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Smoke Alarms Analysis

Ionization Smoke Alarms

An ionization detector consists of two metal plates with a voltage across them, along with a radiation source of americium. When alpha particles from the americium collide with oxygen and nitrogen atoms in the air, electrons from the atoms are freed. The electron has a negative charge, and the atom with the missing electron, a positive charge. The positive charged atoms are called ions. The ions are attracted to the negative plate, and the free electrons are attracted to the positive plate (opposites attract). The flow of electrons and ions is an electrical current, which is sensed by a detector. Smoke particles attach to the ions and neutralize them (zero charge). This reduces the electrical current, which is sensed by the detected.

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Typical Ionization Smoke Alarm Sensor
An Ionization Smoke Alarm Sensor consist of a Radiation Source (241 Americium) and Two Metal Plates.
Americium 241 Radiation Source from Kidde Smoke Alarm Model, i4618.

Kidde Ionization Smoke Alarm, Model i4618

Components in Kidde i4618 Smoke Alarm.
Components inside Kidde Smoke Alarm, Model i4618.
Kidde Ironization Chamber and Sensor
Ionization Chamber and Sensor - Kidde Model i4618 Smoke Alarm.
Kidde Sensor Connection to IC
One of the Sensor Plates is directly connected to the Custom Analog Integrated Circuit below the Ionization Chamber.
Americium 241
Americium 241 Radiation Source from Kidde Smoke Alarm Model, i4618.

Acoustic Agglomeration or Enhanced Soot Depositions around Smoke Alarm Horns.

In many cases whether a smoke alarm sounded can be determined by enhanced soot around the horn. Reference: 2017 NFPA 921, Sections

Smoke Alarm Induced Enhanced Soot Deposition
Acoustic Aggolmeration or Enhanced Soot Deposition caused by the Smoke Alarm Horn (F14-059).