Frostproof  insulation  is  generally  constructed  of five layers of felt. There are three layers of pure wool felt and two layers of asphalt-saturated asbestos felt. Frostproof insulation is 1 l/4 inches thick and comes in 3-foot lengths with a canvas cover. The pipe coverings shown in this section are some of the types of coverings that are installed easily, primarily because each section is split in half and has a canvas cover with a flap for quick sealing. Joint collars are furnished to cover joint seams on insulation exposed to outside conditions. Cheesecloth is used on some types of insulation instead of canvas. To install the cheesecloth, use a paste to hold it in place. Allow enough cheesecloth to extend over the end of each 3-foot section to cover the joints. After  you  have  applied  the  cheesecloth  and smoothed  it  out,  install  metal  straps  to  hold  the insulation firmly in place, as shown in view H, figure 4-24. Valves and Fittings Cover with wool felt, magnesia cement, or mineral wool  cement  of  the  same  thickness  as  the  pipe covering.  These  materials  are  molded  into  shape  to conform  with  the  rest  of  the  insulation.  When magnesia or mineral wool cement insulation is used, cover the insulation with cheesecloth to help bind and hold it in place. Boilers and Storage Tanks If the boilers and storage tanks are unjacketed, cover them with an approved insulation. Use only insulation  approved  by  the  MIL-STD.  Some  of  the approved types of insulation for boilers and tanks are magnesia, mineral wool, calcium silicate, cellular glass, or other approved mineral insulation at least 2 inches thick. Insulation may be of either the block or the blanket type and must be wired securely in place in an approved manner. When applying insulation to the outside of a boiler or storage tank, put it over 1 1/2-inch wire mesh. The mesh is held away from the metal surface by metal spacers that provide an air space of at least 1 inch. When you use blanket or block material, fill the joints in the insulation with magnesia, mineral wool, or other suitable cement. Cover the surface   of   the   insulation   with   a   thin   layer   of hard-finished  cement,  troweled  smooth,  and reinforced with 1 l/2-inch wire mesh. Q12. Q13. Q14. Q15. What minimum dosage of chlorine is required to disinfect  a  well  under  normal  conditions? An 8-inch pipe contains how many gallons of water per foot of pipe? What velocity of water through a pipe is required for proper scouring action? What is the purpose of a thrust block? SHORING AND SCAFFOLDING LEARNING OBJECTIVE: Recognize safety and construction requirements of shoring and scaffolding. As a Utilitiesman, it is part of your job to see whether there is a need for shoring or scaffolding on the job. Most of the time, job problems and accidents are a direct result of inadequate planning. As you plan each job, ensure that you have provided the equipment necessary to do the job safely. In this section, safety and health requirements are addressed. For more information,  see the Safety and Health Requirements Manual, EM 385-1-1, U.S. Army Corps of Engineers. SHORING The  need  to  protect  personnel  who  work  in trenches   is   important.   Following   the   ground investigation, you should make a decision as to how the sides of the trenches are to be protected. All necessary materials must be obtained and delivered to the site (figs. 4-25 through 4-28 and table 4-1). All trenches deeper than 5 feet must have their sides supported  or  protected  by  sloping  or  battering. Trenches can sometimes be made in the case of hard rock, when it becomes clear to experienced engineers on the site (as the trench proceeds) that the rock is solid and has no dangerous cleavage planes that could cause the side of the trench to collapse. The requirements are listed below. 1. Banks more than 5 feet high should be shored, laid back to a stable slope, or provided with other equivalent protection whenever workers must move around or are exposed to a cave-in. Trenches less than 5 feet in depth must be protected when examination of the ground indicates that hazardous ground movement may be expected. The safe angle of repose for soil conditions and bracing systems should be determined by a qualified person. 4-20