Noise induced hearing loss (PowerPoint)

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					Noise Induced Hearing Loss (NIHL)

If you have to shout to be heard by fellow worker standing 2 m away

There may be a noise problem

• • • • • Sound & Noise How do we hear ? What is NIHL ? Occupational Exposure Limits Control of NIHL

Sound and Noise
Sound exists in the form of waves and is described by its tone (sharpness, measured in Hz or KHz) and its loudness (measured in decibels, dB) Noise is any sound that causes damage to hearing. This includes noise from :
– Occupational Exposures – Non-occupational Exposures (e.g. loud music)

Why Bother About Noise ?
The damage is gradual but certain The change may not be noticeable The loudness and the duration of the exposure are two important factors

How do we hear ?
• Sound waves are trapped by the external ear and channeled into the ear canal towards the ear drum (tympanic membrane) • The ear drum will vibrate, converting sound energy into mechanical energy

• Vibrations are passed onto a fluid-filled chamber called the cochlea which is lined with thousands of nerve cells (also called hair cells)
• These hair cells sense vibration, converting them to nerve signals which are sent to the brain and recognized as sound

How do we hear ?
• Human beings are sensitive to the “speech” frequencies (0.5 – 3 kHz)

• At birth, the human ear has about 20,000 hair cells
• These hair cells are very sensitive and are easily damaged by loud noise, giving rise to hearing loss • The damage in NIHL is irreversible • Initially, the hearing loss experienced is in the higher frequencies (4-8 kHz). Later, lower frequencies are affected

Signs and symptoms of NIHL
• Muffled sound. Early NIHL with high frequency hearing loss does not usually give rise to symptoms except some difficulty in hearing clearly with the presence of background noise • Later, when speech frequencies are affected, the sufferer will experience difficulty in hearing • About 1/3 of sufferers will experience tinnitus or ringing in the ears • Needing to turn up the TV too loud • Finding it hard to use the telephone

How to detect NIHL ?
• Because sufferers of early NIHL are usually asymptomatic, pre-employment (base-line) and periodic hearing tests (audiometry) are required. • Audiometry is conducted in a soundtreated booth and pure tone sounds are introduced one ear at a time. The subject then indicates at what loudness level he is able to hear the pure tones.

Occupational Exposure Limits (OEL)
noise level (dBA)
82 85 88 91 94 97 100 103 106 109 112

exposure limit
16 hr 8 hr 4 hr 2 hr 1 hr 30 min 15 min 7.5 min 4 min 2 min 1 min

OEL for noise is typically reflected as 85 dBA over an 8-hr workday, 40 hr work-week

Prevention of NIHL
• Control of noise in the workplace
– Engineering controls
• design layout • equipment selection • use of baffles, screens, enclosures, barriers

– Administrative Control
• minimizing exposure duration • sign posting

• Use of appropriate PPE
– Attenuation – Proper use and maintenance of PPE

• Health surveillance
– Pre-employment and periodic audiometric examinations


Wear ear protectors in the right way. Make sure that : 1.Seals on the ear muffs fit tightly on ears 2. If you wear glasses, use ear -plugs as the frame makes the seals leak 3. Ensure ear plugs are clean

Some Don’ts
• Don’t take your ear protectors off where it is noisy, even for a short time. • It does not take much noise to damage your hearing • Don’t think you can get used to noise • Don’t overstretch the headband on earmuffs. Out of shape - out of work • Don’t modify the muffs - drilling holes etc. It’s your hearing - abuse it or lose it !

What to do
• Mark “ Ear Protection Zones” • Provide adequate information & trg. On how to use noise control equipment • Control noise • Provide ear - protection - ear plugs or ear muffs for exposure levels exceeding 85dB(A) • Make sure they wear protection when exposed to noise levels 90dB(A)

Types of ear protection
1. Muffs 2. Plugs 3. Canal caps Consult the assessor on type of ear protection required and also if they can be used with the other protective equipment Whatever be the type - it must be comfortable

Supervision in ear protection
• Someone in authority to be the overall in-charge • Make sure replacement is available • Introduce Co. rules in consultation with workers and their representatives • Ensure that all managers also set a good example even though they may be unlikely to exceed their daily noise „dose‟.

Sign Posting

Personnel Enclosure

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