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Design Method to Prevent Airborne Infection in an Emergency Department

Design Method to Prevent Airborne Infection in an Emergency Department This study investigated design recommendations to reduce airborne infection risk in an emergency department by using airflow network simulation. The main design concepts include isolating the source of the airborne pathogen and increasing the ventilation rate. A conventional emergency department is selected as a base model, and influenza is selected as the airborne pathogen examined in the study. The Wells–Riley equation is used to model airborne infection risk in a zone. The simulation results indicate that airborne infection risk exists when a patient releases an influenza pathogen in the emergency department with a ventilation rate of 3 ACH according to the Korean building code. The findings reveal that isolating the airborne pathogen source and increasing the ventilation rate are good methods to prevent airborne infection risk. However, the isolation method can increase the infection risk in a zone with an airborne pathogen source. Thus, it is necessary to simultaneously increase the ventilation in a zone with an airborne pathogen source. Additionally, airborne infection risk continuously increases the cumulative exposure time, and it is desirable to increase the ventilation rate required for a zone based on the residing time of a patient releasing airborne pathogens in a target zone. Keywords: airborne infection; ventilation; isolation room; Wells–Riley equation; emergency department 1. Introduction ventilation rate of the emergency department when the Recently, airborne infections in hospitals have cost is not considered (Nardell, 1991; Zhou, Qi, et al. emerged as a social problem in South Korea. Patients 2017; Qian, Hua, et al. 2010). with respiratory symptoms of an airborne disease can However, in the case of existing buildings or small easily visit hospitals. Additionally, medical staff and buildings, it is difficult to change an HVAC (heating, visitors are often in the same area as such patients, and ventilation, and air-conditioning) system in a short thus, a cross-infection risk exists (Kowalski 2006). time. Specifically, emergency rooms are associated In developed countries, it is considered that a crucial with high risks of spread of airborne infection owing design factor to prevent airborne infection in a hospital to their open floor plans and lack of adequate facilities is to increase the ventilation rate from 6 ACH (air (Cheong & Seo, 2016). Previous studies (Li et al., change per hour) to 12 ACH (AIA, 1996–97). However, 2007) did not provide strong scientific evidence for in the case of South Korea, design standards to prevent infection control. Therefore, it is helpful to provide airborne infection in hospitals are not clearly presented design guidelines that can be applied in early stages to date in terms of building code requirements. of the design implementation of hospital facilities. Various attempts to build new constructions for Hence, this study presents a case study detailing the airborne infection control have been implemented. performance of airborne infection risk evaluation in a However, suitable countermeasures for preventing conventional emergency department and verifies the airborne transmission in a conventional emergency design recommendation. room are absent in South Korea. Evidently, the most effective method involves significantly increasing the 2. Methods 2.1 Simulation Tools In this study, CONTAMW ver 3.2 is used to analyze the transmission of airborne pathogens. This program *Contact Author: Seonhye Lee, Assistant Professor, utilizes airflow network, and it can simply analyze Department of Nursing, Gyeongnam National University of airflow patterns and airborne pollutant concentrations Science and Technology, Korea in a multi-zone building. Existing studies used Tel: +82-55-751-3653 Fax: +82-55-751-3659 CONTAMW to analyze airborne pathogen transmission E-mail: shlee@gntech.ac.kr in hospitals (Noakes, 2008; Park, et al. 2011). ( Received March 30, 2017 ; accepted July 23, 2018 ) DOI http://doi.org/10.3130/jaabe.17.581 Journal of Asian Architecture and Building Engineering/September 2018/588 581 2.2 Wells–Riley Equation waiting room is the space where the patient's caregiver In this study, CONTAMW is used to identify the waits while the patient receives medical treatment. concentration of airborne pathogens in a specific zone. Generally, it is located extremely close to the entrance However, the concentration of airborne pathogens area (vestibule/lobby) and triage, and thus, airborne obtained by CONTAMW does not correspond to the pathogens generated from the triage area are easily probability of airborne infection. Therefore, to analyze transferred to this area. Figure 1 the risk of airborne infection in a specific zone, it is necessary to convert the concentration value of the airborne pathogen to the probability of airborne infection. Generally, the Wells–Riley model is used to evaluate the risk of airborne infection (Wells, 1995; Rudni ck, 2003; Issa row, 2015; Z hu, 2011, Qua n, 2009). Equation 1 presents a general expression of the Wells–Riley model for a well-mixed condition as follows: ೟೛೜಺ ஼ ି ܲ ൌ ൌ ͳെ݁ ……………(1) ௌ Fig.1. Diagram of the Areas in an Emergency Department where Table 1. Representative Areas in an Emergency Department P : airborne infection probability of a susceptible Spaces Features Usage person - Determine severity of Triage Opens to the C: number of infection cases patient's condition Area lobby -Perform a simple diagnosis I: number of infectious individuals General p: breathing rate of a susceptible individual (m /min) -Patients usually receive treatment Open area q: quantum generation rate by an infectious individual medical treatment. area s: number of susceptible individuals in the space Waiting Separated t: duration of exposure -Waiting area for a caregiver room area 2.3 Target Area The emergency department is functionally divided 2.4 Major Variables into various areas. Therefore, it is necessary to In this study, methods considered for preventing distinguish between the space in which an airborne airborne transmission are as follows: pathogen is emitted and the space in which infection occurs. It is assumed that a patient with an airborne ① Isolating the source of the airborne pathogen infection pathogen visiting an emergency department ② Increasing the ventilation rate in the area first travels through a triage area located near the entrance. Subsequently, a simple diagnosis Architecturally, it is possible to divide an open space is performed in the triage area, which lasts for into partitioned individual spaces. The use of partitions approximately 30 min. The patient is thereafter moved to separate an area is an easy method to prevent to the general treatment area or acute treatment area airborne pathogen transmission without replacing the to receive medical treatment. In the study, a situation HVAC system. Thus, a patient's family or caregiver can is selected in which a patient's circulation begins from wait in the waiting room of an emergency department. the entrance and proceeds to a triage/general treatment Generally, these individuals are not considered to be area. infected by the airborne disease. Thus, it is necessary Fig.1. conceptually illustrates the assumed risk of to prevent the transmission of the airborne pathogen each area in an emergency department with respect to from other areas of the hospital to this waiting room. the transmission of airborne infection. It is assumed The waiting room area is adjacent to the entrance and that the risk of airborne infection corresponds to the lobby. Two types of waiting rooms are considered. The openness of the area and the densities of patients, first type of waiting room opens to a lobby and a triage companions, and medical staff. area. The second type of waiting room is isolated