Ethylene oxide sterilizing gas (EO)

Due to the active type of ethylene oxide gas, strong bactericidal force, wide bactericidal spectrum, minor damage to articles and other advantages, the mixed gas of ethylene oxide and carbon dioxide has become one of the most important daily low-temperature sterilization methods, widely used in the field of sterilization of medical equipment products.　　

I.Sterilization principle and process of ethylene oxide:　　

Ethylene oxide sterilization principle is through its thiol and protein molecules (SH), amino group (NH2), hydroxyl (OH) and carboxyl (-cooh) group - and nucleic acids and amino - NH - alkylation reaction, cause protein loss of reactive groups, hindered the normal biochemistry and metabolism of protein, killing microorganisms, so as to achieve the sterilization effect.

Although ethylene oxide has a highly effective disinfection and sterilization effect, due to its wide explosion limit, the active effect on the container, as well as its irritation and toxicity, resulting in harsh conditions of use. In order to maximize the sterilization effect of ethylene oxide and ensure the safety of its use, the current popular is to mix ethylene oxide and inert gas, so that the activity of ethylene oxide is reduced, change the explosion limit, so as to improve the safety of use. Because the specific gravity and molecular weight of carbon dioxide are similar to that of ethylene oxide, a mixture of 70 percent carbon dioxide and 30 percent ethylene oxide is commonly used for sterilization.

Because ethylene oxide is flammable, explosive, and toxic to human body, it must be carried out in a closed ethylene oxide sterilization cabinet. The ethylene oxide sterilizer consists of a leak-proof, explosion-proof steel chamber, which is first temperature-regulated through a heating (pretreatment) process, then vacuumed, humidified by a humidifier to achieve sterilization conditions, and then fed with preheated and gasified sterilizing gas. The packaging material must be permeable to air, steam and ethylene oxide so that suitable sterilization conditions can be easily achieved.

The temperature, humidity, concentration, time, pressure and packing mode in the sterilizer are all important factors affecting the sterilizing effect. Due to the potential carcinogenicity, mutagenicity and acute toxic reaction of ethylene oxide, for the safety of the staff, the atmospheric concentration, the temperature and humidity of the chamber, the pressure, the concentration of ethylene oxide gas and the sterilization time should be closely monitored during the sterilization process. Sterilization effectiveness is usually monitored using a biological indicator. It is difficult to control the sterilizer, the whole sterilization process should be under the supervision of skilled personnel. After sterilization treatment, filtered sterile air should be fed through the vacuum air circulation process to safely remove residual ethylene oxide.

II.Safety and Environmental Protection

Due to the explosive characteristics of ethylene oxide, ethylene oxide sterilization device should meet the corresponding standards. The management of sterilization workshop should follow the requirements of the implementation rules for the production of disposable sterile device products (notes and conveyance devices) :

1. Formulate perfect proven and feasible sterilization process scheme and ethylene oxide storage, delivery system, special personnel hold the certificate to work, in strict accordance with the operating procedures
2. EO storage should be isolated from sterilization production, explosion-proof walls should be set up, storage room shaded, ventilated, sunscreen, flammable, explosive, toxic signs, and equipped with fire fighting equipment.
3. There shall be no open fire operation, substation equipment and other equipment or operations that may produce sparks within 30-50 meters around the sterilization workshop
4. In the process of sterilization, it is forbidden to wear nailed shoes to enter the site, and it is forbidden to smoke in the operation site to prevent explosion accidents
5. During operation, pay close attention to pressure and temperature changes and adjust at any time
6. When the sterilizer is opened at the end of the sterilization process, doors, Windows and ventilation equipment must be opened first. When the odor of ethylene oxide is very strong in the room, it is not allowed to turn on electric lighting and flashlight lighting, except for explosion-proof lamps.
7. The residual gas of ethylene oxide discharged after sterilization should be properly treated and meet the environmental protection requirements

III. Factors affecting sterilization　

The factors that affect the sterilization effect are temperature, humidity, concentration, time, pressure and packing method.

1. Temperature:

The conventional limit of temperature is generally 37 ° C ~ 63 ° C, and the most commonly used temperature is generally 50±5 ° C. But when the temperature is high enough to make the maximum effect of the drug, and then increase the temperature, the bactericidal effect will no longer improve. The determination of sterilization temperature is related to the following conditions: 1) the temperature tolerance of the destroyed product. 2) Loading quantity and loading method, the loading quantity is required to be less than 80%, do not contact the wall of the cabinet, and there is a gap of not less than 5cm between each box. 3) Thickness, size and bulk density of packaging materials.

 

2. Humidity

The sterilization effect of EO is affected by the moisture content of the sterilized article, the dryness degree of the microorganism itself and the relative humidity of the environment. When the relative humidity is lower than 30%RH, the sterilization effect is obviously affected. Therefore, wet microorganisms are easier to kill than dry ones, but the killing effect is not directly proportional to the relative humidity. If the humidity is too high, EO will be diluted and hydrolyzed. Therefore, the humidity before dosing should be controlled within the range of 30%RH ~ 80%RH after vacuum pumping.

3.Pressure

The degree of pre-vacuum determines the amount of residual air, and the amount of residual air affects the pressure after the addition of EO and the easy degree of moisture and heat entering the inside of the article, so the pressure, especially the pressure before humidification, has a great impact on the sterilization effect. The pressure setting should be based on the sealing performance of the peripheral equipment of the broken bridge aluminum alloy doors and Windows itself and the positive and negative pressure bearing of the destroyed items. In the range of equipment operation and items, negative pressure sterilization generally has better effect than positive pressure sterilization.

4.Ethylene oxide concentration

As an important factor affecting the sterilization effect, the sterilization effect can be improved by increasing the concentration. In a certain concentration range, temperature and humidity and other conditions are the same, with the increase of concentration, the shorter the time required to kill microorganisms of a certain concentration, the better the killing effect.

5.Time

Under the same conditions, the longer the sterilization time, the smaller the survival probability of microorganisms, and the better the sterilization effect. The shortest effective action time (half cycle) of ethylene oxide without viable bacteria was determined under the condition of constant other parameters except time, and the action time specified by the process should be twice of the half cycle.

6. Determine process parameters

According to the above factors, determine the verification procedure and formulate the process parameters.