The Hand-Crank Siren Indoors: One Roof Siren Against Six Corridor Sounders in a Two-Floor School

A hand-cranked siren on the roof is the traditional way to warn a whole school, but its sound must cross a roof or a wall and then fill rooms that open off a corridor. This paper models a stated building — two floors of 60 m by 14 m, sixteen classrooms per floor — with a warning criterion of 75 dBA at the far corner of every room. The roof siren (125 dB at 1 m at full cranking speed, with stated path losses of 25 dB through roof and ceiling and 22 dB through the external wall) reaches the criterion in 24 of the 32 rooms: 14 of 16 on the ground floor and 10 of 16 on the first floor, with the quietest room at 70.2 dB. Six indoor corridor sounders (110 dB at 1 m, three per floor at corridor positions x = -26.25 m, -3.75 m, and 26.25 m, with a 10 dB loss through each closed door) reach the criterion in all 32 rooms, with the quietest room at 77.6 dB. The sounder system also costs less (USD 770 against USD 850) and sounds 85 seconds sooner: 5 seconds after the alarm switch against 90 seconds for an operator to walk to the crank station and crank the siren to full speed. On these stated assumptions the single roof siren does not warn the whole building, and the common belief that it does is not supported by the arithmetic. SIMULATED, NOT MEASURED.