An aspirating smoke detector (ASD) is a system used in active fire protection, consisting of a central detection unit which draws air through a network of pipes to detect smoke. The sampling chamber is based on a nephelometer that detects the presence of smoke particles suspended in air by detecting the light scattered by them in the chamber. ASDs can typically detect smoke before it is visible to the naked eye. In most cases aspirating smoke detectors require a fan unit to draw in a sample of air from the protected area through its network of pipes. 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 engaged the CSIRO to investigate technologies that could prevent service interruption due to fire. After selecting a sample site to carry out 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 no commercially available fire detection technology suitable for preventing damage to telephone equipment. One technology that did show great promise however was the nephelometer itself. In 1979, Xtralis, then IEI Pty Ltd., produced and sold an air sampling device they called VESDA (Very Early Smoke Detection Apparatus). The company redesigned the detector in 1982 to provide the reliability, features, size and reduced cost for export markets. ASD systems have gained popularity due to their ability to sense smoke long before a catastrophic incident. Design ASD design corrects shortcomings of conventional smoke detectors by using a sampling pipe with multiple holes. The air samples are captured and filtered, removing any contaminants or dust to avoid false alarms and then processed by a centralized, highly sensitive laser detection unit. If smoke is detected, the systems alarm is triggered, and signals are then processed through centralized monitoring stations within a few seconds. Unlike passive smoke detection systems, including spot detectors, ASD systems actively draw smoke to the detector through bore holes within a piping system that runs throughout the protected area. Furthermore, ASD systems incorporate integrity monitoring to ensure an alert is raised at any time the ASD's ability to detect smoke is compromised. This