Smoke Detectors

Smoke detectors and heat detectors. Know the difference!   Pictured here is a photo electric smoke detector. You cannot tell by simply looking at the detector if it’s a photoelectric or a ionization smoke detector. Both are fire protection devices and are suitable for residential and commercial installations. However, one maybe be better suited for a specific kind of installation. Ask your professional if you don’t know which one to use..  Smoke detectors and heat detectors both detect fire yet have different applications. Smoke detectors are primarily "life saving" devices. Heat detectors are considered "property saving devices." Smoke kills long before the a fire does. Smoke detectors detect fire (s) that heat detectors may not detect for until the fire is fully involved.  The two types of smoke detectors are Photoelectric and Ionization. Not all fires are real hot on onset and thus a smoldering object would be best detected by a smoke detector. The NFPA and other legal standards require all smoke detectors to sound in a fire alarm condition For example, in a two story residence, if a smoke detector goes into alarm upstairs then by law all detectors in the house need to sound. Alarm systems that have smoke detectors as part of the protection system is subject to the same legal requirements. In a alarm condition, all sirens need to sound and meet the NFPA and other criteria set forth by the NEC and other regulatory agencies known as "Authorities having jurisdiction" (AHJ) Be sure to contact a alarm professional if you need assistance in fire safety issues.   Ionization Smoke Detectors:

Figure 1.

These detectors contain a small amount of radioactive material that is capable of ionizing the air around it. This material is kept in a chamber between two electrodes in a circuit. When the air is ionized, it becomes conductive. Smoke particles attract the ions, reducing the conductivity of the air in the chamber. The alarm activates when the air drops below a certain level of conductivity. Ionization smoke detectors are useful in moderate or high hazard areas where flaming is likely to occur.

Another way at looking at it. The ionization of air by the radioactive particle causes a very small flow of electrical current. When smoke from a fire enters the chamber, its presence causes a reduction in the current's flow. The electronic circuitry senses the reduced flow and triggers the alarm horn

Photoelectric Smoke Detectors:

Figure 2.

These detectors operate on a principle of light obscuration. A beam of light reflects back from an emitter to a receiver. When this beam is obstructed by particles of smoke, the alarm sounds. They work much like the automatic eyes used to open doors. When smoke is present in the chamber, a photocell located at right angles to the light source senses the light scattered off the smoke particles and, at a certain level of illumination, triggers the alarm horn (See Figure 2.) When there's no smoke, the chamber is dark. Photoelectric detectors are faster than ionization detectors, but are more prone to false alarms due to particulate from cooking, smoking, or dust. They are most often used in large, open areas, where there is little ambient pollution to obscure the light. They are particularly useful in areas prone to smoldering fires.

 Common causes of false alarms

1. Lack of maintenance Smoke detectors require cleaning. Smoke detectors often (over time) collect dust. A dirty detector will cause false alarms. Best way to avoid false alarms caused by a smoke detector is to keep the sensing chambers free if dust and dirt.  Technicians usually use canned air to clear the chamber of contaminants. Have smoke detectors serviced and cleaned once a year by your alarm company. You can do allot by simply keeping your house dust free as possible.

2. Battery issues (low battery in panel) will cause false alarms. If you have battery operated smoke detectors check the batteries. Replace them if they are bad. If you have hard wired smoke detectors you could have a power problem inside the panel. The system needs to be looked at by a qualified technician.

3. Painting and related activities will cause smoke detectors to send a false alarm.  They will also cause smoke detectors to malfunction. A dirty smoke detector may not work in a real fire. Always mask off your smoke detectors when painting. Be sure to remove masking when done. Never leave a smoke detector disconnected. It could cost you your life or the life of another if a fire breaks out and is not detected.

4. Home improvements  projects often cause smoke detectors to report false alarms. Any construction activities that generates dust, fumes, etc. will contaminate the air and potentially cause smoke detectors to report a false alarm. Tile and painting contractors are notorious for setting off smoke detectors. Make sure you masks off smoke detectors before any home improvement where dust and fumes will fill the air.

5. Smoke detectors should be replaced every five to six years in a commercial applications.  Especially in restaurants and warehouse installations.  In residential applications you can expect seven to eight years of use if they are maintained properly. A faulty smoke or contaminated smoke detector may or may not work in an actual fire. So be sure to test them.

Summary

Fire safety is contingent upon the proper maintenance,  installation and application of the fire protection device. Improperly designed fire alarm systems not only cause false alarms but human lives.  Fire department responding agencies often find faulty smoke detectors as a contributing factor in loss of life and property.

In addition,  fire investigators often find no smoke detectors or disconnected smoke detectors in fire related fatalities.  Many were simply not maintained or simply unplugged.

False Alarms cause the unnecessary dispatch of the local fire department  This is costly and puts the general public at risk while fire trucks are responding in a emergency response mode.  The enormous cost in responding to false fire alarms has made it necessary for municipalities to impose fines for false fire alarm dispatches resulting in the deployment of fire personnel.  Fire departments that utilize volunteer fire fire fighters face even a bigger financial challenge as budgets often are fixed and false alarms take much needed funds from the volunteer fire department.