from Table 2. presents the target spaces analyzed in the the lobby and triage area and opens to the vestibule. study. Specifically, patient medical treatments are In this case, the door between the vestibule and lobby performed in the general treatment area, and it is (triage area) is closed. assumed that there is a high possibility of airborne Increasing the ventilation rate is a classical and transmission in this area. The triage area is a place certified method of reducing the concentration of where patient urgency is determined. Thus, all patients airborne pathogens, resulting in reduced airborne visit the triage area. Therefore, in the triage area, infection risk. The building code guidelines in South there is a high latent possibility of cross-infection Korea do not specify the detailed design guidelines between the patient and medical staff at all times. The for HVAC systems in an emergency department. The 582 JAABE vol.17 no.3 September 2018 Chang Heon Cheong Figure 2 existing building code only necessitates a ventilation rate of 36 m /person·hour in large hospitals with floor areas exceeding 2000 m . This corresponds to approximately 2.4 ACH when the minimum floor area required for a patient is considered (Sung, 2015). Table 2. lists the air change rates in an emergency department as specified by previous studies (Cho et al., 2016; Sohn et al., 2014; Park & Kim, 2012; ASHRAE). The baseline for the ventilation rate in an emergency department area is assumed to be 3 ACH. The following two variables are considered to identify the effect of increased ventilation rate on the dispersion Fig.2. Floor Plan of a Target Emergency Department of an airborne pathogen in an emergency department: ventilation rates of 6 ACH and 12 ACH. The air supply Table 3. Features of the Target Emergency Department is entirely obtained from outdoor air (100%). Floor area Volume Ventilation Spaces 2 3 Table 2. Ventilation Rate in Conventional Hospital Design (m ) (m ) Condition Vestibule 16.0 43.2 Authors Total Outdoor air Recirculation (year) supply air of Indoor air Waiting room 52.0 140.4 Cho et al. 6 ACH 2 ACH Not specified Triage area + Lobby 121 326.7 Supply:3ACH (2016) Aisle 107 288.9 Return:3ACH Sohn et al. 6–12 - Not specified Acute treatment area 93.0 251.1 (2014) ACH General treatment 555.0 1498.5 Park & 6 ACH - Not specified area Kim (2012) Toilet 15 40.5 Return:6ACH ASHRAE 12 ACH 5 ACH Not permitted 4. Simulation Outline HVAC (With the applications exception of HEPA 4.1 Boundary Condition of the Base Model filter application) Fig.3. illustrates the CONTAMW modeling of an existing emergency room. In the simulation model, 3. Target Emergency Department the operation room and the closed areas are excluded. 3.1 Floor Plan The doorways between rooms are set with respect to An existing emergency department is selected a two-way flow model (single opening). The model as a sample space to evaluate the effect of design simultaneously reflects the incoming and outgoing factors of an emergency department on preventing the airflows by using the buoyancy effect. Detailed transmission of airborne pathogens. equations with respect to the two-way flow model are Fig.2. illustrates the floor plan of a selected provided in the CONTAMW user manual. However, emergency department. A waiting room, triage area, the simulation is focused on the ventilation rate and and acute treatment area are located near the vestibule airflow by pressure difference. The indoor temperature and lobby spaces. The two spaces open to the lobby, at each zone is set to 20 °C. Figure 3 triage area, and aisle. The aisle is connected to the general treatment area. Consequently, it is possible Vestibule Acute treatment area General treatment area Waiting room for an airborne pathogen to travel to any part of the Toilet emergency department. Additionally, two toilets are located in the waiting room and lobby. Generally, Aisle a toilet is maintained at a pressure lower than that Triage area opened to lobby of other areas to prevent unpleasant odors and the Destination area dispersion of contaminants. (Waiting room) Table 3. lists the floor area, volume, and ventilation Toilet condition of each space. As previously stated, the 2 3 (negative pressure) 1 5 basic ventilation rate is set as 3 ACH based on identical supply and return air volume conditions. The Airflow model ventilation rates of the toilets are set to 6 ACH and are Droplet nuclei emission source (Triage area opened to lobby) only based on return air. These types of ventilation Fig.3. Simulation Model (CONTAMW 3.2) settings permit indoor airflows from the general treatment area and entrances to toilets. The measured data from a previous investigation (Jo et al., 2007) are used to determine the air-tightness of an envelope system and an entrance door. The discharge coefficient and exponent of the large opening are 0.78 and 0.5, respectively. JAABE vol.17 no.3 September 2018 Chang Heon Cheong 583 Table 5. Simulation Case I Table 4. shows the detailed airflow models of the (airborne pathogen source is located in the triage area) openings. Cases Controlled variable Conditions Table 4. Airflow Components Waiting room access Base I - from lobby Size No Type Properties Ventilation rate: 3 ACH h(m)×w(m) Entrance location of the Waiting room access 1 2.7×3.9 Case 1 Discharge coefficient: waiting room from the lobby vestibule 2 2.7×2.4 Two-way flow 0.78 Case 2 Ventilation rate: 6 ACH 3 2.7×5.4 Increased ventilation rate One-opening Ventilation rate: 12 4 2.7×3.2 at lobby Case 3 Exponent: 0.5 ACH 5 2.1×0.9 6 One-way flow - 430 CMH at 50 Pa Table 6. Simulation Case II using power 2 2 7 - EqLA 1.51 cm /m (airborne pathogen source is located in the general treatment law area) Cases Controlled variable Conditions The type of airborne pathogen is considered to be Waiting room access influenza, and its emission intensity is set based on a Base II - from lobby previous study. Ventilation rate: 3 ACH In the simulation modeling, the emission intensity of Case 4 Ventilation rate: 6 ACH Increased ventilation rate the airborne pathogen is set at 1 kg/min. It is considered in the general treatment Ventilation rate: 12 Case 5 equivalent to approximately 9 airborne pathogens area ACH emission per minute (Marsden, 2003). Subsequently, area. The simulation model reflects the patient the concentration of pathogens in a specific area is circulation when the patient first stays in the triage changed to a dimensionless value and finally to the area for 30 min and subsequently stays in the general number of airborne pathogens per unit volume. The treatment area for 4 h. Case II reflects the changed quantity of air inhaled by a susceptible individual is access to the waiting room. The ventilation rate in this set at 9.6 L/min. It is assumed that the sources of the case is 3 ACH. Cases 4 and 5 represent conditions with airborne pathogen are located in the triage area and increased ventilation rates of 6 ACH and 12 ACH, general treatment area based on patient circulation. respectively, in the general treatment area. Natural deposition of influenza virus at the inner surface of each zone is not considered in the simulation. 