居室における感染リスク評価手法に関する研究
新型コロナウイルスの感染拡大により，室内の空気環境への関心が高まっており，感染リスクの小さい安全な空間が求められている。呼吸器系の感染経路の中で，室内気流とともに感染原因物質が拡散するエアロゾル感染に着目し，居室の感染リスク評価を行う手法とそのクライテリアを提案する。
この評価手法では感染確率の空間分布を考慮するため，居室の座席レイアウトと感染者を事前に設定し，CFD解析で室内の気流とエアロゾル濃度の分布を求める。各座席位置における感染確率から算出した居室の二次感染者数が1人未満で感染が収束すると考え，この値を感染リスクのクライテリアと定めた。
本報では天井吹出と床吹出の2種類の空調方式で，冷房時・暖房時における１人の感染者がいる場合の感染リスクを評価した。その結果，吹出口と吸込口の配置の影響が大きいことがわかった。また，捕集率50％以上のフィルタを設置することが効果的であることを確認した。
キーワード：感染症対策，換気計画，CFD解析，エアロゾル，感染確率，感染リスク評価
＊１ 技術センター 都市基盤技術研究部 空間研究室
Research into a Method for Assessing Infection Risk in Indoor Spaces
The rapid spread of COVID-19 has led to increased interest in indoor air environments, necessitating safe spaces that have a minimal risk of infection. Focusing on aerosol transmission, one of the routes of respiratory infection, we propose a method and its criteria for assessing infection risks in indoor spaces, particularly in terms of which infectious substances are dispersed by indoor airflow.
As the proposed assessment method takes account of the spatial distribution of infection probability in indoor environments, a seating layout in a room and an infected person are predefined to determine the distribution of airflow and aerosol concentration using CFD analysis. When the number of secondary infections in a space that is calculated based on the infection probability at each seating location is less than one, the infection is considered to have converged; therefore, we have set this value as the infection risk criterion.
In this study, we assessed the infection risk when there is one infected person in a room while the room is being heated and being cooled using two types of heating/cooling systems: ceiling diffusers and floor diffusers. The results showed that the locations of the supply and return air vents had a significant impact on infection risk, and also confirmed that installing filters with a capture rate of 50% or higher was effective.
Keywords: infectious disease control, ventilation planning, CFD analysis, aerosol, infection probability, infection risk assessment
*1 Valuable Space Research Section, Urban Engineering Research Department