A Mexican study investigating the incidence of noise related hearing loss among 85 workers at a cement factory found 55 percent of the workers suffering from some degree of noise induced hearing loss. Among those, 70 percent suffered from binaural hearing loss, while 30 percent had reduced hearing in one ear.
The degree of hearing loss varied from 20-30 dB to more than 60 dB. 72 percent of employees were suffering from a binaural hearing loss between 20 and 30 dB at 4000 Hertz.
The age of the employees ranged from 18 to 55 years, and the number of working years in the factory varied from 1 to 31.
Years working and post relevance
The number of years working in the factory was found to be relevant. Those working from 1 to 7 years were a little less likely to suffer from any degree of hearing loss than those working from 8 to 31 years. The first group had a 50 percent risk, while the second group had an incidence of almost 70 percent.
Noise levels of more than 90 dB were measured in some processing areas such as crushing, crude milling and cement milling sites. The highest percentage of workers with damaged hearing, up to 85%, was found in the calcination area. Although this area was not the noisiest it was reached by the employees after going through all the other areas.
The impact of decibels
The study showed that 65 percent of workers exposed to noise levels of more than 90 dB suffered from hearing loss. Among those exposed to noise levels between 85 and 90 dB, 44 percent had hearing disorders.
The study published in the journal Salud Pública de México, in March-April 2000, was conducted by personal interviews, audiometric tests and noise level measurements. However, no mention was made in the study of the use of hearing protection by the workers.
Hearing protection and measures to be taken
Working in a noisy environment is hazardous to the hearing ability.
The official Mexican standard of Health and Safety Conditions in noisy Workplaces was updated in 2001, considering 8 hours a day of 85 dB as the maximum permissible noise level in a workplace instead of the previously accepted limit of 90 dB.
Workers must wear hearing protection provided by the employer and must receive hearing evaluations. In addition, actions should be taken at the source of noise and other remedies should be implemented to lower noise levels in the work environment if the recommended maximum noise levels are exceeded.
Source: “Prevalence and correlates of hearing loss in a cement factory,” Salud Pública de México, vol. 42, num. 2, March-April 2000, and Official Mexican Standard NOM-011-STPS-2001