Occ health: NIHL Difference taking mean loss of 40dB versus mean loss of 60dB as action level



The logarithmic scale as used for decibels has major idiosynchracies. One underestimates the impact of dB changes. 40 dB has a 100 times as strong effect on air pressure striking the ear drum than 1 decibel would have. 60 Decibels has a 1000 times larger change on air pressure striking the eardrum than 1 decibel.  Being deaf to a 40 decibel sound is much, much more deaf than being deaf to a 60 decibel sound. Conversely, having lost mean decibels of 40dB is much, much less disabling than having lost 60dB.

Using the same argument, 100 dB has a 100 000 times effect on air pressure strikibg the ear drum than 1 dB. The air movement from 100dB sound will strike the ear drum 100 000 times harder than a 1 dB sound. (140dB strikes the eardrum 10 000 000 times harder)

The difference between a 60dB and 40dB action level is major. Health practitioners, employees, management, law makers and union representatives can easily underestimate the true meaning of such differences

Older people become deaf. This implies that employees just due to fact of normal ageing can drift towards the noise-disability level irrespective of excessive noise exposure or noise protection usage. Older persons become more deaf in the higher frequencies than the lower frequencies. Noise-induced hearing loss also affects the higher frequencies more than the lower frequencies. There is therefore a diagnostic dilemma when evaluating gross age-related presbucusis and gross noise-induced hearing loss.

The effect of gross age-related presbucusis and gross NIHL looking so similar is that the Compensation Commissoner will give noise compensation for employees how have predominantly ageing effects. On the human resources and labour side it may be that a person becomes hearing disabled from his noise job due to ageing (which could be classified as discriminatory practice). There are also ethical implications as to what the OMPs or ONPs functions are; to comply with the law, to get an employee as disabled, and then in effect cause to lose income or lose their job (as there may not be an accommodated position in the company)

A mean average loss of 40 dB over the 250Hz, 500Hz, 1000Hz, 2000Hz, 3000Hz 4000Hz, 6000Hz and 8000Hz frequency bands could make one deaf to the rumble of a refridgerator, the rustling of leaves and the tweet of birds. With accomopanying notching as seen in NIHL (where there is additional loss over the 4000Hz frequency band) you wil start losing hearing on high-pitched sounds such as “p”,”k” and “sh” sounds. In comparison there is a dramatic reduction in hearing ability when the 60 dB loss is taken as the action level. All speech hearing can disappear as well as the ability to even hear a vacuum cleaner.

The above indicates the problems surrounding NIHL in Second World countries such as South Africa. Do you want to die of hunger (due to the loss of your job) or are you and your employer prepared that you lose your hearing?