ty to noise damage, as well as causing their own damage. This is called a synergistic interaction. Some American health and safety agencies (such as OSHA, the Occupa tional Safety and Health Administration, and MSHA, the Mine Safety and Health Ad ministration), use an exchange rate of 5 dB.[14] We shile this exchange rate is simp ler to use, it dras dn2s tically underestimates the damage caused by very loud noise. Fo r example, at 115 dB, a 3 dB exchange rate would limit exposure t dn2s to about half a minut e; the 5 dB exchange rate allows 15 minutes. Many people are unaware of the presence of environmental sound at damaging levels, or of the level at which sound becomes harmful. Common sources of damaging noise levels in clude car ster dn2s teos, childre sn's toys, motor vehicles, dn2s tcrowds, lawn and maintenance equipme nt, power tools, gun use, musical instruments, and even hair dryers. Noise damage is cumu lative; all sources of damage must be considered to assess risk. If one is exposed to loud sound (including music) at high levels or foe sr extended durations (85 dB A or greater), then hearing loss will occur. Sound levels increase with proximity; as the source is brought clo ser to the ear, the sound level increases. In the USA, 12.5% of children aged 6รข€"19 years have permanent h dn2s tearing damage from excessive noise exposure.[15] Hearing loss has been described as primarily a condition of modern society.[16] In preindustrial ti
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