Estimated relative potential for airborne SARS-CoV-2 transmission in a day care centre.

We estimated the hourly probability of airborne severe acute respiratory coronavirus 2 (SARS-CoV-2) transmission and further the estimated number of persons at transmission risk in a day care centre by calculating the inhaled dose for airborne pathogens based on their concentration, exposure time and activity. Information about the occupancy and activity of the rooms was collected from day care centre personnel and building characteristics were obtained from the design values. The generation rate of pathogens was calculated as a product of viral load of the respiratory fluids and the emission of the exhaled airborne particles, considering the prevalence of the disease and the activity of the individuals. A well-mixed model was used in the estimation of the concentration of pathogens in the air. The Wells-Riley model was used for infection probability. The approach presented in this study was utilised in the identification of hot spots and critical events in the day care centre. Large variation in the infection probabilities and estimated number of persons at transmission risk was observed when modelling a normal day at the centre. The estimated hourly infection probabilities between the worst hour in the worst room and the best hour in the best room varied in the ratio of 100:1. Similarly, the number of persons at transmission risk between the worst and best cases varied in the ratio 1000:1. Although there are uncertainties in the input values affecting the absolute risk estimates the model proved to be useful in ranking and identifying the hot spots and events in the building and implementing effective control measures.

Large-scale decontamination of disposable FFP2 and FFP3 respirators by hydrogen peroxide vapour, Finland, April to June 2020.

BackgroundThe shortage of FFP2 and FFP3 respirators posed a serious threat to the operation of the healthcare system at the onset of the COVID-19 pandemic.AimOur aim was to develop and validate a large-scale facility that uses hydrogen peroxide vapour for the decontamination of used respirators.MethodsA multidisciplinary and multisectoral ad hoc group of experts representing various organisations was assembled to implement the collection and transport of used FFP2 and FFP3 respirators from hospitals covering 86% of the Finnish population. A large-scale decontamination facility using hydrogen peroxide vapour was designed and constructed. Microbiological tests were used to confirm efficacy of hydrogen peroxide vapour decontamination together with a test to assess the effect of decontamination on the filtering efficacy and fit of respirators. Bacterial and fungal growth in stored respirators was determined by standard methods.ResultsLarge-scale hydrogen peroxide vapour decontamination of a range of FFP2 and FFP3 respirator models effectively reduced the recovery of biological indicators: Geobacillus stearothermophilus and Bacillus atrophaeus spores, as well as model virus bacteriophage MS2. The filtering efficacy and facial fit after hydrogen peroxide vapour decontamination were not affected by the process. Microbial growth in the hydrogen peroxide vapour-treated respirators indicated appropriate microbial cleanliness.ConclusionsLarge-scale hydrogen peroxide vapour decontamination was validated. After effective decontamination, no significant changes in the key properties of the respirators were detected. European Union regulations should incorporate a facilitated pathway to allow reuse of appropriately decontaminated respirators in a severe pandemic when unused respirators are not available.

Performance of Asbestos Enclosure Ventilation: Laboratory Evaluation of Complex Configuration.

The aim of the study was to find out good practices for effective air distribution inside a complex shaped asbestos enclosure and for control of pressure differences between the enclosure and the surroundings. In addition, sufficient pressure difference for asbestos containment was tested. The effect of air distribution was studied in laboratory conditions by constructing an L-shaped asbestos enclosure and connecting it to a negative pressure unit. The efficiency of six different ventilation configurations was compared using a tracer decay method and the local air change indexes as the performance indicator. The sufficient negative pressure for containment was assessed by simulating person traffic to and from the enclosure and recording the pressure difference continuously. The effect of a pressure controller unit in maintaining the target pressure difference was also tested by simulating filter loadings of the negative pressure unit causing changes in the air flow rate. The results showed that high nominal air change rates alone do not guarantee good air distribution. Effective air distribution within an asbestos enclosure can be arranged by locating additional air supply openings far away from the air exhaustion point, using recirculation air with a pressure controller, or extending the exhaust location to the poorly ventilated areas. A pressure difference of at least -10 Pa is recommended to ensure a sufficient margin of safety in practical situations.

