Air pollution in hospitals is one of the important factors causing hospital infections, and the detection and control of air quality in a hospital environment is attracting more and more attention, and intensive care unit (ICU), drug exchange room, maternity ward, and other hospital class II environments are key aspects of air quality control. Air purifiers are widely used in air disinfection in recent years.  Air purifiers use the principles of electrostatic adsorption, negative ion, and activated carbon adsorption to design purification devices and circulate air for disinfection and purification. This article is based on real experiments to explain.

Let’s dive right in now, and you can click on the question that interest you, 

1 Choose an air purifier and methods

1) Choose an air purifier

UAP003 Air Purifier with 2000 m³ /h CW-HPC600 handheld laser dust particle counter, 6300 SEM scanner (JEOL), thermometer, and hygrometer.

2)  Methods 

Two ICUs with the same area (about 60 ㎡), floor (8th floor), orientation (west), building structure, and similar indoor layout were randomly selected as test sites in a tertiary care hospital in Changsha, Hunan Province. One of them was equipped with UAP003 Air Purifier as the experimental group for dynamic air disinfection; the other one was equipped with no air purifier as the control group, and both groups were equipped with air conditioning.

<1>Particle concentration detection

According to the range of aerodynamic equivalent diameter (AED) of dust particles, PM was measured in 6 particle size ranges in this test, and the PM results were calculated for 5 particle size ranges, and the actually measured PM particle size ranges were defined as: ( 1) particles with AED ≥0.3 μm, denoted as PM ≥0.3. (2) Particles with AED ≥ 0.5 μm, denoted as PM ≥ 0.5. (3) AED ≥ 1.0 μm particles, recorded as PM ≥ 1.0. ( 4) AED ≥2.5 μm particles, recorded as PM ≥2.5. ( 5) AED ≥5.0 μm particles, recorded as PM ≥5.0. ( 6) Particles with AED ≥10.0 μm are denoted as PM ≥10.0. The calculated particle size range is defined as ( 1) 0.3 μm ≤ AED<0.5 μm, denoted as PM 0.3~0.5. (2) Particles with 0.5 μm ≤ AED < 1.0 μm are denoted as PM 0.5~1.0. (3) 1.0 μm ≤ AED < 2.5 μm particles, recorded as PM 1.0 ~ 2.5. ( 4) 2.5 μm ≤ AED < 5.0 μm particles, recorded as PM 2.5 ~ 5.0. ( 5) 5.0 μm ≤ AED < 10.0 μm particles, recorded as PM 5.0 ~ 10.0. According to GB/T16292-1996 “Test method of suspended particles in a cleanroom (area) of pharmaceutical industry” [1] standard, the PM ≥0.3, ≥0.5, ≥1.0, ≥2.5, ≥5.0, ≥10.0 in the air of the test and control groups were measured by a handheld radiant particle counter with a flow rate of 28.3 L/min. A total of 5 sampling points were set up at the corners and the center of each ICU, with a horizontal distance of >1 m from the wall and a vertical distance of about 150 cm from the ground, and each point was sampled 3 times consecutively to obtain the average value.

<2> Measurement and recording of temperature, relative humidity, and number of people

The number of people in the room (including physicians, nurses, patients, and samplers in the room at the time of sampling) was recorded at the same time as the number of PM particles in the air of different particle sizes in the test and control groups were sampled and measured.

<3> Test procedure 

The temperature and relative humidity of the test and control groups were adjusted to 27-30 ℃ and 44%-50% relative humidity, Particle detection sampling time for 8:30, 9:30, 10:30, 11:30, 15:30, 16:30, 17:30, each count pumping 21 s, the control group with the same method sampling, statistical results, compared to calculate the concentration level of particulate matter. Particle samples were scanned and observed under the electron microscope to compare the morphological differences of different particle sizes.

3) Statistical processing  

The data were entered by two persons to establish a database, and the data were calculated as mean The data were expressed as mean ± standard deviation (x ± s), and SPSS 13.0 statistical software was used, The data were expressed as mean ± standard deviation ( x ± s), and the SPSS 13.0 statistical software was used to compare the means of multiple samples by ANOVA. The difference was considered statistically significant.

