EL CRITERIO DE PROTECCIÓN AUDITIVA NRR
Los protectores auditivos son dispositivos de singular importancia en el control pasivo de ruido. Ellos garantizan (cuando la selección es correcta), la atenuación necesaria que asegura la disminución de la exposición efectiva al ruido. Se requerirá el uso de protectores auditivos, por ley, cuando el nivel de exposición al ruido supere los 85 dBA de nivel sonoro continuo equivalente para 8 horas. Es importante acotar que se corre riesgo de daño auditivo con valores inferiores al reconocido oficialmente como de riesgo atendible en ambientes laborales. Es común la selección de dispositivos de protección auditiva sin considerar, seriamente, si realmente el modelo que se trabaja es capaz de asegurar la mejor protección. Es preciso realizar un estudio previo de las características del ambiente sonoro para el cual se busca el resguardo más efectivo. El ingeniero de planta debe velar por la calidad del medio de protección auditiva. Para ello, deberá considerar la información del fabricante (o suministrador), y confrontarla con los datos reales del ambiente acústico donde se desea la protección, para así evaluar la eficacia del protector. Existen varios criterios para la selección de un protector auditivo. Tenemos los criterios HML y SNR (según ISO 4869), el NRR según OSHA y el método de selección más eficaz, que obtiene un nivel efectivo considerando la atenuación por bandas de octavas normalizadas. En esta NOTA se atenderá únicamente a la selección según el valor NRR. La Tasa de Reducción de Ruido (Noise Reduction Rating, NRR, legislado para los fabricantes de Estados Unidos y de aplicación en otros países), es un valor que debe ofrecer el fabricante y se obtiene en condiciones de laboratorio rigurosas. Resulta la tasa de reducción teórica, inalcanzable en condiciones prácticas de la industria. La determinación empírica de la atenuación real del protector se determina por el protector (o combinación de éstos) que brinde el nivel de ruido efectivo más bajo. La determinación del nivel de ruido efectivo (dBA*) para protectores auditivos según este método es como sigue:
- Cuando es conocido el nivel de ruido, medido con la aplicación de la escala de ponderación C (dBC):
dBA* = dBC – NRR [dBA]
- Cuando es conocido el nivel de exposición al ruido, medido con la aplicación de la escala de ponderación A (dBA, la más utilizada mundialmente):
dBA* = dBA - (NRR - 7) [dBA]
- Cuando es necesario, debido a la agresividad del ambiente sonoro, utilizar doble protección auditiva (tapones y orejeras): en este caso, se debe tomar al que presenta mayor tasa de reducción de ruido (NRR), para calcular el nivel de ruido efectivo.
dBA* = dBA - (NRR-2) [dBA]
A todos los cálculos anteriores se les recomienda afectar en un 50% la tasa efectiva de reducción de ruido [NRR, (NRR-7), (NRR-2), según la variante para calcular el nivel de ruido efectivo (dBA*)]. Esto, sin duda, restringe todavía más, la atenuación real que pudiera imputársele al protector que se analiza. Sin embargo, se recomienda tal afectación debido a que el uso de protectores auditivos en condiciones reales no garantiza, bajo ninguna circunstancia, el nivel de atenuación declarado ni siquiera aproximadamente. Resulta curioso que estos detalles nunca se declaran en el producto.
8 comentarios
Luis Guevara -
dBA: 109
NRR fabricante: 24
resultado: 92
Me gustaría saber si lo calcule correctamente y que debo hacer al notar que no esta disminuyendo notablemente el nivel de presión sonora
Miguel camacho -
Comentarios?
Saludos....
Driliople -
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