Cleanroom Ozone Disinfection Validation Program

1. Overview

1.1 Ozone sterilization and disinfection effect

a. Ozone is a broad-spectrum and highly effective sterilizer with strong sterilization and disinfection effects.

b. The molecular structure is unstable at room temperature and pressure, and it quickly decomposes into oxygen and single oxygen atoms. The latter is highly active and has a strong oxidizing effect on bacteria. Ozone oxidizes and decomposes the enzymes necessary for glucose inside bacteria, thereby destroying its cell membrane and killing it. The excess oxygen atoms will recombine into oxygen molecules, and there is no toxic residue, which is a pollution-free disinfectant.

(Figure 1: Clean room ozone disinfection)

1.2 Technical features of ozone generator equipment:

Now choose a JY-BX-160A water-cooled ozone generator produced by xx Ozone Equipment Co., Ltd., equipment technical features:

• Using air as the gas source, the treated clean gas source enters the discharge tube of the odor generator to produce high-concentration odor gas.

• The ozone discharge chamber adopts an external circulation water cooling system to ensure that the heat generated when ozone is generated can be quickly taken away, so the ozone output is stable and can work continuously.

• The new high-frequency high-power development power supply and inverter power supply are adopted, so that the ozone output of a single machine can be adjusted arbitrarily using the panel adjustment knob. It can be used for multiple HVAC systems with different volumes in one machine to maintain the ozone concentration of different HVAC systems.

• The advanced PLC control and alarm system is selected to implement online monitoring, alarm and protection of water temperature, water flow, current, air pressure and other parameters to ensure the safe and normal operation of the equipment.

• The advanced microcomputer control system can set the operating time according to the needs, which is easy to operate and can be unattended.

(Figure 2: Ozone generator)

2. Verification purpose

Through the test of the ozone concentration in the clean room (area) at a certain time, verify whether the ozone concentration in each clean room in the clean area meets the standard requirements within the predetermined disinfection program time;

Through the microbial challenge test, determine the disinfection effect of ozone on the clean room (area) within the predetermined disinfection program time.

3. Verification scope

Ozone disinfection of quality control Class A/C and Class d Clean Rooms (areas).

4. Verification team members and responsibilities

• Production Department

• Engineering Department

• Quality Department

• Quality Assurance Department

• Quality Control Department

5. Verification operation content

5.1 Pre-confirmation

a. Selection of ozone generator.

①Ozone disinfection concentration (C): According to the 1991 standard of the Ministry of Health's "Disinfection Technical Specifications" and the efficiency of ozone disinfection, the concentration of ozone sterilization for floating bacteria in the air is (2~4)x10-6; for sedimentation bacteria on the surface of objects, the concentration of ozone sterilization is (10~15)x10-6.

②Natural half-life of ozone (S): about 20 minutes under reference conditions; 1 hour decay rate is about 62.25%; design and use ozone disinfection to reach relative concentration after 60 minutes, and continue to maintain for a period of time (1-1.5 hours) to achieve the purpose of killing bacteria settled on the surface of machines, equipment and buildings. 

(Figure 3: Air conditioning unit)

③Disinfection space volume (V):

Based on the selection of a suitable ozone generator, the clean area volume is V1, the HVAC system duct volume is V2, and the ozone consumption of the fresh air supplemented to maintain the positive pressure of the clean area is V3.

Determination of V3 Based on disinfection, a more reliable empirical formula is summarized: V3 = total circulating Air volume of HVAC system (m3/h) x 25% (assuming that the fresh air supplement is 25%) x 10% (the fresh air volume supplemented to maintain the positive pressure of the clean area) x 33.75% (the budget value for calculating the half-hi rate of ozone application)

That is: V3 x total circulating air volume of the system x 0.944% 

Then the volume of the disinfection space is: V = V1 + V2 + V3 According to the above requirements, the ozone concentration (C) in the air should reach 10x10-6, which is converted to 19.63mg/m3; after the ozone generator works for 1h, the natural decay rate of ozone (S) is 62.25%: then select the ozone generation volume W (mg/h) of the ozone generator.

