ASHRAE ST-16-004-2016 Assessing Effectiveness of Ceiling-Ventilated Mock Airborne Infection Isolation Room in Preventing Hospital-Acquired Influenza Transmission to Health Care Wor.pdf

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1、 2016 U.S. Government 35This paper is based on findings resulting from an ASHRAE 2015-2016 Graduate Student Grant-In-Aid award.ABSTRACTExposure to airborne influenza (or flu) from a patientscough and exhaled air causes potential flu virus transmissionto the persons located nearby. Hospital-acquired

2、influenza isa major airborne disease that occurs to health care workers(HCW).This paper examines the airflow patterns and influenza-infected cough aerosol transport behavior in a ceiling-venti-lated mock airborne infection isolation room (AIIR) and itseffectiveness in mitigating HCWs exposure to air

3、borne infec-tion. The computational fluid dynamics (CFD) analysis of theairflow patterns and the flu virus dispersal behavior in a mockAIIRisconductedusingtheroomgeometriesandlayout(roomdimensions, bathroom dimensions and details, placement ofvents and furniture), ventilation parameters (flow rates

4、at theinlet and outlet vents, diffuser design, thermal sources, etc.),and pressurization corresponding to that of a traditional ceil-ing-mounted ventilation arrangement observed in existinghospitals. The measured data shows that ventilation rates fortheAIIRareabout12airchangesperhour(ach).However,th

5、enumerical results reveals incomplete air mixing and that notalloftheroomairischanged12timesperhour.Twolife-sizedbreathing human models are used to simulate a source patientandareceivingHCW.Apatientcoughcycleisintroducedintothe simulation and the airborne infection dispersal is trackedin time using

6、a multiphase flow simulation approach.The results reveal air recirculation regions that dimin-ishedtheeffectofairfiltrationandprolongthepresenceofflu-contaminated air at the HCWs zone. Immediately after thepatient coughs (0.51 s), the cough velocity from the patientsmouth drives the cough aerosols t

7、oward the HCW standingnexttopatientsbed.Within0.7s,theHCWisatriskofacquir-ing the infectious influenza disease, as a portion of these aero-sols are inhaled by the HCW.As time progresses (5 s), the aerosols eventually spreadthroughout the entire room, as they are carried by the AIIRairflowpatterns.Su

8、bsequently,aportionoftheseaerosolsareremoved by the exhaust ventilation. However, the remainingcoughaerosolsreenterandrecirculateintheHCWszoneuntilthey are removed by the exhaust ventilation.The infectious aerosols become diluted in the HCWsregion over a period of 10 s because of the fresh air suppl

9、iedinto the HCWs zone. The overall duration of influenza infec-tion in the room (until the aerosol count is reduced to less than0.16%ofthetotalnumberofaerosolsejectedfromthepatientsmouth) is recorded as approximately 20 s. With successivecoughing events, a near-continuous exposure would be possi-ble

10、. Hence, the ceiling-ventilation arrangement of the mockAIIR creats an unfavorable environment to the HCW through-out his stay in the room, and the modeled AIIR ventilation isnoteffectiveinprotectingtheHCWfrominfectiouscoughaero-sols. The CFD results suggest that the AIIR ceiling ventilationarrangem

11、ent has a significant role in influencing the flu virustransmission to the HCW.INTRODUCTIONInfluenza is a virulent human flu that can cause a globaloutbreak or serious illness. The annual number of influenzadeaths is 250500 thousand worldwide (WHO 2014; Thomp-sonetal.2003)andrequires114,000hospitali

12、zations(BridgesAssessing Effectiveness of Ceiling-VentilatedMock Airborne Infection Isolation Room inPreventing Hospital-Acquired InfluenzaTransmission to Health Care WorkersDeepthi Sharan Thatiparti Urmila Ghia, PhD KennethR.Mead,PhDStudent Member ASHRAE Member ASHRAEDeepthi Sharan Thatiparti is a

