346 



NOISE 



the engine room crew will suffer distinct loss 

 of hearing, which will persist to some extent 

 for hours, but, in all but the most susceptible, 

 will undergo complete recovery in time." 



Moreover, the noise spectrum peaked at 

 400 cycles per second (c.p.s.) with very little 

 energy above the 5,000 band. This type of 

 spectrum is not one that would be especially 

 annoying (see later section). 



These measurements of noise level are not 

 necessarily typical of all submarines. A re- 

 port of over-all noise levels of 70 fleet sub- 

 marines while underway at 40 r.p.m. shows 

 that the USS PERCH is the third quietest 

 (51). The RATON was not included in the 

 70 studied. 



Noise Deafness 



Goldner (28) has distinguished between 

 two types of occupational deafness, acute 

 and chronic, the first being due to blasts and 

 the second resulting from frequent exposures 

 to moderately loud noise. The latter type 

 has a gradual onset and hence is not always 

 noticeable to the individual. 



Blast 



A great many reports deal with the effect 

 of gun blast and similar high intensity noise 

 of short duration (31, 36, 38, 40, 41, 54, 56, 

 62, 64, 65, 87, 88, 91, 98) to which service 

 personnel have been repeatedly exposed (ar- 

 tillery men, naval gun crews, rifle coaches). 

 In general these reports deal with field or 

 clinical observations of men who have had 

 auditory mechanism complaints. They tend 

 to agree in showing a hearing loss centered 

 in the 2,000 to 4,000 range of frequencies. 

 Some investigators (77, 88, 98) have made 

 audiograms before and after exposure to such 

 noises and have thus demonstrated in general 

 (a) a temporary deafness localized between 

 2,000 and 5,000 c.p.s., and (b) permanent 

 auditory injury in the same range extending 

 fan-wise on the audiogram (increases in 

 spread of frequencies affected and magnitude 

 of loss) with continued exposure and depend- 

 ing upon the duration and intensity of noises. 



It is to be noted that the range of frequencies 

 thus affected is partially included in the 

 upper range of the secondary speech sounds; 

 and for the most part such injuries, even if 

 permanent, affect only slightly the individ- 

 ual's ability to understand spoken language. 

 However, auditory signals such as those 

 which might be involved in sonar or radio 

 code reception might be adversely affected. 



Continuing High Intensities 



Insults to the auditory mechanism com- 

 parable to those resulting from gun blasts 

 have been discovered in personnel subjected 

 to high intensities of a relatively stable na- 

 ture over an extended period of time. Such 

 people include flying personnel, tankers, and 

 submariners. The majority of such studies 

 have dealt with flying personnel, although 

 the noise intensities are of approximately the 

 same order as those found in submarines and 

 small surface vessels (8, 10, 11, 12, 13, 22, 

 29, 37, 56, 77, 78, 90). 



It is to be noted that the frequencies ad- 

 versely affected by either blast or high inten- 

 sity exposures of relatively long duration do 

 not exactly correspond to the predominate 

 frequencies in the exposure noises. Instead, 

 the bulk of reports indicate the major dam- 

 age centers on 4092 c.p.s. Possible expla- 

 nations of this finding have been suggested 

 by Campbell (8). 



The only report discovered which has dealt 

 specifically with submariners covered 1500 

 otological examinations. It concluded that 

 the major hearing loss due to Diesel engine 

 noise occurs in the first hour of exposure, 

 with further but slight decreases in acuity 

 for two-, three-, and four-hour exposures. 

 Following a one-hour exposure, five hours 

 are required for recovery to normal auditory 

 acuity, while a four-hour exposure often re- 

 quires as long as 20 hours for recovery. 

 Some evidence was discovered of permanent 

 hearing loss as the individual's exposure in 

 engine rooms was prolonged (82). 



A laboratory study (17) suggested that the 

 higher the frequency of the exposure tone, 