The air conditioning unit is JK-1, and the air supply volume: 25000 m3/h, controlled purification area 395.02m2, cleanliness requirements (A/C, D); external ozone generator, connected to the air conditioning box with a pipeline, when in use, the Air conditioning system box and air duct and Clean Room are disinfected at the same time.

Calculate the required amount of odor according to the volume of the clean room and the volume of the air conditioning system duct:

The volume of the clean room is V1; the volume of the HVAC system duct is V2, and V3 is the amount of ozone in the fresh air supplemented to maintain the positive pressure of the clean room.

The volume of the disinfection space is: V=V1+V2+V3

Where V3=HVAC system circulation total air volume (m3/h) x25% (fresh air supplement) x10% (fresh air volume required to maintain the positive pressure of the clean area) x37.75% (calculation of the budget value of the applied ozone half-life) ~ total circulation system air volume x0.944%6.

IK-1: V1=987.55m3: V2=27.5m3: V3=25000x0.944%=236m3;

V=V1+V2+V3=987.55m3+27.5 m3+236m3=1251.05 m3.

Disinfection space volume V=1251.05+1225.33=2476.38 m3.

④Calculation of ozone concentration (C):

The ozone concentration (C) in the air should reach 10x10-6, which is converted to 19.63mg/m3. After the ozone generator works for 1h, the natural decay rate (S) of ozone is 62.25%; then select the ozone generation amount W (mg/h) of the ozone generator.

b. Selection of ozone generator.

The above calculation results show that the maximum amount of ozone required for the purification area controlled by the quality control clean room is 130gh. Therefore, an ozone generator with an ozone generation amount of 130gh can meet the requirements.

5.2 Installation confirmation

a. Purpose: To evaluate whether the installation of the ozone generator meets the design specifications and process requirements.

b. Method: Check the electrical part, the supporting conditions of auxiliary facilities, the installation of the machine, the installation area of the machine, etc.

c. Standards:

• Electrical part: integrated power control system and ozone generator; power supply 380V/50HZ, correct connection method, firm contact, good grounding.

• Auxiliary facilities:

Cooling water: inlet pipe 4'PVR pipe, valve controls water inlet; outlet pipe 4'PVR pipe, direct discharge, unobstructed outlet. Compressed air intake system includes: Jaguar EV51 air compressor, oil-water filtration device, adsorption drying oxygen production device, precision filter, pressure reducing device, etc. Jaguar EV51 air compressor has a safe and reliable structural design; stable operation, low noise; automatic pressure switch and automatic unloading system and other functions. Exhaust volume: 0.21m3/min (12.6 m3/h).

Installation:

Ozone generator installation location: The ozone generator is placed outside the supply and return air ducts of the purification system. The self-purifying ozonated gas is directly connected to the return air section of the two air conditioning units through a 4' stainless steel pipe, filled into the HVAC system, and then sent to each clean room. Valves cannot be installed on the oxygen outlet pipe. The ozone generator and the main control cabinet are basically horizontal, and the cabinet height direction is vertical to the ground. 

d. Result analysis

5.3 Operation confirmation (OQ) ozone concentration test

(Figure 4: Ozone concentration test)

a. Purpose: To confirm that the ozone concentration in the clean area meets the design requirements within 2 hours of the normal disinfection time of the ozone generator.

b. Qualification standard:

• All steps of the ozone generator run normally and are consistent with the operating instructions.

• Ozone concentration: The ozone concentration in the clean room is 210ppm (19.63mg/m3) within 40 minutes after the ozone generator is turned on; and the ozone concentration in all clean areas is 10ppm.

• Disinfection time: The time starts when the ozone concentration in all clean areas reaches 10ppm, and ends when the ozone generator stops working and the ozone concentration drops to 10ppm, and the time is ≥60min;

• After ozone sterilization, the time required for the ozone concentration to be reduced to the safety standard of 0.15ppm should be ≤30min.

c. Test conditions

Environmental conditions: Ambient temperature 16~28℃; Relative humidity 45~65%; no strong airflow from the outside, strong sunlight or other heat radiation in the room.

