Hearing loss from long term exposure to noise has been recognized as a hazard for a long time. However, what the non-auditory effects of noise are is still not certain. In general, the suspected effects include cardiovascular function (hypertension, changes to blood pressure and/or heart rate), and changes in breathing, annoyance, sleeping problems, physical health and mental health. This wide range of effects has led researchers to believe that noise has the ability to act as a general, non-specific stressor. It is very difficult to pin point what the effects of noise are versus the effects of other general stressors.

In the workplace, non-auditory effects of noise include problems with oral communications. It has also been shown that absenteeism appears to be higher among workers in noisy industries. It has not been concluded whether this is from psychological aversion to noise or from physiological consequences of noise stress.

Non-auditory effects can be divided into two categories - physiological effects and performance effects.

The physiological effects can be temporary or permanent.

Examples of temporary physiological effects are:

• the startling response to loud noise, where muscles burst into activities, generally, with the intention to protect
• the muscle tension response, where muscles tend to contract in the presence of loud noise
• the respiratory reflexes, where the respiratory rhythm tends to change when noise is present
• changes in the heart beat pattern
• changes in the diameter of the blood vessels, particularly in the skin

All those effects are similar to the response of the body to other stressors.

As for the permanent effects, there is no consensus on the issue: some researchers tend to favour the theory that there are permanent effects, while others are skeptical on the issue.

Noise can interfere with verbal communications and can be distracting and annoying. Below are some examples of how these factors can affect work performance.

Speech intelligibility

Speech intelligibility is the ability to understand spoken words. The presence of noise interferes with the understanding of what other people say. This includes face-to-face talks, telephone conversations, and speech over a public address system.

In order to be intelligible the sound level of speech must be greater than the background noise at the ear of the listener. People with otherwise unnoticeable hearing loss find it difficult to understand spoken words in noisy surroundings.

In noisy work situations, people are able to converse with difficulty at a distance of one meter for a short time in the presence of noise as high as 78 dB(A). For prolonged conversations, the background noise level must be lower than 78 dB(A).

In social situations people often talk at distances of 2 to 4 meters. In such cases noise level should not exceed 55 to 60 dB(A).

Source: C.M. Harris. Handbook of Noise Control, 2^nd Ed. New York: McGraw-Hill, 1979.

Annoyance

Noise is annoying. In noisy environments, people generally prefer to reduce the noise loudness, avoid it, or leave the noisy area if possible. The same noise could be annoying to some people but acceptable to others. There is no definite relationship between the degree of annoyance or unpleasantness of noise and the risk of adverse health effects. For example, very loud music may be pleasant to one group of people and annoying to another group. Both groups will be equally at risk of hearing loss.

Besides loudness of sound, several other factors contribute to annoyance. The following table lists examples of such factors:

Source: C.M. Harris. Handbook of Noise Control, 2^nd Ed.. New York: McGraw-Hill, 1979.

Job interference

Depending of the type of activity, noise can severely affect efficiency of a task performance. The following examples will illustrate this point:

• a conversation nearby will distract a person and affect their concentration, hence reducing the employee's efficiency
• a noisy environment could create an additional hazard, since audible alarms might not be heard
• a noisy environment interferes with oral communication and thus, interferes with the activity