The extended exposition to high levels of sound pressure, at the work´s environment, is one of the main etiological factors of the hearing loss or the increase of the hearing threshold above the normal values.

It is necessary to take in account that the subject doesn´t sense the injury until it is irreversible, so that which the prevent steps play an important role in the incidence of the hearing alterations.

Although the noise is considered a highly dangerous pollutant (it can produce sleeping distress, decrease of the work´s productive, difficulty for the concentration, digestive disorders and discomforts such as duodenal ulcers, gastritis …, breathy issues, disorders in the nerve system, so that psychological pain like irritability, anxiety, sleeplessness…) the only disease which is clearly demonstrable is the appearance of hearing disorders as a consequence of the exposition to the noise.

There is four factors the firs order that they determinate the risk of the hearing loss:

1.- The level of sound pressure

2.- Type of noise.

3.- Time of exposition to the noise.

4.- Age.

The majority of the Organizations which are in charge of the occupational health establish their judgement in base to the level of sound pressure (first risk´s factor), that is, to the increase of the hearing threshold at different frequencies. And generally, the measures to counteract the occupational noise effects are established from 85 dB (level which was established by the current regulation. Real Decreto 1316/1989 del 27 de octubre)

The doctors which directly and daily face the hearing disorders they don´t dude in establishing a relationship between the sound pressure and the hearing injury.


  • fatigue or fatigue.
  • irritability or tension.
  • difficulties in sleeping and sleep disorders.
  • Blood flow (paleness).
  • digestive disorders.
  • general discomfort.




It is an interesting concept from an ergonomic point of view, because it is going to make an influence in the grade of hearing comfort of the workers.

When the sound waves crash with an obstacle, one part is absorbed and the other one is reflected, moving forward again with less energy. It can crash again, losing more energy and moving forward again. The sound which is sensed by the worker will be the mixt between the sound of the initial crash and the reflections which continue to be produced, even though the focal point has stopped to emit.

The Reverberation Time (RT) of a room, for a frequency which has been given, is defined as the necessary time (in seconds) to that the acoustic pressure level decrease 60 dB once that the focal point, which caused the sound, has been eliminated. This time is going to depend on the local´s geometric of the local, its materials, etc.

If the RT is so much extended it will continue hearing the previous sounds when the new sounds appear, it will cause some distortions which will decrease the intelligibility of the word. Furthermore, it tends to produce an increase in the level of the environment´s noise.

If the RT is too short the sounds sound weak, over all if it is far of the source.



Motors (muscular contractions), vegetative (variations in heart rate, peripheral vasoconstriction, increase in blood pressure, slowing of respiratory movements, etc.) and electroencephalographic.

The answers could be:

In short term: immediately psychophysiological answers being caused for qualitative or quantitative changes in the noise. As for example is the “orientation´s reflect” and the “shock´s reflect”. The first one is related with the attention processes and it implies the redirection of the sensitive organs to the sound source and an amount of physiological answers, as the decrease of the heart rate, the flow and pressure blood, and an increase in the secretion of the swat glands. The Shock´s Reflect supposes blinking, muscle shaking and increased heart and respiratory rates. Both answers are short and weak and they don´t usually have any important consequences, but they are still good as indicators of the noise´s capacity to get distracted the attention.

In the large term: the noise produces physiological modifications which can affect to the health. This effects depend on the type of the activity too, the demanding of the task, of the conditions of the execution, of the length of the work with exposition to the noise and the characteristics of each person. The effects can be classified in:

Cardiovascular effects: They are the most studied. It has been checked that during the exposition to the noise is produced peripheral vasoconstriction and it is increased the diastolic pressure. It is known too, that between workers, who are exposed to the noise, is more frequently the cardiovascular disorders, over all, the hypertension. However, the heart disorders depend too on factors like the vegetative reactivity of the worker, of the nature to be expected or not of the noise, the activity and of other factors.


The noise affect to the secretion of the “stress´s hormones”: catecholamine (adrenaline and noradrenaline) and corticosuprenal hormones (cortisol), but this effect changes depending on the activity, the task and the physical and psychosocial factors. It has been checked the significant increase of the Growth Hormone too (GH), which is an important sign of stress.



The people expose to the noise during the day can suffer some dream´s changes as much in quality as in quantity of it. It is decreased the number and the length of the dream´s cycles. The noise can cause the opposite effect too, to induce to the dream, specially in case of the low frequency noises, monotonous and repetitive noises.


The subjective effect most known which is produced by noise, is the sense of annoyance and displeasure.

It is too difficult to establish some values from which is produced the displeasure sense, because each person is going to value the noise in a different way. For example, the same acoustic environment it could be displeasure for a person and not to be it for another. This situation makes a difficult in the objective study of the problem. The valuation of the aspects which are regarding with the noise production (frequency and intensity) are easier to determinate, however, other type of factors that make an essential influence, like the psychosocial context, the personal attitude to the noise source, the activity, the task, etc, are much more complicates to value objectively.

The subjective evaluation of the noise is made trough questionnaires and self-evaluation scales. Of the relation between these subjective evaluations and the physical quality of the noise, come up the psychoacoustic bases of the noise, which had allowed the developing of series of acoustics index whom objective is to value the annoyance´s grade in a more objective way.