UAP003 Air Purifier

2 Laboratory results

1) Particulate matter detection results

The mean PM 10 concentration in the test group was ( 197 951 ± 12 498.9) particles/m 3 , The mean PM 2.5 concentration was (197,440 ± 12,533.0) particles/m 3 , and the mean PM 2.5 concentration was (197,440 ± 12,533.0) particles/m 3 . 3 , both significantly lower than the control group (P < 0.5). The mean PM 2.5 concentration was 197,440 ± 12,533.0/m 3 , which was significantly lower than that of the control group (P < 0.01). The smallest particle size that could be measured by the laser particle counter used in the experiment was 0.3 μm. The minimum particle size of 0.3 μm could be measured by the laser dust counter, and the number of PM ≥0.3 was used as the total number of dust particles in indoor air. The number of PM ≥0.3 was used as the total number of dust particles in indoor air. The PM composition ratio for each particle size range was calculated as follows PM 0.3~0.5 (pcs/m 3 ) = PM ≥0.3 – PM ≥0.5 PM ≥ 0.3 – PM ≥ 0.5; PM 0.5 – 1.0 (pcs/m 3 ) = PM ≥ 0.5 PM 0.5~1.0 (pcs/m 3 ) = PM ≥0.5 – PM ≥1.0; PM 1.0~2.5 (pcs/m 3 ) = PM ≥1.0 PM ≥1.0 – PM ≥2.5; PM 2.5~5.0 (pcs/m 3 ) = PM ≥2.5 m 3 ) = number of PM ≥2.5 – number of PM ≥5.0; PM 5.0~10.0 (pcs/m 3 ) = PM ≥5.0 – PM ≥10.0 PM 5.0 to 10.0 (particles/m 3 ) = PM ≥5.0 – PM ≥10.0. The difference in the distribution of total dust particles (PM ≥0.3) between the two groups was statistically The difference in the distribution of total dust particles (PM ≥ 0.3) between the two groups was statistically significant (P < 0.05), and the test group was lower than the control group.

UAP001 Air Purifier

2) Dynamics of particulate matter concentration  

The differences in the distribution of PM in various particle size ranges between the experimental group and the control group at different time periods were statistically significant, and the PM in various particle size ranges in the experimental group was lower than that in the control group.

3) Composition of particulate matter of different particle sizes  

The composition of PM in indoor air was 0.3~0.5 > PM 0.5~1.0 > PM 1.0~2.5 > PM 2.5~5.0 > PM 5.0~10.0 > PM ≥10.0. 10.0, and the difference between the test group and the control group was statistically significant ( P < 0.01) .

4) Morphology of particles with different particle sizes under electron microscopy  

In electron microscopic observation, The surface of the particles was all sculpted with small pockets and small particles protruding. The morphology of different particle sizes was mainly based on the morphological size, the obviousness of the pore film and the presence of The differences were statistically significant in terms of morphological size, pore film, and the presence or absence of irregular blocky protrusions.


3 The benefits of using air purifiers in ICU wards

In this study, PM with particle size <5.0 μm was found to dominate the air in the ICU, accounting for 89.32% (p < 0.05) of the total number of dust particles in the indoor air. Particle size <0.5 μm should be the focus of hospital air disinfection and purification and the development of appropriate standards. Existing studies suggest that the risk of microbial aerosols to humans is mainly related to the size of particles and the type and number of bacteria carried. In China, the “Qualified Standards for Disinfection of Hospital Air” were established as early as 1966, followed by the “Techniques for Identification of Disinfection Effect of Air Disinfection Apparatus” and the “Methods for Dynamic Disinfection of Hospital Class II Ambient Air” in November 1999 and May 2000, respectively. These regulations proposed that Class II ambient air should be dynamically disinfected, but only the sampling methods and qualification standards for static air disinfection were available, and no sampling and evaluation standards for bacterial colony counts and dust particle counts for dynamic disinfection and purification of Class II ambient air in hospitals were available. In the unoccupied non-working condition, even if the indoor air culture is sterile, it does not reflect the actual situation and increases the potential risk of infection in the hospital. The foreign regulations for PM in clean rooms (areas) in hospitals with Class II environments only cover the standards for particle size ≤ 0.5 μm and dust particle count ≥ 5.0 μm.

Currently, the main methods of air disinfection in hospitals are air filtration, UV lamp irradiation, chemical disinfectant fumigation, and spraying, and air disinfection cleaners. The UV lamp irradiation method, chemical disinfectant fumigation method, and spray method all require air disinfection under unoccupied conditions, and only the air filtration method and air disinfection purifier purification method are suitable for air dynamic disinfection, and the air purifier adopts electrostatic adsorption and high-efficiency filtration, and kills microorganisms through high-pressure electrostatic and filters, thus achieving the purpose of removing dust particles. The medical purification and disinfection machine has high efficiency of particle purification and can circulate the purified air, which solves the problem of air disinfection in the case of people. The air purifier has a good effect on killing and removing dust in the air, and an air disinfects or can eliminate >90% of natural bacteria in the air under static conditions, but when there are people in the room, the elimination rate of natural bacteria in the air is only 30% to 60%, so the effective disinfection method in the unoccupied condition is not necessarily ideal in the occupied condition. The development of sanitary standards for dynamic air disinfection in hospitals can not only effectively control hospital infections, but also regulate and promote the development of dynamic air purification disinfects.


[1] Ye Xianghong,Chen Yueying,Peng Nanhai,Li Weiqin,Li Jieshou.Analysis of air bacterial contamination before and after ICU partitioning[J]. Journal of Graduate Medical Science:715-718.

[2]Qin Hong Shen Yimei,Gu Zhengwei,Tang Zhengyuan.Air quality analysis and significance of disinfection method at different time points in ICU[J]. Journal of practical clinical medicine: nursing edition:55-55.