Document mpZM7LZ9jYEveVG1bvJQznzwd

1066 CHAPTER 42 1957 Guide very thick bituminous coatings applied in molten condition. The best results are obtained by applying the bituminous coatings over a standard priming coat such as red lead or a bituminous paint, and for long service it has been found that after the bituminous coatings are applied, a wrap ping of asbestos fabric, saturated with bitumens will prevent movement and displacement of the bituminous coatings, and add greatly to the length of time satisfactory protection will be maintained. Cathodic Protection Protection is obtained by rendering the structure cathodic to the sur rounding water or soil by means of a controlled difference of. potential. This method, which has proved satisfactory and economical bn a number of gas and oil pipe lines underground, has also been applied with some success to the protection of the inside of water storage tanks and other structures that are in contact continuously with water. Protective coatings that insulate .a large portion of the metal surface will reduce very materially the total amount of protective current that must be impressed on bare anodic areas to arrest corrosion. Because of differences in environmental conditions, it is necessary to determine or estimate the minimum current density required for each structure, and design the anode or anodes so that the necessary protection can be obtained most economically. In water having relatively high electrical conductivity such as in sea water, this is comparatively easy compared with fresh water. In the latter, the composition of the water is a major factor. It is theiefore desirable to obtain an accurate estimate of the minimum current density required. The current is then controlled by the potential between the anode and the structure to be protected. Rectifiers have generally proved to be the most practical means for supplying the necessary current for protection of surfaces in contact with neutral waters.88 HANDLING WATER TREATING CHEMICALS Virtually all the chemicals used in water conditioning are injurious if taken internally in large doses. Many also cause severe skin irritation. Thus, they should be handled with caution. Caustic soda, lime, and concentrated sulphuric acid will burn the flesh. In addition, if mixed with small amounts of water, sufficient heat may be generated so that spattering occurs or the container becomes too hot to handle. The chlorophenol compounds, even in the low concentrations used in water conditioning, have been reported89 to produce dermatitis. Chromitch is not uncommon among workers handling chromates. The amines are said to be absorbed through the skin.40 Morpholine is said to cause kidney and lung trouble when so absorbed. Chlorine gas irritates the skin, eyes, and mucous membranes. Concen trations as low as 0.004 percent by volume in air cause dangerous illness in 0.5 to 1 hour. When relatively large amounts of the non-gaseous chemicals are to be handled, protective clothing, including goggles, should always be pro vided, and a shower head or its equivalent provided at or very near the point where the chemicals are mixed. Chemicals should always he washed from the skin with large volumes of water. For the handling of chlorine and chlorinators, the U. S. Public Health Service41 stipulates the following safety requirements: Corrosion and Water Formed Deposits, Causes and Prevention 1067 1. Suitable gas masks and a small bottle of ammonia for testing for leaks should be kept at convenient points immediately outside the room or enclosure in which chlorine is being stored or is in use. Gas masks should be inspected at regular inter vals and kept in serviceable condition. Note:--All-purpose masks offer adequate protection only when the concentration of acid gases does not exceed two percent-- see Safe Practices Pamphlet #64 National Safety Council. 2. Chlorinating equipment and cylinders of chlorine should be housed preferably in separate buildings above the ground level. 3. The room or building housing chlorinators in service should be maintained at a temperature above 60 F, but never in excess of the normal summer temperature. The cylinders of chlorine should be shielded, where necessary, from excessive heat or cold. Direct heat should hot be applied to cylinders of chlorine, nor should hot water be poured over them or come in contact with the cylinder valve. 4. Adequate ventilation should be provided for all enclosures in which chlorine is being fed or stored. 5. All joints of tubing connecting chlorine cylinder and chlorinators should be kept absolutely tight and inspected frequently to insure tightness. Tubing should slope upward from the cylinder. Table 7. Recommended Maximum Allowable Content in Wateb Supply* Substance Max. Concen tration, ppm Substance Max. Conc em ulation, ppm Iron & Manganese (Total) . Zinc...................................... Fluorine............................... 3.0 0.3 125.0 15.0 0.1 1.0 Selenium.............................. Phenols (Total)................... Poly-phosphate of Sodium. pH Value @ 25C................ 0.05 0.05 0.001 10.0 10.6 * V. S. Public Health Service. ' LEGAL REGULATIONS In a number of states, the water used for humidification, even in in dustrial plants, is required to meet drinking water standards insofar, as bacteriological quality is concerned. A ruling of the U. S. Department of Agriculture, Meat Inspection Division, prohibits the use of chromate in water used for air washing when the air later contacts, foodstuffs.48 There is an ever growing consciousness on the part of public health officials, of the necessity for regulations to protect potable water supplies. Attesting this is an ordinance48 now in effect in Detroit, Michigan, which, stipulates in part: "No physical connection shall be maintained between lines carrying city water and pipes, pumps, or tanks supplied from any other source. Where dual supplies are necessary or desired, lines carrying city water must be protected against back flow of polluted water by an atmospheric gap. Secondary supplies and emergency Bources shall include: surface waters from rivers, lakes, ponds, lagoons, andreservoirs; well waters both deep and shallow; any supply of water which has been stored, held, or reserved after being used for industrial purposes; cooling water, or water which has in any way been treated, processed, or has been subjected or exposed to any contamination of a bacteriological or chemical nature; and water from any other source than the city supply." The U. S. Public Health Service stipulates: "Salts of barium, hexavalent chromium, heavy metal glucosides, or other sub stances with deleterious physiological effects, shall not be allowed in the water supply system." The same agency recommends that the concentration of the substances listed be held below the values cited in Table 7. The Board of Directors