Sodium is classified as a hazardous material, primarily because of its
extreme reactivity when it comes in contact with water and many other
substances. Because of its
reactivity, sodium is seldom encountered in the pure metallic state, except
when it is being used in an industrial process or for some extremely special
application. It must be shipped in sealed containers, because it will react
even with the moisture in the air on a humid day.
Sodium is a constituent of several non-hazardous compounds that
are in common use, such as table salt (sodium chloride) and several
pharmaceutical products. The metallic form of sodium is used in
applications that require unusual heat transfer and electrical conductivity
properties. Pure sodium is encountered more frequently, however, as an
agent in the processing of other substances. It is an extremely powerful
reducing agent, with the ability to strip oxygen atoms and other atoms or
molecules from otherwise stable molecules. These reactions usually release
large amounts of energy and additional chemical by-products are often
created, some of which are hazardous in themselves.
Sodium is most widely recognized for its violent reaction with water.
Pure sodium will break apart water molecules, separating the hydrogen
atoms from the oxygen atoms. The sodium combines with the oxygen and
liberates the hydrogen. The oxidation of the sodium is a combustion
process, in which the sodium burns with a yellow flame to produce an ash
(sodium oxide), which is liberated as a dense white acrid smoke. The
hydrogen is released as a gas, which usually explodes in the air as the
hydrogen recombines with oxygen from the ambient atmosphere.
In addition to creating sodium oxide and hydrogen gas, contact with
moisture can create sodium hydroxide, a corrosive liquid, which can cause
corrosion bums to exposed skin.
The power of sodium to break apart other compounds that contain
oxygen atoms and/or atoms with similar properties to oxygen make it an
extremely valuable reducing agent with numerous applications in the
processing of other materials. Sodium is a solid at normal ambient
temperatures but melts at the relatively low temperature of 208 degrees
Fahrenheit. Above 208 degrees, it can be transferred and mixed with other
substances as a liquid, however, it must be kept in a closed system because
it will auto-ignite in air at temperatures only slightly above its melting
temperature. Liquefied sodium flows easily, with a viscosity similar to
water.
Once ignited, sodium is very difficult to extinguish. It will react
violently with water, as noted previously, and with any extinguishing agent
that contains water. It will also react with many other common
extinguishing agents, including carbon dioxide and the halogen compounds
and most dry chemical agents. The only safe and effective extinguishing
agents are completely dry inert materials, such as Class D extinguishing
agents, soda ash, graphite, diatomaceous earth, or sodium chloride, all of
which can be used to bury a small quantity of burning sodium and exclude
oxygen from reaching the metal.
The extinguishing agent must be absolutely dry, as even a trace of
water in the material can react with the burning sodium to cause an
explosion. Sodium chloride is recognized as an extinguishing medium
because of its chemical stability, however it is hydroscopic (has the
property of attracting and holding water molecules on the surface of the
salt crystals) and must be kept absolutely dry to be used safely as an
extinguishing agent. Every crystal of sodium chloride also contains a trace
quantity of moisture within the structure of the crystal.
Molten sodium is extremely dangerous because it is much more
reactive than a solid mass. In the liquid form, every sodium atom is free
and mobile to instantaneously combine with any available oxygen atom or
other oxidizer, and any gaseous by-product will be created as a rapidly
expanding gas bubble within the molten mass. Even a minute amount of
water can create this type of reaction. Any amount of water introduced
into a pool of molten sodium is likely to cause a violent explosion inside
the liquid mass, releasing the hydrogen as a rapidly expanding gas and
causing the molten sodium to erupt from the container.
When molten sodium is involved in a fire, the combustion occurs at
the surface of the liquid. An inert gas, such as nitrogen or argon, can be
used to form an inert layer over the pool of burning liquid sodium, but the
gas must be applied very gently and contained over the surface. Except for
soda ash, most of the powdered agents that are used to extinguish small
fires in solid pieces or shallow pools will sink to the bottom of a molten
mass of burning sodium -- the sodium will float to the top and continue
to bum. If the burning sodium is in a container, it may be feasible to
extinguish the fire by placing a lid on the container to exclude oxygen.
Most municipal fire departments rarely, if ever, come in contact
with pure sodium, particularly molten sodium, in any significant quantities.
It is shipped in sealed containers and can only be used under extremely
controlled conditions in closed industrial processes. It is most often used
within large industrial complexes, where municipal fire departments are
unlikely to become involved with it. Industries that use sodium must be
extremely careful with it, because of the consequences of using it unsafely;
many have plant fire brigades trained to handle small sodium incidents.
It is also used in high energy/high temperature systems as a heat
transfer medium. In this application it may be encountered at some
nuclear power facilities and in experimental installations that are involved
in high energy power generation and transmission.
Next » Disposal of Waste Sodium
Save to del.icio.us