13、doctoral candidate and Urmila Ghia is a professor in the Department of Mechanical Engineering, Universityof Cincinnati, Cincinnati, OH. Kenneth R. Mead is a mechanical engineer with the Center for Disease Control and Prevention, National Insti-tute for Occupational Safety and Health (NIOSH), Cincinn

14、ati, OH.ST-16-004 (GIA 15-16)Published in ASHRAE Transactions, Volume 122, Part 2 36 ASHRAE Transactionset al. 2002). Influenza outbreaks occur frequently in healthcare facilities and often more than once in a single facilityduring an influenza season (Patriarca et al. 1985; Drinka et al.2000; Sugay

15、a et al. 1996; Zadeh et al. 2000). In the case of ainfluenza outbreak, health care workers (HCWs) are at highrisk as they are typically in close contact with influenzapatients. HCWsoftencontinuetoworkdespitebeingill(CDC1999; Wenzel et al. 1977; Wilde et al. 1999). Influenza canthen spread rapidly am

16、ong other patients and HCWs, partic-ularly in closed hospital settings (Cunney et al. 2000; Evans etal. 1997).RelevancetoNationalOccupationalResearchAgenda(NORA)TheNationalInstituteforOccupationalSafetyandHealth(NIOSH) developed the National Occupational ResearchAgenda (NORA) for improving the healt

17、h of workers inindoorworkenvironments.Itidentifiedpriorityresearchareasto substantially decrease the work-related illnesses and deathsintheupcomingyears.NORAsHealthCareandSocialAssis-tance (HCSA) Agenda is one element of the larger NORAendeavor. There are over 15 million healthcare-associatedemploye

18、es in the U.S. that are covered by the HCSA researchagenda. According to the NIOSH NORA HCSA Sector, anestimated 18.6 million people are employed within the HCSAsector (CDC 2013). About 80% of HCSA workers are inhealth care industries and 20% in social assistance industries.Comparedtootherindustrial

19、sectors,theHCSAsectorhadthesecond largest number of occupational injuries and illnesses(CDC 2009). One specific research priority within the HCSAresearch agenda is the prevention of occupationally-acquiredtransmissions of infectious disease among HCSA workers.The research discussed in this manuscrip

20、t is in direct responseto this HCSA research priority.The HCSA Sector Council has developed five goalsdesignedtoaddresstopsafetyandhealthconcerns,toadvanceprotection to HCWs and, at the same time, ensure patientsafety (CDC 2009). The HCSA Sector Council five strategicgoals are1. Safety and health pr

21、ograms2. Musculoskeletal disorders3. Hazardous drugs and other chemicals4. Sharps injuries5. Infectious diseases.MotivationThe mission of the research discussed in this manuscriptistopreventoccupationaltransmissionofinfectiousinfluenzadisease to HCWs.Airborne Infection Isolation Room (AIIR)Use of an

22、 airborne infection isolation room (AIIR) isprescribed by various federal and state health organizations(Ninomura et al. 2001; FGI 2014; ASHRAE 2013) whenHCWshavetoconductcough-generatingproceduresoninflu-enza patients. In using an AIIR, the infectious flu virus iscontained within the room and its c

23、oncentration in the room isreduced via dilution ventilation. This is done by followingASHRAE and Facility Guidelines Institute (FGI) guidelines(Ninomura and Bartley 2001; FGI 2014; ASHRAE 2013;Heiselberg1996)ontheconstructionofAIIRsandtheirventi-lation system design. The airflow and ventilation desi

24、gnparameters are controlled in AIIRs to reduce the potential forairborne migration of infectious aerosols into other areas ofthe hospital.ObjectiveThe objective of this study is the computational analysisof the airflow patterns and influenza-infected cough aerosoltransport behavior in a ceiling-vent

25、ilated AIIR and determi-nation of the ceiling ventilations effectiveness in mitigating aHCWs exposure to airborne infectious aerosols.METHODOLOGYProblem StatementThe Mock AIIR layout and its ventilation parameters atNIOSHs Alice Hamilton Research Laboratories in Cincinnati,OH, is considered for the

