Abstract: An optical smoke detector for detecting particulates in an air sample. The detector includes a detection chamber defining an enclosure for the air sample. At least one opening is in fluid communication with the detection chamber whereby the air sample can be introduced and discharged from the detection chamber. A cleaning port defines a passageway to the detection chamber from a position external to the smoke detector and a resilient valve seals the cleaning port with a substantially air-tight seal. The valve member is accessible from a position external to the smoke detector. The valve member is openable, permitting passage of air through the cleaning port into the discharge chamber, by engaging the valve member with a nozzle, such as an air nozzle mounted on a canister of pressurized air.