Project title: Noise exposure to marine foghorns: Assessment and control strategies
Completed in: 2020 | Faculty advisor: Christopher D. Simpson
An occupational noise exposure assessment aboard a U. S. Coast Guard vessel typically involves area noise monitoring and yields recommendations to prevent noise-induced hearing loss. This particular study included the use of a type 2 sound level meter to measure sound pressure levels in 24 different locations aboard a 210 ft Medium Endurance Class Coast Guard Cutter, as well as personal noise dosimeters to measure sound pressure levels for five different watch-standing positions over a 4-hr period. The measurements were taken to assess hazardous noise levels following significant engineering and equipment modifications. The recent assessment near Port Angeles, Washington, revealed a higher than expected exposure for employees on deck of the vessel, due to the activation of the ship’s whistle every two minutes on account of a thick marine layer of fog. The personal monitoring results indicated that the bridge lookout may be overexposed at approximately 98 decibels A-weighted (dB(A)) at an 8-hr time weighted average (TWA) when the foghorn is in use. Most notably, these individuals are required to “maintain a proper lookout by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision.” Thus, unhindered hearing is necessary to locate or identify other vessels or aids to navigation. This finding highlights the potential exposure of a relatively overlooked population, which could be expanded to include other personnel whose hearing is vital to their occupation in the maritime industry and other transportation sectors that utilize loud sound signals. The subsequent recommendations focused on mitigation strategies for prolonged exposure to continuous foghorn use due to vessel operation in fog or reduced visibility, rather than the occasional exposure from infrequent foghorn use. With limited control methods, the most appropriate options to mitigate the effects of this continuous hazardous noise appear to be either limiting the duration of exposures, or use of active noise cancelling headphones electronically connected to the activation of the vessel’s foghorn and also integrated with microphone technology to amplify ambient noise as to not detract from the user’s detection of other navigational sounds.