Detect-A-Fire®
Heat Detectors

DETECT-A-FIRE® (DAF®) units
have met with wide acceptance
because they are designed with
rate compensation. This
provides a unique advantage
over both fixed temperature and
rate-of-rise types of detectors
because only the DAF® unit
accurately senses the surrounding
air temperature regardless of the
fire growth rate. At precisely the
predetermined danger point,
the system is activated.

Fixed temperature detectors must
be completely heated to alarm
temperature and therefore a
disastrous lag in time may occur
with a fast rate fire.

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Rate-of-rise devices, on the other hand, are triggered by the rate of increase in ambient temperature and are subject to false alarms caused by harmless, transient thermal gradients such as the rush of warm air from process ovens.

The secret of the unit's sensitivity is in the design. The outer shell is made of a rapidly expanding alloy which closely follows changes in surrounding air temperature. The inner struts are made of a lower expanding alloy. Designed to resist thermal energy absorption and sealed inside the shell, the struts follow temperature changes more slowly.

A slow rate fire will heat the shell and struts together. At the "set point", the unit will trigger, actuating the alarm or releasing the extinguishant. A transient rush of warm air up to 40ºF /min. may expand the shell, but not enough to trigger the unit. By ignoring transient warm air excursions, the DAF® unit virtually eliminates false alarms prevalent with rate-of-rise devices.

If a fast rate fire starts, the shell will expand rapidly. The struts will close, actuating the alarm or releasing the agent. The faster the fire rate of growth, the sooner the DAF® unit will react.