must be made for the particular fire conditions of interest. Although not specifically
recommending any one fire model, the ISO committee directed that the choice of a
laboratory combustion device be consistent with a good understanding of the characteristics
of the real fire to be simulated.
\
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30
TABLE 4-3. Classification of fires.
1
.
Fi re Oxygen Ratiob Temperatureb IrradianceC
(%) (CO3/CO) ~ °C) (l`W/m2)
_
Decompositon ~ ~ ~ ~ I.
Smoldering (self-sustained) 21 N/A <100 N/A
Nonflaming (ox~dative) 5 to 2 ~ N/A <500 <25
Nonflaming (pyrolytic) I <5 | N/A I ~ COO | N/A |-
Developing fire (flaming) ~ 10 to 15 ~ 100 to 200 ~ 400 to 600 ~ 20 to 40 ~
_ _
Fully developed (flaming)
Relatively low ventilation I to 5 <10 600 to 900 40 to 70
Relatively high ventilation ~ 5 to 10 ~ <100 ~ 6001' 1200 ~ 50 to 150 |
a Mean value in fire plume near to fire.
b General environmental condition (average) within compartment.
c. Incident irradiance onto sample (average).
Source: ISO, 1989.
The Biological Mode!
The issue of relevance of an animal in modeling human exposure was addressed by
considering the effects of asphyxiants and irritants separately. Comparisons of the amounts
of the major toxic gases producing a given effect (e.g., lethality or incapacitation) with
rodents to those estimated to be required for humans revealed that laboratory animals are a
reasonable model in the case of the asphyxiant fire gases, CO and HCN (Hartzell, 1989~.
Similar analysis showed that rodents are also a reasonable movie! for lethality due to
exposure to pulmonary irritants. For sensory irritants, the rodent models were judged to be
inadequate (Purser, 1988~.
Smoke toxicity should be evaluated on the basis of measuring the response of test
animals exposed for a specified period of time (Klimisch et al., 19871. Rodents, usually rats
or mice, are normally to be used. Lethality is to be the most commonly measured response,
although some test methods also obtain a measure of the animal's incapacitation.
For the biological response, the relationship Is determined between the response of the
test animals and exposure to different concentrations of smoke. This Is accomplished by
conducting a series of experiment in which the quantity of material combusted or the flow
rate of diluting air Is varied to produce different concentrations of smoke. The number of
animals that show a response, such as lethality or incapacitation, increases as the
concentration is increased. In combustion toxicology, smoke concentration is traditionally
expressed either as the quantity of test material used per chamber unit volume (the material
charge concentration) or the material mass loss per chamber unit volume (the smoke
concentration). Test methods that employ dynamic or flow-through generation of smoke
usually express concentration simply as the mass of material charged. (The mass per unit
volume can be calculated from the air flow rate.) If the percentage of animals responding
within a specified time is plotted as a function of the logarithm of the concentration, a
straight line is approximated. Such a plot represents the concentration-response relationship
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31
of smoke produced by a material under the experimental conditions of the particular test
method. The concentration that would produce a response or effect in 50 percent of the
animals upon exposure for the specified time is obtained from the data by use of a statistical
calculation. This concentration, commonly termed the EC50, is a measure of the potency of
the smoke. The EC50 is a general term and may be used in reference to any measured
response (i.e., effect) of the animal. When lethality is the measured response, the LC50
(lethal toxic potency measured in gums for a specified period of time) is used as a more
specific term to denote the concentration of material or smoke that produced death in 50
percent of the animals. Although some test methods do report other response measurements,
the LC~0 is the most commonly reported measurement of toxic potency in smoke toxicity
testing.
Being a statistical result, the LCS0 value is accompanied by confidence limits, usually
at the 95 percent level. This gives a range of values for the LCSo, the significance of which
is that an investigator testing a particular material would have 95 percent confidence that
the LC50 would fall within the given range.
