How loud does noise have to be before its dangerous?
Because permanent hearing loss is usually a long-term process, it is impossible to know at exactly what point noise becomes loud enough to cause damage to the ears. The U.S. Environmental Protection Agency has established 70 dBA as a safe average for a 24-hour day. (This figure is based only on the risk to hearing, and does not take into account other health factors such as loss of sleep.) Since sound intensity doubles with every increase of 3 dB, the time of safe exposure would be cut in half with each such increase. Thus a worker should wear ear protection if exposed to a steady 75 dBA for eight hours, 78 dBA for four hours, and so on. Brief exposure to noises of up to 100 dBA is not considered risky, provided the average remains within the prescribed levels. Actual limits for labour tend to be more permissive. In most jurisdictions, workers are permitted to be exposed to up to 85 or even 90 dBA for eight hours. Using the higher of these figures, the sound level in a typical nightclu
