CLASS DELTA FIRE
DYNAMICS OF A FIRE
The fact that there is a large variety of materials
Class DELTA fires are also known as combustible
aboard any ship which can burn and should be
metal fires. This class of fire results when materials
considered as fuels cannot be overemphasized. As
such as magnesium, phosphorus, sodium, or titanium
stated before, for a solid fuel to burn, it must be changed
are ignited. Certain types of aircraft wheels are
into a vapor state. This chemical action is known as
manufactured from these materials, as well as various
pyrolysis and is defined as a chemical decomposition
pyrotechnic smokes and flares. Although some ships
due to the application of heat. This decomposition
creates a fuel vapor. When this vapor is mixed with
have pyrotechnic (referred to as "pyro") magazines
oxygen at the right temperature, a fire is produced.
below decks, typically most occurrences of DELTA
A solid fuel will burn at different rates depending
fires happen topside, where storage is more common.
upon its size and configuration. For example, a pile of
wood chips or wadded paper will burn faster than an
Pyrotechnics often contain their own oxidants and
equal amount of solid wood or a case of paper. This fact
therefore do not depend on atmospheric oxygen for
is true because there is a larger surface area exposed to
combustion. For this reason, the exclusion of air, such
the heat; therefore vaporization occurs faster. Because
as by use of PKP, foam, or other extinguishers, will
more vapor is available for ignition, the fire burns more
typically be ineffective.
intensely and the fuel is consumed at a faster rate.
A liquid fuel releases vapor much as a solid fuel
WARNING
does. However, it does so at a higher rate and over a
larger temperature band. Because liquids have more
loosely packed molecules, heat increases their rate of
Class DELTA fires burn with an intense
vapor release. These dynamics result in the fact that
heat of up to 4,500F, and action must be taken
pound-for-pound liquid fuels produce about 2 1/2 times
to shield your eyes from the brilliance of the
more heat than wood, and this heat is given off much
flame. High velocity fog should be used to
more rapidly.
cover and cool these fires. If possible, remove
the burning material by jettisoning it over the
If a flammable liquid is spilled (or is atomized and
side of the ship. To prevent the fire from
sprayed out under pressure) it covers a very large
spreading, you should apply large quantities of
surface area and gives off much more vapor. This is one
water at low pressure to cool the surrounding
reason flammable liquid (class BRAVO) fires burn so
area. Class DELTA fires give off extreme
violently.
amounts of heat and can produce explosions.
As mentioned earlier, the lowest temperature at
Therefore, you must maintain a safe distance
which a liquid gives off sufficient vapor to form an
from the source of the fire while applying the
ignitable mixture is known as the flashpoint for that
water fog.
liquid. An ignitable mixture is a mixture of vapor and
air that is capable of being ignited by an ignition
source. As an example, gasoline has a flashpoint of
WARNING
-45F (-43C). This factor makes gasoline a constant
hazard because it produces flammable vapor at normal
During a class DELTA fire, certain
temperatures. Like gasoline, the other shipboard fuels
chemical reactions are occurring as the water
have specified minimum flashpoints.
is applied to cool the surrounding area. This
To ignite, a flammable gas or vapor of a liquid has to
water reacts with the burning metal and forms
mix with air in the proper proportion. The lowest
hydrogen gas, which will either burn or
percentage of gas that will make an ignitable mixture is
explode, depending on the intensity of the fire
called its lower explosive limit (LEL). If there is less
and the amount of burning material. In any
vapor or gas than this percentage, then the mixture is too
case, maintain a safe distance from the fire and
lean to burn. Conversely, there is also an upper explosive
shelter yourself and your team from any
potential explosions.
limit (UEL) above which the mixture is too rich to burn.
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