During disinfection, close the fresh air outlet and return air discharge valve, so that the air in the entire clean area to be disinfected forms a cycle through the purification system air duct, and the ozone generator starts working.

Ozone concentration test instrument: ZG-1 vacuum manual sampler, manufacturer: Beijing Labor Protection Technology Development Co., Ltd.

Test principle: The test tube test adopts the chemical colorimetric principle and directly reads the analysis data.

Ozone concentration test method: Cut off the seals at both ends of the test tube; insert the test tube into the air inlet of the sampler, pull the sampler handle to the second gear, sample 100ml, wait for the indicator in the test tube to stop changing color, and read the odor volume concentration (ppm) data from the scale caused by the white column. 

(Figure 5: Clean room purification system air duct)

The relationship between the oxygen detection concentration unit mg/m3 and ppm and the conversion formula: Ozone concentration (mg/m3) = ozone molecular weight (M)/22.4 (molar volume B of gas under standard conditions) x volume concentration (ppm) x (273/(273+T)) x (Ba/101325).

Volume concentration (ppm) = mass concentration (mg/m3)/(ozone molecular weight (M)/22.4 (molar volume B of gas under standard conditions))/(273/(273+T) x (Ba/101325).

e. Two parallel samples should be tested at each test point at the same time;

f. During the test, the tester should wear a gas mask to prevent ozone poisoning.

g. Test process

①The following work should be ready:

The equipment is firmly installed;

Electrical connection:

Check whether the ozone outlet is unobstructed:

Open the external cooling water inlet valve; Set the ozone generator disinfection time to 2 hours on the main control cabinet programmable timer. 

②Press the start button, the green indicator light is on, the timer starts timing, and the odor pipe starts working at the same time, slowly adjust the concentration knob to the normal value area. For detailed operating procedures, see (JY-BX-160A Ozone Generator Standard Operating Procedures".

h. Ozone concentration-time distribution test.

①Purpose: When testing the air disinfection in the clean area, set the ozone generator disinfection working time within 2 hours, the ozone distribution density and action time in the air:

• Determine the time for the ozone concentration to reach 10ppm: ≤40min;

• Determine the time when the ozone concentration in all clean areas reaches 10ppm and start timing until the ozone generator stops working and the ozone concentration drops to 10ppm. The maintenance time should be 260min: Determine the time required for the ozone concentration to drop to the safety standard (0.15ppm) after ozone disinfection: ≤30min. 

②Test location: Select the room farthest from the air outlet of the air conditioner and with the least air outlet (D101 men's undressing room) for testing.

③Test plan: Start the test when the ozone generator is turned on, and use the ZG-1 vacuum manual sampler to sample and test once every 10 minutes; after the generator is turned on for 40 minutes, the ozone concentration rises slowly and approaches a platform; monitor continuously for 2 hours; when the ozone generator is turned off, test once when the air conditioner is supplying air, test once after 10 minutes, and monitor continuously for 1 hour (monitor the attenuation of ozone concentration when the air conditioner is supplying fresh air).

④Result analysis.

5.4 Performance confirmation (microbial challenge test)

(Figure 6: Microbiological experiment)

a. Purpose: To confirm that the predetermined ozone disinfection procedure has a microbial killing rate of ≥90% after disinfection of the clean area space.

b. Staphylococcus aureus challenge test.

• Preparation of biological indicators: Prepare bacterial solution from Staphylococcus aureus; after 48 hours of culture, dilute to 1200/ml. Before use, add 1ml of the above bacterial solution to the nutrient agar medium plate and evenly distribute it on the surface of the culture medium.

• Select key rooms and place 2 plates in each room.

• Open the cover of the culture dish filled with bacterial solution while turning on the ozone generator until the ozone disinfection procedure is completed.

• Place the culture dish in a 37℃ constant temperature incubator for 48 hours and calculate the colony. At the same time, use a culture dish that has not been treated with ozone as a blank control.

• Calculate the killing rate.

6. Verification Results Synthesis and Evaluation