Several Standards For The Use Of UV Disinfection Lamps In Medical Institutions

This paper provides a reference for the use of UV disinfection lamps in medical institutions by testing the performance of several common power ordinary straight UV disinfection lamps in clinical use.

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1 Materials and Methods

Irradiance measurement method
UV disinfection lamps threshold value determination
Selection of UV disinfection lamps
Bacterial culture dish preparation
UV irradiation sterilization test

2 Results

Radiation sterilization test
Relevant parameters of commonly used UV sterilization lamps

3 Discussion

UV irradiation is a common disinfection method that is convenient, fast and effective, and is widely used for air, object surfaces, environment, drinking
Although today’s air disinfection equipment is becoming increasingly diverse, UVC germicidal lamp irradiation is still one of the main means of air purification in China’s hospitals. Nowadays, hospitals use different specifications of UVC lamps. The experiment of a hospital now uses three types of UVC lamps, 20 w, 30 w, and 40 W, with the numbers 245, 230, and 7 respectively. Therefore, we use a 20 w, 30 w UV lamp irradiation sterilization test to confirm the sterilization performance of the lamp, and the clinical common power of the UV lamp standard to summarize.

1 Material and Methods

1)Irradiance measurement method

In accordance with the standardized monitoring method provided by the expert group of Beijing Hospital Infection Quality Control and Improvement Center, the SUV I-3 ultraviolet irradiance meter of China Metrology Institute Technology Development Company was used for measurement. The irradiometer is calibrated annually by the Beijing Institute of Metrology and Inspection Science. According to the “Technical Specification for Disinfection of Medical Institutions” (hereinafter referred to as “Technical Specification for Disinfection of Medical Institutions”) method, the measurement was performed at 60%-70% relative humidity and 20-25 °C. Before the test, the indoor 13 lights, draw the curtains to keep the dark and weak light, and wipe the UV lamp with a 75% ethanol cloth towel before turning on. After turning on the UV lamp for 5 min, the UV irradiation meter probe with the measurement wavelength of 253.7 nm was placed at the center of the vertical distance l m under the UV lamp under test, and after the instrument was stabilized, the data shown was read as the irradiance value of the UV lamp. Each lamp was measured three times and the average value was taken.

2) UV disinfection lamps threshold value determination

A. The critical value of 30 W UV disinfection lamp replacement

The Technical Specification for Disinfection of Medical Institutions states that the irradiation intensity of an ordinary 30 W straight UV lamp in use should be no less than 70 μW/c㎡. Therefore, the critical value of the 30 W UV lamp is 70 μW/c㎡.

B. 20 W UVC lamp replacement threshold value

According to GB 19258 – 2012 “UVC Germicidal Lamps”: 20 w double-ended straight tube UVC germicidal lamps new tube illumination 1 m distance under the rated value of 75 μW / c square meters. The initial radiation illumination of the new lamp cannot be less than 93% of the rated value. Therefore, the initial intensity value of the new 20 w lamp should be no less than 75 X 93% = 69.75 W / c ㎡. According to the “Technical Specification for Disinfection in Medical Institutions”: the use of UV lamps with power <30 w, the irradiation intensity should be no less than 70% of the original new lamp intensity. Therefore, the irradiance of the 20 w UV lamp in use at a distance of l m should be no less than 69.75×70%=48.825 μW/c㎡, according to which the critical value of the 20 w lamp is set at 49 W/c㎡.

3) Selection of UV disinfection lamps

The use of ultraviolet illuminance meter on all the lamp’s intensity measurement, 226 30 w ultraviolet lamps, to find 5 l m distance irradiance of 70 μW / c square meters of ultraviolet lamps; in 245 20 W ultraviolet lamps, to find 5 l m distance irradiance of 49 μW / c square meters of ultraviolet lamps. These 10 critical lamps were used for sterilization tests.

4) Bacterial culture dish preparation

A. Petri dishes

Petri dishes were made of 90 mm diameter ordinary nutrient flat dishes.

