Segregation
of Stored Chemicals
Summary:
To minimize
the problems that might occur in the event of a major accident
in a lab full of chemicals, reagents are grouped in five
or six separate locations to reduce the chance of mixing
in case of a disaster (shelf collapse or cabinet tipping
over).
The groups are:
- Strong
acids
- Strong
bases
- Flammables
and combustibles (including weak acids)
- Oxidizers
- General
chemicals
Additional
locations or containers might be set up for: radioisotopes,
extremely toxic compounds, compounds that require desiccation
or low temperature .
Details:
It is
important to separate stored chemicals based on their chemical
properties to avoid serious problems that can occur if certain
combinations are accidentally mixed. This mixing is not
from someone preparing a concoction in a beaker (which also
could be disastrous), it refers to mishaps involving bottle
breakage that can occur if a shelf collapses† or a
worker bangs one bottle into another while accessing the
cabinet. Certain combinations can produce a violent reaction
that could involve fire or explosion.
Most
documents on incompatible chemicals merely provide a list
of combinations that are a problem [see "Incompatible
Chemical Mixtures"]. This is of some value, but
another approach is to list groups that are compatible and
which can be stored together as a unit. People should use
both types of information to help them decide how to safely
store their chemicals. I have included some examples of
things commonly used in Biology labs.
Major
Groups:
1.
Strong Acids: e.g. hydrochloric,
sulfuric, nitric, perchloric, phosphoric
Must be stored separate from weak acids (acetic and formic
are combustible) or flammable solvents. Mixing either of
these with Strong acids will produce heat and may result
in a fire or explosion.
Special
cases:
- nitric
acid - is also a strong oxidizer (see below).
- perchloric
acid: is a very strong oxidizer when heated and can be
dangerous; should always be held in a secondary container
(e.g. a plastic tub).
- chloric
acid: is also a very strong oxidizer.
Such
strong oxidizers must not be stored near any compounds that
can be oxidized (like acetic acid or any flammable solvents/solids).
2.
Strong Bases: e.g. sodium hydroxide, potassium hydroxide,
ammonium hydroxide, calcium oxide. Isolate in a cabinet
away from Strong acids.
3.
Weak Acids: e.g. acetic, formic, propionic, butyric.
Store separate from Strong Acids and Oxidizers. Acetic acid
and formic acids are combustible and might be stored in
the Flammable storage cabinet if you do not have location
reserved for Weak Acids.
4.
Flammables/Combustibles: store large containers (>1
L) in a Flammable Storage cabinet. These cabinets are insulated
and designed to keep the contents cool for a period should
there be a fire in the lab (thus giving people time to escape
before the solvents "get involved"). See related
topic "Flammable
and Combustible Liquids".
Some examples:
- alcohols:
methanol, ethanol, isopropanol
- ethers:
petroleum ether, diethyl ether
- organic
"solvents": hexane, pentane, acetone, xylene,
methylene chloride, diethylamine (although this is an
organic base, it is also flammable), methyl ethyl ketone,
ethylene glycol monomethyl ether (Cellosolve) and many
more.
Workers
need some flammables stored on the bench for easy access
but try to keep as much as possible and any larger bottles
(>1L) in the Flammable Cabinet. The Alberta Fire Code
places limits on the quantities of Flammable/Combustible
liquids that can be stored in a Flammable Storage cabinet
or in a room (see "Flammable and Combustible Liquids").
5.
Oxidizers: these compounds are the ones most commonly
stored incorrectly with the general chemical inventory.
Oxidizers can cause spontaneous ignition if mixed with a
combustible material. Often these compounds contain oxygen
atoms that can be donated to a reaction and increase the
rate of combustion (analogous to someone fanning the kindling
to try and get a camp fire going). Oxidizers must be separated
from other chemicals and stored in a separate cabinet. It
should be noted that the bomb used to blow up the federal
building in Oklahoma City in 1995 consisted of ammonium
nitrate (a lawn fertilizer and a strong oxidant) mixed with
kerosene (which is combustible and can be oxidized). Further
information on oxidizers can be found at the University
of Nebraska site: http://bifrost.unl.edu/ehs/ChemicalInfo/oxidize.html
some
examples of oxidizers:
- nitrates
/ nitrites: sodium nitrate, potassium nitrite - used in
fireworks among other things
- chlorates
and perchlorates: magnesium perchlorate is used as a drying
agent.
- dichromates:
sodium or potassium dichromate, might be used in acid
cleaning solution.
-
hydrogen peroxide: 30% (or 70%) solution - don't store
in Flammable cabinet with solvents; refrigerate at 4C.
- nitric
acid: store with strong acids
-
perchloric acid: store with strong acids and within a
secondary container (beaker or tub).
-
iodine, bromine, fluorine: don't contain oxygen but are
strong oxidizers.
6.
General Chemicals: most of the rest of chemicals you
have in the lab. There may be a few special treatments for
things like very toxic substances (arsenic, cyanide) or
carcinogens which might be placed in plastic bags or plastic
containers to help contain the material if the bottle is
dropped and to indicate to users that these require a bit
more care in handling. See "Some
Chemicals with Special Hazards".
Thus
you may need up to 5 or 6 discrete cabinets/storage areas
to house these different groups. Make sure everyone in the
lab understands why these separations are made. Provide
clear lables on the cabinets. The Office of Environmental
Health and Safety at the University of Alberta usually recommends
that people not store chemicals below sinks or in other
cabinets with utilities that may need repair. However, most
labs do not have the luxury of not using spaces like this
and I think it is acceptable to use them as long as you
understand you will be responsible for clearing it out should
workers need to make repairs in that area. It might be good
to store items in a plastic bin or dishpan so they can be
removed quickly and easily.
Cabinet
Signs:
Depending on your workspace, you may have one or several
discrete storage groups. To avoid mixing things up after
they have been organized, put a sign with LARGE letters
on the cabinet identifying the group and list a few members
as well as a few things that should not be added. Here are
a few examples that you may need to alter for your situation:
STRONG
ACIDS:
hydrochloric,
sulfuric, nitric acid
NOT for weak acids (acetic, formic, propionic)
or Flammables
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STRONG
BASES:
ammonium
hydroxide, potassium hydroxide, sodium hydroxide
NOT for Acids or Flammables
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FLAMMABLE/COMBUSTIBLES:
(including
weak acids: acetic, formic)
NO Strong Acids
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OXIDIZERS
ONLY:
nitrates,
nitrites, dichromates, iodine, persulfates
NO Flammable/Combustibles
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†
Note added it Proof: Sometime around May 1999, there
was a chemical spill in the chemistry department that resulted
from failure of shelf clips. Several bottles of chemicals
broke and mixed on the floor and the Edmonton Emergency
Response Team and Fire Department responded.
reviewed:
December 15, 2000
BGMcC Department of Biological Sciences, University of Alberta
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