Physiological responses are usually dose related (i.e., the magnitude of the effect
increases with increasing dose or accumulated body burden of a physiologically active
agent). Since the real dose of toxicants from smoke inhalation cannot be directly measured,
it is assumed that the dose is a function of smoke (or toxicant) concentration (C) and
exposure time (t) (MacFarland, 1976~. This Closes is really an expression of the insult to
which a subject is exposed. Thus, Exposure doses (Ct) has become the preferred term in
combustion toxicology to quantify an exposure either to smoke or to pure fire gases.
Concentrations of common fire gas toxicants, such as CO and HCN, are usually
expressed as parts per million (ppm) by volume. Therefore, the exposure dose can be
expressed as the product of the concentration and time (i.e., ppm · min). In the case of a
changing concentration of a gaseous toxicant, the exposure dose is the integrated area under
a concentration vs. time curve.
Often, the concentrations of fire gas toxicants may not be known. In that event one
can still deal with the concept of exposure dose as it applies to smoke. Since smoke
concentration cannot be quantified, an approximation is made that it is proportional to the
mass loss during a fire. The integrated area under a mass loss per unit volume versus time
curve thus becomes a measure of smoke exposure dose (e.g., g~m~~.min).
Of the numerous smoke toxicity test methods that have been used, only a few are
plausibly relevant to uncontrolled fires, are adequately documented in the literature, and/or
are in sufficiently common use to warrant description here.
TEST METHODS
National Bureau of Standards Cup Furnace Test
The National Bureau of Standards (NBS) test (Levin et al., 1982) employs a cup or
crucible furnace, often referred to as the Potts furnace,. named for the investigator who
first reported its use in combustion toxicology (Figure 4-~. Heating is considered to be
. . . .. ., . ., , .. . . ~ . ~ , ~ ~ ~
largely conductive, with the bottom and lower portions ot the quartz cup constltutmg tne
hot zone. Test materials of up to ~ g are introduced into the cup, which has a volume of
about ~ I. Procedures for testing materials involve combustion at just below (nonflaming)
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32
and just above (flaming) an
autoignition temperature.
Concentration- response
(lethality) relationships for
30-min exposures (14-day
postexposure observation)
are determined by using rats
held in tubular restrainers
for head-only exposure. Six
rats are used per test.
Concentration is controlled
by varying the sample
weight charged to the cup.
There has been
· .
~ PORTS FOR ANIMALS
W0
W~ a T
r ~ ~
it,
EXPOSURE CHAMBER
FURNACE ENCLOSURE
particular concern regarding
air flow into the cup,
although it does
communicate with a volume
of 200 1 of air contained in FIGURE d-1. National Bureau of Standards (NBS) apparatus. Source:
the exposure chamber. With Lenin et al., 1982.
the variable sample sizes
used and an ill-defined fuel/air ratio, the system has been criticized for failing to carry out
combustion in a well-characterized manner. A further criticism has been that various
materials are not tested under the same conditions but often at considerably different
temperatures.
The method provides a good mode! for nonflaming oxidative decomposition. It is also
a good model for simulating the decomposition conditions during a well-ventilated, early-
stage fire. It cannot produce the high-temperature, oxygen-vitiated conditions of a fully
developed, postflashover fire.
Once in fairly common use in a number of laboratories in the United States, the NBS
cup furnace test has been well documented, with considerable data available (Levin et al.,
1983~. Its use has declined, however, in recent years.
University of Pittsburgh Test
In the University of Pittsburgh (UPTrr) test method (Alarie and Anderson, 1979; New
York State, 1986), the combustion device is a muffle or box furnace, which is often used in
an inverted position to provide for a pedestal connected to a mass sensor (Figure 4-2~. With
this arrangement, continuous monitoring of sample weight is conducted. Combustion is
accomplished by using a linearly rising temperature of 20°C/minup to as high as 1100°C,
. . < ~ ~ ~ ~ . ~ . . c. ~ . ~ ~ . ~ ~ ,~c ~ ~ ~ ~ ~ .
while 1 1 1/mln ot~ air is pulled through the furnace. ( line smoke atmosphere produced IS
diluted with an additional 91/min of cool air prior to exposure of test animals.) The smoke
concentration is varied by changing the weight of material charged to the furnace. The
fuel/air ratio can therefore vary widely depending on the weight of the sample and its rate
of decomposition.
