Watch those ears. (Gallo Images)

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Johannesburg - Researchers have produced evidence, based on tests at a soccer match with blaring vuvuzelas, that the sound level inside a 2010 stadium could lead to permanent hearing damage.

"The findings of this study demonstrate a real risk of noise-induced hearing loss," they say in an article in the latest edition of the SA Medical Journal.

The study was authored by Dr De Wet Swanepoel of the University of Pretoria's department of communication pathology, and Dr James Hall of a sister department at the University of Florida.

They said they tested the hearing of 11 spectators before and after they attended a Premier Soccer League match at a FIFA-approved training stadium with 30 000 seats.

During the match, ten of the 11 wore personal sound exposure meters fixed to their shoulders, and four of them blew vuvuzelas.

The researchers said the average sound exposure experienced by the participants during the almost two hours they spent in the stadium was 100.5 decibels.

The peak exposure exceeded 140 decibels for eight of the ten participants, with the maximum peak reaching 144.2.

The four who blew vuvuzelas had the most exposure to noise.

Swanepoel and Hall said South African standards for occupational noise required hearing protection for workers exposed to levels of 85 decibels and above.

The decibel scale was logarithmic, implying a doubling of hearing loss risk with every three decibel increase.

This meant participants in the stadium study were "exposed to high-intensity sound far exceeding the current legislated average exposure and peak exposure levels for occupational noise".

Tests on the 11 after the match showed a "significant" decrease in hearing sensitivity.

Though the decrease was probably temporary, the changes usually preceded permanent hearing damage.

Swanepoel and Hall said their findings supported a recommendation for hearing protection for soccer spectators.

"Official match stadiums for the 2010 FIFA World Cup will house 90 000 spectators, three times more than the stadium used in this study.

"It is reasonable to suspect that sound intensity will be even higher in the larger official venues."

Though they could not pinpoint the vuvuzela's contribution to the overall sound level, the instrument was certainly "a major factor".

In a previous study, also published in the SA Medical Journal, they reported on tests conducted at the university that showed exposure to vuvuzela noise for more than a few minutes put people at risk of hearing loss.

A South African company is marketing foam earplugs specially designed for the World Cup.