Residential Fire Sprinklers are designed to:

• activate at 160 degrees F
• only discharges water from the head that is activated
• apply water at a rate of 13 to 18 gallons per minute during the initial stages of fire
• provide early fire warning (augments, but does not replace smoke detectors)
• allow one to escape from the fire
• activate by heat only. Smoke without heat will not cause a sprinkler to activate.

Today's fire sprinklers operate on a much more sophisticated approach than the methods I am going to describe, but some still are activated by thermal expansion in a bi-metallic strip. These sprinklers cycle on and off as the air temperature around them changes. They are activated once the ambient temperature reaches 160 degrees F. Once the temperature reaches 160, the bi-metalic strip has curved to the point where it triggers a valve that controls the operation of the sprinkler. Once the temperature goes below 160, the sprinkler cycles off.