Exposures of mice (four in each test) are for 30 min. plus 10 min postexposure,
starting when ~ percent of the sample weight has been lost. Bioassays include concentration
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33
to
response and time to death for lethality. An early version of the test utilized respiratory
rate depression as a measure of sensory irritation (Barrow et al., 19761. In the UPI11 test,
the concentration term in the LCso refers to the weight of test specimen charged to the
furnace. Thus, LC50 values for this test are not directly comparable with those from the
NBS method.
The test begins in a nonflaming oxidative mode, and at some stage transition to
flaming usually occurs. At this time the CO2/CO ratios tend to be low (under 20, usually
less than 10), while the temperature is still low (less than 600 °C). This combination of
conditions does not, therefore, fit well into the scheme of fire classes shown in Table 4-3.
It can represent the rather special situation of a small fire load under restricted ventilation.
Although the oxygen concentration is rather low, there are some similarities to the chemical
decomposition environment in the early stages of ~ developing fire. The method does not
simulate the conditions of a large, fully developed, postflashover fire; however, it could be
used to measure the toxic potency of products resulting from the decomposition conditions
of developing fires.
A problem of small explosions has been encountered with some materials that
thermally decompose or burn very rapidly once ignition occurs. This phenomenon, possibly
the rapid emission of gases whose volume exceeds that being pulled from the furnace, has
not been reported to be sufficiently severe to rupture the apparatus. Another criticism of
this method is the 20°Cimin temperature increase, which is quite stow and is not
representative of uncontrolled fires. It results in a gradual fractionation of the pyrolysis
products, with a disproportionately high percentage of low-temperature decomposition
products in the fire effluent that is analyzed and presented to the test animals early in an
exposure.
Despite these problems, the UPt t-T test Is required for certain construction products in
the state of New York (New York State, 1986~. As a result, the test is offered by eight
~ . ~ ~
I FLOW METER PUMP _
F I LTER EXPOSUR E
r CHAMB:
W
~ ~ 7\ LellGTH: 10cm l.D. 19mm
AN I MA L PLETH YSMOGR APH
SAMPLING PORT
LENGTH: 25 cm
DIAM.: 10.5 cm
FIGURE d-2. University of Pittsburgh apparatus.
DILUTING AIR
1~1
ICE BATH
| FURtMACE
1 25x23x34cm
r
rS
WE IG HT
SENSOR
~ 'C
RECORDER
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34
laboratories certified by New York state. The requirement is such that only test data be
submitted. The data are not used for classifying products.
DIN 53436 Test
The DIN 53436 test is characterized by the use of a moving annular tube furnace
operating at a constant temperature from 200 ° to 1000°C (German Standards Institution,
1981, Prager, 1988) (Figure 4-3~. The furnace is programmed to travel the length of a
quartz tube containing the sample. Decomposition, taking place in an air stream
countercurent to the direction of furnace travel, is intended to result in the continuous flow
of fire effluents of constant composition. Radiant heat is the major source of energy
transfer. This test device, used in six European countries, offers a rather wide range of
well-controlled combustion conditions. Ratios of CO2/CO can be widely varied through the
choice of the air flow rate; thus, both freely ventilated and ventilation limited fires may be
simulated.
Specimens may undergo either flaming or nonflaming combustion, depending on the
imposed heat flux level and/or the presence of an ignition device. Some difficulty has been
experienced in controlling, flaming conditions; however, work using sample segmentation
has shown promise with this mode of combustion (EinbroUt et al., 1984~. Such procedures
can alter the type of atmosphere produced.
An air stream countercurrent to the direction of flame propagation, in contrast
generally to the uncontrolled fire situation, is used to prevent uncontrolled preheating
DISTRIBUTION CHAMBER
DILUTION AIR
PRECISION FLOW-METER \
C777777
1
COMBUSTION _
AIR _
\ MOBILE FURNACE
QUARtZ CRUCIBLE AS SAMPLE HOLDER
FIGURE dog. DIN SS4" apparatus. Souce: Klimisch et al., 1980.
