Information on how the impact of occasional loud noise is measured
Occasional loud noise is usually measured in the UK using Sound Exposure Level (SEL). An SEL footprint shows the geographical area in which a particular SEL is reached from a single noise incident – such as a plane taking off.
Large-scale studies have found that SEL over 90dBA generally leads to sleep disturbance (dBA are A-weighted decibels. The A-weighting system reduces the decibel values of sounds at low and high frequencies, because the human ear is less sensitive to these). Using an SEL footprint, it is possible to work out the areas where a take-off creates an SEL over 90dBA, and so see where sleep disturbance could occur.
This could then inform decisions about whether or not a particular type of aircraft should be allowed to operate from an airport during the night time, or about airport construction or extension in populated areas.