Keoghs Insight

Author

Abbie Witherington

NIHL killed the radio star

AWARE15/08/2014
Disease Aware Issue 5

Radio use in the workplace is not uncommon. In factories, workshops and garages across the country, radios are common place (although subject to licensing controls). Music is often thought to be of benefit by increasing productivity and boosting morale amongst employees.

An employer however, will, all too often, give little thought as to how radio adds to overall noise levels in the workplace and the possible deterrent effect it may have against the use of hearing protection, where the same is provided for use.

In claims for noise-induced hearing loss (NIHL), radio usage is perceived to significantly increase noise levels in the workplace. The HSE have identified radios as a potential hazard to hearing in the work environment. Acoustic engineers and lawyers alike have generally accepted, when dealing with NIHL claims, that where a radio can be heard above the noise of machinery, that this must mean at least a doubling of the sound intensity and a consequently an increase in noise levels of at least 3 dB.

Such a generalisation pays scant regard to the differences in the type of noise output, or the intricacies of the human ear. The starting point in any assessment of the impact of radio noise on the working environment is an analysis of what a claimant means by being able to hear the radio above the machinery noise.

If this is reference to a claimant being able to hear speech on the radio, whilst in a working factory environment, then tests have demonstrated that a claimant can recognise speech on a radio where the signal to noise ratio (SNR) is -6 dB (i.e. the words in the speech are 6 dB less intense than the surrounding noise). This is in an environment which assumes that the surrounding noise is at the same frequency spectrum as the radio noise, as a constant source with no variation or fluctuation (which would be the most difficult type of environment to distinguish the radio noise).

In a factory environment of course, the machinery noise is unlikely to be at the same or similar frequency output as the radio. For interrupted, intermittent or fluctuating noise, the SNR for complete speech recognition would fall to -16 dB. If one factors in the natural fluctuating pattern of human speech or song, then the SNR falls to as low as -22 dB.

Where the frequency spectrum of the environment noise is very different to the frequency of the radio, then it becomes even easier to hear the radio at lower outputs.

The above may all sound rather technical, but, in essence, means that the approach of engineers simply adding 3db to noise readings to factor in any radio noise, is an approach that should be challenged. Just because a claimant can hear a radio, does not mean a doubling in the sound intensity.

It is also important to consider the location of any source of radio noise. Sound intensity will reduce by 3db with each doubling of the distance away from the source. The location of the individual can therefore be a significant factor in assessing the overall impact of the radio. Whether the radio is played over a tannoy system therefore might bear greater consideration than where an individual is 30 meters away from a portable radio.

The type of radio is also of relevance. For most portable radios, distortion of sound will occur when played at maximum volume and, for this reason, radios are often not set at full volume.

It is imperative in NIHL cases therefore, particularly where radio noise could be the difference between culpable and non-culpable levels, for a detailed analysis, challenging any assumptions made by an engineer.