ER-200 Personal Noise Dosimeter

LED	Dose %	Risk Factor
green (slow flash)	< 25%	No risk of hearing loss
green (fast flash)	25%	No risk of hearing loss
green	50%	1/2 daily dose reached
yellow	100%	Limit of permissible exposure
red	200%	2x allowable daily dose
red	400%	4x allowable daily dose
red	1600%	16x allowable daily dose
red	3200%	32x allowable daily dose

Simply stated, noise dose is a measurement of noise exposure. It is the combination of the amount of sound and the amount of exposure time. Think of 100% as the limit of safe exposure, 200% as two times the permissible exposure limit, 400% as four times the limit, etc. The risk of hearing impairment grows with increasing noise dose. In some susceptible persons, a 100% dose indicates enough noise exposure to cause a small amount of hearing loss over time.

The dosimeter uses color-coded LEDs to display noise dose in percent.

Green (Safe): Noise dose is below 100% Yellow (Borderline): Noise dose is greater than 100% and less than 200% Red (High Risk): Noise dose is greater than 200%

Rate

A slow flashing LED at 25% means that the noise dose is at or below 25% (i.e., between 0% and 25%). When the noise dose reaches 25%, the 25% LED flashes rapidly indicating that it is between 25% and 50%. Similarly, when the dose exceeds 50% but is less than 100%, the 50% LED flashes rapidly, etc.

Hearing loss from loud sound affects millions of people. Noise-induced hearing loss is preventable, but most people don’t know how long they can listen to loud sound without risking hearing damage. A single noise exposure may not result in hearing loss, but permanent damage to the inner ear from noise adds up over time. The accumulation of too much noise day by day, year after year, is the determining factor in hearing loss risk. A sound level meter is a device that measures noise at a particular point in time, while a dosimeter measures sound levels for many hours and calculates the cumulative noise dose in percent.

Daily noise dose is determined by both the intensity of the sound and the amount of exposure time. A 100% dose means that a person has reached the maximum noise exposure for the day, and continued exposure to loud sound could lead to hearing loss. Ideally, hearing protection should be used before the dose reaches 100% since dose limits are based on averages, and some ears are more susceptible to noise damage than others. When the noise dose exceeds 50% a person has reached half the maximum noise exposure for the day and it’s a good idea to use hearing protection to prevent over-exposure, particularly if a 50% dose reading is reached early in the day.

In cases of gunfire and other impulse noise, no conventional dosimeter measures the risk accurately. More specialized equipment is required to measure impulse noise.