• The main indicators of fire are smoke and abnormal heat, which are detected by smoke and heat sensors in automatic fire detection systems. These sensors alert the fire alarm control panel, prompting appropriate response actions. Addressable smoke detectors enhance this process by assigning a unique identifier to each unit, allowing the control panel to locate specific areas affected by smoke or fire. Unlike conventional detectors, addressable units provide real-time information, enabling quicker emergency responses. They feature two-way communication with the control panel, advanced sensitivity, programmability for environmental adjustments, and integration with other building systems to improve safety and minimize false alarms.

• The primary function of the smoke sensor is to detect the presence of smoke within its coverage area. Upon detecting smoke, the sensor sends a signal to the control panel and continuously provides real-time smoke density readings. The control panel assesses the severity based on the smoke density and, after a time delay, triggers a pre-alarm. If the smoke density exceeds a certain threshold, the main alarm is activated to signal a potential fire.

• The primary function of the thermal sensor is to detect changes in temperature, particularly rising heat levels that may indicate a fire. When the sensor detects a temperature increase beyond a preset threshold, it sends a signal to the control panel and continuously provides real-time temperature data. The control panel evaluates the severity of the temperature rise. If the temperature increase is significant, a pre-alarm is triggered after a time delay. If the heat intensity reaches a critical level, the main alarm is activated, warning of a potential fire hazard.

• The multi-sensor integrates both smoke and thermal sensors, combining their capabilities to enhance fire detection. Each sensor operates independently to detect specific fire indicators: the smoke sensor detects the presence of smoke, while the thermal sensor monitors temperature changes. When both sensors detect potential fire conditions, their individual signals are sent to the control panel for analysis. This dual detection approach allows for more accurate fire identification by cross-referencing both smoke density and temperature rise, reducing the likelihood of false alarms and ensuring a faster response to actual fire hazards. If the combined data reaches a certain severity, the control panel triggers a pre-alarm, followed by the main alarm if the conditions indicate a significant fire threat.

Conventional Smoke Detector:

• Conventional smoke detectors use a fixed threshold to detect smoke and produce a binary output (ON/OFF) for the alarm. In normal conditions, they draw minimal current (quiescent current), but when smoke is detected, the current increases (alarm current). This change is monitored by a fire panel, which signals a potential fire

Addressable Smoke Detector

• Addressable smoke detectors detect smoke density and trigger an alarm when it exceeds a set threshold. They offer advanced features such as pre-alarms, main alarms, false alarm management, dust contamination alerts, automatic health monitoring of individual detectors, and isolation control . These detectors communicate digitally with the control panel, enabling customizable settings, sensitivity adjustments, and unique ID assignments, providing flexibility for various building requirements.

• When selecting a smoke detector, it’s crucial to consider its sensitivity, which determines its efficiency in detecting smoke. Smoke detectors have varying sensitivities; some can detect smoke at as low as 0.05 obscuration per foot, while others require a higher threshold, such as 2%. Sensors with higher sensitivity offer quicker response times, providing earlier fire detection, while those with lower sensitivity may trigger alarms more slowly. For optimal performance, choose a detector with a sensitivity of 0.05 obs/sqft for fast, early fire signals. Detectors with higher thresholds will provide delayed responses.

• Buyer can identify the sensitivity of a smoke detector by checking the OEM’s technical data sheet.

The lifespan of a smoke detector is relatively short, with sensors typically offering accurate readings for only about two years. Smoke detectors operate on the photoelectric principle, and the smoke chamber and LED circuitry degrade over time, reducing sensitivity. As a result, periodic calibration is necessary to restore the detector’s original sensitivity.

Regular calibration is not only important for accuracy but is also mandated by codes and standards. Calibration records are required for fire safety inspections, and are necessary for NOC renewal submissions.

Key Considerations When Choosing a Smoke Detector:
1. Choose a high-sensitivity smoke detector.
2. Ensure the manufacturer offers calibration services at a reasonable cost.
3. Confirm availability of smoke detectors for future replacements and system expansions.

While periodic checks using incense sticks (agarbathi) may suggest the sensor is working, this method is not a reliable way to verify its functionality. Even if a smoke detector seems to work properly, it may still be deteriorating internally, compromising its effectiveness. Regular professional calibration is critical to ensuring the detector performs as expected, as neglecting calibration can jeopardize fire safety and affect insurance coverage in case of a fire. All stakeholders, including building owners, fire authorities, and contractors, must ensure that smoke detectors are properly calibrated and functioning for maximum safety.

Life of smoke detector is too short, it may  give correct measurements hardly for two years. Smoke detector works on photo electric principle. Smoke chamber LED and its allied circuit gets deteriorate due to aging, hence the sensitivity of smoke detector losses it’s sensitivity. Out of range sensitivity detector may not deliver its function. Hence the smoke detector required periodical calibration. ( refer IS 2189 )