The Temporal Pattern Takes Precedence in Total Evacuations

Communication is critical when a fire breaks out in a building of any kind. If the fire alarm system is not properly designed for the task at hand, the occupants, as well as responding firefighters, can perish. How the fire alarm communicates using the relatively new temporal pattern is integral to the task of saving lives. Whether you use it or not is determined by a number of factors that fire technicians must know.

Handling Partial, Total Evacuations

Traditionally, as most fire technicians are aware, there are two distinct ways to deal with the occupants of a building in a fire situation. You can either evacuate an entire building or you can do a partial evacuation.

However, there appears to be a question on the minds of some fire technicians as to what form audible notification must take where relocation or selective evacuation vs. full building evacuation is practiced.

When to Use the Temporal Pattern

The answer to that question is well documented and easy to find in NFPA 72, National Fire Alarm Code, 1999 Edition, published by the National Fire Protection Association (NFPA).

The quick answer is:
• When the objective is to fully evacuate an entire building, you must use temporal pattern.
• When the objective is to partially evacuate or relocate people, use voice evacuation.
According to The Moore-Wilson Signaling Report, published by Baltimore-based Hughes Associates Inc., “[In a] small building, fire alarm notification … must use the American National Standard [Institute] (ANSI) Evacuation Signal because management intends that everyone should evacuate when a fire occurs.”

The ANSI Evacuation Signal, better known as the temporal pattern, utilizes a three-pulse temporal pattern in accordance with the ANSI S3.41, Audible Emergency Evacuation Signal standard, effective July 1, 1996. It consists of a tonal sequence of 0.5 seconds ON and 0.5 seconds OFF, lasting for three successive cycles. Between these three-pulse cycles, there must be 1.5 seconds of silence. According to Section A-3-7.2(a), NFPA 72, 1996 Edition, this sequence must be repeated for no less than 180 seconds.

How Voice-Evac Systems DifferVoice-evacuation systems differ in that they seek to inform the occupants of a building where they must go and what they must do during a fire situation. Most of the time, these systems involved audible commands, recorded and real-time by nature.

For example, in a large, multifloor, high-rise building, it is customary to install speakers with strobes as notification appliances. The speakers are connected to a zoned audio amplifier, which allows management or firefighters to target specific areas of the building when sending voice commands.

However, according to The Moore-Wilson Signaling Report, when a voice-evac system is unable to transmit voice commands, real-time or recorded,  the fire alarm system must issue the temporal pattern.

Al Colombo is a technical writer in the electronic security and fire protection markets, providing technical direction for security dealers since 1986. Send your fire-related questions and comments to [email protected].

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