 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, such as is the case for Wagner, Safe Fire Detection's ProSeries and Xtralis ASD systems.In 1970 the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) used a nephelometer to carry out research into forest fires.