Työntekijöiden suojaaminen ilmavälitteisiä taudinaiheuttajia vastaan toimistoympäristössä - Työsuojelurahaston tutkimushanke #210099 (SUOJAILMA)

The COVID pandemic showed that airborne transmission is an important route for pathogen spreading among office workers. People carrying pathogens may be completely unaware of it so protection against airborne transmission is important in office environments. Different face masks became familiar for most as a protection method during the recent pandemic but there are also other means to protect people such as air purifiers and partitions acting as flow obstruction. Also, air distribution can be used to reduce contaminant concentrations in the occupied zone. In this Finnish Work Environment Fund project laboratory measurements and computer simulations were used to study the effect of air purifiers, masks, and air distribution onto pathogen exposure when an infected person spreads aerosols in a room either through breathing or coughing. A coughing machine and a breathing thermal manikin were used to spread and receive aerosols, respectively. Airborne pathogens were modelled with paraffin oil -based aerosol and MS2 viruses, and effectiveness of different protection methods was studied. Additionally, ventilation effectiveness and contaminant removal efficiency were investigated with SF6 as a marker gas. Computer simulations were conducted with CFD.

The measurement results showed that masks and air purifiers were the best means of protection against pathogens transmitted via breathing whereas flow obstruction with e.g. partitions or the infector wearing a mask or visor was effective against coughing. With mixing ventilation contaminant concentrations were similar throughout the occupied zone but displacement ventilation introduced both temporal and spatial differences. Both the best and the worst local concentrations were achieved with displacement ventilation. CFD simulations showed that in a large open office an infector at the center of the space spreads contaminants efficiently in all directions. When the infector was seated in the corner, the contaminants became attached to walls and moved alongside them outside the occupied zone. As expected, the best situation was when the infector sat near the exhaust. Even with an undersized (purifier airflow equal to space supply airflow) air purifier, the size of high-concentration zones in the open office could be clearly reduced. It can be deduced from the results that there are many effective ways to protect workers against airborne transmission of pathogens in office environments, and the best outcome can be achieved by combining them. Masks can prevent pathogens from entering the space, air purifiers remove pathogens already in the space or entering it, and flow obstruction with e.g. partitions prevents fast-moving pathogens originating from coughs and sneezes from reaching the exposed person. Proper air distribution on the other hand helps transfer the pathogens away from the occupied zone.