This page contains a Flash digital edition of a book.
INFECTION CONTROL


Partition 1000 100 10 1


Square cone diffuser Liner slot diffuser


0 810


180 630


270 540


450 360


/hr between the square cone diffuser and the liner slot diffusers. Partition 1000 100 10 1


Square cone diffuser Liner slot diffuser


0 810


180 630


270 540


450 360


/hr between the square cone diffuser and the liner slot diffusers.


810 0


Figure 5: Mean concentration and standard error for the exhaust over Patient 1 when we divided the 810 m3


the average concentration to 34% is smaller than the 55%. There was an exhaust over Patient 1 and the area was kept at negative pressure. However the average air velocity to flow in from the gap was only 0.02 m/sec. Therefore, the air velocity may be larger by the air-flow from the diffuser or the difference in temperature. However, there may have been an air-flow leakage. On the other hand, the average


concentration was decreased by 92% without the rolling screen when we used the liner slot diffuser. The average concentration was decreased by 95% when we added the rolling screen. The air velocity of the liner slot diffuser was only 0.6 m/sec. However, it is thought that the liner slot diffuser formed an air curtain, which decreased leakage. According to the results of the CFD analysis, calculated before the experiments, the particles were delivered to the upper area without spreading and were removed from the exhaust. In this result, even the step side concentration of Patient 1 was greatly decreased. The result of the exhaust concentration increase was similar to the experiment. The increase was 3.7 times at the liner slot diffusers and the rolling screen. Previous studies showed that particles near a patient were delivered to upper areas from


22


updrafts caused by the patients’ temperature. In this study, it is considered that the liner slot diffusers not only formed an air curtain but also formed an air-flow to prevent the spread of particles delivered to the exhaust over the patient by updrafts. When we used both the square cone


diffuser and the liner slot diffusers, the average concentration of Patients 2 to 4 was decreased by increasing the air volume of the liner slot diffusers ratio. According to the additional experiments of total air volume 1,080 m3


/hr (12 ACH), the average


concentrations were almost the same when the total air volume of the liner slot diffusers exceeded 810 m3


In other words the air-flow did not reach the floor when the air volume of the liner slot


the air-flow from the liner slot diffusers needs more than 810 m3


/hr. This result suggests that /hr to reach the floor.


(m3 (m3


/h) /h)


810 0


(m3 (m3


Figure 4: Mean concentration and standard error for the average of Patient 2 to 4 when we divided the 810 m3


Partition + Rolling screen


/h) /h)


Partition + Rolling screen


diffusers was decreased, which in turn increased the leakage. According to these results, it is considered


that we can reduce the airborne infection risk in a four-bed room by using liner slot diffusers, rolling screen and partition walls to isolate every bed. The risk can be reduced when the gap of the rolling screen is decreased.


Conclusion In this study, we discuss the reduction methods of droplet nuclei concentration to reduce the airborne infection risk of a four- bed room by experiments and obtained the following results. • The particle concentration of the patient area excluding the source was decreased by 34% when we set exhausts over every bed and isolated the source patient area by partition walls and a rolling screen. However this was insufficiently effective.


• The particle concentration decreased by 92% when we used liner slot diffusers and partition walls. The concentration decreased by 95% when we added a rolling screen.


• Isolation by partition wall, rolling screen, or air-flow can reduce the airborne infection risk.


Acknowledgement This study was cooperatively carried out with Juntendo University, Waseda University Joint Research Group. This article was reprinted from proceedings of Indoor Air 2014, Hong Kong.


References • CDC. Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings. Centers for Disease Control and Prevention 2007.


• Healthcare Engineering Association of Japan. 2013. Healthcare Engineering Association of Japan Standard (HEAS-02-2013). (in Japanese)


• Morimoto S, Hori S, Sakimura S, Ito A, Hiramatsu K. Performance Assessment of the


Actual Negative Pressure Room and the Layouts to Reduce Droplet Nuclei by Computational Fluid Dynamics. Proceedings of ASHRAE IAQ Conference Malaysia 2010.


• Okajima A, Tsutsumi H, Tanabe S, Isahaya T, Ito T, Morimoto S, Hori S, Ariga T. Transmission Characteristics of Coughed air using Cough Generator with Simulated Oral Airway. Proceedings of Healthy Buildings 2012.





‘Japan is a TB intermediate danger country and many patients host TB. For this reason prevention of the transmission of TB within the hospital environment is an important issue.’


IFHE DIGEST 2015


Concentration (p/3.5L)


Concentration (p/3.5L)


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96