Document zKJGrQbwDz1nEv4ke0kKqvy3

any kind of inserts other than approved de vices Mufl Type Cup or muff type devices cover the exter nal ear to provide an acoustic barrier (Fig 38-8c) The attenuation provided by ear muffs vanes widely due to differences in size, shape, seal material, shell mass and type of suspension Head size and shape also influence the attenuation characteristics of these protectors The type of cushion used between the shell and the head has a great deal to do with attenuation efficiency Liquid or grease filled cushions give better noise suppression than plastic or foam rubber types, but may present leakage problems Amount of protection Commercially available earplugs if pro perly fitted and used, generally reduce noise reaching the ear by 25-30 dB in the higher frequencies (Fig 38-8a), which are conceded to be the most harmful This will provide ample protection against sound levels of 115 to 120 dB The better type of ear muffs may reduce noise an additional 10 to 15 decibels (Fig 38-8b), making them effective against sound levels of 130 to 135 dB Com binations of ear plugs and muffs give 3 to 5 more dB of protection In no case will total attenuation be greater than about 50 dB be cause at this point, bone conduction becomes significant Face and Eye Protection The protection of the eyes and face from injury by physical or chemical agents, or by radiation is of prime importance m any in dustrial safety program The eye and face protection standard. Prac tice for Occupational and Educational Eye and Fate Protection (Z87 1), is a fairly com prehensive document It sets performance standards, including detailed tests, for a broad area of hazards --excluding only X rays, gamma rays, high-energy particulate radia tions, lasers, and masers Besides general requirements, applying to "all occupations and educational pro cesses," the standard provides requirements on the following Rigid welding helmets Welding hand shields Nonngid welding helmets Attachments and auxiliary equipment-- lift fronts, chin rests, snoods, aprons, mag nifiers, etc Flammability Face Shields Goggles--eyecup (chipper's), dust and splash, welder's, and cutter's Spectacles--metal, plastic, and combina tion Some of the requirements are stated gen erally For example "Aprons or bibs for helmets shall be of nonflammable, noncon ducting matenal that is flexible and capable of withstanding disinfection " Other requirements are more precise As regards flammability, for example--"The thinnest section of the ngid helmet or hand shield shall not bum at a rate greater than 3 in per minute when tested by inserting one end of a 5 by I*/* in stnp of the helmet matenal in a blue-flame Bunsen burner The most significant changes of Z87 from the previous Z2 1-1959 Standard are An increase in the severity of the impact resistance test for lenses The revision il lustrates the test block with two figures and prescnbes that "A 100-in diameter steel ball, weighing approximately 2 4 oz shall be dropped in free fall from a height of 50 m onto the honzontal upper surface of the lens, impinging the lens within a circular area of a %-in diameter centered at the lens mechan ical [geometnc] center The lens shall not be chipped and the lens shall not be displaced from the frame eye m this test " Supplement ing this test for lens m frame--glass and plas tic--are impact resistance tests for lens on block and breakage pattern Also specified are tests for penetration resistance (plastic), flammability (plastic), haze (plastic), and ul traviolet, luminous, and infrared transmit tance (plastic and glass) A new requirement for lenses in welder's and cutter's goggles to be hardened to meet impact resistance requirement "All glass filter lenses or plates shall be heat-treated 1155