*2.1.2 Noise exposure and limit values*

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

### 1.Worker (genetic predisposition)


Generally, the potential and stage for hearing loss by noise are related to the workers' duration of noise exposure and stage of noise loudness.

Halving acoustic energy can be done reducing sound pressure level by the 3 dB or halving the exposure time [10].

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


#### **Table 1.**

*Overview of noise level and impact on human body.*


International standards recommend an "equivalent sound pressure level of 85 dB(A) at 8-h working day average as the exposure limit for occupational noise" for preservation of the personnel's hearing when working in a noisy environment. However, in reality, it shows that this limit does not guarantee safety, especially for the hearing system of workers, since 80 dB(A) is already indicating harmful effects [11].

Therefore, Noise at Work Regulations recommend a "three action levels for occupational noise level" depending on equivalent noise level for 8-h working day (see **Table 2**)*.*

#### **2.2 Overview of hearing loss**

Hearing loss can be categorised depending which parts of the hearing system are damaged. There are three basic types of hearing loss: conductive hearing loss, sensorineural hearing loss, and mixed hearing loss [12].

Conductive hearing loss occurs due to damage of outer structures of the auditory system.

The sound waves are not properly conducting through the outer ear canal, the eardrum and ossicles of the middle ear. It is characterised by a reduction of sound level perception or the ability to hear weak sounds. Good treatment options are surgery or medication depending on issue.

**7**

stimuli.

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

**Action level LAeq8h** First action level (minimum) provide protection 80 dB(A) Second action level mandatory protection 85 dB(A) Maximum exposure limit value 87 dB(A)

Causes of conductive hearing loss are as follows:

• Ear infection (otitis media or otitis externa)

• Obstacle such as cerumen, tumour or foreign body

muffled. Unfortunately, there is no treatment option.

cochlea or to the nerve pathways from the inner ear to the brain.

Sensorineural hearing loss appears in case of damage to inner structures such as

Characteristically, it is described by the reduced ability to hear faint sounds. Even when speech is loud enough to hear, it may still appear to be unclear or sound

NIHL is one of the most common occupational illnesses, because it is often

Factors that especially predispose one to NIHL are found in high-frequency noise exposure, which is known to be much more harmful than low-frequency noise, and also continuous stimuli are more damaging than interrupted

NIHL starts with a temporary threshold shift (TTS). Physiologically explained, while the ear is exposed to the noise, there originates a release of ATP from stria cochlearis, which provides the necessary energy for the function of the hair cells. In case of prolonged elevated noise exposure, a mismatch occurs between energy supply and consumption, as the ATP needs to reach the hair cells by diffusion. The hair cells get tired due to energy depletion and result to be less sensitive. This leads

ignored since there are no visible effects or pain sensation in early stages.

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

• Fluid in the middle ear

*Three action levels for occupational noise level.*

**Table 2.**

Examples:

• Ageing

• Head trauma

• Ototoxic medication

• Genetic or hereditary

• Exposure to loud noise

*2.2.1 Noise-induced hearing loss*

• Poor eustachian tube function

• Trauma, e.g., perforated eardrum

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


**Table 2.**

*Noise and Environment*

**Noise level and body reaction**

30–65 dB(A) Mental reaction

65–90 dB(A) Physical reaction

90–120 dB(A) Hearing loss, ear

**I**

**II**

**III**

pain

**Table 1.**

• 80 dB for 8 h

*Overview of noise level and impact on human body.*

• 83 dB for 4 h

• 86 dB for 2 h

• 89 dB for 1 h

effects [11].

(see **Table 2**)*.*

tory system.

**2.2 Overview of hearing loss**

sensorineural hearing loss, and mixed hearing loss [12].

surgery or medication depending on issue.

