Citation

Starck J, Toppila E, Pyykko I. Noise Health 2003; 5(20): 63-73.

Affiliation

Occupational Health, Helsinki, Finland. jukka.starck@ttl.fi

Copyright

(Copyright © 2003, Noise Research Network, University College London)

DOI

unavailable

PMID

14558894

Abstract

Impulse noise causes evidently more severe hearing

loss than steady state noise. The additional effect of occupational impulse

noise on hearing has been shown to be from 5 to 12 dB at 4 kHz audiometric

frequency. Reported cases for compensated for hearing loss are prevalent in

occupations where noise is impulsive. For impulse noise two measurement methods

have been proposed: the peak level method and energy evaluation method. The

applicability of the peak level method is difficult as even the recurrent

impulses have different time and frequency characteristics. Various national

risk criteria differ from international risk criteria. In France the maximum

A-weighted peak level is 135 dB, and in the United Kingdom the C-weighted peak

sound pressure is limited to 200 Pa (140 dB). This criterion of unweighted 200

Pa (140 dB) is used in European Union (EU) directive 86/188 and ISO 1999-1990

regardless of the number of impulses. The American Conference of Governmental

Industrial Hygienists (ACGIH) has recommended that no exposure in excess of a

C-weighted peak sound pressure level of 140 dB should be permitted. At work

places these norms do not cause any practical consequences since the impulses

seldom exceed 140 dB peak level. In several occupations the impulses are so

rapid that they contribute only a minimal amount to the energy content of noise.

These impulses can damage the inner ear even though they cause reduced awareness

of the hazard of noise. Based to the present knowledge it is evident that there

is the inadequacy of the equal energy principle in modelling the risk for

hearing loss. The hearing protectors attenuate industrial impulse noise

effectively due to the high frequency contents of impulses. Directive regarding

the exposure of workers to the risks arising from noise requires that in risk

assessment attention should be paid also to impulsive noise. So far there is no

valid method to combine steady state and impulse noise. A statistical method for

the measurements of industrial impulse noise is needed to get a preferably

single number for risk assessment. There is an urgent task to develop risk

assessment method and risk criteria for impulsive noise to meet the requirements

of the upcoming European Union noise directive.