SPONSOR CPD PROGRAMME 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 Ensuring healthy building environments with mechanical ventilation systems completed module is equivalent to 1.5 hours of CPD. Modules are also available at www.cibsejournal.com/cpd This module explores the demands on mechanical ventilation systems to maintain healthy indoor environments, as well as considering the emerging application of UV-C in air handling units For building services engineers, the prerogative to deliver healthy and productive environments is not new, but the focus on this has increased because of the recent overriding imperative to minimise the exposure of building occupants to SARSCov-2. In many cases, particularly in commercial and institutional applications, the provision of appropriately healthy indoor air will depend on mechanical ventilation. This CPD article will consider the demands on the ventilation systems to maintain healthy internal environments, and briefly explore the application of ultraviolet germicidal irradiation (UVGI) in air handling units (AHUs) as a means of providing energy efficient microbial cleaning. Air in buildings is likely to contain contaminants, including particulate matter (some biological in origin), gases, and vapours,1 and there is a plethora of guidance on the acceptable limits of common and not so common air pollutants that could impact the internal environment. Sources for many of these contaminants may be located indoors from building components, occupants and occupant activities outdoors, or both indoors and outdoors. The range of possible substances is daunting (as comprehensively illustrated in the World Health Organization (WHO) Air Quality Guidelines for Europe2) but, in terms of typical European applications, there are key chemical contaminants3 of carbon monoxide (CO) and nitrogen dioxide (NO2), and the volatile organic compounds (VOCs) formaldehyde, benzene and naphthalene. There are several of lesser significance, and their impact will be dependent on exposure levels this, notably, includes carbon dioxide (CO2). Additionally, there are bacteria and viruses, particulate matter (PM2.5, PM1.0 and ultrafine particles) and, in some locations, gases such as radon. Moderating gaseous contaminants and ultrafine particles requires air-cleaning devices in addition to general particle filters. As explained in CIBSE Technical Memorandum TM40 Health and wellbeing in building services, exposure to air pollutants can have both acute and chronic health effects, from mild to severe and the pollutants may not even be perceived by occupants. The effects can include temporary discomfort and annoyance (or pleasure) from odours, while some pollutants can have negative impacts on cognitive performance. Poor indoor air quality (IAQ) can lead to headaches, fatigue, lack of concentration, and irritation of the eyes, nose, throat and lungs; conversely, optimised ventilation providing improved IAQ has been shown to significantly improve cognitive functioning of office workers, including in areas such as crisis response, information usage and strategy.4 TM40 relates to several studies that have found benefits in improving IAQ by avoiding pollutant sources, providing adequate ventilation rates, and filtering the air supply. TM40 refers to a number of studies that found benefits in increasing fresh air rates beyond current best practice recommendations; for example, reducing non-specific symptoms, such as headaches, irritation, or self-reported lethargy, and sick leave. However, it is noted that most of these studies are inconclusive about the possible www.cibsejournal.com June 2021 63 CIBSE June 21 pp63-66 CPD 180.indd 63 21/05/2021 16:31