Ann. occup. Hyg., Vol. 47, No. 4, pp. 337, 2003
© 2003 British Occupational Hygiene Society
Published by Oxford University Press
Letters to the Editor |
The Comfort and Effectiveness of Hearing Protection Devices
Corus plc, Swinden Technology Centre, Moorgate, Rotherham S60 3AR, UK
Received 19 November 2002;
The article by Arezes and Miguel (2002) is valuable in quantifying an important issue—hearing protection will be less effective if it is less comfortable, because it will be tend to be worn for shorter periods of time. Unfortunately, the conclusions drawn are misleading in that they imply that earplugs are significantly more effective than earmuffs.
The first conclusion states: ‘There is no significant difference in the sensations of comfort between the same type of Hearing Protection Device (HPD).’ However, it goes on to say that only two (!) types of each defender were compared. A more accurate statement would be: ‘The two earmuffs had similar comfort indices, as did the two earplugs which were more comfortable.’ A reasonable recommendation would be that this work be extended to a wider range of HPDs.
The third conclusion states: ‘There are substantial differences between nominal (catalogued) attenuation and effective (real) attenuation. This feature is more evident for earmuffs.’ This implies that the real performance of earplugs is superior to earmuffs. Unfortunately, this conclusion is based on manufacturers’ data based on the standard test regimes (such as BS EN 352-2 and ANSI S3.19) (ANSI, 1974; BS, 1993). There are now many studies that show that the ‘real-world’ attenuation of some earplugs is often considerably worse than such tests indicate. For example, Berger et al. (1996) report studies showing noise reduction ratings for two types of earplugs of 1.4 and 2.2 dB, compared to manufacturer’s reported values of 26 and 23 dB, respectively.
In the UK, the HSE (1998) have summarized this by stating ‘...research has shown that the attenuation provided by earmuffs, when used in the work environment, is about 5 dB less than predicted by manufacturers’ average attenuation data. For earplugs a greater variability is found, with differences up to 18 dB observed. This increased variation is principally due to the poor fitting of plugs.’
From Arezes and Miguel’s Table 11, the average attenuation for two plugs tested can be calculated to be ~10 dB better than the two muffs. This difference may well not be significant if an ineffective type of ear plug is used.
The best outcome of this debate would be for realistic test methods to be adopted as international standards. In the USA, ANSI 12.6:1997 has been developed where the ‘experimenter-fit’ protocol of ANSI S3.19:1974 is replaced either by ‘experimenter-supervised- fit’ or ‘subject-fit’ (ANSI, 1974, 1997). The latter technique seems to correlate better with the ‘real-world’ performance of earplugs (Berger et al., 1998). These methods are under development as international (ISO) standards.
The comfort index developed by Arezes and Miguel could perhaps provide another valuable parameter, if the correlation with time of use can be shown to be robust for a variety of HPDs.
REFERENCES
ANSI. (1974) S3.19-1974. American national standard method for the measurement of real-ear protection of hearing protectors and physical attenuation of earmuffs. New York: American National Standards Institute.
ANSI. (1997). S12.6-1997. American national standard methods for measuring real-ear attenuation of hearing protectors. New York: American National Standards Institute.
Arezes PM, Miguel AS. (2002) Hearing protectors acceptability in noisy environments. Ann Occup Hyg; 46: 531–6.
Berger EH, Franks JR, Lindgren F. (1996) International review of field studies of hearing protector attenuation. In Axlesson A, et al., editors. Scientific basis of noise-induced hearing loss. New York: Thieme. pp. 361–77.
Berger EH, Franks JR, Behar A et al. (1998) Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices, Part III. The validity of using subject-fit data. J Acoust Soc Am; 103: 665–72.[CrossRef][Medline]
BS. (1993) EN 352-2. Hearing protectors. Safety requirements and testing. Ear plugs. London: British Standards Institution.
HSE. (1998) Reducing noise at work. Guidance on the Noise at Work Regulations, 1989. L108. Part 6. Selection and use of personal ear protectors—advice for employers. London: Health & Safety Executive. ISBN 0 7176 1511 1.
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  P. M. AREZES and A. S. MIGUEL Reply Ann. Hyg., June 1, 2003; 47(4): 338 - 338. [Full Text] [PDF]
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