Using EEG to characterise drowsiness during short duration exposure to elevated indoor Carbon Dioxide concentrations

Abstract

1 Abstract: Drowsiness which can affect work performance, is often elicited through self-2 reporting. This paper demonstrates the potential to use EEG to objectively quantify changes to 3 drowsiness due to poor indoor air quality. Continuous EEG data was recorded from 23 4 treatment group participants subject to artificially raised indoor CO 2 concentrations (average 5 2,700 ± 300 ppm) for approximately 10 minutes and 13 control group participants subject to 6 the same protocol without additional CO 2 (average 830 ± 70 ppm). EEG data were analysed 7 for markers of drowsiness according neurophysiological methods at three stages of the 8 experiment, Baseline, High CO 2 and Post-Ventilation. Treatment group participants' EEG data 9 yielded a closer approximation to drowsiness than that of control group participants during the 10 High CO 2 condition, despite no significant group differences in self-reported sleepiness. Future 11 work is required to determine the persistence of these changes to EEG over longer exposures 12 and to better isolate the specific effect of CO 2 on drowsiness compared to other environmental 13 or physiological factors. 14 15 16 17 18 Practical implications: 19 This study introduces EEG as a potential objective indicator of the effect of indoor 20 environmental conditions upon drowsiness 21  Participants exposed to 2,700 ppm for 10 minutes showed greater evidence of a 22 progression towards drowsiness (as measured by EEG) than that of participants who 23 received the same protocol without additional CO 2 (mean 830 ± 70 ppm), despite 24 similar ratings of subjective sleepiness. 25 Subjective and objectively measured indications of drowsiness were reduced following 26 ventilation of the room. Future work could explore the potential of regular ventilation 27 episodes in knowledge work spaces to retain alertness. 3 28 29 Introduction 30 Being a product of human respiration, carbon dioxide (CO 2 ) increases in indoor spaces when 31 ventilation of the space is insufficient to replace stale air [1,2]. CO 2 is thus a useful indicator 32 of ventilation and, by extension air quality indoors, in occupied spaces [3,4]. A large body of 33 literature exists relating poor ventilation to mild health symptoms [2,5-7] and lowered 34 cognitive performance [4,8-10]. Office-realistic levels of CO 2 are reported to be typically < 35 3,000 ppm, but whether CO 2 itself negatively impacts cognitive performance, or whether other 36 pollutants such as volatile organic compounds (VOCs), including human bio-effluents, are 37 responsible, is still unclear [11,12]. Human performance effects have been recorded in studies 38 both where CO 2 is accompanied by human bio-effluents (e.g. the CO 2 concentration is a 39 product of poor ventilation in occupied spaces) [4,13,14] and where pure CO 2 gas is added to 40 a room to achieve steady-state concentrations [12,13,[15][16][17][18].41 At a room concentration of 3,000 ppm, human bio-effluents are found to cause an increase in 42 respired -end-tidal-CO 2 (ETCO 2 ), increased b...

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