PRECISION-FLOW METER ~—I—I
i'
/1
~ \
ID
G
LU
Cal
In
ANIMAL TUBES
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35
effects by the combustion products. However, cocurrent conditions have been used
(Boudene et al., 1976~. The lack of continuous monitoring of sample weight is compensated
by the continuous decomposition process, which enables one to relate the exposed mass,
volume, or surface area to the bioassay and/or analytical test data.
The DIN 53436 test is clearly useful for toxic potency testing. It is capable of
producing the chemical decomposition environment of any of the fire types shown in Table
4-3, and it is the only method that closely simulates the high-temperature, oxygen~vitiated,
conditions in a postflashover fire. Care must be taken with simulating the CO2/CO ratios of
growing, well-ventilated fires, since such ratios tend to be rather small under standard
operating conditions. Self-sustained smoldering is also difficult to simulate in small
samples, as is the case with most small-scale methods.
The DIN 53436 test has been well documented and widely used. Considerable work
demonstrating its validity has been reported (Prayer et al., 1987; Prager, 19881. It is quite
flexible in being able to accommodate a range of controlled ventilation conditions, with
CO2/CO ratios from below 5 to more than 200 being obtained.
The major disadvantages of the system are the difficulties in quantifying the exposure
dose of smoke (although it can be estimated) and in controlling both smoldering and flaming
combustion.
U.S. Radiant Furnace (Modified) Testt
The combustion device
used In the U.S. radiant
furnace (modified)
methodology (Grand, 1990)
consists of a horizontally
mounted, cylindrical quartz
combustion cell, 130 mm
inside diameter and
approximately 320 mm in
length (Figure 4-4~. It is
connected to an animal
exposure chamber through a
rectangular stainless steel
chimney, which is
approximately 30 tic 300 x
300 mm in height. The
chimney is divided into three
channels, creating a heat I,
pump action by inducing COMBUSTION
smoke to flow up the center CELt
channel, while air from the FIGURE dot. U.~. pant flee (modified).
exposure chamber circulates
down the outer channels. External to the combustion cell are four tungsten-quartz radiant
heat lamps focused onto the plane of the specimen. A platform, accommodating test
specimens of 76 x 127 mm and up to 51 mm in thickness, is connected to a load cell located
~ SMOKE SHU l l en ANIMAL EXPOSURE TORTS
~ 1- ~ -- A--- i--- A--- ~ -- A---- ~
~ i] ~ ~ SPECIMEN PLATFORM
/ \~ LOAD CE' L
This test is also referred to as the NIBS (National Institute of Building Sciences) test.
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36
underneath the combustion chamber to monitor continuously the specimen weight. A high-
energy spark plug is used as an ignition source.
Heat fluxes ranging from 0 to 75 kW/m2 have been used. Ratios of CO2/CO have
ranged widely, usually being well in excess of 20. This combustion device, therefore,
appears to produce good simulation of an early developing, flaming fire. However,
insufficient data are presently available to establish the exact characteristics. Developmental
work still in progress, should permit better characterization of the properties of this
combustion device.
Unique to this method is a proposal that the test method be used to develop an linden
of potential toxic hazard. for screening of test materials by procedurally combining time to
ignition, rate of decomposition, and toxic potency. Alternatively, it has been proposed that
these separate parameters be extracted from the test for use in toxic hazard engineering
calculations. Such a proposed test is currently undergoing the ASTM consensus process.
In this method, a test specimen is subjected to ignition while exposed to radiant heat,
with the smoke produced being collected for 30 min within a 200-! chamber
communicating with the combustion assembly. Concentrations of the major gaseous
toxicants are monitored over the 30-min period, with Ct products for each being
determined from integration of the areas under the respective concentration-time plots.
The Ct product data, along with the mass loss of the test specimen during the test, are then
used in calculations to estimate the 30-min LC50 of the test specimen. The estimated LC50
is then validated by use of exposure of rats. Validation assures that the monitored toxicants
account for the observed toxic effects and that there is no unusual toxicity.
Although there Is still a lack of documentation and availability of data from the test
method, several laboratories have the apparatus. Considerable work using an earlier version
of the radiant furnace test is described by Alexeeff and Packham' 1984.
