According to data gathered by a Canadian Occupational Safety and Health study, a potentially new source of hearing damage risk may have been revealed by a hazardous, environmental combination.

Findings appear to indicate that exposure to a mixture of loud noise together with carbon monoxide from car exhaust emissions is an even more potent cocktail, which carries an increased risk of suffering long term hearing loss.

It is being increasingly pointed out that noise levels within the urban environment are rising, as exposure to everyday sounds appear above the recognised safe level of 80 decibels, and are often within the hazardous range of 90 to 140 decibels, and likely to lead to permanent noise-induced hearing loss.

The research conducted amongst 8, 600 workers, exposed one group to noise levels lower than 90 decibels for 8 hours and another group to noise levels above 90 decibels, and a sample of workers from both groups was also exposed to carbon monoxide at the same time.

The study demonstrated that workers who were exposed to carbon monoxide together with noise levels above 90 decibels displayed significantly poorer hearing thresholds at high frequencies (from 3 to 6 kHz).

One of the suggested explanations is that the presence of carbon monoxide and the resulting reduced oxygen level in the blood stream accelerates the deterioration of the sensory cells of the inner ear.

Findings also showed that garage mechanics, truck drivers, forklift operators, welders, fire fighters and miners are among the most exposed groups vulnerable to contracting varying degree of industrial deafness.

However, any damaging effects or symptoms from carbon monoxide are only likely to appear as a progressive hearing loss after at least 15 years of working in excessive noise level workplaces or similar environments.

Recommended hearing loss advice is to also evaluate the risk of chronic exposure to carbon monoxide when assessing particular working environments also prone to excessive noise levels.