Ventilation and COVID-19 transmission risks on board of Dutch governmental ships

The Dutch government (specifically the ‘Rijksrederij’, the governmental shipping company) owns a fleet of just under 100 ships that are equipped to service the internal waterways and parts of the North Sea. Think in this context of e.g. Coast Guard ships, ships that help to fight oil accidents or ships that maintain buoys. Just after the COVID-19 pandemic had started the ‘Rijksrederij’ decided that it was necessary to investigate to what extent the fleet might pose a risk for cross contamination of this new disease on board. This was approached with a specific focus on ventilation and the airborne route. The objective was to find out whether the most important spaces on board of the ships were adequately ventilated and to evaluate how ships can be made or kept ‘COVID-resistant’ as far as the airborne route is concerned. A sample of 16 ships of different types, most of them mechanically ventilated, were surveyed. This included a general inspection, an inspection of relevant HVAC system characteristics and measurements of e.g. air supply flows. Also, ships were equipped with monitors that measured CO2 concentration (e.g. in galleys and wheelhouses) that were left on board for at least one week. As reference for the supply flow measurement outcomes we used ISO 7547 guideline values and the Germanischer Lloyd ventilation requirements. On board of 6 of the 16 ships that were investigated we found serious problems with the fresh air supply and/or measured CO2 concentrations. On the positive side, the majority of the ships had ventilation capacities in line with the two reference standards, and almost all did not use central recirculation. We also found that many of the ships had adequate options, at room level, for individual control of both fresh air supply and temperature. The results of the study will be used to further improve ‘COVID safety’ on board of the whole fleet and to ameliorate future, new ships and their HVAC systems.Support AE+

Respiratory infection risk-based ventilation design method

A new design method is proposed to calculate outdoor air ventilation rates to control respiratory infection risk in indoor spaces. We propose to use this method in future ventilation standards to complement existing ventilation criteria based on the perceived air quality and pollutant removal. The proposed method makes it possible to calculate the required ventilation rate at a given probability of infection and quanta emission rate. Present work used quanta emission rates for SARS-CoV-2 and consequently the method can be applied for other respiratory viruses with available quanta data. The method was applied to case studies representing typical rooms in public buildings. To reduce the probability of infection, the total airflow rate per infectious person revealed to be the most important parameter to reduce the infection risk. Category I ventilation rate prescribed in the EN 16798-1 standard satisfied many but not all type of spaces examined. The required ventilation rates started from about 80 L/s per room. Large variations between the results for the selected case studies made it impossible to provide a simple rule for estimating the required ventilation rates. Consequently, we conclude that to design rooms with a low infection risk the newly developed ventilation design method must be used.Support AE+

Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks

Some infectious diseases, including COVID-19, can undergo airborne transmission. This may happen at close proximity, but as time indoors increases, infections can occur in shared room air despite distancing. We propose two indicators of infection risk for this situation, that is, relative risk parameter (Hr) and risk parameter (H). They combine the key factors that control airborne disease transmission indoors: virus-containing aerosol generation rate, breathing flow rate, masking and its quality, ventilation and aerosol-removal rates, number of occupants, and duration of exposure. COVID-19 outbreaks show a clear trend that is consistent with airborne infection and enable recommendations to minimize transmission risk. Transmission in typical prepandemic indoor spaces is highly sensitive to mitigation efforts. Previous outbreaks of measles, influenza, and tuberculosis were also assessed. Measles outbreaks occur at much lower risk parameter values than COVID-19, while tuberculosis outbreaks are observed at higher risk parameter values. Because both diseases are accepted as airborne, the fact that COVID-19 is less contagious than measles does not rule out airborne transmission. It is important that future outbreak reports include information on masking, ventilation and aerosol-removal rates, number of occupants, and duration of exposure, to investigate airborne transmission.Support AE+

A paradigm shift to combat indoor respiratory infection

Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Indoor EnvironmentSupport AE+