the wick. The hot spot will continue to give off sufficient
Fuel Vapors. Fuel vapors form when a liquid fuel
vapors to sustain the flame.
undergoes the process of evaporation. When F-76 and
JP-5 are mixed with air in certain proportions,
Candles and kerosene lamps are good examples of
flammable vapors result.
wicking. Rags soaked with fuels also make excellent
wicks. For this reason, you should always consider
Fuel vapors are heavier than air. This is important
fuel-soaked rags to be potential fire hazards.
for you to understand because fuel vapors will tend to
collect in the lowest levels of your ship's compartments,
Fuel mists can form when a rupture or small leak
such as the bilges. Fuel vapors can travel rapidly from
occurs in a pressurized fuel line. Fuel mist formation can
compartment to compartment through existing
also be caused by fuel vapor condensation that results
openings. You may not be aware of these vapors until
from sudden cooling. Mists from fuel droplets mix with
they ignite by an unsuspected source. Some sources that
air, forming a flammable mixture. When exposed to an
can cause fuel vapors to ignite are open flames, electric
ignition source, these mists can ignite. Once ignited, the
sparks, sparks produced from striking metals, heat from
fuel mists will continue to bum because the fuel spray
exposed hot piping, and smoking.
droplets entering the flame zone will continue to
vaporize as long as they are exposed to the heat of the
Spontaneous Ignition Temperatures. The
flame.
spontaneous ignition temperature (SIT) is also called the
autoignition or autogenous ignition temperature (AIT).
It is vitally important for you to understand the fuel
The SIT or AIT is the minimum temperature at which a
characteristics we have just described and the prescribed
fuel or fuel blend will ignite spontaneously in air without
safety guidelines and precautions you must use
the aid of a spark or flame. The importance of the SIT
whenever you come in contact with these products.
or AIT is that it identifies the lower limit of fire hazard
Remember, these characteristics are always present
whenever you are handling fuels near hot surfaces. In
wherever fuels are handled, tested, stowed, transferred,
other words, to conform with prescribed military
or used aboard ship. They will always be dangerous
standards and safety guidelines, you must not handle
sources of potential fire hazards.
fuels in areas in which temperatures exceed the SIT or
OILS. Even though oils have a much higher flash
MT.
point than fuels, they are still dangerous if they are not
For both F-76 and JP-5 fuels, the SIT values can be
properly handled. The potential for fire always exists,
as low as 450F (232.2C). For this reason, you should
Like fuels, oils operate in some systems under high
consider these two fuels to be equally hazardous.
pressure. This is why strict attention must be paid to
General specifications for the building of naval ships
system integrity (prevention and control of leaks). The
require that any surface that might exceed a temperature
policy of no leaks in any system carrying flammable
of 400F (204.4C) must be suitably insulated so that
liquids is a good one. If oil should be forced out of a
temperatures of the exposed surface will not exceed this
system in the form of a fine mist, the results could be
critical level.
disastrous.
The procedure by which the SIT or AIT rating of a
Fire hazards are not the only danger associated with
fuel is determined is very complex. To do your part in
petroleum products. They can also be harmful to
preventing fire hazards, you must respect and accept the
personnel by irritating the skin and eyes. Aboard ship,
established laboratory SIT values. In your oil lab duties,
fuel and oil products are handled daily. To most people,
always consider the SIT value of any fuel you must
the vapors from these products are irritating. To some
handle and try to take every precaution to prevent the
people, physical contact with these products can cause
fuel from dripping onto a hot surface.
severe skin disorders. This is why you must use
Wicking and Mist Formation. Normally, fuels do
protective clothing, such as rubber gloves, a face shield,
not form flammable vapor-air mixtures at temperatures
and an apron whenever you handle these products.
below their flash points. There are two exceptions to this
Although the oil used in the gas turbines is not a
rule: (1) wicking and (2) mist formation. Both of these
petroleum-based product, you need to be aware of
conditions provide the means by which fuels can ignite
certain safety precautions. This oil is an synthetic
even at temperatures below their flash points.
ester-based product that can cause dermatitis after
Wicking occurs when a fuel is drawn onto an
prolonged contact with the skin. If you come into contact
absorbent solid material that can be ignited locally.
with this oil, wash your skin thoroughly and remove any
When a flame is applied to a wick, a hot spot forms on
saturated clothing immediately.
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