ion devices Hearing defender

Highly effective and moderate cost.

Essential for - tarmac and

4

workshop areas.

DAMAGE NOISE IS THE GREATEST ENVIRON-

mental hazard to the aviation and general community. Every year in Australia, around 10,000 people

are awarded a total of $35 million in compen-sation payments for noise-induced hearing loss. Awards exceed $100,000 in some cases.

When aviation noise is superimposed on other noise sources in our daily lives (industri-al, road traffic and recreational), individual and collective exposure can become significant.

Regardless of your occupation within the avi-ation environment, you should understand the health consequences of hazardous noise levels, how to protect yourself against potential injury, and how to protect others such as passengers.

If you are an employer, manager or supervi-sor, you also need to be aware of your "duty of care" to provide an adequate warning of the noise hazard in your work environment and to provide protective hearing devices. You should also be aware of your responsibilities to reduce injurious noise in the workplace, regularly monitor the noise hazard and organise hearing assessments for staff at risk.

Engine noise, particularly from jet engines, creates most of the hazardous noise in aviation. Other sources include auxiliary power units

(APU), pro-pellers and heli-

Headset copter rotors, Strongly recom- aerodynamic

mended for flight noise trans- crew. Enables

communication mission and

whilst providing accessory gear %:~P good protection boxes, avionics

from noise. and other aircraft systems, air con-

Ir units, ground power

units, motor vehicles around the tarmac areas and maintenance workshops.

Noise measurement

Measurement and evaluation of noise involves: • Measurement of the sound energy. • Evaluation and estimation of its effect on those exposed, where possible.

Sound pressure is measured in decibels, which is a logarithmic scale where dB = 20 10gb (P1/P0) in which P1 is the measured sound pres-sure and P0 is a reference sound pressure.

The current unit of pressure is the pascal (Pa). The reference level (P0) is a pressure of 20 micropascals (20 x 10-6 Pa)

Noise measurements are made using elec-tro-acoustic methods. The sound meters used must comply with international and national standards.

If you want to do the mathematics, you will see that by doubling the sound energy (inten-sity) you will alter the measured noise level by 6dB. Therefore, a four-fold increase in sound energy means a 12dB increase in the measured noise level.

Therefore, if you are trying to reduce noise in your workplace, a 6dB reduction represents a halving of the environmental noise intensity.

Sound meters are usually calibrated elec-tronically to match sound measurement to human loudness perception.

Noise and health

The effects on health from excessive noise can be divided into two broad classifications - auditory and non-auditory. Auditory effects a high volume noise of any kind (continuous or impulse noise) can cause temporary or permanent damage to the hear-ing apparatus.

Noise induced hearing loss (NIHL) occurs because exposure to excessive noise perma-nently damages the delicate hearing mechanism of the inner ear. The noise initially causes a tem-porary hearing loss (or Temporary Threshold Shift - TTS). Normal hearing is recovered fol-lowing TTS.

The extent of TTS depends on the intensity of the noise, length of the exposure and the characteristics (such as frequency) of the noise. There are certain frequencies where the ear is very sensitive to damage.

Noise between 500-3,000Hz encroaches on the speech frequency range - damage occur-ring in this range can result in difficulty hear-ing speech.

Damage occurring below 1500Hz can be critical to people (LAMEs, for example) who rely on hearing for tuning piston engines or diag-nosing engine/accuracy faults noise for detec-tion of faults.

Repeated exposure to excessive noise can transform this temporary threshold shift into a permanent, irreversible threshold shift. Both temporary and permanent threshold shift can

FLIGHT SAFETY AUSTRALIA AUTUMN 1997 19

bearing) located in the inriet skull. These hair cells are designed to respon

to discrete frequencies sound energy. Onc

they have bee I1 W71 T11 Fl

excited, tli

I.w1in chochle transforn

(the m

t h e s hair cel

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i n t IJ I I 10)0 LIII 00 3111(111 LJJI lOS III LI II electria

stimulate specialised hair cells signals. inside the organ of Corti (organ of T h e s

electric signals at

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ry centre of the bral via electrical pathways.