The factors which are most related with these effects are:

  • Intensity: If the level of noise increases, the increase of the annoyance´s level will be proportional, but between both different noises not always the most annoying is which has most intensity.
  • Frequency: The human hearing is more sensitive to the high sound frequencies, so that, these are discerned like noisier in equal conditions.
  • Temporal Variability: When the noise change in the time, there is less risk of objective hurts than if the noise is constant, whereas subjective reactions, the variability is an annoying trait by itself.
  • Relationship signal-noise: When a noise covers up words or sounds which the worker believes relevant (signals), it is considered specially annoying.
  • Informative Content: If the informative content is useful (noises which warn about something anomalous, etc), the noises are considered more acceptable than if they didn’t carry on any information.
  • Predictability and Controllability: The unpredictable noises annoy more than the routine or regular noises. When a worker can control the production of a noise, he is less annoy respect the noise than when he can´t do it.
  • Attitude regarding to the noise source: A worker who is reluctantly with a machine, he will be specially annoy with this machine´s noise.
  • Activity in process: In the subjective evaluation the demands of the task and the workload makes an influence.
  • The need of noise: A noise is considered more acceptable when it is an unavoidable consequence of the activity developed.
  • Individual differences: It exists interindividual different regarding the sensitive to the noise, so that at the same acoustic environment it causes answers which can be very different in different people.


In the labour scope, the effects most studied of the noise on the behaviour have been which affect to the efficiency and the social behaviour, specially in the communication.


The effects of the noise on the efficiency ( understanding as the efficiency of the subject in the making of its job) are complex and affect in a different way to different activities, depending on factors like the characteristics of the noise (intensity, frequency, type, significance…), the possibility of forecast and control of itself, nature and demands of the task, duration, psychological variables of the person (sensitive, functional state, motivation…) and the presence of other annoying environment factors.

There are no effects clearly defined of the noise on the efficiency of the task. A same type of noise could decrease the gathering in some cases or to be stimulating in others. In tasks which require a high level of focus, to put in a noise could affect in a negative way, whereas the same noise present in repetitive and routine tasks cold be stimulating.

The adverse effects of the noise seem to be fundamentally regarding with tasks where the workers have to apply knowledge, to think stop and to achieve some conclusions. This involves the memory in short and large term. It has been proved (Weinstein, 1977) that in a reading test, a noise between 68 and 70 dB (A) prevents significantly the detection of grammatical mistakes (task based in the knowledge), but it doesn´t affect to the ability of detecting orthographic mistakes (task based in rules).

So that, the noise causes decrease in the attention and worsen specially the making of Works which require focus, quick or skill. The worker should make a supplementary effort to cut off from the noise, which is translated as a bigger wear and an increase of the mind´s fatigue. Although it must also be borne in mind, that sometimes noise may not affect, it may even be a positive aspect, for the performance for example of routine tasks or based on dexterity.

In general, it can be observed that the noise almost always is annoying for the work, and that the activities which demand an effort of attention higher and holder they are more sensible to the noise.


The mere presence of noise, by itself and independent of its characteristics, causes an amount of displeasing and annoying emotions which can show up in the social and individual behaviour of the workers expose. If the exposition is chronic, the workers become irritable, the show up aggressive inclinations, they are less attentive with the colleagues and little inclined to help them. The relationship between people are made more difficult, as much for the fatigue which is generated as for the recovering time of hearing after the work and the change in the behaviour that it can cause. The effects that in this level might be produced are:

  • Difficulty in the communication, how it will be show forward
  • Disturbing in rest
  • Disturbing in night dream
  • Decrease in the concentration ability
  • Feeling of physical discomfort: It starts to show up from 35dB(A), being the threshold in 65 dB(A), according to the OMS.


The noise might difficult the talk communication in the job (the understanding of the verbal message), which affects to the security, to the productive process and to the personal and professional relationship. The difficulty in communicating with colleagues during working hours increases the isolation of workers and makes working conditions more difficult. The interference of the noise in the verbal communication depends on the next factors:

  • The level of the acoustic pressure (intensity)
  • Spectro of the current noise (frequency)
  • Voice tone employed
  • Distance between the conversational partners
  • Conversational demands of the task.


The communication in noisy environments increases the workload in both the transmitter and the receiver: one of them should to increase the voice and the other one should increase the attention to understand the message.  The difficulty of the understanding increases when the worker must to pay attention at the same time to the verbal message and to the signals which come from another sources.

It exists several methods to establish some maximum or suggested levels of noise that allows keeping the communication into acceptable levels, being the SIL Method (Speech Interference Level) one of the most employed. This method establishes the maximum levels of acceptable noises for the rank of conversational frequencies (between 500 and 400 Hz)


It seems to be that in noisy environments the workers are 2 or 3 times more dangerous than workers in quiet environments, but it have not been demonstrated that the direct cause would be the noise and, so that, it can´t be established a causal relation between the noise and the accidents.

In any case, the noise is a potential factor of risk for the security or, at least, it favours the human mistake, because it masks the noises which carry the useful information (alarm´s signals, warnings…) it interferences in the communication and alter the course of the attention.