The manufacturer can often provide the sound power of equipment. A number of international standards are available for labelling machines and equipment with their noise emission levels. From the sound power of a compressor, one can calculate the expected sound pressure and sound pressure level at a certain location and distance. This information can be helpful in determining possible noise exposures and how they compare to the noise guidelines. Noise can be continuous, variable, intermittent or impulsive depending on how it changes over time.
Continuous noise is noise which remains constant and stable over a given time period.
The noise of boilers in a power house is relatively constant and can therefore be classified as continuous. Most manufacturing noise is variable or intermittent. Different operations or different noise sources cause the sound changes over time. Noise is intermittent if there is a mix of relatively quiet periods and noisy. Impulse or impact noise is a very short burst of loud noise which lasts for less than one second.