Noise at Work Regulations Mick Gray MRSC, LFOH, ROH. MWG Associates - PowerPoint PPT Presentation

Noise at Work Regulations Mick Gray MRSC, LFOH, ROH. MWG Associates Ltd

The Issue • NIHL is a significant occupational disease • 170,000 people in the UK suffer deafness, tinnitus or other ear conditions as a result of exposure to excessive noise at work – Health and Safety Executive • 3 rd European workers are exposed to potentially dangerous levels of noise for at least a quarter of their working time – European Agency for Safety and Health at Work • “ the most prevalent, irreversible industrial disease” - World Health Organisation

Programme • Basic Noise Terminology • The Control of Noise at Work Regulations 2005 • Instrumentation for Workplace Noise

Basic Noise Terminology

An introduction to noise and sound • What is noise? – Noise is usually defined as “unwanted sound” • But unwanted by whom? • Let us consider the more general case of “sound”

Basics of Noise Terminology • One of the 5 human senses - – sight, touch, taste, smell, hearing • Pressure variations in the air caused by something moving • detected by our ears and turned into electrical impulses • ear is divided into 3 parts, – outer, middle and inner ear • brain sorts them out into some form of meaning

The physics of hearing • we hear sounds over a wide range of frequencies – measure frequency in Hz – Hz is short for Hertz or cycles per second (cps) • we hear sound over a wide range of levels – measure levels in dB – dB is short for decibels • we hear sound over a wide range of times – measure time in seconds, minutes or hours

dB Scale

What do we hear? • Air pressure fluctuations are caused by vibrating objects or by air flows • low speed variations cause low frequency sounds – few tens of variations per second • high speed variations cause high frequency sounds – few thousands of variations per second • variations are called frequency or tone or pitch • limits of normal healthy hearing is about 20 to 20,000 Hz in the very best case

The inequality of human hearing - 1 • We do not hear all sounds with equal intensity • our ears are less sensitive to some frequencies than others • this is more noticeable at the lower frequencies of sound • consider some sounds as examples…… • Hum of power transformers, air conditioning, etc

The inequality of human hearing - 2 • our hearing is non-linear unlike the response of a hi-fi amplifier • it is also non-linear with the loudness (or strength) of the sound • research has established 3 main areas of interest associated with noise measurements • standardized correction curves have been written into the way measurements are carried out

The equal loudness curves • Lowest curve shows the threshold of hearing (audibility) for normal adult male • Phon curves

Frequency weighting curves -1 • For low level measurements correction curve is quite steep – the A weighting curve • for medium level measurements the correction is less steep – the B weighting curve • for high level measurements the correction is only at the extremes – the C weighting curve

The frequency correction curves • The „A‟ curve is at 40 Phons, the „B‟ curve is at 70 Phons, the „C‟ curve is at 100 Phons

The standard broadband frequency weightings for noise measurements

Frequency weighting curves - 2 • for some measurements the “true” or un - corrected frequency response is needed – (sometimes called Linear or un-weighted or All- Pass) – this can be different for different manufacturers and for different instruments from the same manufacturer depending on microphone fitted • the Z weighting curve sets limits of 20 to 20kHz

What do we hear? • How loud is it? • Very wide range of sound pressures experienced • Sound pressure is measured in Pascals (N/m 2 ) • lowest values few tens of micro Pascals (10 -5 Pa) • highest values are about 100/200 Pa • this is a range of at least 10 6 • this is a ratio of over 1 million to 1!!

What range do we hear? • If we measured this like we do with temperature or length,….. – We would need a tape measure that could measure 1 mm and 1 km!! (1 thou to 83 ft) • This would be very difficult to express results if we had to use absolute units of sound pressure, so….

How do we measure sound? • We use a relative scale rather than an absolute scale • we say a sound is bigger (or smaller) than another sound by a certain amount • logically we would choose a pressure of 1 Pa – (like 1 Volt for electrical signals) • but then we would end up with a scale of smaller and bigger values, so….