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The result is the sound we hear, which roughly in the frequency range of 2(

How we hear with hairs

N oise is sound energy which is produced by energising air. It stimulates our

hearing as sound pressure on the eardrum. The eardrum (tympanic mem-

brane) vibrates when excited by this energy, and stimulates a tiny chain of 3 small bones in the mid- dle ear (the ossicles: malleusincus and stapes). Thrr thrr en II 1,,r1 irl II

be accompanied by "ringing in the ears" or tinnitus, which can also become permanent. There is no medical cure for tinnitus and treatment for it is generally less than satisfac-tory. Hearing loss is bad enough, but if it is accompanied by tinnitus, life can be miser-able.

People suffering from occupational deaf-ness experience a distortion of the sounds they hear and they may no longer be able to distinguish between some spoken words. Hearing aids offer limited benefit for people with NIHL.

Many jobs in aviation depend on good hearing. This is the case for pilots and ATC5, as well as for LAMEs, who can depend on sharp hearing for special noise detection.

Tarmac workers depend on good hearing to detect hazards and prevent accidents.

Cabin crew rely on good hearing to com-municate with passengers, other crew and to listen for auditory alarms or for indications of mechanical problems. They have an impor-tant monitoring function.

Non-auditory effects: There has been much debate over the interpretation of research into these effects, but the strengthening consensus is that unwanted continuous noise can inter-fere with human performance, resulting in:

• Increased reaction times. • Reduced performance in reading, writing and listening tasks, including reduced com-prehension and short-term memory. • Reduced communication performance. • Reduced performance in tasks which

demand continuous attention and accuracy. • Irritability and mood swings. • Interference with some visual tracking tasks and visual performance generally. • Increased susceptibility to fatigue. • Dizziness, headache, nausea and other non-specific symptoms, consistent with stress dis-order.

If your hearing is impaired you will be unable to communicate effectively - mistakes will be made. Worse still, stress added to a noisy environment results in a more severe reduc-tion in performance, and the onset of that per-formance reduction will occur earlier. Additional stressors can include: • Large temperature changes (heat and cold). • Hypoxia. • Vibration. • Poorly controlled humidity. • Increased pilot workload.

Clues to hearing loss

In the early phases of hearing loss, you may have no indication that there is a problem. The loss can be subtle and therefore go unno-ticed.

You may only start to suspect a problem if you find yourself having increasing difficulty listening to others speak, particularly if there is already distracting background noise; if others are having difficulty attracting your attention; or if you find yourself asking for read-backs on the radio. You should also be suspicious of hearing loss in others who have had near misses with vehicles on the tarmac area or are "accident-prone' in a noisy work

environment such as a workshop or hangar. Passengers who have significant hearing

impairment can also present problems. They can easily walk too close to live propellers without suspecting danger. Tarmac crew should ensure that all passengers keep to tar-mac walkways.

In emergency evacuations, cabin crew must take account of the need to communicate with those who suffer a hearing impairment.

Also remember that if you are responsible for the safety of others and are forced to wear hearing protection, you will find yourself more vulnerable to traffic hazards if you cannot hear or see approaching vehicles, or hear people try-ing to communicate with you.

It is very important to make yourself as vis-ible as possible around a busy tarmac, espe-cially at night.

Audiometry

Audiometry is the assessment of the sensitivity of hearing. The threshold of hearing is mea-sured for a number of frequencies and the graphical plot which results is an audiogram.

To be done properly the test should follow a standardised protocol, be conducted in the absence of any background noise, and be per-formed with a properly calibrated audiometer.

Audiograms can be used as a basic screen-ing test, or in conjunction with other audio-metric tests using diagnostic equipment.

An example of a typical normal audiogram and an audiogram showing bilateral (both ears) noise induced hearing loss are shown below. Note significant threshold losses at the higher frequencies (3,000, 4,000, 6,000 Hz).

