Smoke detector – Types of detectors

Smoke Detector is a tool for detecting smoke that arises from sources of fire. Smoke involves the thermal release of large quantities of solid and liquid particles into the surrounding atmosphere.  These particles that are suspended in the air are termed aerosols.

The aerosol particles that are produced in a fire are classified into two types of fire signatures according to their light scattering properties. Namely, invisible and visible fire signatures.

And there are two types of  smoke detectors, Ionisation detector and Photoelectric detector.

Ionization detectors are most effective with invisible smoke particles and Photoelectric detectors are most effective with visible smoke particles and are applied where smouldering fires are anticipated.

Ionisation smoke detectors

Ionization Smoke Detector can react quickly to rooms with flammable materials, such as chemical chambers, with particles from 0.01 to 0.3 micron.

The sensor on the ion detector consists of two electrically charged plates and radioactive material between positive and negative plates. Collisions between molecules cause positive and negative ions. The ion will be attracted to both plates and cause a current with a certain value. If the chamber is exposed to smoke, the ion particles will change according to the incoming smoke and affect the current to a certain value and then the detector will work

This smoke detector type works on 2 dielectric pleats and a radiocarbon source to ionize the air between the two plates. Positive ions will be channelled from the positive terminal to the negative terminal, and vice versa electron ions will be channelled from the negative terminal to the positive terminal. If a smoke particle has sufficient levels to block the process of channelling these molecules, the current monitored by this tool will increase, when the current reaches a certain point, the alarm will sound.

Where smoke will enter through the cracks at the end of the smoke detector which will hinder the process of moving ions from negative electrodes to positive or vice versa.

Photoelectric smoke detector

Photoelectric sensors continuously emit light to a receiver diode, if the light power decreases to a certain value because it is blocked by the amount of smoke entering the detector then an alarm will occur.

In addition, there is photo smoke using a reflection system, if there is smoke coming in, then the smoke will reflect the light to the receiver. If the received light reaches a certain value then the Alarm will occur.

Photoelectric is very fast working on smoke particles between 0.3 to 10 microns. In this module used is the smoke detector.

This type of smoke detector works based on a light emitted from a light emitting diode (LED) and is received by a light receiving the sensor. This type works by giving direct radiation to the light sensor receiver. The system will alarm if smoke blocks the light reaching the light receiving sensor.

• Light Source can be an LED.
• The light sensitive tool that can be Photoresistors, Photocells, Photomultiplicators

 Advantages of Photoelectric Smoke Detectors

• Better at detecting visible smoke particles, making them more effective for smoldering fires, like those in upholstered furniture.
• Less likely to trigger false alarms due to cooking smoke, making them suitable for areas near kitchens.
• Do not contain radioactive materials, so they are easier to dispose of and have fewer environmental concerns.

Disadvantages of Photoelectric Smoke Detectors

• May react slower to flames and smaller particles that do not produce a lot of visible smoke.
• Generally more expensive than ionization detectors.
• Not as effective in detecting smaller, invisible particles that arise from fast-flaming fires.

Best Applications of Photoelectric Smoke Detectors

• Suitable for areas where steam and cooking activities might otherwise trigger false alarms with ionization detectors.
• Ideal for places where smoldering fires, such as those from upholstered furniture or electrical sources, are more likely.

Advantages of Ionization Smoke Detectors

• Quick detection of small, invisible smoke particles, typically produced by fast-flaming fires.
• More affordable and widely available compared to photoelectric detectors.
• Effective in areas with highly flammable materials, such as chemical labs, due to sensitivity to small particles (0.01 to 0.3 microns).

Disadvantages of Ionization Smoke Detectors

• Not as effective at detecting larger, visible smoke particles, which are common in smoldering fires.
• Can be prone to false alarms from cooking fumes or steam.
• Contains a small amount of radioactive material, which may raise disposal and environmental concerns.

Best Applications of Ionization Smoke Detectors

• Effective in storage spaces where paper or other easily ignitable materials are present.
• Suitable for areas prone to fast-flaming fires, such as those involving flammable liquids or chemicals.

Comparison of Ionization and Photoelectric Smoke Detectors

When selecting a smoke detector, understanding the differences between ionization and photoelectric types can help ensure optimal fire detection for various environments. The following table outlines the key features, advantages, and limitations of each detector type to assist in choosing the right one for your specific safety needs.