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TWA Equal noise exposure risk combinations for different exchange rate "Q". The number of decibels considered to double (or half) the risk of hearing damage in the workplace. A Q factor of 3 dB represents the equal energy principle and is based on the measured Leq value. A Q factor of 3 is recommended by certain US bodies such as NIOSH and the ACGIH and is mandated in European style noise regulations. A Q factor of 4 dB is mandated in certain US Department of Defense noise exposure regulations. The US OSHA regulations require a Q factor (or doubling rate) of 5 dB such that a noise is considered to be twice as risky (for the same exposure time) if it increases by 5 dB.