Anyone who is regularly exposed to loud noise in the workplace should have an audio-gram done periodically to detect early changes suggestive of hearing loss. How often these

Frequency in Hertz 20 500 100 15) 200 300 40)0 ()00 800

*10

—10

20

30

40

50

60

70 so 90

100

110 41 120

INormal hearing (left and right)

Left ear damaged hearing

Right ear damaged hearing

20 FLIGHT SAFETY AUSTRALIA AUTUMN 1997

THE AUSTRALIAN STANDARD

The national standard for exposure to noise in the occupational environment is an eight

hour equivalent continuous A-weighted sound pressure level, LAeq,8h of 85dB(A). For peak

noise, the national standard is a peak noise level, Lpeak of 1400(lin). The exposure to

noise is taken to be that measured at the employee's ear position without taking into

account any protection which may be afforded by personal hearing protectors.

The standard and a code of practice for management of noise and prevention of hear-

ing loss are available from the Australian Government Publishing Service.

FLIGHT SAFETY AUSTRALIA AUTUMN 1997 21

screening tests need to be performed will depend on your exposure and the quality of hearing protection devices you have been using.

Some screening may need to be done every 3 or 6 months; in other cases annually, two yearly or even less frequently. If you are in doubt, arrange to have an audiometer test to be done by an approved hearing laboratory, a designated aviation medical examiner or your family prac-titioner. Check to see if their practice has an audiometer first.

You need to recognise if you are already at risk in your workplace, and whether or not your workplace has been the subject of a noise survey by an approved testing agency.

Ask your supervisor or manager if there is a hearing conservation program in your area.

There are many methods available to deal with noise, but much of the aviation envi-ronment relies on individuals wearing per-sonal hearing protective devices (HPD5) for protection. Ideally, this should be the last line of protection in the workplace. However, in practice it is usually the first option used for protection because it is usually the cheapest.

Noise induced hearing loss can be exacer-bated by other factors, which include: • Presbyacusis - the deterioration in hearing that occurs with advancing age in the absence of disease or injury. • Previous ear pathology, such as a perforated eardrum from trauma, or chronic ear disease during childhood. • Acute ear infections or disorders, a cold, the "flu", Meniere's disease, which affects the bal-ance organs, and other viral infections. • Some anti-malarial drugs and some antibi-otics. • Alcohol abuse. • Recreational noise hazards, such as sports shooting, or listening to loud music (espe-cially in confined spaces). • Diving barotrauma.

Protection In order of priority, the following strategies should be used to combat hazardous noise: • Noise control at source. • Noise control at the point of reception. • Noise control along the pathway to the sub-ject(s). These can be achieved in a number of ways:

• Regulatory intervention including enforced standards. • Engineering and design. • Sound insulation and absorption. • Enclosures. • Vibration isolation and damping. • Distance. • Reduced exposure time. • Noise attenuating devices.

You should use the personal hearing pro-

tective device that is appropriate to the sever-ity of the hazard. The device must meet Aus-tralian design standards. The options are: • Combination of foam ear plugs and ear defender. • Communication headset. • Communication ear plug. • Active Noise Reduction (ANR),such as elec-tronic noise cancelling headsets.

You should also attend to: Correct fit.

• Regular maintenance and inspection. • Access for users (whether the devices are for personal issue or issue as required). • Proper storage to avoid damage and deteri-oration.

There are grades of protection which depend on the quality of manufacture, cost and functional requirements.

The technical specifications of the HPD should be available from the vendor. The spec-ifications must be compatible with your work environment. If you are in doubt about the requirements, get specialist advice about the needs of your workplace.

Jeff Brock is acting director of aviation medicine, CASA.

The regulatory requirements

The Regulations state that medical certificate holders:

• Must be free of any hearing defect

that is likely to interfere with the safe exercise of privileges, or per-

formance of duties, under the licence

that the person holds or has applied for.

• Must not, when in a quiet room,

have a hearing loss in either ear of

more than: - 35dB at any of the frequencies of

500Hz, 1,000Hz or 2,000Hz; or - 50d13

at 3,000Hz; unless the person passes a speech

test, or an operational check, by an approved person carrying out the

examination in an aircraft of similar

ambient noise level to that in which the relevant person is or will be

operationally involved.