One attempt to identify safe levels assumed that the most appropriate exposure limit for recreational noise exposure in children would aim to protect 99% of children from a shift in hearing exceeding 5 dB at 4 kHz after 18 years of noise exposure.[1] Using estimates from the International Organization for Standardization (ISO 1999:2013),[46] the authors calculated that 99% of children who are exposed from birth until the age of 18 years to 8-h average sound levels (LEX) of 82 dBA would have hearing thresholds of about 4.2 dB greater, indicating a shift in hearing ability. By including a 2 dBA margin of safety which reduces the 8-hr exposure allowance to 80 dBA, the study estimated a hearing change of 2.1 dB or less in 99% of children.