Hot forgings, steam or bored hammers shall be permitted when located at least one thousand feet from any zoned residential district and/or existing residential use and such operation shall be located within a masonry building or suitably reinforced concrete mat, or solid rock, and mounted on shock absorbers that reduce vibration to a reasonable minimum. The noise in decibels, as measured at the street or property line, shall not exceed sixty-five decibels of sound and shall be muffled so as not to become objectionable due to intermittence, beat, frequency or shrillness. Such noise shall not in any case exceed the street traffic noise during a normal day, when the employees arrive or leave the place of manufacturing. Smoke, dust, dirt, and fly ash shall not exceed three-tenths grains per cubic foot of flue gas at stack temperature of five hundred degrees Fahrenheit, and not exceed fifty percent excess air, and shall in no instance be unclean, destructive, unhealthful, hazardous, nor shall visibility be impaired by the emission or a haze which unduly impedes vision with an apparent opaqueness equivalent to No. 2 of the Ringelmann Chart.