Sirens Installed for Safety


This article appeared in the City of Dayton Annual Report for 1943

 

Sirens Installed for Safety

By

Perry Benton

Superintendent, Division of Telegraphs and Signals

 

     The sudden attack upon Pearl Harbor, December 7, 1941, found not only our government unprepared for war, but also found the manufacturers of public warning apparatus unprepared for the unprecedented demand for their products.

     Sirens, air driven and electrically operated, have long been used by small communities as fire alarms.  These communities generally cover a small area and an adequate coverage was obtained by use of these sirens.  The densely populated cities, however, were unable economically to provide a sufficient number of them to get adequate coverage in their unheard of use as air raid warnings.  This was no fault of the manufacturers, whose equipment had heretofore served satisfactorily the purpose for which they were intended.

     Recognizing this inadequacy, the Bureau of Standards in Washington, D. C., requested interested manufacturers of sound equipment to submit to them a sound producing unit of their make for the purpose of establishing a decibel (unit of sound measurement) output rating on that apparatus.

     The results of these ratings proved that some apparatus which was being used as air raid warning signals were woefully inadequate.  It must be borne in mind that a sound produced for use in a small area, say one-quarter to one-half a mile in radius, loses its effectiveness in an area a mile or more in radius, even though the sound may be audible at this distance.  To be really effective, a siren must be heard above street noises, etc., otherwise it is useless as a warning medium.

     This City, classified as a highly strategic one, set to the task of installing warning signals immediately following the Pearl Harbor attack by installing six five-horse-power, four two-horse-power, and fourteen one-half horse power sirens.  The latter were placed at selected points in the noisy sections in the downtown business area.  The five and two-horsepower sirens were located at points designated to give coverage for the area involved.  These were our first installations.  More will be said of them later.

     Copper wire was even at this time a critical material, since so much of it was being held for our lend-lease program.  Because of this we were compelled to plan our siren control on the basis of existing facilities.  We were fortunate to have, already installed, cables with spare wires that could be used for part of our control.  Where spare wires did not exist, we pressed into use our police signal flasher circuits.  These circuits are of the series type, battery operated.  Polarized relays were installed at siren locations, in these circuits; thus, by the simple expedient of reversing the polarity of the outgoing operating battery, we were able to sound the sirens at will and this without disturbing the functioning of the police flasher system.  We were able to operate our one-half-horsepower sirens directly off the contact of the flasher relays.  For the larger sizes, it was necessary to start the sirens by means of an intermediate power relay, operated by the flasher relay.

     Since so many of the sirens were operating on the police flasher system, it was appropriate that its flashing transmitter be used to code the signals of the sirens.  A code wheel was cut with long impulse teeth to provide the required modulated signal tone.  By re-tuning the flashing transmitter slightly, we were able to create with four revolutions of the code wheel, an exact two minute period of signals. The steady tone was accomplished by operating a master control key.

     Eventually all sirens were ready for operation and a test was planned.  This plan consisted of the placement of 502 civilian defense lieutenants at their posts throughout the City.  Each was to turn in a report as to the dependable audibility of the signal at this particular post.  The results of the tests were very disappointing since less than forty per cent of the reports indicated that the signal was satisfactory.

     Since the local Utility Company purchased and loaned to us our sirens, specified on our own planning, it is apparent that we could not go to them and ask for a sixty per cent additional siren gift, and, since the Defense fund allocated by the State of Ohio could not be used at that time for such a purpose, we waited for the completion of the development of a new type siren that promised to outdo in sound output, anything yet heard.

     We were rewarded for our patient waiting by a demonstration of this new equipment, called the “Victory Siren,” in September, 1942.  This siren was a mobile one and was spotted at Deeds Park in order that the truck upon which it was mounted might be turned in a 360 degree movement, thus giving coverage in a complete circle.

     To check the effectiveness of the sound output of this unit, a group of observers were located at points throughout the city all being on a mile and seven-tenths radius from the siren.  This radius was the coverage which the siren would make and give a dependable signal of 72 decibels in the areas selected.  The test was most satisfactory since it was heard with good volume at all given points.

     Local members of the Council for Civilian Defense organization, a number of our City officials, and visitors from Oakwood, Richmond and Fort Wayne, Indiana, were present at this demonstration.  All were immensely pleased with the results since it did exceed in tone volume anything ever heard in sound tests.

     It was not until early in the spring of 1943 that we were able to see our way clear for purchase of four of this type siren which were then ordered from the Chrysler Motor Corporation of Detroit, Michigan.

     The task of erecting the supporting towers for the sirens fell upon the Signal Division. The towers consist of four fifty-foot cedar poles set in the ground on seventeen-foot centers with a convergence of ten feet to the top of the structure making the top seven feet on centers.  Because of the tremendous weight of the sirens (two and one-half tons) a very substantial platform was constructed at the top of the tower and a “catwalk” sixteen feet square was constructed three feet below the siren platform.  This “catwalk” permits operators to walk completely around the siren while servicing or operating it.

     The actual mounting of the heavy sirens was performed by Muth Brothers, riggers, who cooperated with the Council for Defense in this work.

     The task of erecting the towers and mounting the sirens was not a small one.  Our efforts, however, were rewarded by the satisfactory tests that were made for overall coverage.  We feel that if the need ever came for their use in an actual air raid that the Council for Defense and its volunteer workers will be adequately alarmed.

     The question of post war use of the sirens has been asked.  To this we can reply that one siren can be used at our Municipal Airport as a “crash siren” or public fire alarm.  The remaining three may be disposed of to other airports for the same use as we would put ours to, or to a community for use as a fire alarm.

     Differing fundamentally from our electrically operated sirens which the Signal Division maintained, the Victory Siren is strictly mechanical and can be maintained by anyone familiar with the rudiments of an automobile engine.  This being so, the operation and maintenance of the sirens is directly under the office of the Dayton Council for Defense.

     We hope that actual need for an alerting alarm will never arise, but if it should—“We are ready.”