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 cleaning out. 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 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. 5-33