Humidification in healthcare facilities

An important exception are buildings that are used for healthcare, especially hospitals. There, e.g. in operating theatres, relative humidity (RH) generally is controlled stringently at levels around 50%. From an energy point-of-view humidification is an energy-intensive activity.
Currently, more than 10% of the total energy used in buildings for healthcare is spent on humidification. The basis for an RH of around 50% is however, unclear. Therefore, we pursued a scoping review to find evidence for specific RH thresholds in such facilities. In addition, an inventory was made of the current practice in the Netherlands. In the literature review, references were selected based on keywords. Guidelines and current practice were analyzed by referring to existing (inter)national guidelines and standards, and by contacting experts from Dutch hospitals through a survey and semi-structured interviews. The literature review was grouped into four topics: 1) microbes including viruses, 2) medical devices, 3) human physiology and 4) perception. No scientific evidence was found for the currently generally applied RH set-point of approx 50%. Some studies suggest a minimum RH of 30% but the evidence is weak. A lack of research that addresses more long-term exposure (a couple of days) and includes frail subjects, is noted. Following current practice related to humidification, it was found that RH requirements are strictly followed in all hospitals consulted, some only focusing on the hot zones, but in many cases extended to the whole hospital. For humidification, steam is mostly applied due to hygienic reasons. Alternatives are available but nearly not considered yet. The conclusion, therefore, is that there is no solid evidence to support the RH- setpoints as currently applied in the Netherlands. It is merely a code of practice