only treatment before discharge to the distribution
system, as in the chlorination of groundwater supplies
and previously unchlorinated purchased supplies.
Prechlorination is the application of chlorine to raw
water before coagulation, sedimentation, or filtration.
Postchlorination is the application of chlorine after
filtration, but before the water leaves the treatment
plant. Rechlorination is the application of chlorine into
the distribution system or into a previously chlorinated
purchased supply to maintain the chlorine residual.
The above applications are normally continuous.
Very heavy chlorination for a limited period is
sometimes applied at specific points in the distribution
system to destroy localized contamination.
OTHER USES OF CHLORINE.Chlorine is
also used to control tastes and odors in water. It reacts
with the substances causing taste and odor, such as
hydrogen sulfide, minute organisms, algae, and
If the reaction is incomplete, the taste and odor of
some substances may be intensified or become more
objectionable. Chlorine is also used to a limited extent
to oxidize iron and manganese and to remove color.
SAFETY.Safety is important in the handling of
chlorine. Some of these important factors are as
Provide self-generating oxygen-breathing
apparatus or self-contained oxygen-breathing
apparatus designed to cope with chlorine.
Maintain only the supply of chlorine in any
chlorinator room that will do for normal daily
demands. Store the main supply in a detached
noncombustible building or in a fireproof room
that is vented only to the outside and separated
from the main part of the building. Keep the
chlorinator and chlorine storage building or
rooms locked to prevent the entrance of
unauthorized personnel and restrict these areas
from any other use.
Allow only reliable and trained personnel to
Handle containers carefully to avoid dropping or
Avoid hoisting containers; if hoisting is
necessary, use safe lifting clamps.
Store cylinders in a cool place, away from
dampness, steam lines and fire, and in an upright
position secured from tilting and falling.
Keep protective valve caps on containers when
not in use; never tamper with safety devices on
Never connect a full cylinder to a manifold with
another cylinder unless the temperatures of both
are nearly the same.
When not withdrawing chlorine or when
cylinders are empty, keep the valves closed.
Disconnect the valves as soon as the containers
are empty, and check for chlorine leaks at the
valve outlets. Test for leaks by passing an
opened bottle of strong ammonia solution
around the valve. White fumes of ammonium
chlorine will appear if there is any leakage.
Leaks around fittings, connections, and line can
be detected in the same way. Do not apply
ammonia solution to plated metal parts, as it will
remove the plating.
When chlorine is noticed, workers should avoid
panic, refrain from coughing, keep mouth
closed, avoid deep breathing, keep head high,
and get out of the affected area. Only qualified
personnel with suitable respiratory equipment
should be assigned to investigate and correct the
cause of chlorine leaks. If chlorine is being
discharged, close the container valve
immediately. If chlorine is escaping in liquid
form, turn the containers so the chlorine escapes
as gas. This will reduce leakage. Do not apply
water to the leak; this dangerous practice causes
corrosion that may increase the leakage.
Electronic chlorine gas detector warning devices
are widely used in plants and mechanical rooms
that contain chlorine.
The handling of a persistent chlorine leak in a
plant is best left to the chlorine supplier or local
Never apply a flame, blowtorch, or other direct
heat to chlorine containers; discharge them in a
room with a temperature of about 70°F.
Never ship a defective or leaky cylinder unless it
is completely empty. Paint DEFECTIVE
plainly on all such cylinders.
Follow all regulations on shipping, storing, and
using compressed gas cylinders.
Provide proper means of exit from areas where
chlorine is stored or used.
Never use a chlorine cylinder except to hold