How do we measure sound? • We choose the lowest pressure that the normal ear can hear as our reference point • in this way all other sounds are always bigger than that sound • First we need to have a reference pressure level – 20 micro Pascal at 1 kHz has been internationally agreed

The dreaded decibels!! • Actual equation used to find the dB value of a given sound pressure is found from - • dB = 20 log (P/P ref ) P ref = 0.00002 Pa • because of the logarithmic nature of the dB scale • 70 dB + 70 dB (does not =) 140 dB • 70 dB + 70 dB = 73 dB

The maths of dB‟s • The reference sound pressure corresponds to the lowest sound that can be normally heard • now we refer all other sounds to this level • a sound 10 times more would be +20 decibels (dB) • a sound 100 times more would be +40 dB • a sound 1000 times more would be +60 dB • a sound pressure twice as much would be 6 dB • (Note that a sound with twice the noise energy increases by 3dB)

The R.M.S. time constants • We use the result of the R.M.S. circuit to see the noise level on the display • for steady noises we use the time averaged levels – slow (1 sec), fast (1/8 sec), impulse (1/32 sec) • these settings are standardized on meters to allow comparisons to be made • There is a Peak setting on some meters to capture the true highest level (equivalent to <1/10,000sec)

What do we measure? • Definitions of some of the popular noise units as we come across them in the sessions later on • Instantaneous sound pressure level L • maximum sound pressure level L mx • minimum sound pressure level L mn • peak sound pressure L pk • time average sound pressure level L eq

Example of the steady level 90 L AEQ = 83 dB L A 80 70 TIME

How do we state the result? • Need to specify the frequency weighting – A, C or Z (non) • need to specify the time weighting – S, F or I

Expression of typical noise result • For example, the noise level from a source - – maximum A weighted Fast sound pressure level was 85 dB over a 3 min period – written as L AFmx = 85 dB (3 min)

Lepd for a 4 Hour Shift • Steady LAeq 90 90dB 89 • Noise is measured for 4 88 hours 87 LAeq • Energy is Lepd 86 “spread” over 85 8hrs 1 2 3 4 5 6 7 8 9 10 11 12 LAeq • Therefore Lepd is 87dBA

Lepd for an 8 hour Shift • 8 hour LAeq 90 = Lepd 88 • Steady noise 86 of 90dBA for LAeq 84 8 hours = Lepd 82 90dBA Lepd 80 1 2 3 LAeq 4 5 6 7 8

Lepd for 12 hour shift • Employee is exposed to 4 hours “extra” 94 93 energy, therefore 92 91 Lepd is higher 90 89 LAeq 88 than measured Lepd 87 86 LAeq 85 1 2 3 4 5 6 LAeq 7 8 9 • 12 hours of 10 11 12 steady 90dBA = Lepd of 92dBA

The peak level limit • Although L EP,d is an 8 hours value. • But very high impulses of noise can cause instant damage to hearing. • So instruments have peak hold function to measure any impulsive noises (L CPK ). • Only has to be exceeded once to be considered over action level.

Introduction to noise • Conclusions – noise (sound) has three dimensions • frequency • level • time • Must measure properly to ensure you get the correct values

Physical Agents (Noise) Directive Directive 2003/10/EC The Control of Noise at Work Regulations 2005

Below first action level Employer must: • Reduce risks to lowest practicable level • Keep records and make them available including audiometry (if done) • Buy quiet

Above first action level Employer must: • Identify all employees at risk • Put up signs • Review if any changes to noise levels • Repeat assessment <2 years • Inform employees of risk • Provide choice of PPE on request (first aid) • Provide training / education • Noise Control

Above second action level Employer must: • Demarcate as Ear Protection Zones • PPE must be used at all times • Noise control to reduce exposure • If Lepd is over 95dBA then must use octave band method to check if hearing protection is effective Note: For peak action level, take the same action as for second action level

Why the changes? • Even under current regulations many people are still exposed to unacceptable levels of noise. • 14% of population exposed to noise in the workplace will suffer some long term damage New regulations give new emphasis

What is new emphasis? • Main goal is control of noise risk • Risk assessment to establish what needs to be done • Controls known to work should be implemented • PPE in place • Other systems in place – Maintenance – Training – Health surveillance