Document qk6GQZYGz9Q91BK0oQV3yj4ok

546 G. W. JONES walls of the buildings following an explosion can be obtained by outside glazing and by scoring the glass panes before they are installed.115 It is impossible to have too much ventilation around exceedingly hazardous , operations. Whenever possible the operations should be carried out entirely in the open air, as is done in certain processes in the petroleum industry, with no closed structures, except those to house instruments and other equipment that must be protected from the weather. G. RELEASE DIAPHRAGMS AND VENTS . Adequate release diaphragms should be provided on all equipment in which! explosive mixtures may be present. The ideal release diaphragm is that having zero mass and infinite area. Although this cannot be realized in practice, the* construction and size of release openings should approach the above ideal as closely as possible, yet be strong enough to sustain the operating pressure within1 the equipment without danger of rupture or leakage, except in case of an ex plosion within the equipment. To protect properly a given installation containing explosive mixtures the' following major factors must be known or determined experimentally: (I) the': type and concentration of the combustible vapor or gas that may be present iri: the equipment; () the maximum pressure the equipment will safely stand; (3)1 the maximum pressure developed by the mixtures on explosion; (4) the area of release openings necessary to keep the pressures below the safe maximum pressure) (5) the kind, area, and thickness of the diaphragm, material that will ruptur. at the'desired~pmsure;' '(6)' thei5ropArToeati'on "of'th`r diaplirAgffiS"te"Meaw'tt| pressure developed before excessive pressures are reached. For specific informatio on this subject the reader is referred to published reports.115-121 Release dial phragms are now available that will rupture at definite ..pressures ranging froii less than 1 to .more than 1000 p.s.i. Various types of materials are used, and the, may be obtained with protective coatings where corrosive atmospheres ar> encountered. ./ One example of explosive mixtures of acetone and air will be discussed to show how the proper diaphragms may be determined. Figure 5 gives the pressures- developed when the area of release opening is varied from no opening to 45 squar inches per cubic foot of space in the equipment. These values were obtained eat] perimentKlljriir-arr8=liter-closed"'bomb-with-mixtures"containifig'-5:50.rperrEi of acetone yapor, a concentration that gives the highest pressure on explosion'/1 "*H. R. Brown and R. L. Hanson, Chem. & Met. Eng., 40, 1030 (1929). "*M. E. Bonyun, Chem. <fc Met. Eng., 42, 260 (1935). n' S. Chester, and B. W, Jesser, Trane. Am, Soc. .Mech. .Engrs., 74, 229.. (1952)........ urCTE7Huff, Chem. & Mel. Eng., 44, 715 (193771 'G. W. Jones, E. S. Harris, and B. B. Beattie, U. S. Bur. Mines Tech. Paver No. 553! 1933. "G. F. Lake and N. P. Inglia, Inst. Mech. Engrs. (London), 142, 365 (1940). *T. S. Murphy, Chem. & Met. Eng., 99, 108 (1944). < HAZARDS OF COMBUSTIBLE GASES AND VAPORS 547 AREA OF OPENING, per cuff, of mixture, tq.in Figure 5. Relation of pressures produced to area of opening, 5.50 per cent acetone-air mixtures (8.05 liter bomb). Let it be assumed that the equipment should not be subjected to a pressure Igreater than 10 p.s.i.; then from the results given in Figure 5 the area of release gpenings should be at least 5 square inches per cubic foot of space. Next is determination of the proper size and thickness of the diaphragm aterial that will provide release of the gases from the equipment at a pressure of 10 p.s.i. or less. In general, lead, tin, aluminum, copper, gold, platinum, and special alloys have been found to be most, suitable for release materials at low ressures. An example is shown of tests made on aluminum foil of 0.001-inch jckness in an 8-liter bomb using acetone-air mixtures. The rupturing pressures ,or openings of different sizes and for different concentrations of acetone in air hi explosion are given in Figure 6. The rupturing pressures increase as the area Fjgure 6. Aluminum diaphragm testa (0.001 inch thick). jtthe_Qpening_is_reduced--Io-this-exampler-w.here~the-pressure-must-not-exoeed |9 p.s.i., the curves show that the diaphragms must be at least 3 inches in Jameter for this particular aluminum foil; and, as previously determined, he number of release openings should be such as to give 5 square inches of iaphragm release opening per cubic foot of space in the equipment.