Fog Signal

When bad weather obscured a lighthouse beacon, navigators relied on the fog signal. Swirling snow and pea-soup fog could even make Split Rock Lighthouse invisible during the day, and navigators aboard ore boats used the signal to determine their location. The signal had a unique characteristic: a two-second blast of sound followed by eighteen seconds of silence. It was about 120 decibels, on par with an ambulance siren, and could be heard in Beaver Bay, four miles away. The fog signal building housed two Franklin tandem air compressor engines connected to air tanks and then to roof-mounted sirens. To activate the fog signal, keepers powered up the engines, forcing air into the compressor tanks and out through the sirens. The original gas-powered engines were replaced with diesel models in 1932.

Minnesota · United States