**2. Literature review**

### **2.1 Basics of acoustics**

Noise can be described as rapid fluctuations in atmospheric pressure, which affects the human body as vibrations that are perceived by the human ear and finally can be classified as sound.

Sound propagates as a pressure wave and is able to travel through any elastic medium (e.g., air, water, wood, and metal).

Important units for measurements of noise attributes are hertz (Hz) and decibels (dB), and together with some basic knowledge of physics of waves, frequency, wavelength, amplitude, refraction, absorption and transmission, we are able to understand the behaviour of noise and can develop controls and preventions. When molecules start to move due to atmospheric pressure changes, the moving air molecules pass their energy on to neighbouring molecules, which results in the spread of their energy over and over until an increasingly larger volume is created. This principle can be compared to the ripples when a stone is thrown into water. These described pressure changes are detected by the eardrum, which in return vibrates as response. In return, the vibrations are further transferred to the middle ear, which is constructed of three tiny bones facing towards the fluid-filled inner ear. The inner ear contains tiny inner and outer hair cells, which convert the vibrations into electrical nerve impulses that then are sent to the brain. Finally, the brain is then able to process these impulses into meaningful sounds [5, 7].

The perception of loudness of a sound is determined by two factors: sound pressure and frequency. The frequency (number of vibrations per second) is

**5**

the same:

*Influence of Noise in Ambulance Vehicles on Emergency Service Personnel*

related to "pitch". The higher the frequency, the shaper the sound heard by the

Important issues about noise perception are as follows: Sound pressure levels are measured in (dB). They describe the amplitude of the sound waves. They are related to the loudness of the sound. The A-weighted sound pressure levels are measured in dB(A). A-weighting considers the non-linear response to sound of the human ear, and also its non-homogeneous response to sounds of different frequencies and intensities. This level is determined by using a standardised weighting at different frequencies and then, summing logarithmically these sound pressure levels. The A-weighted sound pressure levels better represent the auditee's perception of noise. They are used for many applications, from community noise ordinances to occupa-

Every day, we are naturally exposed to loud, distracting and possibly hazardous noise. A common experience for everyone may be the example of continues ringing after a great concert or muffled sounds after working with loud tools (chainsaw,

Noise at prolonged exposure at 80 dB has unsafe effects to the auditory system

Studies proved that the risk for NIHL increases exponentially in noise-exposed

**Table 1** shows critically how noise is correlated with health that is shown in three

A standard conversation is measured at approximately 50 dB(A), which at a prolonged exposure may lead to mental reactions (e.g., low concentration and annoyance); at 80 dB(A), for communication, the voice needs to be elevated remarkably that interferes with health shown in physical reactions (e.g., hypertonus); and at 90 dB(A), communication is not possible anymore, which in return in long term is

Determining the limit of noise exposure is crucial to take three components in

Generally, the potential and stage for hearing loss by noise are related to the

Halving acoustic energy can be done reducing sound pressure level by the 3 dB

For better understanding, see the following examples. These noise exposures are

At the example of "Conversation", it can be nicely illustrated in what manner

population, who are exposed to noise level beyond 85 dB(A) for a prolonged

*DOI: http://dx.doi.org/10.5772/intechopen.91898*

tional noise exposure regulations.

*2.1.1 Noise as a dangerous hazard*

but also to general health [5, 7, 8].

different stages of noise levels in dB(A).

unbearable and triggers pain threshold.

1.Worker (genetic predisposition)

3.Duration of exposure

or halving the exposure time [10].

2.Character of noise: sound pressure level and frequency

workers' duration of noise exposure and stage of noise loudness.

*2.1.2 Noise exposure and limit values*

noise level has an impact on health.

grass cutter, etc.).

time [9].

consideration:

subject [7]*.*

#### *Influence of Noise in Ambulance Vehicles on Emergency Service Personnel DOI: http://dx.doi.org/10.5772/intechopen.91898*

related to "pitch". The higher the frequency, the shaper the sound heard by the subject [7]*.*

Important issues about noise perception are as follows: Sound pressure levels are measured in (dB). They describe the amplitude of the sound waves. They are related to the loudness of the sound. The A-weighted sound pressure levels are measured in dB(A). A-weighting considers the non-linear response to sound of the human ear, and also its non-homogeneous response to sounds of different frequencies and intensities. This level is determined by using a standardised weighting at different frequencies and then, summing logarithmically these sound pressure levels. The A-weighted sound pressure levels better represent the auditee's perception of noise. They are used for many applications, from community noise ordinances to occupational noise exposure regulations.
