Emission of bacteria from air humidifiers

Abstract An experimental study was undertaken to determine the emission of bacteria from two different types of air humidifier. In one of the humidifiers, which is of spray type, the air is humidified by very small droplets of finely dispersed water being sprayed by nozzles into the air stream. The other humidifier is of evaporative type, in which the air is humidified by water being evaporated from a humid contact body. The emission of bacteria from the humidifiers was studied by adding Pseudomonas aeruginosa to the humidifier water. In addition, the emission of bacteria was simulated by metering polystyrene particles with a diameter of 2 μm into the humidifier water. The carry-over factor, defined as the ratio of the bacteria concentration in the humidified air to the bacteria concentration in the humidifier water, was found to be about 10 −7 for the spray-type humidifier and about 5·10 −10 for the evaporative humidifier of standard design. A modified evaporative humidifier was found to have a carry-over actor of less than 5·10 −12 when tested with particles.