26、present study. Figure 1 presents theisometric view of the geometric model and the configurationdetails of the mock AIIR modeled at the NIOSH facility. Themodeled room dimensions were: length = 170 in. (4.318 m),width = 96 in. (2.4384 m), height = 192 in. (4.879 m). The corre-sponding computer-aided

27、design (CAD) model was constructedforthemockAIIR,andacomputationalgridwasgeneratedusingthe ANSYS ICEM computational fluid dynamics (CFD) soft-ware (ANSYS 2016a).Thismockisolationroomconsistsoftwoceilinginletsupplyvents (square and linear supply) and one ceiling exhaust grille, aFigure 1 Schematic la

28、yout of the mock AIIR.Published in ASHRAE Transactions, Volume 122, Part 2 ASHRAE Transactions 37bathroom with an exhaust vent, and a room entrance/exit maindoor for the patient and HCW. The ceiling air supply diffusersused in the mock AIIR are shown in Figure 2.The supply diffusers for the mock AII

29、R are selected toprovide minimum ventilation rates and indoor air quality that isacceptable to the patient and HCW as per ANSI/ASHRAE/ASHE Standard 170 (ASHRAE 2013).A rectangular linear diffuser (Figure 2a and 2b) with two airslots is used for the ceiling installation. The standard diffusermodulele

30、ngthis48in.(1.219m).Thelengthofeachslotis46.25in. (1.17 m) and the thickness of each slot is 0.718 in. (0.018 m).The two slots are equipped with air deflectors so the direction ofair discharge can be adjusted. Supply air flows at an angle of 45fromtheslotclosesttothewindowanddirectlydownward(verti-c

31、al air distribution) for the second slot furthest from the window.The total supply flow rate from the linear diffuser is 81.49 cfm(138.45 m3/h).Asquarediffuserwithtwoslotsisusedfortheceilinginstal-lation (Figure 2c and 2d). The standard diffuser module length is24 in. (0.6 m). The thicknesses of the

32、 outer and inner slots are2.7and 2.9 in. (2.685 and 0.073 m), respectively. Supply air flows atan angle of 45 outward into the room. The total supply flow ratefrom the square diffuser is 66.67 cfm (113.27 m3/h). The supplyair temperature from the linear and square diffusers is 69.72F(20.96C).The pat

33、ient and HCW are modeled using the NASA anthro-pometric data from the Human Integration Design Handbook(NASA 2014). Table 1 gives the patients and HCWs dimen-sions.Thepatientislyingonthebedinclinedat30andtheHCWis facing the patient at a distance of 3.46 in. (0.087 cm) from thepatient on the side of

34、the monitoring instrumentation location.The mouth diameter is taken to be 1.18 in. (0.03 m) (VanS-civeretal.2011)createdatthepatientsfaceforcoughflowfromthepatientsmouth.Thenoseopeningdimensionsweremodeledwith an area of 0.116 in.2(7.5105m2) (Gupta et al. 2009) at thepatients and HCWs face centers f

35、or breathing. Figure 3 showsthe two semicircular nose openings and mouth opening at theHCWs face.Boundary and Operating ConditionsThe fresh air inflow of 148.16 cfm (251.72 m3/h) into theAIIR is caused by the airflow from the main supply (the linearinlet diffuser inflow rate is 81.49 cfm 138.45 m3/h

36、 and thesquare supply inflow rate is 66.67 cfm 113.27 m3/h) and theFigure 2 (a) Linear supply slot diffuserisometric view.(b) Linear supply slot diffuser with dimensions(in.)front view. (c) Square supply diffuserisometric view. (d) Square supply with dimen-sions (in.)plane view.Table 1. Patient and

37、HCW Dimensions (NASA 2014)BodyPartLength,in. (m)Width,in. (m)Height,in. (m)Head 14.96 (0.38) 6.29 (0.16) 11.14 (0.283)Trunk 19.68 (0.5) 9.84 (0.25) 25.66 (0.652)Hands 3.93 (0.1) 3.93 (0.1) 30.82 (0.783)Legs 5.11 (0.13) 5.11 (0.13) 5.9 (0.15)Mouth Diameter: 1.18 in. (0.03 m)Figure 3 Patient and HCWs

