# What is Dose and how is it Measured?

Dose is a measure of noise exposure similar to Lex. It is dependant on exchange and criterion levels. In the UK, where the criterion level is 90dBA, dose can best be described with the following statement:

100% Dose = 90dBA for 8 hours

It is related to exposure time and Lex. The following tables give examples of dose levels using different changing factors, a criterion level of 90dBA is used throughout.

### Effects of Changing Lp

 Lp (dBA) Exposure Time (Hours) Dose (%) Lex (dBA) 99 8 800 99 96 8 400 96 93 8 200 93 90 8 100 90 87 8 50 87 84 8 25 84

### Effects of Changing Exposure Time

 Lp (dBA) Exposure Time (Hours) Dose (%) Lex (dBA) 90 16 200 93 90 12 150 91.76 90 8 100 90 90 4 50 87 90 2 25 84 90 1 12.5 81

Each time the sound level increases by 3dB (the exchange rate), the dose doubles given the same exposure time. Similarly, if the sound level decreases by 3dB, it will halve for the same exposure time.

Doubling the exposure time doubles the dose and halving the exposure time halves the it, given the same sound level.

### The operation can be mathematically described by the following equation which relates the percentage exposure, D, to the integrated sound power. Where

• D = percentage exposure
• Tc = criterion sound duration
• T = measurement duration (in hours)
• L = weighted sound level
• Lc = criterion sound level

### With respect to Lc, criterion levels of 90dBA and 85dBA are most often used. For discrete time intervals at a constant sound level the equation can be written as: Where

• time = exposure time, in hours
• Q = exchange rate (typically 3dB)