5. Results and Discussions It is a more conservative condition that increases the 5.1 Airborne Pathogen Sources in the Triage and concentration of airborne pathogens in air. Lobby Areas A t r a n si e n t si m u l a t i o n u si n g C ONTAMW i s 1) Base I performed to analyze the distribution pattern of With respect to the overall pressure distribution in an airborne infection within the emergency department. emergency department, negative pressure in a toilet is 4.2 Simulation Cases the main driving force for the airflow. Hence, airflows Simulation cases are established by considering are formed from the general treatment area and patient circulation with respect to airborne pathogens. outdoor areas to the toilets. Specific airflow routes that Table 5. presents the simulation cases in cases in which influence the airborne pathogen concentration in the an airborne pathogen source (patient) is located in the waiting room and lobby (triage area) are as follows: triage area (lobby). In these cases, individuals located in the lobby (triage area) and waiting room are at a risk Entrance (outdoor) → vestibule → lobby → of airborne infection. It is assumed that a patient who ① waiting room → toilet releases airborne pathogens remains in the triage area General treatment area → lobby → waiting room for 30 min. The triage area is located in the lobby. ② → toilet Base I model corresponds to a conventional condition in which an airborne pathogen source is Fig.4. illustrates the concentrations of airborne located in the triage area and the waiting room is pathogen and infection risk for Base I. The concentrations accessible from the lobby (triage area). of airborne pathogen in the lobby (triage area) and waiting Case 1 corresponds to the modified plan type room increase for a period of 30 min when a patient in which the waiting room is accessible from the releasing airborne pathogens (hereafter referred to as a vestibule. The conventional door placed between the PRAP) enters the triage area. A period of approximately 1 lobby (triage area) and waiting room is closed. h is required to remove airborne pathogens in the spaces Case 2 and 3 correspond to increased ventilation rate after a PRAP leaves the triage area. However, infection in the lobby and triage area. Ventilation rates in Case 2 risk is related to the overall exposure of a susceptible and Case 3 are set as 6 ACH and 12 ACH, respectively. person (hereafter referred to as an SP) to airborne In simulation case II, the patient who releases the pathogen, which increases continuously although the airborne pathogen is located in the general treatment 584 JAABE vol.17 no.3 September 2018 Chang Heon Cheong PRAP leaves the triage area. The infection risks after 2 h According to Fig.6., the infection risks in the waiting of exposure in the waiting room and lobby (triage area) room and the lobby are significantly reduced to 2.3% are 3.8% and 10.0%, respectively. and 6.1%, respectively. Figure 6 Figure 4 Concentration(Case 2-waiting room) Concentration(Case 2-lobby) Concentration(Base I-waiting room) Concentrstion(Base I-lobby) Infection risk(Case 2-waiting room) Infection risk(Case 2-lobby) Infection risk(Base I-waiting room) Infection risk(Base I-lobby) 0.40 16% 0.40 16% 0.35 14% 0.35 14% 0.30 12% 0.30 12% 0.25 10% 0.25 10% 0.20 8% 0.20 8% 0.15 6% 0.15 6% 0.10 4% 0.10 4% 0.05 2% 0.05 2% 0.00 0% 0.00 0% Fig.6. Infection Risks (Case 2) Fig.4. Infection Risks (Base I) 2) Case 1: Changed access to the waiting room When the ventilation rate in the lobby (triage area) is Case 1 changes the access to the waiting room from increased to 12 ACH, the infection risk in the waiting the lobby to the vestibule. The results of the alternative room is 1.3%, and that in the lobby is 3.5%. The arrangement are shown in Fig.5. The changed access implementation of a ventilation rate of 12 ACH in the type to the waiting room influences the airflow pattern lobby (triage area) is an extremely effective solution to to the waiting room. prevent the dispersion of airborne pathogen (Fig.7.). Figure 7 The main airflow to the waiting room is determined Concentration(Case 3-waiting room) Concentration(Case 3-lobby) as follows: entrance (outdoor) → vestibule → waiting Infection risk(Case 3-waiting room) Infection risk(Case 3-lobby) room → toilet. An airborne pathogen from the triage 0.40 16% area is not transmitted to the waiting room. In this case, 0.35 14% the infection risk in the waiting room is 0%. Changing 0.30 12% the access from the vestibule to the waiting room 0.25 10% effectively isolates the waiting room from the airborne 0.20 8% pathogens generated in the lobby. The results indicate 0.15 6% that isolating a specific area from airborne pathogen 0.10 4% sources is an effective solution for preventing the 0.05 2% spread of airborne infections. However, the infection 0.00 0% risk in the lobby is slightly increased. The infection risk in the lobby (triage area) is 11.9%. Additional solutions are required to prevent expected increases Fig.7. Infection Risks (Case 3) in the infection risks at the zone where airborne pathogens are released. 5.2 Pathogen Source in the General Treatment Area Figure 5 1) Base II Concentration(Case 1-waiting room) Concentration(Case 1-lobby) Base II considers the condition in which a PRAP Infection risk(Case 1-waiting room) Infection risk(Case 1-lobby) remains in the general treatment area for 4 h after 0.40 16% visiting the triage area. As shown in Fig.8., the 0.35 14% airborne infection risk in the general treatment area 0.30 12% continuously increases during the patient's occupancy 0.25 10% period. The airborne infection risk in the general 0.20 8% treatment area increases to approximately 24.1% after a 0.15 6% period of 6 h after the PRAP visits the emergency area. 0.10 4% The infection risk in the general treatment area linearly 0.05 2% increases after the airborne pathogen concentration 0.00 0% reaches a steady state. The simulation result indicates that the transmission of airborne pathogen from the general treatment area to the aisle is restricted, because Fig.5. Infection Risks (Case 1) no available opening at the general treatment area is 3) Cases 2 and 3: Increased ventilation rate modeled. An airflow rate of 6.7 m /h is generated from In Case 2, the ventilation rate of the triage is doubled the general treatment area to the aisle. This indicates and is 6 ACH with respect to the source control. that a maximum of approximately 0.76 infectious JAABE vol.17 no.3 September 2018 Chang Heon Cheong 585 Airborne pathogen concentration Airborne pathogen concentration (particles/m ) (particles/m ) 0:00 0:00 0:15 0:15 0:30 0:30 0:45 0:45 1:00 1:00 1:15 1:15 1:30 1:30 1:45 1:45 2:00 2:00 Infection risk(%) Infection risk(%) Airborne pathogen concentration Airborne pathogen concentration 3 3 (particles/m ) (particles/m ) 0:00 0:00 0:15 0:15 0:30 0:30 0:45 0:45 1:00 1:00 1:15 1:15 1:30 1:30 1:45 1:45 2:00 2:00 Infection risk(%) Infection risk(%) particles per hour move from the general treatment rate of 12 ACH is potentially too high. Hence, it is area to the aisle. The transmission of airborne pathogen extremely important to identify a latent PRAP in the increases if an operable door and window exist in the triage area and to isolate such PRAP in advance. general treatment area. Thus, an architectural design to acquire an adequate As shown in Fig.9., there is a negligible increase in area to isolate PRAPs is required even when the area the infection risk in the lobby and waiting room after a does not correspond to an isolation room with heavily PRAP moves to the general treatment area. equipped HVAC systems. Additionally, it is necessary The results indicate that, if the ventilation system that the ventilation rate required to prevent airborne works properly with an appropriate air volume, it is infection in a zone should reflect the residing time of Figure 10 possible to effectively prevent the transmission of the PRAP. airborne pathogen between each zone. Evidently, it is Concentration(Case 4-general treatment.) Concentration(Case 5-general treatment.) desirable to increase the ventilation rate to a suitable Infection risk(Case 4-general treatment.) Infection risk(Case 5-general treatment.) level if the number of PRAPs increases. 0.40 16% Figure 8 0.35 14% Concentration(Base II-general treatment area) Concentration(Base II-aisle) 0.30 12% Infection risk(Base II-general treatment area) Infection risk(Base II-aisle) 0.25 10% 0.40 40% 0.20 8% 0.35 35% 0.15 6% 0.30 30% 0.10 4% 0.25 25% 0.05 2% 0.20 20% 0.00 0% 0.15 15% 0.10 10% 0.05 5% Fig.10. Infection Risks in the General Treatment Area 0.00 0% (Case 4 and Case 5) Fig.8. Infection Risks in the General Treatment Area and Aisle 5.3 Discussions (Base II) In this study, airborne infection risks in the triage Figure 9 area, waiting room, and general treatment area are Concentration(Base II-waiting room) Concentration(Base II-lobby) analyzed based on the simulation results. The airborne Infection risk(Base II-waiting room) Infection risk(Base II-lobby) pathogen from a PRAP is considered to be influenza. 