SPONSOR CPD PROGRAMME Hospital indoor air quality Continuing professional development (CPD) is the regular maintenance, improvement and broadening of your knowledge and skills, to maintain professional competence. It is a requirement of CIBSE and other professional bodies. This Journal CPD programme can be used to meet your CPD requirements. Study the module and answer the questions on the final page. Each successfully completed module is equivalent to 1.5 hours of CPD. Modules are also available at www.cibsejournal.com/cpd This module explores the various elements that come together to determine overall indoor air quality in healthcare facilities Indoor air quality (IAQ) in hospitals will significantly impact occupant health and wellbeing. Aside from the more recent impacts of the spread and containment of SARS-CoV-2 in healthcare facilities, there are many other airborne pollutants that, together with the air temperature and humidity, will determine hospital IAQ. This CPD will explore some of the key variables that combine to provide the allinclusive IAQ. In England alone, as well as providing a safe environment for the 35 millionplus patient bed-days, hospital air is shared by approximately one million health workers. As indicated in Figure 1 (overleaf), the sources that contribute contaminants to the indoor air are numerous and often interrelated and these will affect the quality of the environment for patients, staff, and visitors. In spaces that have at least some ventilation, CO2 is unlikely to reach levels that cause any health concerns. A CO2 limit is often set in the design specification as a proxy for the sufficiency of ventilation. However, the recent review2 by Fonseca et al notes that it can be challenging to develop ventilation strategies to address the different simultaneously-occurring indoor air pollutants with the formation of secondary pollutants from the reaction between the primary pollutants, as well as with other chemicals or those introduced by ventilation. In healthcare settings there are many microorganisms bacteria, viruses, parasites and fungi that are potentially airborne and can lead to nosocomial infections otherwise known as healthcare associated (or acquired) infections (HAI). A study by Guest et al,3 based on pre-Covid 2016-17 data, estimated that there were 834,000 cases of HAIs annually in the NHS in England. The proportion of infections that can be directly associated with the IAQ and the airborne load is unknown and likely impossible to establish. The 2020 review paper4 by Hiwar et al notes that IAQ parameters such as temperature, relative humidity, CO2 level, particle mass concentration, and particle size are, in any case, important for the comfort, health and wellbeing of those in hospitals, and will likely impact the bioburden in the environment. This relates to the whole hospital population Fonseca et al noted2 that headaches, fatigue, dryness and irritation of the eyes and skin are common complaints of healthcare professionals, which are often associated with poor IAQ. Air temperature and particularly humidity are linked with the survival of microorganisms, with many bacteria and fungi favouring more humid conditions and some evidence of virus survival increasing at lower humidities (typically below 40% relative humidity). Low relative humidity, as is typically encountered in heated healthcare premises in winter, also keeps large droplets suspended in air for extended periods of time.5 In this context, the term aerosol is widely applied and is variously defined but commonly understood to have a characteristic dimension smaller than 5m. As explored by Randall et al,6 there are various definitions of aerosols, with most contemporary sources relating the 5m threshold to particles that remain suspended in the air for longer periods. However, he explains that this distinction is erroneous, and is actually based on what reaches deepest in the lungs. This has likely confused the understanding of the droplet and aerosol transmission mechanisms as defined by a 5m threshold. As well as the much-investigated SARSCoV-2, there are many other airborne microorganisms that remain viable in the air in an aerosol state.7 The stability of viruses in aerosols is affected by relative humidity through several physical mechanisms, but the role of these mechanisms in virus inactivation is not fully understood. Hiwars review found conflicting results linking IAQ parameters and microorganism prevalence and survival, with any relationship being dependent on the specific microbe. Typically, the pollutants in the outdoor air that impact occupant wellbeing are the www.cibsejournal.com October 2023 61