B. Strain selection

The strain used for the test was the standard strain of Staphylococcus aureus, ATCC 25923.

C. Turbidimeter

Use the sub-turbidimeter manufactured by BD, USA.

D. Preparation of Petri dishes for test

Prepare bacterial suspensions with the corresponding Mackenzie turbidity as required. Use a sterile quantitative spiking gun to quantitatively aspirate the bacterial suspension to 90 mm ordinary nutrient dishes, and prepare into culture dishes containing different amounts of bacteria by dense coating and ascribing. After the irradiation test, the dishes were incubated in a 35℃ incubator for 48 h. The bacterial growth was observed after 48 h. Negative and positive control was set up for each test.

5) UV irradiation sterilization test

Using the principle that bacteria can be killed when the total dose of irradiation received by microorganisms reaches the bacterial inactivation rate, that is, the irradiation dose (“μW-s/㎡) = irradiation time (S) × intensity (μW / c㎡). The Technical Specification for Disinfection of Medical Institutions stipulates that the irradiation time of 30 w UV lamps should be i>30 min each time, so 30 min was chosen as the irradiation length for this test.

First, the lamp was turned on for 5 min, and after stabilization, the dishes containing bacteria were prepared and irradiated for 30 min at a distance of 1 m vertically under a 30 w (70 μW/c㎡) lamp, and immediately after completion, the irradiated dishes were placed in a 35 °C incubator and the bacterial growth was observed after 48 h. The maximum amount of bacteria that could be completely killed was found by using different amounts of Petra dishes. The dishes with the maximum bacterial amount were prepared and irradiated at 1 m under a 20 w critical value (49 μW/c㎡) UV lamp in the same way as the 30 w UV lamp. 20 w UV lamp irradiation test was conducted at different time lengths to observe the dishes that reached complete sterilization after incubation, and the shortest sterilization time was recorded.

2 Results

1) Radiation sterilization test

A. 30 W critical value lamp gradient sterilization test

Parallel tests were conducted with 2 bacterial amounts of wheat turbidity: 5.0 wheat turbidity (1.5 x 109 cfu/ml) and 2.0 wheat turbidity (0.6x 109 cfu/ml). Different amounts of bacteria were taken and prepared into concentration gradient flat dishes. The irradiation test was carried out with 30 W (70 μW/c㎡) UV lamp, and the maximum sterilization amount of the 2 turbidity dishes was the same as 1.2×10⁷ cfu/dish, and the bacterial culture after irradiation is shown in Table 1.

Table 1 30W critical value UV lamp after 30min vertical irradiation 48 h bacterial culture results

5.0 Mack turbidity/μl	Average residual amount of bacteria / cfu	2.0 Mack turbidity/μl	Average residual amount of bacteria / cfu
200	109.0	200	46.0
100	51.0	100	21.4
50	23.0	50	12.2
40	17.8	40	8.6
30	12.0	30	5.2
20	9.2	28	3.2
18	7.6	26	2.4
16	5.8	24	1.2
14	3.2	22	0.6
12	1.8	21	0.2
10	1.0	20	0
9	0.4	19	0
8	0	18	0
7	0	17	0
6	0	16	0
1 μl positive control	>10 000	1 μl positive control	>10 000
Negative control	0	Negative control	0

B. 20 W critical value lamp sterilization time test

The minimum time required to sterilize a standard Staphylococcus aureus culture dish at a distance of 1.2 × 10⁷ cfu/dish (2.0 Mackay turbidity 20 μl) was 43 min using a 20 W critical value UV lamp (49 μW/cm²) at a distance of l m. The bacterial growth after different times of exposure to the 20 W critical value UV lamp is shown in Table 2.