0.40 16% T he dom i na nt a i rfl ow pa t t e rn i n a n e m e r ge nc y 0.35 14% department is determined by the exhaustion rates in the 0.30 12% toilets located near the lobby and waiting room. With 0.25 10% respect to this condition, airborne infection risks exist 0.20 8% at a zone containing the airborne infection source and 0.15 6% zones located on the route of transmission of airborne 0.10 4% pathogen. 0.05 2% The results of the case studies indicate that the 0.00 0% probability of airborne infection varies based on the concentration of airborne pathogens and exposure time. At a ventilation rate of 3 ACH, the general Fig.9. Infection Risks in the Lobby and Waiting Room treatment area is the most dangerous zone as a PRAP (Base II) resides in this area for a long time (4 h). In cases in 2) Cases 4 and 5: Increased ventilation rate which the general treatment area can become a source Cases 4 and 5 correspond to cases with increased of infection, findings suggest that the probability ventilation rates of 6 ACH and 12 ACH, respectively, of infecting surrounding individuals increases in the general treatment area (Fig.10.). The maximum significantly when a PRAP remains in the room for a cumulative airborne infection risks in the general long period. The infection probability is based on the treatment area in Case 4 and Case 5 are 12.9% and assumption that cumulative exposure to an airborne 6.7%, respectively. The results also indicate that pathogen is sustained during a period exceeding 6 increasing the ventilation rate is a good solution h. This indicates that medical staff working in an for preventing airborne infection. However, the emergency department is most vulnerable to airborne residing time of a PRAP in a specific zone evidently infection and the medium of cross-infection. Patients significantly contributes to the infection risk of an SP in present in the general treatment area for long periods an identical zone. This indicates that the infection risk also present the risk of airborne infection. in the general treatment area of 6.9% at the ventilation 586 JAABE vol.17 no.3 September 2018 Chang Heon Cheong Airborne pathogen concentration 3 Airborne pathogen concentration (particles/m ) (particles/m ) 0:00 0:00 0:30 0:30 1:00 1:00 1:30 1:30 2:00 2:00 2:30 2:30 3:00 3:00 3:30 3:30 4:00 4:00 4:30 4:30 5:00 5:00 5:30 5:30 6:00 6:00 Infection risk(%) Infection risk(%) Airborne pathogen concentration (particles/m ) 0:00 0:30 1:00 1:30 2:00 2:30 3:00 3:30 4:00 4:30 5:00 5:30 6:00 Infection risk(%) The triage area exhibits the second highest risk of ③ The required ventilation rate should be increased 10.0% in the base condition. It is assumed that a PRAP in a manner proportional to the residing time of a remains for 30 min in the triage area. The waiting room PRAP in a specific zone. has an infection risk of 3.8%. ④ Accumulated exposure time to airborne pathogen The simulation results indicate that it is possible significantly influences the infection risk. Thus, to decrease the airborne infection risk in the waiting medical staff, patients, and family members present room by changing the entrance from the lobby to the in the emergency department for long periods also vestibule such that outside air can easily flow into present higher risk of airborne infection. Appropriately the waiting room instead of the air from the lobby designed architectural features such as proper partition (triage area). However, solutions isolating the airborne installation, airflow modification among rooms, and pathogen source result in increased infection risks isolated occupancy circulation can reduce the airborne in the zones in which a PRAP remains for extended infection. periods such as the triage area and general treatment ⑤ This study is based on the generation of airborne area. Thus, it is desirable to increase the ventilation pathogens by a PRAP. Considering the worst case rate at the aforementioned zones where PRAPs remain where there are many PRAPs present, highly increased for extended periods while simultaneously isolating the ventilation rate may be required. zones. The study results indicated that negative pressures A useful method involves increasing the ventilation in the toilets are the main driving force for the r a t e i n a z o n e wh e r e t h e a i r b o r n e p a t h o g e n i s transmission of airborne pathogens. With respect to generated. In this condition, it is possible to minimize unexpected situations characterized by uncontrollable the transmission of the airborne pathogen to adjacent variables (such as strong wind, stack effects, strong zones. If proper ventilation is implemented at zones airborne pathogen generation, or other risky human near the airborne pathogen source, further transmission behavior), increasing the overall ventilation rate of the airborne pathogen can be prevented. in an emergency department is also a potential Particularly in the case of the general treatment solution. A future study will reflect the effects of the area, it is considered that increasing the ventilation aforementioned external forces. rate is essential to ensure that the occupancy period of a PRAP is significantly long. According to the South Acknowledgements Korean building code (Sung, 2015), the required This study was supported by the Basic Science ventilation rate in a hospital is approximately 2.4 ACH. Research Program through the National Research Thus, it is necessary to increase the ventilation rate in Foundation of Korea (NRF) funded by the risky zones such as the general treatment areas, triage Ministry of Science, ICT & Future Planning (No. areas, and waiting rooms. In this case, the required 2015R1C1A1A01051740). ventilation rate must reflect the intensity of generation of airborne pathogen and the residing time of PRAPs. Authors Contributions Chang Heon Cheong designed the research plan, 6. Conclusions performed CFD simulation, and drafted the manuscript. This study analyzed the effectiveness of two design Beungyong Park analyzed the simulation results. factors—namely isolating the airborne pathogen Seonhye Lee reviewed the results of the study with source and increasing the ventilation rate—on airborne respect to hospital environment, airborne infection, and infection control by using CONTAMW simulation. It public health. All authors read and approved the final is also expected that the results of the study can help version of the manuscript. in evaluating airborne infection risks in an emergency room and in improving the architectural design of Conflicts of Interest emergency rooms within a short period. The authors declare that there are no conflicts of The main results of the study can be summarized as interest. follows: ① Potentially optimal solutions for airborne Note The original value given by Marsden, A.G. (2003) is 515 infection control are isolating the airborne pathogen pathogens per hour. source and increasing the ventilation rate. ② It is necessary to simultaneously implement isolation of the airborne pathogen source and an increase in the ventilation rate at the airborne pathogen source to prevent increased infection risk in the zone where airborne pathogens are generated. 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(2017) The lock-up phenomenon of exhaled flow in a stable thermally- stratified indoor environment, 116, pp.246-256. 21) Zhu, S., Srebric, J., Spengler, J.D., and Demokritou, P. (2012) An advanced numerical model for the assessment of airborne transmission of influenza in bus microenvironments, Building and Environment, 47, pp.67-75. 588 JAABE vol.17 no.3 September 2018 Chang Heon Cheong http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Asian Architecture and Building Engineering Taylor & Francis

