The Science:

The decibel scale is a logarithmic scale applicable to any parameter, used to make quantities with a wide range of values more manageable. In the measurement of sound, we are concerned with the amplitude of the acoustic pressure, measured in pascals (Pa). The range of acoustic pressures that the human ear can detect is very wide - from the lower limit of hearing at around 20 micro Pa (2 x 10-5 Pa) to the threshold of pain at around 20 Pa. This very wide range of values is unwieldy, so it is converted into a logarithmic scale. This changes the range of values shown above to the more manageable range of 0 dB to 140 dB. Thus 0 dB is roughly the lowest level a normal person can hear.

The pitch of a note is described by its frequency. Frequency is measured in hertz (Hz), or cycles per second. The general range of hearing for young people is 20 Hz to 20kHz. The upper frequency limit decrease with age, and so the older a person gets, the less well they can hear high notes. Also, the male hearing range decreases more quickly than the female, and so women can generally hear higher pitch notes than men of similar age (National Physics Laboratory (NPL), 2014).

The World Health Organization (WHO) describes the distinction between occupational and environmental noise: Noise is present in every human activity, and when assessing its impact on human well-being it is usually classified either as occupational noise (i.e. noise in the workplace), or as environmental noise, which includes noise in all other settings, whether at the community, residential, or domestic level (e.g. traffic, playgrounds, sports, music) (Groothoff, 2012, p. 1).

Sound consists of very small pressure changes, which are superimposed on the atmospheric pressure. Air molecules move in a pendulum motion backwards and forwards from their resting position, causing momentary compression and rarefaction of the air pressure. The air molecules pass some of their energy on to neighbouring molecules and so spread their energy over an increasingly larger volume, much like the ripples when a stone is thrown into water. The pressure changes are detected by the eardrum, which vibrates in response. The vibrations are transferred via a lever system consisting of three tiny bones in the middle ear to the fluid-filled inner ear. In the inner ear, tiny hair cells convert the vibrations into electrical pulses that are sent to the brain. The brain is then able to process these electrical pulses into meaningful sounds. (Groothoff, 2012, p. 5).

Risk Potential:

The health impacts of noise hazards are well recognised with noise-induced hearing loss identified as a priority work-related disease for Australian workers.   Although noise-related legislation focusing on reduction at source has existed for many years, provision of hearing protectors is still the predominant control strategy in many workplaces.  As a future OHS professional, it is understood that there is a need for a better control than PPE according to the hierarchy of controls.  

Environmental noise or community noise: is defined as noise emitted from all sources except noise at the industrial workplace.  It can be found to cause: stress, annoyance, sleep disturbance, interference with concentration and activities, increased blood pressure and heart rate, and ischaemic heart disease, intellectual development of children in noisy suburbs may be compromised.  Of particular community concern is the increase in the use of personal music/media devices.  (Groothoff, 2012, p. 9)

Acoustic Shock:

Acoustic shock is a term used to describe the physiological and psychological symptoms a person may experience after

hearing a sudden, unexpected, loud sound (referred to as an acoustic incident),  It is found in instances of telephone use, either handset or headset.  Symptoms can be broken into three categories: 

Primary (immediate) symptoms, which can include but are not limited to: 

• a feeling of fullness in the ear 

• burning sensations or sharp pain around or in the ear 

• numbness, tingling or soreness down the side of face, neck or shoulder 

• nausea or vomiting 

• dizziness, and

• tinnitus and other head noises such as eardrum fluttering.

Secondary symptoms, which include but are not limited to:  

• headaches 

• fatigue 

• a feeling of being off-balance, and 

• anxiety.

Tertiary symptoms, which include but are not limited to: 

• hypersensitivity (sensitivity to previously tolerated sounds such as loud noises, television and radio); and 

• hyper vigilance, i.e. being overly alert.

(Groothoff, 2012, p. 11)

Ototoxicity: Ototoxic agents are chemical substances that either alone or in concert with noise may have a more detrimental effect on hearing than noise (oto = ear, toxic – poisonous) There are three main classes of ototoxins: solvents, heavy metals and asphyxiants. Also, some medications such as anti-inflammatory, anti-thrombolitic and antibiotic drugs, and salicylic acid (aspirin) are considered to be ototoxic. (Groothoff, 2012, p. 11)