Emitted droplets and aerosols and their transmission when drying hands under an air-jet dryer

When drying hands with a high-speed air jet dryer, the jet impingement on hands can quickly atomize the remnant water on the hand skins into droplets and aerosols. Emission of droplets and liquid aerosols, their spatial transport and the possible inhaling exposure to the hand dryer user remain unclear. This investigation measured the jet flows from a downward air jet dryer, by the particle image velocimetry (PIV), the helium bubble trajectory analysis, and an ultrasonic anemometer. Emission of the droplets when turning over the hands, the droplet spatial motion, and their deposition on human body were photographed by a high speed camera. Concentrations of the liquid aerosols were monitored and the total emitted aerosol numbers and size spectrum were analyzed. The possible inhalation exposure to the emitted liquid aerosols was examined. It is found that number of droplets in size of 0.1 to 0.6 mm can deposit on the mouth and nose and the surrounding face. A typical hand drying process may emit approximately 10⁵ liquid aerosols, of which 93 % are in the submicron size. A hand dryer user may inhale thousands of the emitted liquid aerosols if drying hands without wearing face mask.