Design Method to Prevent Airborne Infection in an Emergency Department

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Taylor & Francis
Copyright
© 2018 Architectural Institute of Japan
ISSN
1347-2852
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1346-7581
DOI
10.3130/jaabe.17.581
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Abstract

This study investigated design recommendations to reduce airborne infection risk in an emergency department by using airflow network simulation. The main design concepts include isolating the source of the airborne pathogen and increasing the ventilation rate. A conventional emergency department is selected as a base model, and influenza is selected as the airborne pathogen examined in the study. The Wells–Riley equation is used to model airborne infection risk in a zone. The simulation results indicate that airborne infection risk exists when a patient releases an influenza pathogen in the emergency department with a ventilation rate of 3 ACH according to the Korean building code. The findings reveal that isolating the airborne pathogen source and increasing the ventilation rate are good methods to prevent airborne infection risk. However, the isolation method can increase the infection risk in a zone with an airborne pathogen source. Thus, it is necessary to simultaneously increase the ventilation in a zone with an airborne pathogen source. Additionally, airborne infection risk continuously increases the cumulative exposure time, and it is desirable to increase the ventilation rate required for a zone based on the residing time of a patient releasing airborne pathogens in a target zone. Keywords: airborne infection; ventilation; isolation room; Wells–Riley equation; emergency department 1. Introduction ventilation rate of the emergency department when the Recently, airborne infections in hospitals have cost is not considered (Nardell, 1991; Zhou, Qi, et al. emerged as a social problem in South Korea. Patients 2017; Qian, Hua, et al. 2010). with respiratory symptoms of an airborne disease can However, in the case of existing buildings or small easily visit hospitals. Additionally, medical staff and buildings, it is difficult to change an HVAC (heating, visitors are often in the same area as such patients, and ventilation, and air-conditioning) system in a short thus, a cross-infection risk exists (Kowalski 2006). time. Specifically, emergency rooms are associated In developed countries, it is considered that a crucial with high risks of spread of airborne infection owing design factor to prevent airborne infection in a hospital to their open floor plans and lack of adequate facilities is to increase the ventilation rate from 6 ACH (air (Cheong & Seo, 2016). Previous studies (Li et al., change per hour) to 12 ACH (AIA, 1996–97). However, 2007) did not provide strong scientific evidence for in the case of South Korea, design standards to prevent infection control. Therefore, it is helpful to provide airborne infection in hospitals are not clearly presented design guidelines that can be applied in early stages to date in terms of building code requirements. of the design implementation of hospital facilities. Various attempts to build new constructions for Hence, this study presents a case study detailing the airborne infection control have been implemented. performance of airborne infection risk evaluation in a However, suitable countermeasures for preventing conventional emergency department and verifies the airborne transmission in a conventional emergency design recommendation. room are absent in South Korea. Evidently, the most effective method involves significantly increasing the 2. Methods 2.1 Simulation Tools In this study, CONTAMW ver 3.2 is used to analyze the transmission of airborne pathogens. This program *Contact Author: Seonhye Lee, Assistant Professor, utilizes airflow network, and it can simply analyze Department of Nursing, Gyeongnam National University of airflow patterns and airborne pollutant concentrations Science and Technology, Korea in a multi-zone building. Existing studies used Tel: +82-55-751-3653 Fax: +82-55-751-3659 CONTAMW to analyze airborne pathogen transmission E-mail: shlee@gntech.ac.kr in hospitals (Noakes, 2008; Park, et al. 2011). ( Received March 30, 2017 ; accepted July 23, 2018 ) DOI http://doi.org/10.3130/jaabe.17.581 Journal of Asian Architecture and Building Engineering/September 2018/588 581 2.2 Wells–Riley Equation waiting room is the space where the patient's caregiver In this study, CONTAMW is used to identify the waits while the patient receives medical treatment. concentration of airborne pathogens in a specific zone. Generally, it is located extremely close to the entrance However, the concentration of airborne pathogens area (vestibule/lobby) and triage, and thus, airborne obtained by CONTAMW does not correspond to the pathogens generated from the triage area are easily probability of airborne infection. Therefore, to analyze transferred to this area. Figure 1 the risk of airborne infection in a specific zone, it is necessary to convert the concentration value of the airborne pathogen to the probability of airborne infection. Generally, the Wells–Riley model is used to evaluate the risk of airborne infection (Wells, 1995; Rudni ck, 2003; Issa row, 2015; Z hu, 2011, Qua n, 2009). Equation 1 presents a general expression of the Wells–Riley model for a well-mixed condition as follows: ೟೛೜಺ ஼ ି ܲ ൌ ൌ ͳെ݁ ……………(1) ௌ Fig.1. Diagram of the Areas in an Emergency Department where Table 1. Representative Areas in an Emergency Department P : airborne infection probability of a susceptible Spaces Features Usage person - Determine severity of Triage Opens to the C: number of infection cases patient's condition Area lobby -Perform a simple diagnosis I: number of infectious individuals General p: breathing rate of a susceptible individual (m /min) -Patients usually receive treatment Open area q: quantum generation rate by an infectious individual medical treatment. area s: number of susceptible individuals in the space Waiting Separated t: duration of exposure -Waiting area for a caregiver room area 2.3 Target Area The emergency department is functionally divided 2.4 Major Variables into various areas. Therefore, it is necessary to In this study, methods considered for preventing distinguish between the space in which an airborne airborne transmission are as follows: pathogen is emitted and the space in which infection occurs. It is assumed that a patient with an airborne ① Isolating the source of the airborne pathogen infection pathogen visiting an emergency department ② Increasing the ventilation rate in the area first travels through a triage area located near the entrance. Subsequently, a simple diagnosis Architecturally, it is possible to divide an open space is performed in the triage area, which lasts for into partitioned individual spaces. The use of partitions approximately 30 min. The patient is thereafter moved to separate an area is an easy method to prevent to the general treatment area or acute treatment area airborne pathogen transmission without replacing the to receive medical treatment. In the study, a situation HVAC system. Thus, a patient's family or caregiver can is selected in which a patient's circulation begins from wait in the waiting room of an emergency department. the entrance and proceeds to a triage/general treatment Generally, these individuals are not considered to be area. infected by the airborne disease. Thus, it is necessary Fig.1. conceptually illustrates the assumed risk of to prevent the transmission of the airborne pathogen each area in an emergency department with respect to from other areas of the hospital to this waiting room. the transmission of airborne infection. It is assumed The waiting room area is adjacent to the entrance and that the risk of airborne infection corresponds to the lobby. Two types of waiting rooms are