Update of the scientific evidence for specifying lower limit relative humidity levels for comfort, health, and indoor environmental quality in occupied spaces (RP-1630)

Abstract

Nearly 600 papers were located in citation and keyword searches regarding the effects of humidity on comfort, health, and indoor environmental quality (IEQ). Of these, around 70 papers reported the effects of low humidity (RH≤40%) and were analyzed in detail. Information in some categories was well chronicled, while other categories had significant knowledge gaps.Low humidity decreased house dust mite allergens. Due to different envelopes, generalizations could not be made for all bacteria and viruses. However, lower humidity increased virus survival for influenza. For comfort, low humidity had little effect on thermal comfort, but skin dryness, eye irritation, and static electricity increased as humidity decreased. For IEQ, low humidity had non-uniform effects on volatile organic compound (VOC) emissions and perceived indoor air quality. Across many low humidity studies, ventilation rates and exposure times were noted as confounding variables. A majority of studies that used human subjects utilized exposure times of three hours or less with adult subjects; few studies used children, adolescents, or elderly subjects.

Environmental and Health Effects of Ventilation in Subway Stations: A Literature Review

“…On the other hand, humidity affects the formation and spread of air pollutants such as particles, aerosols, and microbes. But the underlying mechanisms among humidity, air pollutant, and human health need further studies [57][58][59][60][61]. High humidity may promote the accumulation and growth of microbial pathogens [62] and increase off-gassing, for example, an increase in RH of 35% can increase the missions of formaldehyde by a factor of 1.8-2.6 [25].…”

“…Low RH may cause desiccation or dehydration of nasal epithelium and, therefore, worsen the inflammations [67,68]. Thirdly, cold and low RH conditions are conducive to the survival and transmission of some influenza viruses like respiratory syncytial virus, human rhinovirus, and avian influenza virus [57,69,70], but the opposite has been observed for dust-mite allergens and other virus types [57,71,72].…”

Biological fluid dynamics of airborne COVID-19 infection

“…As far as the effect of this environmental parameter on the viral transmission is concerned, combined with that of the ambient temperature, the literature does not draw firm conclusions (Wen et al 2020). Environmental conditions corresponding to low relative humidity associated with low temperature seem to favor the stability and transmission of certain influenza viruses such as respiratory syncytial virus, human rhinovirus and avian influenza virus (Derby et al 2017;Davis et al 2016;Ikäheimo et al 2016). On the contrary, it has been observed that for dust mite allergens and other virus types (Derby et al 2017;Morawska et al 2006;Weber and Stilianakis 2008) such environmental conditions appear unfavorable to the spreading of the infection.…”

Preparation of Reversible Photoresponsive Poly(SPA‐co‐MMA) Films by Electrospinning: A Possible Route to Smart Materials for Regulating Wettability and Humidity

“…Optimum humidity is closely related to human life, both very high or low ambient humidities may contribute to severe health issues such as mouth parched, eye astringent, virus survival, and so on . Therefore, improving the microclimate and creating a suitable living environment have become a hot research topic, exploring an effective new method and producing a smart material to regulate the surrounding humidity are required urgently.…”