Improved Fire- and Smoke-Resistant Materials for Commercial Aircraft Interiors A Proceedings (1995) / Chapter Skim
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Chapter 12. Smoke Toxicity
Chapter 12. Smoke Toxicity
Pages 175-196
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From page 175... ...
* When aircraft cabin occupants are exposed to fire effluent the first hazard encountered is usually smoke, containing particulates and toxic gases that cause immediate visual obscuration and painful irritation of the eyes and respiratory tract.
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From page 176... ...
In this situation the key factors are the time within which the passengers can disembark compared with the rate of fire growth and particularly the time within which toxic smoke and heat impair or prevent egress. This paper examines fire scenarios in terms of toxic smoke and heat profiles and presents methods for estimating behavioural impairment and incapacitation.
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From page 177... ...
The second method is used mainly for evaluating materials with regard to the lethal toxic potency of potential fire atmospheres. In order to enable the effects of exposure of people to fire hazards to be calculated, a series of algorithms has been developed for calculating time to incapacitation or death, which is published in The SFPE Handbook of Fire Protection Engineering (Purser, 1988)
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From page 178... ...
This aspect is largely beyond the scope of this paper but some aspects are mentioned in the next section. Evaluation of the Effects of Optically Dense, Irritant Smoke on the Eyes and Respiratory Tract Optically dense smoke affects way-f~nding ability and the speed of movement of occupants, and a smoke barrier may be perceived as being impenetrable.
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From page 179... ...
In evaluating this aspect of irritancy the aim is to predict what concentration of mixed irritant products is likely to cause such pain and difficulty in breathing that escape attempts would be stowed or rendered less efficient, and what concentration is likely to seriously disrupt or prevent escape (a degree of incapacitation approximately equivalent to that at the point of collapse resulting from exposure to narcotic gases)
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From page 180... ...
A reasonably good relationship has been found between the mouse RDso concentrations for a range of irritant vapours and the concentrations reported as being painfully irritant to humans (Alane, 19811. The test has been applied to a wide range of irritant substances, many of which occur in fire atmospheres, and also to mixed combustion product atmospheres.
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From page 181... ...
majority of materials have RDso values lying between 0.05 and 0.5 g/m3 under nonflaming oxidative decomposition conditions. This means that if the products of decomposition of between 0.05 and 0.5 grams of material are clispersed into each cubic metre of air, then the resultant atmosphere is predicted to be painfully irntant to the eyes and respiratory tract.
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From page 182... ...
Calculation of Time to Incapacitation Due to Effects of Narcotic Gases Narcotic gases (carbon monoxide, hydrogen cyanide, carbon dioxide, and reduced oxygen) affect the nervous and cardiovascular systems, causing confusion followed by loss of consciousness, followed ultimately by death from asphyxiation (Purser, 19881.
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From page 183... ...
x VCO2 + FEDS or FIN, (3) where FEDS fraction of an incapacitating dose of all narcotic gases; FEDS fraction of an incapacitating dose of CO; FEDS = fraction of an incapacitating dose of HCN; FEDS-fraction of an irritant dose contributing to hypoxia; VCO2-multiplication factor for CO2-induced hyperventilation; FEDS = fraction of an incapacitating dose of low oxygen hypoxia; and FED~Co2 - fraction of an incapacitating dose of CO2.
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From page 184... ...
Details of the calculation methods are given in Purser, 1988 and 1989. APPLICATION OF THE INCAPACITATION MODEL TO DIFFERENT FIRE SCENARIOS In terms of the basic scenarios, the hazards in terms of the yields of heat, smoke, and toxic products, and the effects on escape behaviour, fires can be considered in several different categories.
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From page 185... ...
In the context of aircraft fires, the first three categories are of concern mainly in the inflight situation, where cabin occupants and crew may be exposed to fire effluent for several hours. Although fires in categories 2 and 3 may also present a hazard on the ground, it is to be expected that the aircraft would be cleared before such fires become a serious threat.
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From page 186... ...
which is likely to cause fatal lung damage. TABLE 4 Concentrations of Toxic Gases and FEDs in Target Room for Smouldering Followed by Flaming Ignition of Standard Foam Armchairs versus Time (in minutes)
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From page 187... ...
Early-Flannog, WeN-Ventilated Fires In a Room with an Open Doorway In early-flaming fires, the decomposition conditions, particularly the air/fuel ratio, and the type of fuel are major determinants of the yields of toxic gases. In early-flaming, wellventilated fires involving non-fire-retarde`d materials, combustion is usually efficient, so that the main products are heat, carbon dioxide, and water, the yields of toxic products and smoke being relatively low.
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From page 188... ...
4. An occupant escaping or rescued after the fourth minute would suffer severe postexposure effects due to skin burns, possible laryngeal burns with accompanying oedema and danger of obstructive asphyxia, and also lung oedema and inflammation which might well be fatal (due to the combined effects of inhaled hot gases, chemical irritants, and the pulmonary secondary effects of skin burns)
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From page 189... ...
In this situation a smouldering or especially a flaming fire quickly uses up the available oxygen, and as the oxygen concentration falls after a minute or so the combustion becomes inefficient, producing a dense smoke rich in carbon monoxide and other toxic products. These, together with the lowered oxygen concentration in a room, can produce a rapidly lethal atmosphere.
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From page 190... ...
The rapid involvement of the cabin contents gave rise to a dense smoke containing large amounts of carbon monoxide and hydrogen cyanide at a measurement point halfway down the fuselage. It is predicted that escape capability is likely to be severely inhibited after approximately I-~.5 minutes due to the effects of exposure to the dense smoke containing high concentrations of acid gases and organic irritants.
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From page 191... ...
Table 7 shows the results of another Boeing 707 fuselage test, which was conducted under the same conditions as those used for the test whose results are shown in Table 6, except that a fine water spray mist was applied to the zone of the cabin interior opposite the fuel fire. In contrast to the previous fire, the water mist prevented significant decomposition of the cabin interior materials, so that the cabin remained tenable for up to approximately 7 minutes.
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From page 192... ...
It is considered that the combined concentration of these and other irritants would have some irritant effect on the eyes and respiratory tract, but probably not sufficient to cause serious incapacitation or seriously impair escape attempts, or cause serious post-exposure lung damage. The total particulate concentration is much lower than observed in the nonsprayed and fully sprayed tests.
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From page 193... ...
Fires involving wire and cable can present a problem in smoldering or small flaming fires due to the organic irritants and acid gases that evolve. Materials with an improved flame propagation and higher decomposition temperature performance may be advantageous, provided that they do not evolve high toxicity products when they are overheated (Purser et al., 19941.
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From page 194... ...
Improved ignitability and fire-growth performance of materials have gone some way towards improving the fire performance of seats and other cabin materials, but large external fuel fires are still capable of igniting cabin materials in a short time. Low-volume water mist systems have been shown to provide a significant benefit in some situations by delaying cabin interior involvement in the fire.
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From page 195... ...
1989. Modelling time to incapacitation and death from toxic and physical hazards in aircraft fires.
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