38、face showing nose and mouthopenings.Published in ASHRAE Transactions, Volume 122, Part 2 38 ASHRAE Transactionsoutflowof225cfm(382.27m3/h)isduetotheairflowthroughthemain exhaust and the leakage into the bathroom. The boundaryand operating conditions of the ceiling-ventilated mock AIIR arepresented i

39、n Table 2.The bathroom exhaust flow rate is 80 cfm (135.92 m3/h). Itisassumedthatthebathroomreceives10%ofitsexhaustmakeupair from leaks other than the bathroom entry door. Thus, a flowrate of 72 cfm (122.32 m3/h) was specified at the gap around thebathroom door.A pressure of0.01 in.w.g. (2.49 Pa)was

40、 spec-ified as the boundary condition at the gaps around the AIIRsmain entry door.The geometric model, ventilation parameters, and roompressurization of the ceiling-ventilated mock AIIR are numeri-cally simulated along with the HCWs potential to inhale thepatients cough aerosols as follows and as in

41、dicated in Table 2.1. At Patients Mouth. Cough flow boundary condition isspecified at the patients mouth. The patient introducescough aerosols 1 micron (m) in diameter during coughing.This aerosol size is consistent with deep-lung penetrationand airborne infectious disease transmission and thus wast

42、hefocusofthemodel.Thepatientscoughcycle,takenfromtheresearchbyGuptaetal.(2009),isshowninFigure4,andthe cough flow parameters are represented in Table 3.2. At HCWs Mouth. A no-slip boundary condition isspecified at the HCWs mouth.3. At Patients and HCWs Noses. The patient and HCWare breathing out-of-

43、phase with a maximum volumeairflow of 0.5 L (0.132 gal). Figure 5 and Table 4 shownormal breathing cycle of patient and HCW and thecorresponding breathing profile parameters obtained bydigitizing the volume of breath curve, taken from theresearch by Hall (2011). It is observed that expirationtakes a

44、 relatively longer time (2.29 s) than inspiration(1.71 s). Also, expiration starts at a faster pace in initialtime instants (between 1.71 and 2.5 s) and slows down asit approaches 4 s.4. At Patients and HCWs Bodies. To account for a fever,it is assumed that the patients head is at a temperature of10

45、0.72F (36.51C) and the rest of the body is assumed tobecoveredwithasheetatroomtemperature.FortheHCW,a normal body temperature of 97.71F (36.51C) is speci-fiedfortheHCWsheadandtherestofthebodyisassumedto be covered with clothes at room temperature.5. For Furniture. The patients bed is modeled as wall

46、boundary and maintained at a normal room temperatureof 69.72F (20.96C).6. At Window. The window in the room is considered anisothermal wall. The temperature for the window facingTable 2. Ceiling-Ventilated Mock AIIRBoundary and Operating ConditionsNo. Boundary Boundary Condition Boundary Value Requi

47、red1. Linear inlet diffuserNumber of slots in the linear diffuser 2Flow rate 55% of Qin= 81.49 cfm (138.45 m3/h)Angle 45Direction of flow: Toward the window (for the slot closest to window);directly downward for the second slot furthest from window.2. Square supplyFlow rate 45% of Qin= 66.67 cfm (11

48、3.27 m3/h)Angle 45Direction of flow: Outward, air flows into the room.3. Main room exhaustFlow rate 225 cfm (382.27 m3/h)Direction of flow: Into the exhaust vent, air extracted from the room.4 Bathroom exhaust Flow rate 80 cfm (135.92 m3/h)5 Main door gaps Pressure at the main door gaps 0.01 in. w.g. (2.49 Pa)6.Bathroom door gaps (assuming bathroom receives10% of its exhaust makeup air from leaks otherthan the bathroom entry door)Flow rate 72 cfm (122.32 m3/h)Direction of flow: Into bathroom, room air escapes through bathroom door gaps.7. Overhead lights Power (W) 08. HCW lower bodyTempera