Aparatos auditivos para protección acústica

Protección auditiva contra el ruido industrial

Development of Mexican Standard on Hearing Protection Devices HPDs

Daniel P. Salomon
Comaudi. Patriotismo 706. Colonia Mixcoac. México D.F. 03730 México.

José N. Razo
Centro Nacional de Metrología. División de Vibraciones y Acústica. Carretera a Los Cués km 4,5. El Marqués, Qro. 76241 México.

A working group was called by the Secretaria del Trabajo y Prevision Social (STPS), similar to OSHA in the USA, to work on a standard whose objective is to protect workers from noise by trying to predict the performance of HPDs as personal protection equipment at the work center. Standards analyzed included ISO 4869 [1, 2], AS/NZ 1270 [3] and ANSI S12.6 [4, 5]. All of them evaluate attenuation as a performance descriptor. Experimenter fit methods tend to overrate field performance due to very different field versus laboratory conditions [6, 7]. Subject Fit methods result in lower attenuation values which are more likely to be achieved at work centers, specially when workers are inadequately motivated and trained. Subject Fit methods encounter big resistance. Difficulties to find naive subjects for laboratories, commercial interests of manufacturers, risk of overprotection, etc. [6,7]. Having settled for Experimenter Fit Method, the intent is to do more to help protect workers hearing through other means available. A thorough yet fairly simple HPD Selection and Usage Guide was prepared as an Informative Appendix. Relevant information must be provided to the user with the Packaging. “NRR wars” should be avoided. Standard includes list of contents, instructions and warnings that must be included. A sample label containing key information is detailed in Informative Appendix.

PACS numbers: 1) 43.50.Hg or 2) 43.66.Vt

I. INRODUCTION

This standarization effort was promoted by the Secretaria del Trabajo y Prevision Social (STPS) which is the highest federal authority in all aspects of workers and employers relationships and their rights and obligations. In 1999 the Direccion General de Seguridad e Higiene en el Trabajo requested a National Committee for Standarization of products provided as Personal Protective Equipment at the work centers. More than a million workers may be exposed to potentially hazardous noise levels. Noise induced hearing loss (NIHL) has one of the highest ratings of occupational disease in Mexico. A Subcommittee (SC) on Hearing Protection Devices (HPD) was formed.

This paper presents some aspects of the analysis performed by this SC on other Standards, and how these influenced our work and criteria. Those sections of this new Mexican Standard NMX-S-053-SCFI-2000 that are considered more relevant or innovative are also commented.

II. ANALYZING ATTENUATION STANDARDS

Being that a HPD is intended to provide protection from noise, the logical first choice in trying to measure and standardize its performance is to quantify the attenuation parameter. The interaction between the HPD and the human ear as well as the way in which the HPD is fitted are critical elements affecting attenuation values. Therefore, laboratory testing must be performed with humans as opposed to acoustic testing devices such as artificial ears. Thus the term "real ear attenuation".

HPD SC analyzed attenuation standards from around the globe and how their application had resulted. Some of the attenuation standards revised were the ISO standard, and the corresponding documents from USA and Australia among others.

For many years, HPD purchasing decisions have been based, on many occasions, only on higher attenuation values. An NRR (Noise Reduction Rating) war has been going on among manufacturers avid of a comparable superiority through higher NRR values helped by end users seeking numbers for "objective" comparisons. Lacking any mandatory standard applicable worldwide, any manufacturer that wants to provide responsible information with any sort of lower NRRs could be committing commercial suicide. One unwanted result of this NRR war is that it tends to distract attention from the features of a Hearing Conservation Program (HCP) that make it successful like worker training, motivation and supervision.

III. TEST SITE - BACKGROUND NOISE COMPARISONS

One of the key issues of the test site is background noise. Table 1 shows requirements of several Standards for this parameters.

It can be noted that values in Table 1 are specified for ISO 4869.1 and AS/NZS 1270 in third octaves while in ANSI S12.6 it is only octave bands. Even integrating the values in third octaves specified in the first two standards, values of up to 10 dB below ANSI are obtained. These additional dB are quite costly to any test laboratory. The SC decided for ANSI values thus increasing the likelihood of the establishment of a certifiable lab in Mexico.