• 92 dB for 30 min

International standards recommend an "equivalent sound pressure level of 85 dB(A) at 8-h working day average as the exposure limit for occupational noise" for preservation of the personnel's hearing when working in a noisy environment. However, in reality, it shows that this limit does not guarantee safety, especially for the hearing system of workers, since 80 dB(A) is already indicating harmful

**Type of noise Sound pressure** 

Fine ticking of a clock,

whispering

**levels in dB(A)**

Library, bedroom at night 40 dB(A) Pretty quiet Conversation 50 dB(A) Normal

Loud factory hall 90 dB(A) Very loud Car horns in 7 m distance 100 dB(A) Very loud to

Full symphony orchestra 110 dB(A) Very loud to

Jet engine, live rock band 120 dB(A) Unbearable to painful

Quiet office 60 dB(A) Moderate to loud

Shouting, car in 10 m distance 70 dB(A) Loud to very loud Street noise in heavy traffic 80 dB(A) Very loud

30 dB(A) Very quiet

130 dB(A) Intolerable

**Sound sense**

unbearable

unbearable

Therefore, Noise at Work Regulations recommend a "three action levels for occupational noise level" depending on equivalent noise level for 8-h working day

Hearing loss can be categorised depending which parts of the hearing system are damaged. There are three basic types of hearing loss: conductive hearing loss,

Conductive hearing loss occurs due to damage of outer structures of the audi-

The sound waves are not properly conducting through the outer ear canal, the eardrum and ossicles of the middle ear. It is characterised by a reduction of sound level perception or the ability to hear weak sounds. Good treatment options are

**6**

*Three action levels for occupational noise level.*

Causes of conductive hearing loss are as follows:


Sensorineural hearing loss appears in case of damage to inner structures such as cochlea or to the nerve pathways from the inner ear to the brain.

Characteristically, it is described by the reduced ability to hear faint sounds. Even when speech is loud enough to hear, it may still appear to be unclear or sound muffled. Unfortunately, there is no treatment option.

Examples:


#### *2.2.1 Noise-induced hearing loss*

NIHL is one of the most common occupational illnesses, because it is often ignored since there are no visible effects or pain sensation in early stages.

Factors that especially predispose one to NIHL are found in high-frequency noise exposure, which is known to be much more harmful than low-frequency noise, and also continuous stimuli are more damaging than interrupted stimuli.

NIHL starts with a temporary threshold shift (TTS). Physiologically explained, while the ear is exposed to the noise, there originates a release of ATP from stria cochlearis, which provides the necessary energy for the function of the hair cells. In case of prolonged elevated noise exposure, a mismatch occurs between energy supply and consumption, as the ATP needs to reach the hair cells by diffusion. The hair cells get tired due to energy depletion and result to be less sensitive. This leads

#### *Noise and Environment*

to a shift in hearing threshold but has still potential to recover completely when the harmful stimulus is removed [13].

If the exposure to the harmful noise still continues, the cellular integrity of the hair cells of the Corti organ disrupts gradually and ultimately the nerve fibres that innervate the hair cells will disappear, thus resulting in permanent threshold shift (PTS), and henceforth, irreversible hearing loss at higher frequencies will be noted. In most cases, it is described affecting both ears symmetrically [14].

NIHL can be classified into four stages: mild, moderate, severe and profound [15].

1.Mild NIHL is a high-frequency hearing loss of sounds between 20 and 40 dB.

2.Moderate NIHL, between 40 and 60 dB.

3.Severe NIHL, between 60 and 80 dB.

4.Profound NIHL, greater than 80 dB.

Limitations in hearing are evident when listening to high frequencies. First noticed problems are trouble understanding speech during present background noise. NIHL progresses gradually, and people have difficulty understanding highpitched voices (e.g., women and children) even in quiet conversational situations, whereas conversation on the telephone is generally unaffected.

TTS slowly progresses to PTS, post exposure tinnitus, and TTS serves as warning signs of impending permanent NIHL [14].

### *2.2.2 Audiogram*

Hearing loss is detectable by performing an audiogram and is presented as a graph that shows the weakest sounds a person can hear at different frequencies. It can be used to detect the concrete severity of sensorineural hearing loss or for check-up reasons.

For TTS, there is a chance that the shift regresses again after the noise is removed.

Therefore, the sound pressure level during the recovery period is kept below 70 dB(A) and a recovery time of at least 10 h.

In case the recovery period is not respected, an accumulation of the individual TTS may occur and leads to PTS, which can be detected in the audiogram (see **Figure 1**)*.*

NIHL is typically shown with selective loss of hearing at around 4000 Hz, which is apparent in the audiogram as a notch-like depression.

If exposure to harming noise is continued, the notch gradually deepens and widens. It can also take over to the middle frequencies. In very severe cases, even the lower frequencies may eventually become involved [5].