Table 2 Bacterial growth after 1 m distance 49μW/cm² intensity irradiation of 20W UV lamp

Number	Irradiation for 41 min	Irradiation for 42 min
Tube #1	3	0
Tube #2	5	1
Tube #3	4	1
Tube #4	2	3
Tube #5	3	0

2) Relevant parameters of commonly used UV sterilization lamps

Tests have proven that 20 W UV lamps can achieve the same sterilization effect as 30 W lamps by extending the irradiation time, fully confirming the formula irradiation dose (μW-cm²) = irradiation time (S) – intensity (μW/cm²).

Critical value 30 w lamp irradiation dose = 30 (min) x 60 (s) x 70 (μW/cm²) = 126 000 (μW-cm²): 20 w lamp irradiation time = 126 000 (μW-s/cm²) + 49 (μW/cm²) ÷ 60 (s) = 42.86 (min)

To facilitate clinical disinfection with UV lamps, using the formula we gave a summary of several power UV disinfection lamp standards commonly used in clinical practice, see Table 3.

Table 3 commonly used double-ended UVC germicidal lamps related parameters

Lamp power / W	Radiant illuminance rating (μW/cm²)	93% of rated value (μW/cm²)	Critical value (μW/cm²)	Theoretical time to sterilization standard/min
15	45	41	29	73
20	75	70	49	43
30	107	100	70	30
40	117	109	70	30

Note: (1) UV lamp radiation illuminance rating by GB 19258; (2) ≥ 30W UV lamp critical value of 70μW, <30W UV lamp critical value = rated value x 93% x 70%; (3) sterilization standard theoretical time = 126 000 (μW.s/cm²) ÷ critical value (μW/cm²) ÷ 60 (s)

3 Discussion

Disinfection with ultraviolet light is C-wave ultraviolet, its wavelength is 253.7 nm, its germicidal principle is that the radiation of ultraviolet radiation makes the DNA molecules in the cell undergo various forms of structural changes, preventing the replication of bacteria, transcription, protein synthesis. Because bacteria generally have a short life cycle, they cannot produce proteins, and reproduce bacteria will die quickly.

Through the bacterial concentration gradient sterilization test, we found that 20 w critical value lamps irradiated for 43 min could completely kill 1.2×107 cfu/dish of standard Staphylococcus aureus, fully meeting the sterilization effect specified in the Technical Specification for Sterilization of Medical Institutions. The results are consistent with the theoretical time of projection, indicating that low-power UV lamps can achieve the same sterilization effect by extending the corresponding The same level of sterilization can be achieved by extending the irradiation time. It has also been reported that using the phenomenon of superimposed irradiance values and turning on two old lamps at the same time can extend the use time of UV lamps.

According to the requirements of WS/T 368-2012 “Hospital Air Purification Management Code” for air purification management, hospitals should develop the corresponding air purification management system and organize its implementation according to the provisions of laws, regulations, and standards related to air purification and disinfection, combined with the actual situation of hospitals. In order to facilitate clinical standardization, we summarize several straight UV disinfection lamps are summarized.

The dust and grease on the surface of the UV lamp will hinder the penetration of UV light, and attention should be paid to the wiping and cleaning of the lamp in use. New lamps can be wiped with 75% alcohol cotton balls before use. In use by the output current stability, transformer type mismatch, transformer aging, voltage stability, and other factors, the irradiance of the lamp will be reduced. The UV intensity of the UV lamp should be measured regularly and should be replaced promptly if it drops below the intensity specified in the national standards. UV disinfection lamp life should not be less than 1 000 h. Use time < 1 000 h lamps need to be measured every six months, the use of time to 1 000 h should increase the frequency of monitoring. Currently, only 30 w UV intensity chemical indicator card, power < 30 W UV lamps need to use UV irradiation meter for determination. In addition, the literature points out that the use of the LED light source to replace the traditional light source to make UV sterilization equipment, with energy-saving, high brightness, long service life, long service life, and the ability to be used as a sterilizer. It is noted in the literature that the use of an LED light source to replace the traditional light source for UV sterilization equipment has the characteristics of energy-saving, high brightness, long service life, and lightweight, which will become a better choice for clinical use.