considered. The openness of the area and the densities of patients, first type of waiting room opens to a lobby and a triage companions, and medical staff. area. The second type of waiting room is isolated from Table 2. presents the target spaces analyzed in the the lobby and triage area and opens to the vestibule. study. Specifically, patient medical treatments are In this case, the door between the vestibule and lobby performed in the general treatment area, and it is (triage area) is closed. assumed that there is a high possibility of airborne Increasing the ventilation rate is a classical and transmission in this area. The triage area is a place certified method of reducing the concentration of where patient urgency is determined. Thus, all patients airborne pathogens, resulting in reduced airborne visit the triage area. Therefore, in the triage area, infection risk. The building code guidelines in South there is a high latent possibility of cross-infection Korea do not specify the detailed design guidelines between the patient and medical staff at all times. The for HVAC systems in an emergency department. The 582 JAABE vol.17 no.3 September 2018 Chang Heon Cheong Figure 2 existing building code only necessitates a ventilation rate of 36 m /person·hour in large hospitals with floor areas exceeding 2000 m . This corresponds to approximately 2.4 ACH when the minimum floor area required for a patient is considered (Sung, 2015). Table 2. lists the air change rates in an emergency department as specified by previous studies (Cho et al., 2016; Sohn et al., 2014; Park & Kim, 2012; ASHRAE). The baseline for the ventilation rate in an emergency department area is assumed to be 3 ACH. The following two variables are considered to identify the effect of increased ventilation rate on the dispersion Fig.2. Floor Plan of a Target Emergency Department of an airborne pathogen in an emergency department: ventilation rates of 6 ACH and 12 ACH. The air supply Table 3. Features of the Target Emergency Department is entirely obtained from outdoor air (100%). Floor area Volume Ventilation Spaces 2 3 Table 2. Ventilation Rate in Conventional Hospital Design (m ) (m ) Condition Vestibule 16.0 43.2 Authors Total Outdoor air Recirculation (year) supply air of Indoor air Waiting room 52.0 140.4 Cho et al. 6 ACH 2 ACH Not specified Triage area + Lobby 121 326.7 Supply:3ACH (2016) Aisle 107 288.9 Return:3ACH Sohn et al. 6–12 - Not specified Acute treatment area 93.0 251.1 (2014) ACH General treatment 555.0 1498.5 Park & 6 ACH - Not specified area Kim (2012) Toilet 15 40.5 Return:6ACH ASHRAE 12 ACH 5 ACH Not permitted 4. Simulation Outline HVAC (With the applications exception of HEPA 4.1 Boundary Condition of the Base Model filter application) Fig.3. illustrates the CONTAMW modeling of an existing emergency room. In the simulation model, 3. Target Emergency Department the operation room and the closed areas are excluded. 3.1 Floor Plan The doorways between rooms are set with respect to An existing emergency department is selected a two-way flow model (single opening). The model as a sample space to evaluate the effect of design simultaneously reflects the incoming and outgoing factors of an emergency department on preventing the airflows by using the buoyancy effect. Detailed transmission of airborne pathogens. equations with respect to the two-way flow model are Fig.2. illustrates the floor plan of a selected provided in the CONTAMW user manual. However, emergency department. A waiting room, triage area, the simulation is focused on the ventilation rate and and acute treatment area are located near the vestibule airflow by pressure difference. The indoor temperature and lobby spaces. The two spaces open to the lobby, at each zone is set to 20 °C. Figure 3 triage area, and aisle. The aisle is connected to the general treatment area. Consequently, it is possible Vestibule Acute treatment area General treatment area Waiting room for an airborne pathogen to travel to any part of the Toilet emergency department. Additionally, two toilets are located in the waiting room and lobby. Generally, Aisle a toilet is maintained at a pressure lower than that Triage area opened to lobby of other areas to prevent unpleasant odors and the Destination area dispersion of contaminants. (Waiting room) Table 3. lists the floor area, volume, and ventilation Toilet condition of each space. As previously stated, the 2 3 (negative pressure) 1 5 basic ventilation rate is set as 3 ACH based on identical supply and return air volume conditions. The Airflow model ventilation rates of the toilets are set to 6 ACH and are Droplet nuclei emission source (Triage area opened to lobby) only based on return air. These types of ventilation Fig.3. Simulation Model (CONTAMW 3.2) settings permit indoor airflows from the general treatment area and entrances to toilets. The measured data from a previous investigation (Jo et al., 2007) are used to determine the air-tightness of an envelope system and an entrance door. The discharge coefficient and exponent of the large opening are 0.78 and 0.5, respectively. JAABE vol.17 no.3 September 2018 Chang Heon Cheong 583 Table 5. Simulation Case I Table 4. shows the detailed airflow models of the (airborne pathogen source is located in the triage area) openings. Cases Controlled variable Conditions Table 4. Airflow Components Waiting room access Base I - from lobby Size No Type Properties Ventilation rate: 3 ACH h(m)×w(m) Entrance location of the Waiting room access 1 2.7×3.9 Case 1 Discharge coefficient: waiting room from the lobby vestibule 2 2.7×2.4 Two-way flow 0.78 Case 2 Ventilation rate: 6 ACH 3 2.7×5.4 Increased ventilation rate One-opening Ventilation rate: 12 4 2.7×3.2 at lobby Case 3 Exponent: 0.5 ACH 5 2.1×0.9 6 One-way flow - 430 CMH at 50 Pa Table 6. Simulation Case II using power 2 2 7 - EqLA 1.51 cm /m (airborne pathogen source is located in the general treatment law area) Cases Controlled variable Conditions The type of airborne pathogen is considered to be Waiting room access influenza, and its emission intensity is set based on a Base II - from lobby previous study. Ventilation rate: 3 ACH In the simulation modeling, the emission intensity of Case 4 Ventilation rate: 6 ACH Increased ventilation rate the airborne pathogen is set at 1 kg/min. It is considered in the general treatment Ventilation rate: 12 Case 5 equivalent to approximately 9 airborne pathogens area ACH emission per minute (Marsden, 2003). Subsequently, area. The simulation model reflects the patient the concentration of pathogens in a specific area is circulation when the patient first stays in the triage changed to a dimensionless value and finally to the area for 30 min and subsequently stays in the general number of airborne pathogens per unit volume. The treatment area for 4 h. Case II reflects the changed quantity of air inhaled by a susceptible individual is access to the waiting room. The ventilation rate in this set at 9.6 L/min. It is assumed that the sources of the case is 3 ACH. Cases 4 and 5 represent conditions with airborne pathogen are located in the triage area and increased ventilation rates of 6 ACH and 12 ACH, general treatment area based on patient circulation. respectively, in the general treatment area. Natural deposition of influenza virus at the inner surface of each zone is not considered in the simulation. 