RELATIVE HUMIDITY IN INCUBATORS

The range of relative humidity (RH) that can be achieved in three standard commercial incubators has been investigated under a variety of conditions. The range of control was sometimes limited, and often not linearly related to the control setting. In none of the incubators tested was it possible to achieve a maximum RH of 95% (as currently required by the British Standard specification), even under optimum conditions, without the use of accessory equipment. A means of measuring humidity was only provided with one incubator, and, since this hygrometer was fixed to the canopy in the boundary layer of relatively cold air, the instrument gave a falsely high reading. Marked condensation on to the cold Perspex walls obscured visibility when incubator air was more than threequarters saturated under normal ward conditions; the provision of a double-walled canopy with a sealed cavity reduced the incidence of this problem as well as halving the discrepancy between air temperature and mean radiant temperature within the incubator.