Addressable Smoke Detector

NXPCFS112 - Addressable Smoke Detector

Automatic Fire Detection Using Addressable Smoke Sensor

Purpose

purpose of the Smoke Detector is to detect the presence of smoke within its surveillance area. When the smoke reaches the alarm threshold level, it promptly triggers an alarm signal to the fire panel.

WHAT ARE THE MAIN PARTS OF SMOKE DETECTOR AND IT’S FUNCTION ?

Light Source: A photoelectric smoke sensor consists of LED (Light Emitting Diode) as a light source and a photodetector.

Chamber Design: The sensor chamber is designed to allow ambient air to flow freely while preventing external light from entering the sensing chamber.

Scattering of Light: In normal conditions, the emitted light from the LED does not directly reach the photodetector. However, when smoke particles enter the chamber, they scatter the light, causing some of it to be redirected towards the photodetector.

Detection Process: The photodetector senses the scattered light, and when a certain threshold is reached, it triggers the smoke alarm.

Vulnerablity of false alarm due to Dust contamination:

Smoke sensor chamber shall be maintained dark for effective smoke detection. The smoke chamber is vulnerable to get dust contamination due to pollution . Contaminated sensors tend to provide false alarm signal. Control panel shall have provision to check level of contamination, user should be periodically check the level of contamination, if any contaminated sensors are found those sensors shall be removed for cleaning and other sensors can be kept undisturbed. If any sensors are found more contaminated, control panel will raise a contamination alarm to alert user.

LIFE OF SMOKE DETECTOR AND WHY IT REQUIRES A PERIODIC CALIBRATION ?

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.

Benefits of Addressability in Smoke Detectors

1. Precise Location Identification:

Addressable smoke detectors pinpoint the exact location of a fire or smoke event, improving response times and reducing the need for manual troubleshooting.

2.Faster Response Times:

By identifying the specific detector that triggered the alarm, emergency responders can act quickly, focusing on the affected area to minimize damage.

3. Simplified System Management:

With individual monitoring and remote control capabilities, addressable systems streamline the management and maintenance of fire detection systems.

4. Customizable Settings:

Users can easily adjust sensitivity levels and set alarms based on specific needs, providing flexibility for different environments.

5. Reduced False Alarms:

Addressable detectors help reduce false alarms by providing detailed information on the cause of the alarm and distinguishing between smoke and contamination.

6. Real-Time Monitoring:

Continuous monitoring allows for proactive maintenance, with the ability to identify issues or malfunctions before they become critical.

7. Scalability:

Addressable systems can be easily expanded, making them suitable for growing facilities or changing layouts.

8. Integration with Other Systems:

These detectors can be integrated with other safety systems, such as lighting and HVAC, to ensure a coordinated emergency response.

9. Enhanced Reporting:

Detailed reports on system performance and smoke detection trends improve maintenance and regulatory compliance.

10.Cost-Effective Long-Term Solution:

Though initially more expensive, addressable detectors reduce long-term maintenance costs and minimize false alarms, providing better value over time.

In short, addressable smoke detectors offer improved accuracy, flexibility, and efficiency, making them a smart choice for comprehensive fire safety management.

Smoke Detector Placement and Spacing Guidelines

Sloped Ceilings with Beam Pockets
-Beam Pocket Locations: Spot-type detectors should be located at the bottom of beams.
-Ceiling Height: Measure ceiling height as the average height across the slope.
-Spacing:
– For beam depths ≤ 10% of ceiling height, detectors should be spaced no more than three beams apart, not exceeding smooth ceiling spacing.
– For beam depths > 10% of ceiling height, detectors should be spaced no more than two beams apart, with spacing not closer than 40% of ceiling height, and not exceeding 50% of smooth ceiling spacing.

Sloped Ceilings with Solid Joists
–Detector Placement: Detectors should be installed on the bottom of the joists.

Peaked Ceilings
–Initial Placement: Detectors should be placed within 36 inches (910 mm) of the peak, measured horizontally.
–Additional Detectors: Additional detectors, if needed, should be spaced based on the horizontal projection of the ceiling.

Shed Ceilings
–Initial Placement: Detectors should be placed within 1 mtr of the high side of the ceiling, measured horizontally.
–Additional Detectors: Additional detectors, if necessary, should be spaced according to the horizontal projection of the ceiling.

