Relationship of Alarm Bell To Heart Disease Studied

Relationship of Alarm Bell To Heart Disease Studied

It’s the middle of the night and the fire fighters in Station 3 are sound asleep. Suddenly the big alarm bell rings. Without really waking up, the fire fighters leap out of bed. Adrenalin shoots into their blood. Their heart rate increases. Anxiety instantly develops. What are the physiological and psychological effects of the shock of this alarm on the fire fighters—are these effects detrimental, and if so, can they be eliminated or minimized?

The fire service has long suspected that the alarm bell is detrimental to the mental and physical well-being of fire fighters; however, until recently, this feeling has lacked supporting medical evidence. Studies of fire fighter health hazards are now being conducted at Harvard and UCLA. Preliminary results at UCLA indicate that the shock of the fire alarm bell may have something to do with the generation of heart disease in fire fighters. Furthermore, although the issue has been intensely argued, it is not known whether the suspected detrimental aspects of the awakening shock are due to the intensity of the bell, the sudden sound, apprehension of danger, or some combination of these factors.

The Los Angeles City Fire Department has long been concerned with the medical aspects of station alarms— even without specific evidence that the traditional practice is detrimental to fire fighters.* Therefore, when the development of a new fire communications/dispatch system for the city was initiated a few years ago, a study of techniques for alerting firemen was included. The objective of the study was intended to develop a better (less stressful) technique for alerting men in the stations. It should be noted, however, that the study was not intended to rigorously analyze the physiological and psychological effects of the alarm bell on fire fighters, but rather to identify a less shock-producing technique which could be readily adopted.

Early in the analysis, it became apparent that the optimum method of alerting personnel who must respond to emergency situations has never been experimentally examined. Fire fighters have historically (and probably universally) been alerted by a loud noise. However, the study viewed as reasonable the stimulation of other than auditory sensory systems as potentially effective in alerting the men, possibly without the detrimental “shock” effect.

Nevertheless, whatever the system utilized, three criteria for effectively alerting fire fighters must be satisfied: intensity, significance and uniqueness.


The intensity of the alarm signal required to alert an individual varies according to stages of sleep, as well as between individuals. In general, the deeper the sleep, the greater the intensity required to awaken an individual. A fire station alarm system must, therefore, have an intensity sufficiently high to awaken all fire fighters, each of whom may have different sleeping characteristics and be in different stages of sleep. Thus, the intensity must be keyed to an individual most difficult to awaken.


Research has shown that^ intensity alone is not sufficient to constitute an effective alarm signal. The signal must also be “significant” to each individual, that is, have a personal, special meaning. Examples of alarms having personal significance include your name shouted, a baby’s cry (to a mother), or a voice announcing a fire company designation. The study concluded that the conventional station bell probably meets the criterion of signifance for fire fighters.


The usual station bell may not be truly unique. After all, similar bells are used for many other purposes, such as in schools and factories.

The next step in the study was to identify and evaluate alternative alerting techniques. A theoretical analysis of the alerting process (from a sleeping state) resulted in the selection of four classes of alerting techniques: audible, visual, vibration, and electrical shock. Each of these techniques was evaluated to determine its suitability for use in a fire station alerting system. The results of the evaluation of vibration, visual, and electrical shock techniques can be summarized as:

Previous research indicates that alerting by electrical shock is effective and is not detrimental to the individual.

Moderately intense light can be sensed through closed eyelids and when used in a “flashing” mode can be an effective alerting technique.**

Vibration is an effective awakening technique. And, although it can be very disagreeable, vibration of the body is not necessarily detrimental.


There are, however, some severe practical limitations associated with all three of these techniques—primarily related to alerting personnel during waking hours. It may be noted that a combination of techniques keyed to the station activities of the personnel— recreation, training, sleeping, etc.— may ultimately prove to be the optimum alerting system.

The elimination of electrical shock, flashing light and vibration for reasons of practicality (pending further research) left the audible alarm as the only remaining alternative. Thus, the final objective of the study was to determine the “optimum” audible signal—that is, to simultaneously maximize the effectiveness of the signal while minimizing the medically detrimental aspects.

An audible signal has been designed which seems to meet the above criteria. This signal is a tone of approximately seven seconds’ duration. The first three seconds are low in intensity and pitch to “ease” the individual into the alert state. Then, the signal increases in intensity and pitch for the remaining four seconds to complete the process. This signal seems to meet the criteria of uniqueness and significance to firemen. The intensity can be set empirically at the level required to awaken all personnel in any given station. While not ideal, the variable tone signal should reduce the physiological and psychological shock of the alarm.

The Los Angeles City Fire Department converted to tone alerting in all of its stations in 1973. The system has not been in use long enough to permit a comprehensive evaluation, although at this time station personnel are pleased with the new system and believe that it does reduce the shock of the fire station alarm.

The above article is based upon research performed by Human Factors Research, Inc., Goleta, Calif.

** Alarm clocks are commercially available which utilize the flashing light technique.

*The department is evaluating a tone alerting system which had been installed in one station on an experimental basis.

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