INFECTION CONTROL
Experiment results The results shown in Figure 4, indicate that no measurable difference exists in the cleanliness between the evaporative humidifiers (1 to 3) and the steam humidifier (4). In a comparison of the results of 29 January and 5 March, the cleanliness of the humidified air becomes higher as the operation time becomes longer. As shown in Figure 4, the outdoor air is the lowest in cleanliness, but most of the airborne microorganisms were eliminated passing through the filter. The air becomes even cleaner after heating by the heating coil and passing through the humidifier. It is believed that in steam humidifiers, the air is disinfected by steam spray, whereas in evaporative humidifiers, microorganisms seem to attach to the humidifier element and are washed away. Figure 4 shows no considerable difference among the evaporative humidifiers. In a comparison of the results of the air after passing through the humidifier on 5 March (humidification operation) and on 12 March (ventilation operation without humidification), shown as humidified air in Figure 4, the number of fungi decreased in Humidifiers 1 and 2 and increased in Humidifier 3, while the number of microorganisms decreased in Humidifier 1 and increased in Humidifiers 2 and 3. According to the Architectural Institute of
Japan Environmental Standards (AIJ 2005), the design standard is 200 CFU/m3
and
under, and the maintenance standard is 500 CFU/m3
and under for airborne
microorganisms in general patient rooms. It is considered that each humidified air has sufficient air cleanliness to meet this standard as dilution air. Figure 5 shows the number of
microorganisms on the inside wall surface of the AHUs and of the humidifier elements. As shown in Figure 5(a), the degree of contamination of the inside wall surface of AHUs becomes higher as the operation time becomes longer. However, the increase is slight. As shown in Figure 5(b), the humidifier element is clean at first, but becomes contaminated drastically after the start of the operation, especially for microorganisms of Humidifier 3. In contrast, the number of fungi is small in every humidifier. No Legionella species was detected in the drainage water.
Pollution control in evaporative humidifiers Four types of operating conditions were compared to examine the difference of cleanliness due to the design specification of the evaporative humidifiers. Case A was the normal operation (24 hr humidification), Case B was the operation with compulsory hydro-flow washing for 30 min/day, Case C was the operation with continuous UV light irradiation, and Case D was the operation with compulsory drying for 2 hr/day. Figure 6 shows the layout of the UV light lamp and the measured UV intensity (W/m2
). The IFHE DIGEST 2014
200 180 160 140 120 100 80 60 40 20 0
Fungi
Microorganisms
(Steam) A
200 180 160 140 120 100 80 60 40 20 0
4
1
Humidified air 2
Figure 4: Evaluation of number of airborne microorganisms. Inside wall surface of AHUs
Fungi Microorganisms
1.E+08
Fungi Microorganisms
1.E+06 B Humidifier element
3
humidification
Air before
Outdoor air
1.E+04
1.E+02
1.E+00
41 2 (Steam) Figure 5: Evaluation of number of attached microorganisms.
experiment was conducted from the end of November 2009 through to March 2010. Sampling was conducted three times during the operation of humidifiers. The first sample was taken on 2 December 2009: 120 hr after the start of the humidifier operation; the second sample was taken on 25 January 2010: two months (15.00 hr) after the start of the humidifier operation; and the third
sample was taken on 2 March 2010: three months (23.00 hr) after the start of the humidifier operation.
Results of the experiment Figure 7 shows the evaluation result of the air sampling. Many fungi were detected in the outdoor air and the air before humidification on March 2. However, the humidified air was
73
3
12
3
Number of microorganisms [CFU]
January 29 March 12
January 29 March 12
January 29 March 12
January 29 March 12
Number of microorganisms [CFU/g (mL)]
Initial state January 29 March 12 Initial state January 29 March 12 Initial state January 29 March 12
January 29 March 5
Initial state January 29 March 5 March 12 Initial state January 29 March 5 March 12 Initial state January 29 March 5 March 12 Initial state January 29 March 5 March 12 Initial state January 29 March 5 March 12
Number of microorganisms [CFU/m3
]
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