Chlorine and Ammonia Accident
Date: Winter 2009-2010
I teach Hazwoper, and was reading a novel from the late 1960s
that discussed a chlorine-tanker derailment, and that the response was
to open a bunch of ammonia tanks to neutralize it.This somehow does not
sound right, even though the author is pretty knowledgeable. All I can
find on line is about the obvious "do not mix BLEACH with ammonia," but
nothing about straight chlorine, vs. sodium hypochlorite. I would be
interested to find out what would happen if Cl2 was mixed with NH3.
When Chlorine gas is used for water sterilisation - as in large swimming pool
complexes - Ammonia is often kept on hand to detect leaks!
Chlorine is colourless at low concentrations, but is extremely corrosive and
very very very toxic - causing breathing difficulties and leads to damage of
tissue in the mouth and lungs. A cheap and effective way to test for chlorine
in the plant room is to take a squeezable bottle with some cloudy ammonia and
puff the vapour into the air. Ammonia gas combines with chlorine to produce
(among other products) Ammonium Chloride, which is a white powder. What you
see are clouds that look like white smoke.
Yes. Ammonia will neutralise chlorine, but in using it to deal with a tanker
spill, I imagine it would be as difficult to control the ammonia as much as
the chlorine, and ammonia is also poisonous.
A more practical solution would be to cool the tanker with water which also
dissolves the gas and prevents it drifting in the air. The result is mostly
hydrochloric acid, which can easily be neutralised with caustic soda, or even
crushed marble (sodium carbonate)
Intriguingly, the reason chlorine is used in swimming pools is not only to
kill bacteria, but to neutralise the ammoniated products which result from
urine in the pool!!! The smell you often detect in the evening is chloroamines -
not chlorine. That smell tells you that the chlorine is doing its job!!
The main reason or not mixing bleach (Sodium Hydrochlorite) with ammonia is
that it can release chlorine as a gas. VERY dangerous!
2NaOCl + 2NH3 --> 2NaONH3 + Cl2
Tennant Creek High School
Indeed mixing hypochlorite (bleach) and aqueous ammonia is very hazardous.
The reaction products are
NClx where x=1-3 These are toxic but very irritating, so unless trapped one
would evacuate by necessity.
You have to be careful the use the terms: "chlorine". Does that mean Cl2 or
hypochlorite? The reactions are different. Does "ammonia" mean NH3 or an
aqueous solution. Those too are different reactions. The "best" of not very
good options is anhydrous Cl2 and anhydrous NH3 with a minimal amount of
water, which is always present. There the reaction product is NH4Cl. But
even there the remediation should only be done by trained personnel.
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Update: June 2012