Fire Alarm Detectors (1)

1.     Photoelectric Detectors

Photoelectric smoke detectors use light and how it is reflected to detect smoke. Normally light is projected into a smoke sensing chamber inside the detector assembly. The light hits a black background of the chamber and is absorbed. When enough smoke enters the chamber it reflects the light on to a sensor inside the chamber. This causes the sensor to indicate an alarm. Photoelectric detectors are suitable for most applications giving the fastest response to slow burning fires - the most common start to fire events. Use of photoelectric detectors is highly recommended to provide coverage for escape routes due to their superior ability to detect optically dense smoke that would easily obstruct the use of escape routes.

2.     Ionization Detectors

    Ionization detectors were the first type of detector to be commercially developed and are also a popular choice. These generally contain two chambers. One is used as a reference to compensate for changes in ambient temperature, humidity or pressure. The second contains a radioactive source, usually alpha particle, which ionizes the air passing through the chamber where a current flows between two electrodes. When even invisible smoke enters the chamber and it disrupts the flow of current and generates an alarm.

  

3.      Heat Detectors

The detector shall be a combined unit including both fixed temperature element and rate of rise temperature element. Each heat detector shall incorporate a dual thermal element which responds to either an excessively high temperature or a rate of rise of temperature which is unacceptable. The heat detector shall operate on the principle that one element is exposed to the atmosphere whilst the other is contained in such a way that is not so readily affected by increasing temperature. At a certain rate of rise of temperature or at a pre-set fixed temperature, the imbalance between the two elements shall cause the detector to trigger. The fixed element of the heat detector shall be the type that can be reset or renewed detection. The detector shall be fully operational after initiation of an alarm without any maintenance.