Are Your Smoke Detectors Too Sensitive, Not Sensitive Enough, or Just Right?
Most people simply expect and assume the smoke detectors located in their facility to “just work.” Without complete, scheduled sensitivity testing, there’s no better way to determine whether or not they’re functional and protecting your facility and occupants as intended.
As with any electronic system but more specifically a fire alarm system, the system components can degrade over time. Dust particles, dirt and other airborne contaminants are often the reason for a smoke detector to be too sensitive or not sensitive enough and both of these conditions can be trouble. In the event of an emergency, if your smoke detector is not 100%, you have most likely lost a key component in your first line of fire and life safety defense.
FLSA recommends an ongoing maintenance plan that will assure you that your system is doing precisely what it is intended to do…save lives in the event of an emergency.
A well-maintained smoke detection system will reduce the possibility of false alarms but remember—when a smoke detector goes into alarm—it’s alarming for a reason whether it is a false alarm or not. Within the life safety world, there is no such thing as a false alarm; rather, a nuisance alarm. Nuisance alarms are commonly associated with smoke detection. A proper maintenance plan will reduce the frequency of nuisance alarms and can save a company’s productivity and employee time in the event of an unnecessary building evacuation as well as costly and unbudgeted emergency repairs. Scheduled maintenance can also extend the life of the system and comply with fire codes enforced by the local Authority Having Jurisdiction (AHJ).
According to the National Fire Protection Association National Fire Alarm Code (NFPA 72), sensitivity testing should be checked and calibrated every alternate year after the first test. If, however, after the second required calibration test, sensitivity tests show that the device has remained within its listed and marked sensitivity range (or 4 percent obscuration light gray smoke if not marked), the length of time between calibration tests may be extended to 5 years.
For sensitivity tests, any of the following tests may be performed to ensure that each detector is within its listed and marked sensitivity range using:
- A recognized, calibrated test method with smoke or listed aerosol
- The detector manufacturer’s calibrated sensitivity test instrument
- Listed control equipment (fire alarm control panels) that are arranged to perform sensitivity ranges
- A combination smoke detector/control unit where the detector causes a signal at the control panel unit when its sensitivity is outside its listed sensitivity ranges
Use of any other calibrated sensitivity test methods approved by the code official.
For the sensitivity tests, it is not required that smoke or aerosol be introduced into the detector. However, when conducting a performance test—to ensure that the detector senses smoke and generates an alarm—smoke or listed aerosol must enter the detection chamber. Performance tests and sensitivity tests are intended to achieve different results: the first is to ensure the device works, the second is to verify it remains within its listed range. For additional information, refer to NFPA 72, Chapter 14.
During the sensitivity testing, if the smoke detector fails, it is recommended that the smoke detector be cleaned. This process includes the cleaning of the smoke detector screen and chamber using a non-electrostatic vacuum, specifically designed to prevent damage to the smoke detector. The smoke detector will then be retested and should the device fail again, it will be noted in the inspection report and not reintroduced into the system but rather replaced.
For the purpose of performing sensitivity testing, FLSA uses trutest. Trutest 801 is a revolutionary product that introduces a smoke test aerosol through the vents of the installed detector to the sensing chamber. It operates using a precision closed loop system that measures smoke obscuration and feeds back information to a controlling microprocessor.
Some standards permit sensitivity test frequencies to be extended after proven detector stability. This relies on tracking drift, which can be done only by measuring actual sensitivity readings. Trutest does not need two tests to check the upper and lower limits (which, in itself, does not establish actual sensitivity). Just one test provides an actual reading in %⁄ft. which can be compared year on year to establish drift.