5. Results and Discussions It is a more conservative condition that increases the 5.1 Airborne Pathogen Sources in the Triage and concentration of airborne pathogens in air. Lobby Areas A t r a n si e n t si m u l a t i o n u si n g C ONTAMW i s 1) Base I performed to analyze the distribution pattern of With respect to the overall pressure distribution in an airborne infection within the emergency department. emergency department, negative pressure in a toilet is 4.2 Simulation Cases the main driving force for the airflow. Hence, airflows Simulation cases are established by considering are formed from the general treatment area and patient circulation with respect to airborne pathogens. outdoor areas to the toilets. Specific airflow routes that Table 5. presents the simulation cases in cases in which influence the airborne pathogen concentration in the an airborne pathogen source (patient) is located in the waiting room and lobby (triage area) are as follows: triage area (lobby). In these cases, individuals located in the lobby (triage area) and waiting room are at a risk Entrance (outdoor) → vestibule → lobby → of airborne infection. It is assumed that a patient who ① waiting room → toilet releases airborne pathogens remains in the triage area General treatment area → lobby → waiting room for 30 min. The triage area is located in the lobby. ② → toilet Base I model corresponds to a conventional condition in which an airborne pathogen source is Fig.4. illustrates the concentrations of airborne located in the triage area and the waiting room is pathogen and infection risk for Base I. The concentrations accessible from the lobby (triage area). of airborne pathogen in the lobby (triage area) and waiting Case 1 corresponds to the modified plan type room increase for a period of 30 min when a patient in which the waiting room is accessible from the releasing airborne pathogens (hereafter referred to as a vestibule. The conventional door placed between the PRAP) enters the triage area. A period of approximately 1 lobby (triage area) and waiting room is closed. h is required to remove airborne pathogens in the spaces Case 2 and 3 correspond to increased ventilation rate after a PRAP leaves the triage area. However, infection in the lobby and triage area. Ventilation rates in Case 2 risk is related to the overall exposure of a susceptible and Case 3 are set as 6 ACH and 12 ACH, respectively. person (hereafter referred to as an SP) to airborne In simulation case II, the patient who releases the pathogen, which increases continuously although the airborne pathogen is located in the general treatment 584 JAABE vol.17 no.3 September 2018 Chang Heon Cheong PRAP leaves the triage area. The infection risks after 2 h According to Fig.6., the infection risks in the waiting of exposure in the waiting room and lobby (triage area) room and the lobby are significantly reduced to 2.3% are 3.8% and 10.0%, respectively. and 6.1%, respectively. Figure 6 Figure 4 Concentration(Case 2-waiting room) Concentration(Case 2-lobby) Concentration(Base I-waiting room) Concentrstion(Base I-lobby) Infection risk(Case 2-waiting room) Infection risk(Case 2-lobby) Infection risk(Base I-waiting room) Infection risk(Base I-lobby) 0.40 16% 0.40 16% 0.35 14% 0.35 14% 0.30 12% 0.30 12% 0.25 10% 0.25 10% 0.20 8% 0.20 8% 0.15 6% 0.15 6% 0.10 4% 0.10 4% 0.05 2% 0.05 2% 0.00 0% 0.00 0% Fig.6. Infection Risks (Case 2) Fig.4. Infection Risks (Base I) 2) Case 1: Changed access to the waiting room When the ventilation rate in the lobby (triage area) is Case 1 changes the access to the waiting room from increased to 12 ACH, the infection risk in the waiting the lobby to the vestibule. The results of the alternative room is 1.3%, and that in the lobby is 3.5%. The arrangement are shown in Fig.5. The changed access implementation of a ventilation rate of 12 ACH in the type to the waiting room influences the airflow pattern lobby (triage area) is an extremely effective solution to to the waiting room. prevent the dispersion of airborne pathogen (Fig.7.). Figure 7 The main airflow to the waiting room is determined Concentration(Case 3-waiting room) Concentration(Case 3-lobby) as follows: entrance (outdoor) → vestibule → waiting Infection risk(Case 3-waiting room) Infection risk(Case 3-lobby) room → toilet. An airborne pathogen from the triage 0.40 16% area is not transmitted to the waiting room. In this case, 0.35 14% the infection risk in the waiting room is 0%. Changing 0.30 12% the access from the vestibule to the waiting room 0.25 10% effectively isolates the waiting room from the airborne 0.20 8% pathogens generated in the lobby. The results indicate 0.15 6% that isolating a specific area from airborne pathogen 0.10 4% sources is an effective solution for preventing the 0.05 2% spread of airborne infections. However, the infection 0.00 0% risk in the lobby is slightly increased. The infection risk in the lobby (triage area) is 11.9%. Additional solutions are required to prevent expected increases Fig.7. Infection Risks (Case 3) in the infection risks at the zone where airborne pathogens are released. 5.2 Pathogen Source in the General Treatment Area Figure 5 1) Base II Concentration(Case 1-waiting room) Concentration(Case 1-lobby) Base II considers the condition in which a PRAP Infection risk(Case 1-waiting room) Infection risk(Case 1-lobby) remains in the general treatment area for 4 h after 0.40 16% visiting the triage area. As shown in Fig.8., the 0.35 14% airborne infection risk in the general treatment area 0.30 12% continuously increases during the patient's occupancy 0.25 10% period. The airborne infection risk in the general 0.20 8% treatment area increases to approximately 24.1% after a 0.15 6% period of 6 h after the PRAP visits the emergency area. 0.10 4% The infection risk in the general treatment area linearly 0.05 2% increases after the airborne pathogen concentration 0.00 0% reaches a steady state. The simulation result indicates that the transmission of airborne pathogen from the general treatment area to the aisle is restricted, because Fig.5. Infection Risks (Case 1) no available opening at the general treatment area is 3) Cases 2 and 3: Increased ventilation rate modeled. An airflow rate of 6.7 m /h is generated from In Case 2, the ventilation rate of the triage is doubled the general treatment area to the aisle. This indicates and is 6 ACH with respect to the source control. that a maximum of approximately 0.76 infectious JAABE vol.17 no.3 September 2018 Chang Heon Cheong 585 Airborne pathogen concentration Airborne pathogen concentration (particles/m ) (particles/m ) 0:00 0:00 0:15 0:15 0:30 0:30 0:45 0:45 1:00 1:00 1:15 1:15 1:30 1:30 1:45 1:45 2:00 2:00 Infection risk(%) Infection risk(%) Airborne pathogen concentration Airborne pathogen concentration 3 3 (particles/m ) (particles/m ) 0:00 0:00 0:15 0:15 0:30 0:30 0:45 0:45 1:00 1:00 1:15 1:15 1:30 1:30 1:45 1:45 2:00 2:00 Infection risk(%) Infection risk(%) particles per hour move from the general treatment rate of 12 ACH is potentially too high. Hence, it is area to the aisle. The transmission of airborne pathogen extremely important to identify a latent PRAP in the increases if an operable door and window exist in the triage area and to isolate such PRAP in advance. general treatment area. Thus, an architectural design to acquire an adequate As shown in Fig.9., there is a negligible increase in area to isolate PRAPs is required even when the area the infection risk in the lobby and waiting room after a does not correspond to an isolation room with heavily PRAP moves to the general treatment area. equipped HVAC systems. Additionally, it is necessary The results indicate that, if the ventilation system that the ventilation rate required to prevent airborne works properly with an appropriate air volume, it is infection in a zone should reflect the residing time of Figure 10 possible to effectively prevent the transmission of the PRAP. airborne pathogen between each zone. Evidently, it is Concentration(Case 4-general treatment.) Concentration(Case 5-general treatment.) desirable to increase the ventilation rate to a suitable Infection risk(Case 4-general treatment.) Infection risk(Case 5-general treatment.) level if the number of PRAPs increases. 