### **2.3 Consequences of NIHL**

Consequences of NIHL may severely interfere with both social and occupational environment. NIHL as a reason for limited communication ability with co-workers and family may develop anxiety, irritability and decreased self-esteem resulting in loss of productivity and, eventually, social isolation.

**9**

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

In terms of safety, NIHL often runs together with a reduced ability of assessment

and to monitor work environment such as warning signals or equipment sounds

Noise creates physical and psychological stress that can interfere with health leading to extra aural health risks. Common early symptoms can be found psycho-

Depending on the extent of sound pressure level, it can influence the vegetative system by a shift in favour towards the sympathetic nervous system. Examples are tachycardia, hypertonia, tachypnoea, increased adrenal secretion of stress hormones such as cortisol and decrease in gastric secretion for protection of gastric mucosa. In the long term, these symptoms have potential to interfere severely with health [16].

The data were collected through a retrospective cohort study using a questionnaire with a total sample size of 207 workers from two main emergency ambulance

service centres located in Riga, Latvia, and Aurich, Germany.

socially as sleep disturbances, concentration difficulties and clumsiness.

and immensely increase the danger of injuries.

*2.3.1 Health risks*

*Audiogram characterising early NIHL.*

**Figure 1.**

**3. Methods and materials**

**3.1 Study design**

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

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

#### **Figure 1.** *Audiogram characterising early NIHL.*

In terms of safety, NIHL often runs together with a reduced ability of assessment and to monitor work environment such as warning signals or equipment sounds and immensely increase the danger of injuries.

### *2.3.1 Health risks*

*Noise and Environment*

symmetrically [14].

*2.2.2 Audiogram*

check-up reasons.

**2.3 Consequences of NIHL**

removed.

**Figure 1**)*.*

harmful stimulus is removed [13].

2.Moderate NIHL, between 40 and 60 dB.

3.Severe NIHL, between 60 and 80 dB.

4.Profound NIHL, greater than 80 dB.

ing signs of impending permanent NIHL [14].

70 dB(A) and a recovery time of at least 10 h.

is apparent in the audiogram as a notch-like depression.

lower frequencies may eventually become involved [5].

loss of productivity and, eventually, social isolation.

to a shift in hearing threshold but has still potential to recover completely when the

If the exposure to the harmful noise still continues, the cellular integrity of the hair cells of the Corti organ disrupts gradually and ultimately the nerve fibres that innervate the hair cells will disappear, thus resulting in permanent threshold shift (PTS), and henceforth, irreversible hearing loss at higher frequencies will be noted. In most cases, it is described affecting both ears

NIHL can be classified into four stages: mild, moderate, severe and profound [15].

1.Mild NIHL is a high-frequency hearing loss of sounds between 20 and 40 dB.

Limitations in hearing are evident when listening to high frequencies. First noticed problems are trouble understanding speech during present background noise. NIHL progresses gradually, and people have difficulty understanding highpitched voices (e.g., women and children) even in quiet conversational situations,

TTS slowly progresses to PTS, post exposure tinnitus, and TTS serves as warn-

Hearing loss is detectable by performing an audiogram and is presented as a graph that shows the weakest sounds a person can hear at different frequencies. It can be used to detect the concrete severity of sensorineural hearing loss or for

For TTS, there is a chance that the shift regresses again after the noise is

Therefore, the sound pressure level during the recovery period is kept below

In case the recovery period is not respected, an accumulation of the individual TTS may occur and leads to PTS, which can be detected in the audiogram (see

NIHL is typically shown with selective loss of hearing at around 4000 Hz, which

Consequences of NIHL may severely interfere with both social and occupational environment. NIHL as a reason for limited communication ability with co-workers and family may develop anxiety, irritability and decreased self-esteem resulting in

If exposure to harming noise is continued, the notch gradually deepens and widens. It can also take over to the middle frequencies. In very severe cases, even the

whereas conversation on the telephone is generally unaffected.

**8**

Noise creates physical and psychological stress that can interfere with health leading to extra aural health risks. Common early symptoms can be found psychosocially as sleep disturbances, concentration difficulties and clumsiness.

Depending on the extent of sound pressure level, it can influence the vegetative system by a shift in favour towards the sympathetic nervous system. Examples are tachycardia, hypertonia, tachypnoea, increased adrenal secretion of stress hormones such as cortisol and decrease in gastric secretion for protection of gastric mucosa. In the long term, these symptoms have potential to interfere severely with health [16].