Deposition of respiratory virus pathogens on frequently touched surfaces at airports.

BACKGROUND: International and national travelling has made the rapid spread of infectious diseases possible. Little information is available on the role of major traffic hubs, such as airports, in the transmission of respiratory infections, including seasonal influenza and a pandemic threat. We investigated the presence of respiratory viruses in the passenger environment of a major airport in order to identify risk points and guide measures to minimize transmission. METHODS: Surface and air samples were collected weekly at three different time points during the peak period of seasonal influenza in 2015-16 in Finland. Swabs from surface samples, and air samples were tested by real-time PCR for influenza A and B viruses, respiratory syncytial virus, adenovirus, rhinovirus and coronaviruses (229E, HKU1, NL63 and OC43). RESULTS: Nucleic acid of at least one respiratory virus was detected in 9 out of 90 (10%) surface samples, including: a plastic toy dog in the children's playground (2/3 swabs, 67%); hand-carried luggage trays at the security check area (4/8, 50%); the buttons of the payment terminal at the pharmacy (1/2, 50%); the handrails of stairs (1/7, 14%); and the passenger side desk and divider glass at a passport control point (1/3, 33%). Among the 10 respiratory virus findings at various sites, the viruses identified were: rhinovirus (4/10, 40%, from surfaces); coronavirus (3/10, 30%, from surfaces); adenovirus (2/10, 20%, 1 air sample, 1 surface sample); influenza A (1/10, 10%, surface sample). CONCLUSIONS: Detection of pathogen viral nucleic acids indicates respiratory viral surface contamination at multiple sites associated with high touch rates, and suggests a potential risk in the identified airport sites. Of the surfaces tested, plastic security screening trays appeared to pose the highest potential risk, and handling these is almost inevitable for all embarking passengers.

Production and characterization of bioaerosols for model validation in spacecraft environment.

This study aimed to evaluate the suitability of two bioaerosol generation systems (dry and wet generation) for the aerosolization of microorganisms isolated from the International Space Station, and to calibrate the produced bioaerosols to fulfill the requirements of computational fluid dynamics model (CFD) validation. Concentration, stability, size distribution, agglomeration of generated bioaerosol and deposition of bioaerosols were analyzed. In addition, the dispersion of non-viable particles in the air was studied. Experiments proved that wet generation from microbial suspensions could be used for the production of well-calibrated and stabile bioaerosols for model validation. For the simulation of the natural release of fungal spores, a dry generation method should be used. This study showed that the used CFD model simulated the spread of non-viable particles fairly well. The mathematical deposition model by Lai and Nazaroff could be used to estimate the deposition velocities of bioaerosols on surfaces, although it somewhat underestimated the measured deposition velocities.

Local ventilation solution for large, warm emission sources.

In a foundry casting line, contaminants are released from a large area. Casting fumes include both volatile and particulate compounds. The volatile fraction contains hydrocarbons, whereas the particulate fraction mostly comprises a mixture of vaporized metal fumes. Casting fumes lower the air quality in foundries. The design of local ventilation for the casting area is a challenging task, because of the large casting area and convection plumes from warm moulds. A local ventilation solution for the mould casting area was designed and dimensioned with the aid of computational fluid dynamic (CFD) calculations. According to the calculations, the most efficient solution was a push-pull ventilation system. The prototype of the push-pull system was built and tested in actual operation at the foundry. The push flow was generated by a free plane jet that blew across the 10 m wide casting area towards an exhaust hood on the opposite side of the casting lines. The capture efficiency of the prototype was determined by the tracer gas method. The measured capture efficiencies with push jet varied between 40 and 80%, depending on the distance between the source and the exhaust. With the aid of the push flow, the average capture efficiency was increased from 40 (without jet) to 60%.