0.40 16% Figure 8 0.35 14% Concentration(Base II-general treatment area) Concentration(Base II-aisle) 0.30 12% Infection risk(Base II-general treatment area) Infection risk(Base II-aisle) 0.25 10% 0.40 40% 0.20 8% 0.35 35% 0.15 6% 0.30 30% 0.10 4% 0.25 25% 0.05 2% 0.20 20% 0.00 0% 0.15 15% 0.10 10% 0.05 5% Fig.10. Infection Risks in the General Treatment Area 0.00 0% (Case 4 and Case 5) Fig.8. Infection Risks in the General Treatment Area and Aisle 5.3 Discussions (Base II) In this study, airborne infection risks in the triage Figure 9 area, waiting room, and general treatment area are Concentration(Base II-waiting room) Concentration(Base II-lobby) analyzed based on the simulation results. The airborne Infection risk(Base II-waiting room) Infection risk(Base II-lobby) pathogen from a PRAP is considered to be influenza. 0.40 16% T he dom i na nt a i rfl ow pa t t e rn i n a n e m e r ge nc y 0.35 14% department is determined by the exhaustion rates in the 0.30 12% toilets located near the lobby and waiting room. With 0.25 10% respect to this condition, airborne infection risks exist 0.20 8% at a zone containing the airborne infection source and 0.15 6% zones located on the route of transmission of airborne 0.10 4% pathogen. 0.05 2% The results of the case studies indicate that the 0.00 0% probability of airborne infection varies based on the concentration of airborne pathogens and exposure time. At a ventilation rate of 3 ACH, the general Fig.9. Infection Risks in the Lobby and Waiting Room treatment area is the most dangerous zone as a PRAP (Base II) resides in this area for a long time (4 h). In cases in 2) Cases 4 and 5: Increased ventilation rate which the general treatment area can become a source Cases 4 and 5 correspond to cases with increased of infection, findings suggest that the probability ventilation rates of 6 ACH and 12 ACH, respectively, of infecting surrounding individuals increases in the general treatment area (Fig.10.). The maximum significantly when a PRAP remains in the room for a cumulative airborne infection risks in the general long period. The infection probability is based on the treatment area in Case 4 and Case 5 are 12.9% and assumption that cumulative exposure to an airborne 6.7%, respectively. The results also indicate that pathogen is sustained during a period exceeding 6 increasing the ventilation rate is a good solution h. This indicates that medical staff working in an for preventing airborne infection. However, the emergency department is most vulnerable to airborne residing time of a PRAP in a specific zone evidently infection and the medium of cross-infection. Patients significantly contributes to the infection risk of an SP in present in the general treatment area for long periods an identical zone. This indicates that the infection risk also present the risk of airborne infection. in the general treatment area of 6.9% at the ventilation 586 JAABE vol.17 no.3 September 2018 Chang Heon Cheong Airborne pathogen concentration 3 Airborne pathogen concentration (particles/m ) (particles/m ) 0:00 0:00 0:30 0:30 1:00 1:00 1:30 1:30 2:00 2:00 2:30 2:30 3:00 3:00 3:30 3:30 4:00 4:00 4:30 4:30 5:00 5:00 5:30 5:30 6:00 6:00 Infection risk(%) Infection risk(%) Airborne pathogen concentration (particles/m ) 0:00 0:30 1:00 1:30 2:00 2:30 3:00 3:30 4:00 4:30 5:00 5:30 6:00 Infection risk(%) The triage area exhibits the second highest risk of ③ The required ventilation rate should be increased 10.0% in the base condition. It is assumed that a PRAP in a manner proportional to the residing time of a remains for 30 min in the triage area. The waiting room PRAP in a specific zone. has an infection risk of 3.8%. ④ Accumulated exposure time to airborne pathogen The simulation results indicate that it is possible significantly influences the infection risk. Thus, to decrease the airborne infection risk in the waiting medical staff, patients, and family members present room by changing the entrance from the lobby to the in the emergency department for long periods also vestibule such that outside air can easily flow into present higher risk of airborne infection. Appropriately the waiting room instead of the air from the lobby designed architectural features such as proper partition (triage area). However, solutions isolating the airborne installation, airflow modification among rooms, and pathogen source result in increased infection risks isolated occupancy circulation can reduce the airborne in the zones in which a PRAP remains for extended infection. periods such as the triage area and general treatment ⑤ This study is based on the generation of airborne area. Thus, it is desirable to increase the ventilation pathogens by a PRAP. Considering the worst case rate at the aforementioned zones where PRAPs remain where there are many PRAPs present, highly increased for extended periods while simultaneously isolating the ventilation rate may be required. zones. The study results indicated that negative pressures A useful method involves increasing the ventilation in the toilets are the main driving force for the r a t e i n a z o n e wh e r e t h e a i r b o r n e p a t h o g e n i s transmission of airborne pathogens. With respect to generated. In this condition, it is possible to minimize unexpected situations characterized by uncontrollable the transmission of the airborne pathogen to adjacent variables (such as strong wind, stack effects, strong zones. If proper ventilation is implemented at zones airborne pathogen generation, or other risky human near the airborne pathogen source, further transmission behavior), increasing the overall ventilation rate of the airborne pathogen can be prevented. in an emergency department is also a potential Particularly in the case of the general treatment solution. A future study will reflect the effects of the area, it is considered that increasing the ventilation aforementioned external forces. rate is essential to ensure that the occupancy period of a PRAP is significantly long. According to the South Acknowledgements Korean building code (Sung, 2015), the required This study was supported by the Basic Science ventilation rate in a hospital is approximately 2.4 ACH. Research Program through the National Research Thus, it is necessary to increase the ventilation rate in Foundation of Korea (NRF) funded by the risky zones such as the general treatment areas, triage Ministry of Science, ICT & Future Planning (No. areas, and waiting rooms. In this case, the required 2015R1C1A1A01051740). ventilation rate must reflect the intensity of generation of airborne pathogen and the residing time of PRAPs. Authors Contributions Chang Heon Cheong designed the research plan, 6. Conclusions performed CFD simulation, and drafted the manuscript. This study analyzed the effectiveness of two design Beungyong Park analyzed the simulation results. factors—namely isolating the airborne pathogen Seonhye Lee reviewed the results of the study with source and increasing the ventilation rate—on airborne respect to hospital environment, airborne infection, and infection control by using CONTAMW simulation. It public health. All authors read and approved the final is also expected that the results of the study can help version of the manuscript. in evaluating airborne infection risks in an emergency room and in improving the architectural design of Conflicts of Interest emergency rooms within a short period. The authors declare that there are no conflicts of The main results of the study can be summarized as interest. follows: ① Potentially optimal solutions for airborne Note The original value given by Marsden, A.G. (2003) is 515 infection control are isolating the airborne pathogen pathogens per hour. source and increasing the ventilation rate. ② It is necessary to simultaneously implement isolation of the airborne pathogen source and an increase in the ventilation rate at the airborne pathogen source to prevent increased infection risk in the zone where airborne pathogens are generated. 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Journal

Journal of Asian Architecture and Building Engineering – Taylor & Francis

Published: Sep 1, 2018

Keywords: airborne infection; ventilation; isolation room; Wells–Riley equation; emergency department

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