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INFECTION CONTROL


6 m 1000 Patient 2 Patient 1 100 10 Patient 3 Patient 4


Square cone diffuser Liner slot diffuser Exhaust Partition wall Rolling screen Measuring point Source of particle


Figure 1: Outline of the test room (ground plan).


center of the ceiling. Four exhausts were set in the ceiling above each patient. The air volume was 810 m3


hour (ACH). Next, we examined the combined


effectiveness of four linear slot diffusers and the partition walls. Supply air diffusers were set in the ceiling, a square cone diffuser was in the center and four linear slot diffusers were on the step side of each bed between the wall and the partition wall. We used the same exhausts as in the previous conditions. The total air volume of the square cone diffuser and the linear slot diffusers was 810 m3


for the air volume; 0 m3/hr -810 m3 180 m3/hr -630 m3 450 m3/hr -360 m3


/hr, 270 m3 /hr and 810 m3


/hr (9 ACH). Five conditions were set /hr,


/hr -540 m3 /hr


/hr, -0 m3/hr. We also examined the combined


effectiveness of the rolling screen and the linear slot diffusers. We measured the particle concentrations at the exhaust over Patient 1 and at the breathing areas of Patients 2, 3 and 4.


Results Figure 2 shows the results of mean concentration and standard error for partition walls. There was no remarkable difference in these results, but there were some tendencies. The average concentration of Patients 2 to 4 tended to decrease when the partition walls were set. The average concentration tended to decrease further when we used the rolling screen. However, the effect was insufficient as the average concentration decrease was only 34%. At this time, the concentration of the exhaust over Patient 1 tended to increase inversely proportionally to the average concentration of Patients 2 to 4. Then, Figure 3 shows the results of mean


IFHE DIGEST 2015 1 No partition wall Partition wall Figure 2: Mean concentration and standard error for partition walls. 1000 100 10 /hr – nine air changes per 1 Square cone diffuser Linear slot diffuser


concentration and standard error for diffusers with partition walls. The concentrations of Patient 2 to 4 significantly decreased but the concentration of the exhaust over Patient 1 significantly increased when we used the liner slot diffusers. When we added the rolling screen, the concentrations of Patients 2 to 4 tended to decrease further and the concentration of the exhaust over Patient 1 tended to increase further. Finally, Figure 4 shows the results of mean


concentration and standard error for the average of Patients 2 to 4 when we divided the 810 m3


/hr between the square cone


diffuser and the liner slot diffusers. Figure 5 also shows the results of mean concentration and standard error for the exhaust over Patient 1 when we divided the 810 m3


/hr.


In Figure 4, the average concentration of Patient 2 to 4 was significantly low when the air volume of the liner slot diffusers was 810 m3


‘We used baby powder with a median particle size of 12.6 µm, as the substitute particle for droplet nuclei.’


/hr. The average concentration tended


Linear slot diffuser + Rolling screen


Figure 3: Mean concentration and standard error for diffusers with partition walls.


to increase when the air volume of the square cone diffuser was increased and when the air volumes of the liner slot diffusers were decreased. In these results, the average concentrations tended to decrease when we added the rolling screen. In Figure 5, the exhaust concentration tended to decrease when the air volume of the square cone diffuser was increased and when the air volumes of the liner slot diffusers were decreased. In these results, the exhaust concentrations tended to increase when we added the rolling screen. In this study, as we assumed only one


particle source on the bed, the center of the room became the clean buffer area. Therefore, it is thought that the substantial air change rate increased. The patient volume surrounded by the partition wall and the rolling screen was 13.75 m3


(2.2 m x 2.5 m x


2.5 m). If the area is ventilated by 202.5 m3


/hr, the air change rate is 14.7. This rate


was 1.63 times the room air change rate (9 ACH) and is thought to decrease the concentration by 39%. The result of the partition walls and the rolling screen decreased the average concentration of patients 2 to 4 by 34%. This is considered to be the main reason for the decrease of the average concentration. The gap from the area of Patient 1 was 6.25 m2 at the step side when we set the


partition walls. When we added the rolling screen, the gap from the area of Patient 1 decreased by 55% to 2.83 m2


. The decrease of 21 Exhaust (patient 1) Patient 2-4 + Rolling screen Partition wall


Exhaust (patient 1)


Patient 2-4


6 m


Concentration (p/3.5L)


Concentration (p/3.5L)


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