What describes the Exchange Rate?

• A. The trade-off relationship between an increase (or decrease) in sound level and the corresponding change in allowed exposure duration
• B. The measure of WBGT
• C. The 85 dBA criterion
• D. The survey to define hazardous areas

Answer: (A)

Exchange rate describes how sound level and exposure duration trade off to produce the same noise dose. In practical terms, as the level goes up, the amount of time you can be exposed decreases according to the rate. For example, with a 5 dB exchange rate, a 5 dB increase in level halves the permissible exposure time (so going from 85 dBA to 90 dBA might cut allowed time from 8 hours to 4 hours). Conversely, a 5 dB decrease in level doubles the allowable exposure duration. Different standards use different exchange rates (such as 3 dB or 5 dB), which changes how quickly time limits shrink at higher levels. This is the concept described by the correct choice. The other terms refer to unrelated ideas: a heat-stress measure (WBGT), a fixed hearing threshold (85 dBA criterion), or a survey to map hazardous areas.