Aspirated smoke detector

An aspirating smoke detector is a type of smoke detector, based on a nephelometer that is capable of detecting the presence of microscopic particles of combustion also known as (smoke) suspended in air by detecting the light scattered from the smoke particles in a sampling chamber.

In the context of smoke detection, the word aspirate means to draw in, which illustrates the basis for how these smoke detectors operate. In most cases aspirating smoke detectors require a fan unit to draw in a representative sample of air from the protected area.

History
In 1970 the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) used a nephelometer to carry out research into forest fires. Subsequently, the Australian Postmaster-General's Department (Later becoming Australia Post and Telstra) engaged the CSIRO to investigate technologies that could prevent service interruption due to fire.

After selecting a sample site to carry our research, the CSIRO suggested that the nephelometer should be used as the benchmark for the APO fire tests. This was installed to monitor smoke levels within the return-air ducts of the mechanical ventilation system, utilising a chart-recorder output display.

At the conclusion of several weeks of testing, it was discovered that there was not one commercially-available fire detection technology suitable for preventing major damage to telephone equipment. One technology that did show great promise however was the nephelometer itself.

Smoke detector sensitivity comparisons
Obscuration is a unit of measurement that has become the standard definition of smoke detector sensitivity. Obscuration is the effect that smoke has on reducing visibility. Higher concentrations of smoke result in higher obscuration levels, lowering visibility.