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(c) RADAR ABSORBING MATERIAL (RAM) AND CONVENTIONAL
COATINGS. Due to the lack of burn data
for specific RAM coatings, combustion products are not
assessed as greater health hazard than those of the existing
composite materials or conventional coatings. Conventional
coatings for corrosion and electrostatic discharge
concerns are based on organic polymers with the
addition of metallic compounds. The majority of RAM is
also polymeric based, with the addition of metallic compounds.
Polymeric coatings will burn as described for
the resin releasing similar combustion products. Depending
on the type of RAM additive, the burn characteristic
RAM coatings may differ from those of conventional coatings.
The mishap concern for coatings are the same as
those of the resin, such as emission of toxic combustion
products into the plume any unexpected burn conditions
caused by the addition of additives.
(d) FIBER PATTERN EFFECTS. The fiber form of the
composite layer influences the release of fire-damaged
particulate in the same way it influences a release for
physically damaged composites [3.5(b)(2)e)]. Patterns
in the filament wound part and the cross weave of the
woven fabric holds fibers in place not allowing for the
free movement of the individual fibers. The inability of
the fibers to move freely decreases the amount of particulate
released during flaming combustion. Unidirectional
tape does allow for an easier release and contributes
to most of the carbon fiber particulate release during
a fire and when handling fire damaged carbon fiber
debris.
(4) FIRE SCENARIOS.
(a) FIREBALL. Upon impact fuel and vapor is suddenly
dispersed over a large area of the site. A mist of fuel
vapor ignites, creating the fireball that very rapidly follows
the spread of fuel. Extent of composite damage
caused by fireballs varies depending on where the debris
lands after impact. The fireballs path may miss the
pieces com-pletely, cause slight surface-scorch or entirely
engulfed the debris. Even though fireballs can create
very, very hot flame temperatures (2400°F) extent of
fire damage depends on the time within the fireballs path.
(PHOTOS 34 and 35)
(b) POOL FIRE. Pool fire is the scenario that can create
the greatest amount of fire damage. Quantities of fuel
have collected in a relatively small area creating a pool.
The flaming combustion stage of a pool fire can be much
longer than for a fireball (the fuel is not used up as rapidly
as within a fireball scenario). More time spent at high
temperatures allows the flame and heat to penetrate
many more composite layers causing more damage and
also produces the conditions for a smoldering combustion
stage. (PHOTO 36)
(c) LOW TEMPERATURE HEATING OVER TIME. The
ignition source may determine whether a composite material
burns in the smoldering or flaming mode. A slow
but low temperature heating, such as a heated wire may
lead to smoldering combustion. A restricted air supply,
as in a closed compartment will promote smoldering combustion
that may go undetected for a long time. A transition
to flaming combustion after smoldering for a long
time can produce a very rapid growing fire due to the
preheating of the fuels, and the accumulation of combustible
gases during the smoldering phase.
(d) IN-FLIGHT FIRES. The generation of smoke and
toxic gases provides the first evidence that a fire is developing.
The distinct odor produced by burning composites
is noticeable right away. While visibility is immediately
impaired by the smoke, the rapid generation of
acutely toxic compounds presents an even greater danger.
The confined space of aircraft cockpits increase toxicity
because limited ventilation contributes to the increase
of toxic gas concentrations. If a rapid generation of toxic
gases in confined spaces ignites, a very rapid destructive
fire can result.
(5) HEALTH.
(a) SMOKE PLUME. Smoke contains airborne solid and
liquid particulates, and gases which can be toxic if concentrations
are high enough. Foremost among the hazards
are impaired vision from eye irritation, narcosis from
inhalation of asphyxiants and irritation of the upper/or
lower respiratory tracts. The emergency phase of the
mishap is concerned with the most dangerous or lethal
hazards of the smoke, which are the asphyxiants and
irritants. Carbon monoxide and hydrogen cyanide are the
primary toxic or lethal gases in smoke. The predominant
irritants are the acid gases (hydrochloric acid, hydrogen
bromide, and hydrogen fluoride HCl, HBr, HF), nitrogen
oxide compounds, and organic irritants like acrolein, formaldehyde,
　
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