Tourism is a growing phenomenon in cities, especially in those with important heritage buildings. The conditions of physical and psychological comfort and safety for visitors are not always guaranteed when excessive numbers of visitors gather and when this situation is recurrent throughout the day, or during the tourist season. This must be even more concerning considering that, due to Climate Change, the tourist season has been extended in the destinations and thus the total number of visitors in the cities is increasing. It should be noted that a greater flow of tourists inside the historic buildings leads to an increase in CO2 emissions, especially significant in enclosed and confined spaces, mainly due to human respiration. This situation elevates the risk of deterioration of heritage assets but also poses health risks to visitors. CO2 concentration and indoor air temperature and humidity are measurable parameters within a heritage site, and their real-time monitoring through digital technologies is considered a key tool for preventive heritage conservation and ensuring people's health. For this reason, a practical monitoring experiment has been carried out in the Chapel of the Holy Chalice of the Cathedral of Valencia (Spain). The results reveal the very rapid rate at which, under current circumstances, recommended levels of CO2 to ensure human health are reached, and the long decay time required for CO2 to return to acceptable levels in the absence of mechanical means to ventilate the space. Scenarios for the future management of the site are also described in relation to the number of people that could access the Chapel.
Teruel-Recio et al. (2025) studied this question.