Raised Floors and Suspended Ceilings
–Separate Spaces: Areas beneath raised floors and above suspended ceilings should be treated as separate rooms for smoke detector spacing.
–Detector Requirements: Detectors beneath raised floors or above suspended ceilings cannot replace detectors within the main room.
–Raised Floors: Detectors installed beneath raised floors should comply with general smoke detector spacing guidelines.
–Suspended Ceilings: Detectors installed above suspended ceilings should follow the spacing requirements for the specific ceiling configuration.

INSPECTION, TESTING, AND MAINTENANCE

General
A well-designed and properly installed automatic fire alarm system requires continuous high standards of maintenance and supervision to ensure reliable, trouble-free operation. Regular inspections and scheduled preventive maintenance are essential, covering all system components.

Initial Installation Inspection & Tests
– A visual inspection should be conducted to verify proper placement of all detectors, ensuring they are correctly mounted and connected.
– Smoke detectors should be tested with smoke or an approved aerosol to ensure they initiate an alarm when smoke enters the chamber.
– To ensure smoke detectors are within their sensitivity range, use a calibrated test method, a manufacturer’s approved instrument, or other approved testing equipment.
– Detectors found to have sensitivity outside the approved range should be replaced.

Servicing & Periodic Maintenance
– For reliable servicing, establish a maintenance contract with a qualified contractor or ensure at least one trained employee is responsible for basic servicing, including routine sensitivity checks.
– For institutions like hospitals or hotels, ensure an engineer is available for emergency service, with a 24-hour response time. Protective measures should be taken if the premises are unoccupied.

Maintenance Schedule
– Users must obtain specific instructions from manufacturers or installers regarding routine maintenance and testing procedures.
– Maintenance routines should reflect environmental conditions; for example, detectors in harsh conditions need more frequent checks. Notify occupants if tests will activate alarms.

Annual Inspection Tests
– Annual tests should include the routine checks of detectors. At least 20% of detectors should be tested annually, ensuring that all detectors are tested over a 5-year period.
– Inspect cables and equipment for security and damage.
– Perform electrical tests every three years and document any defects.
– Record any defects found and remedied in the logbook.

General Points About Detectors
Ensure that detectors’ sensitivity ranges meet the specified requirements. Regular sensitivity checks should be carried out to maintain correct sensitivity levels throughout the service life of the installation.

Cleaning and Maintenance
Detectors should be cleaned every 3 months or more often, depending on environmental conditions. Follow manufacturer instructions for cleaning, checking, and adjusting sensitivity.

Tests Following an Alarm or Fire
Test all detectors exposed to fire conditions according to the annual inspection procedures. Inspect battery chargers and check for system-wide damage.

System Disconnection During Testing
To minimize disruption, avoid alarm activation during testing. Replace any detectors removed for servicing to ensure system contin.

What are the Vulnerabilites of false Fire Alarms due to smoke detectors Automatic fire detection primarily relies on smoke detectors

Failure or Delay in Smoke Detection:

Over time, smoke detectors can lose sensitivity, typically within two to three years, though cheaper models may lose sensitivity in under one year. This degradation impairs their ability to detect smoke effectively, leading to delayed or missed alarms and undermining the purpose of their installation.

Solution:

National and international codes and standards mandate periodic calibration of smoke detectors. To ensure reliable performance:

Select a reputable OEM that guarantees calibration services for at least five years.
Ensure availability of spare parts and service support for at least five years.
Managing False Alarms:

Contamination of Smoke Detectors:

Contamination can cause false alarms. Modern control panels and smoke detectors can indicate contamination levels and alert users, helping identify and clean affected detectors to maintain optimal performance. Some control panels can differentiate between dust and smoke, which helps reduce false alarm rates.

Preliminary Stage Alarm to Avoid False Alarms:

Since 95% of smoke incidents are not due to fire, advanced fire alarm panels and smoke detectors provide an initial alert to the control panel. This preliminary alarm allows a 30 to 45-second analysis period to determine if the smoke is from a fire. If not, the system will reset automatically to prevent false alarms, while giving emergency monitoring staff time to verify the situation. If the monitoring staff and fire alarm panel cannot confirm a fire, an external alarm will be triggered.