The noise-reducing measures prevent sounds above 85 decibels from leaving airport boundaries. Noise-cancelling headphones specify the amount of noise they can cancel in terms of decibels. Seattle gained the record by reaching a noise level of 137.6 decibels. Consumer fireworks are also not allowed to be louder than 90 decibels. PEL for noise exposure is 90 decibels (dBA) for an 8-hour TWA. The recommendation for occupational noise exposure is 85 decibels (dBA) for an 8-hour TWA. This phenomenon is called acoustic attenuation and is measured in decibels (dBs). Normal hearing threshold is generally defined as 020 decibels (dB). Gain is often expressed in logarithmic units called decibels (dB). Modern sirens can develop a sound level of up to 135 decibels at . Propane exploders are capable of creating noises of approximately 130 decibels (Wildlife Control Supplies). This is why SPL is measured on a logarithmic scale in decibels (dBs). Amplitude decibels is usually done using formula 25 to define decibels. It is measured in decibels of hearing loss, or dB HL. Published numbers for antenna gain are almost always expressed in decibels (dB), a logarithmic scale.