Other causes include sand, gravel, and greasy or tar-
related materials. A lot of sand, gravel, or just plain
mud reveals a broken or loose sewer joint or pipe.
Explosions in sewers are not uncommon and
should be guarded against. Check with your local
safety office for the most current regulations and
information. Systematic inspection and maintenance
permit early correction of faults before major defects
and failures develop. Trouble calls concerning
stoppages or slow drainage are received occasionally.
The first step in correcting the trouble is to
determine the cause. A sewer line can be inspected
from manhole to manhole by using a flashlight or a
reflecting mirror or both. One person acting as an
observer can look up the sewer line toward the
flashlight held by the second person in a preceding
manhole. Thus the condition of the line can be noted to
determine whether roots or other obstructions need
Before entering a manhole, ensure the air is safe.
You are NOT permitted to enter a manhole until you
have an entry permit, identifying all of the conditions
that must be satisfied before the entry begins.
Additionally, an attendant person shall be stationed
outside the manhole at all times. The attendants sole
responsibility will be for observation of the entrants
into the manhole. The attendant shall have no other
responsibilities or duties during the observation. For
more information on entering confined spaces, refer to
EM 385-1-1, Safety and Health Requirements Manual.
Purging or a fresh air pump may be required.
Sewage gases are very toxic as well as explosive.
Routine sewer maintenance includes flushing,
cleaning, and immediate repair of defective sewers.
Information pertaining to flushing, cleaning, and
repairing sewers is given below.
Flushing helps remove loose organic solids and
sand or grit deposits from sewers. Flushing is not an
efficient method of sewer cleaning unless a high
velocity can be maintained between manholes on a
short run; in other words, you depend on the high
velocity for complete scouring action of the sewer.
Flushing may be done by a number of methods, two of
which are with a fire hose and with a pneumatic ball.
When flushing with a fire hose, you need enough fire
hose to reach between manholes. When using this
method, string a rope or light cable through the sewer
with sewer rods if a plain fire nozzle is used. Start at the
upper end of the system and draw the flowing nozzle
through the sewer. If a self-propelling turbine type of
nozzle is used, the rope is not required. Try to use 2 1/2-
inch fire hose discarded by the Fire Department. Paint
the sewer-flushing hose at the ends with an identifying
color (yellow, non-potable water) to prevent use for
emergency potable water connections.
In pneumatic-ball flushing, inflate a light rubber
ball, such as a beach ball or volleyball bladder, to fit
snugly in the sewer, and place it in a small canvas or
burlap bag with a light rope attached. Place the ball in
the sewer, hold the line until the sewage backs up in the
manhole, and allow the ball to move to the next
manhole. When an obstruction is reached, the pressure
pushes the ball against the crown of the sewer, causing
a jet at the bottom (fig. 5-47). As much as 4 miles of
sewer can be cleaned in 8 hours by this method, and it
works for sewers up to 30 inches in diameter. A
wooden ball with a diameter of 1 inch less than the
sewer can also be used. Where sewage flow is low, the
addition of water to the upper manhole may be
required. In the sand cup method, a sand cup with an
auger is attached to flexible steel sewer rods to run
through the sewer (fig. 5-48). The rubber cup is
perforated to provide flushing action.
WATER PRESSURE BAG (BLOW BAG)
Water pressure bags are made of various types of
rubber and canvas material. The blow bag is very
efficient and requires less time to operate than other
types of drain cleaning equipment. Various sizes of the
blow bags are available. To operate a blow bag,
connect a water source to one end and insert the blow
bag into the line to be cleared or flushed. Ensure that
you are using a blow bag that is compressed when
placed into the line. When the water pressure is turned
on, the blow bag will expand in size, increasing the
pressure and holding the blow bag in the line. Keep in
Figure 5-47.Ball method of sewer flushing.