ROI`E OF ANALYTICAL CHEMISTRY
Babrauskas et al., 1987, stated that early attempts to explain the toxicity of smoke by
analysis of the combustion products were fraught with problems: (~) the number of
identified species was overwhelming (over 400 compounds have been reported from the
decomposition of wood), (2) the toxic potency of every one of these compounds is not
known, and (3) the approach becomes difficult in particular in view of the multiplicity of
combinations of these gases. On the other hand it was once perceived that exposure of
animal models was the only reliable methodology. As an example of support for this
contention' relatively sophisticated instrumental methods failed to detect a highly toxic
bicyclophosphate material produced from the nonflaming degradation of a fire retarded
polyurethane foam (Voorhees et al., 1975~. The bicyclophosphate compound was identified
only after grand mat seizures were observed in rats exposed to the combustion atmosphere
(Petajan et al., 1975~. This example, though rare, serves to illustrate that care must be taken
in relying solely on analytical results.
Experience has since suggested that the toxicity of most fire effluent atmospheres can
be explained largely on the basis of only a few major components. Thus, along with the
advent of engineering calculations for hazard and risk assessment, analytical methods in
combustion toxicology are extremely important in minimizing animal experimentation. In
fact, chemical analysis of fire effluent atmospheres is deemed sufficiently important that it
OCR for page 37
37
is the subject of an ASTM Standard Guide (ASTM, 1988) and a forthcoming ISO Technical
Report (ISO, 1989~. Since such guidance is available, this report will not go into detail on
the methods.
The most common fire effluent constituents, CO and CO2, are routinely measured on a
continuous basis by nondispersive infrared spectroscopy. Oxygen is continuously measured
by use of a paramagnetic detector. HCN and hydrogen chloride (MCI) are normally sampled
with syringes, together with some type of noncontinuous analysis. Commonly used are gas
chromatography, ion-specific electrode titrimetry, and calorimetric procedures for HCN.
Titration and ion chromatography are employed for HCI. However, even HCN and HC!
have been successfully analyzed continuously in some systems by use of continuous
automatic titration methocIs (Grand, 1988~. Fourier transform infrared methods show
considerable promise for continuously analyzing several fire gases simultaneously (Kallonen,
1990~. Gas chromatography/mass spectrometry may be used for analyses of fire effluent
components that do not lend themselves to direct instrumental methods.
CONCLUSIONS
Toxicity data for materials and/or products are obtained from laboratory tests that,
upon utilizing a combination of analytical data along with the exposure of rodents, yield two
useful types of information: l) the principal typets) of intoxication, i.e., asphyxiation,
sensory or pulmonary irritation, etc. and 2) the LC50 of the smoke in units of gums over a
given exposure period. Toxic potency data obtained from laboratory tests are, however,
subject to the following limitation and/or considerations.
1. No single laboratory combustion device Is appropriate for all materials and
products under the condition of all fire types and stages. Therefore, there can be no
universal Smoke toxicity test.. The laboratory combustion device used in a test should be
chosen and operated to approximate as closely as possible the conditions of the type of fire
being examined. (For example, laboratory scale combustion furnaces may, under certain
conditions, produce less CO per unit mass of sample burned than would occur in a real fire.
Thus, laboratory LC~0 values may need to be Adjusted for use in hazard calculations.)
2. All LC ;O values have an associated level of statistical confidence. Furthermore,
interiaboratory comparisons suggest LC~0 determinations can vary by a factor of about 2.5.
3. Although calculated from data based on exposure of rodents, LCS0 values can be
extrapolated to human exposure with reasonable confidence for asphyxiants and for
pulmonary irritation. Sensory irritation Is not addressed with current laboratory smoke
toxicity tests. Also, its relevance to incapacitation of humans has not been demonstrated.
(Hazard assessments currently tend to set threshold tenability levels for acid gases and other
combustion products known to have irritant properties.)
4. Currently employed laboratory smoke toxicity tests do not directly measure
incapacitating effects of smoke inhalation. Incapacitation must be inferred from LC~0
values.
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38
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Representative terms from entire chapter:
combustion products
