Document n99DvxNNx9qeD0aO87YpVwzn1

690 JEROME R. COX, JR. a. Cotton. The upper dashed curve in Figure 32 shows the noise reduction typical of ordinary, dry cotton wads placed in the ears. The protection is poor throughout the low frequency range, but improves slightly at high frequencies. This possibly accounts for the misleading claims of some enthusiastic users of ordinary cotton. The reduction in high frequency noise decreases the annoyance of the noise, and the user believes that his increased comfort means satisfactory protection. b. Impregnated Cotton. The solid curve in Figure 32 shows the typical noise reduction for properly fitted wax-impregnated cotton plugs. These plugs are cylinders Va inch in diameter and about V< inch long. Their average weight Figure 32. Maximum noise reduction to be expected from ear plugs. For average noise reduction : subtract 5 to 10 db. Data were averaged from several sources."'" is a little over 2, grams. They must be warmed and rolled in the hand before, insertion; when the material has the consistency of putty, the plug may be pressed', into the ear. Care must be taken to insure that the plug conforms to the eafi4 canal. At tropical temperatures, the wax softens and becomes sticky and th6{ plugs are, therefore, unsatisfactory. Under all conditions of use, they collect and retain any dirt to which they are exposed. These plugs are relatively expendable,. however, since a new pair each day for each worker would not be unreasonably! expensive. If-the plugs must be removed many times each day, it m&f 'ndt B'f economical to use new plugs each time. Also, it is inconvenient to remold tfi. plugs each time. c. Soft Rubber. The lower dashed curve in Figure 32 shows the typical^ -noise-reduotion-for-properly-fitted-soft-FubbeF-plugSr-These-plugB-Me-oapbalbS^., a soft rubberlike material weighing about V2 gram, shaped to facilitate insertion" and retention in the ear canal. Most manufacturers make the plugs in three sizes -for comfortable fit in small, medium, and large ears. They should be made of a special nontoxic elastomeric material that is resistant to the action of ear;, NOISE AND THE CONSERVATION OF HEARING 691 asKosJvax. The plugs must be carefully inserted to provide adequate protection. They S^Jlhave small tabs on the outside end of the plug to facilitate removal. Unless these ra^Hjigs are cleaned regularly with soap and water, they will collect wax and dirt. B&vfpieir average cost is slightly less than a dollar a pair. Therefore, they are not 'Wi|j expendable as the impregnated-cotton plugs. Attempts have been made to design a plug that excludes noise, but not aBmeech. One such attempt is a "filter" plug, which has a small perforation that '^Bfiows low frequency and mid-frequency sounds to be transmitted. The noise ^^S^Sduction characteristic -is no better than that for cotton up to the 600 to 1200 ' H>.s. band. Above this band the characteristic is about the same as the average for " "Elff rubber plugs. Another attempt at an ear plug that will pass speech utilizes ,`tflPny va^ve fhat closes during an intense pressure pulse of long duration. At 'Ill other times the valve is open and the plug has a noise reduction similar to the "filter" type. d. Muffs and Helmets. Muffs that cover the outer ear and are held in noplace by means of a headband have a noise reduction characteristic silghtly better '^Iplian that of the filter type of ear plug, but usually not as good as the solid plug. ||t is difficult to obtain a good seal between the muff and the ear, and for this Ireason, the low frequency noise reduction may be poor. Muffs thajj have a very ftfirm headband will provide protection equivalent to that of a solid plug; -but they .nZ'j may be uncomfortable if worn for long periods. A new muff with a fluid-filled seal apparently overcomes this difficulty. Helmets are, in general, inferior to niuffs. BL This-.type-of ~protector-.-can-be_put-.on...and removed quickly since' nothing Mgn&ed 'be inserted in the ear canal. Therefore, the muffs and helmets are useful in lituations that require frequent removal of ear protection or for personnel who 3;cannot wear regular protection. They may be worn in addition to plugs if extra Bpfotection is needed. This combination approaches the theoretical limit of ear f|protection.87 sb- if3 S. Medical Considerations W'"'- *? A few employees will require treatment before they can wear ear plugs ^safely. Current medical opinion indicates that eczema and draining of the ears *4are the major reasons for not wearing ear plugs. Usually these difficulties can be jrectedby "treafmenfiirthe planfoFByTlie employee's physician!"The'.employee ..can then participate in the ear-plug program within a short time. During treat ment, the employee may wear ear muffs. ,r . . A few who should be treated may not be aware of their condition. Complete TT^--^Screening of all.,exposed employees may be accomplished by means'.:nf_an:.ntn^ gcopic examination performed by the plant physician. If an audiometer program 'is.to be conducted, this examination will probably be planned for the,time of the . {first audiogram. "H. E. von Gierke, Personal protection, Am. Ind. Hyg. Assoc. Quart., 15, 44 (1954).