Requirments of Hot Air Circulation Tunnel Oven(Dry Heat Sterilization)
Requirments of Hot Air Circulation Tunnel Oven(Dry Heat Sterilization)
Requirments of Hot Air Circulation Tunnel Oven(Dry Heat Sterilization)
November 07, 2022


Dry heat sterilization is a method of killing microorganisms by using high temperature to produce non-specific oxidation of microorganisms or biopolymers such as deoxyribonuclease. According to the heat transfer method, it can be divided into three types of heat transfer: convection heat transfer, conduction heat, and radiation heat. Dry heat sterilization equipment can be divided into batch type (or intermittent type) and continuous type according to the mode of use. The former, such as dry heat sterilization cabinet, can be used for sterilization and depyrogenation of metal appliances and equipment parts; Continuous dry heat sterilization equipment, such as tunnel sterilization ovens, can be used to sterilize ampoules or vials. Dry heat sterilization is suitable for sterilization of high temperature resistant items, such as glass, metal equipment, utensils, oils and fats that do not require moisture penetration, high temperature resistant powder chemicals, etc., but not suitable for rubber, plastic and most drugs sterilization. At the same time, dry heat can also be used for depyrogenation.

Compared with wet heat sterilization, dry heat sterilization has a relatively small application range, which is mainly determined by the following factors: 1. The heat transfer medium of dry heat sterilization has no phase change process. 2. During dry heat sterilization, the pressure in the chamber is relatively low, and there is no phase change, so the uniformity of temperature distribution is poor. Air is somewhat insulating (low heat capacity) compared to saturated steam, resulting in larger temperature differences within the dry heat sterilization chamber and longer heating times. The main factors that affect and determine the effect of dry heat sterilization include: exposure temperature, exposure time, and moisture content of microorganisms.

2.The basic principle of tunnel oven

The vials are sent to the hot air circulation tunnel sterilization oven from the bottle washer and sent to the preheating area, high temperature sterilization area and cooling area of the oven by the conveyor belt. Finally, the sterilized and depyrogenated bottles are sent out of the oven to filling and stoppering machine. The preheating area is composed of blower, dehumidifier, medium-efficiency filter and high-efficiency filter. The high temperature sterilization area consists of a high temperature resistant fan, an electric heater and a high temperature high efficiency filter to form a hot air circulation system. The high-temperature hot air flows through the high-efficiency filter to obtain parallel-flow air with a cleanliness level of A, and then directly heats and sterilizes the bottles. This function not oly meet the sterilization and depyrogenation requirements, but also achieve laminar flow A-level protection. The cooling area consists of a supply fan, high-efficiency filter, medium-efficiency filter, water cooler, (cooling) circulating fan and exhaust fan to form a cooling system, cooling bottle and laminar flow A-level protection.

3.Regulatory requirements for heat-dry sterilization

(1)2010 version of GMP aseptic appendix 1 specific regulations

Sterilization can be done by moist heat, dry heat, ionizing radiation, ethylene oxide, or filter sterilization. Each sterilization method has its specific scope of application. The sterilization process must be consistent with the requirements of registration and approval, and it should be verified. Before any sterilization process is put into use, physical detection methods and biological indicators must be used to verify its applicability to the product or article and that all parts have achieved sterilization effect. The effectiveness of the sterilization process should be revalidated periodically (at least once a year). After great changes to the equipment, revalidation is required. Revalidation records should be kept.
Biological indicators should be stored and used in accordance with the supplier's instructions and their quality confirmed by positive control tests. When using biological indicators, strict management measures should be taken to prevent the microbial contamination. Each sterilization operation should have a sterilization record and serve as one of the basis for product release.

(2)Thermal sterilization should meet the following requirements

1)During the verification and production process, the temperature probe used for monitoring or recording and the temperature probe used for control shall be set separately, and the setting position shall be determined through verification. The time-temperature profile of the sterilization process should be recorded for each sterilization. If the automatic control and monitoring system is adopted, it should be verified to ensure that it meets the requirements of key processes. The automatic control and monitoring system should be able to record system and process failures, and be monitored by operators. The readings from the independent temperature display should be periodically compared with the profiles recorded during the sterilization process.
2) The sterilization process can be monitored using chemical or biological indicators, but should not be used as a substitute for physical testing.
3) The heating time required for each loading method should be monitored and the sterilization time calculated from the time all sterilized products or items reach the set sterilization temperature.
4) Measures should be in place to prevent contamination of sterilized products or items during cooling. Unless it can be demonstrated that any leaking products or items can be removed from the production process. Any cooling medium (liquid or gas) that comes into contact with the product or item should be sterilized or sterilized.
5) During dry heat sterilization, the air in the sterilizer chamber should be circulated and maintained at a positive pressure to prevent the entry of non-sterile air. Air entering the chamber should be filtered by a HEPA filter, and the HEPA filter should be integrity tested.
6) When dry heat sterilization is used for depyrogenation, validation should include a bacterial endotoxin challenge test.
7) The temperature, time and pressure difference between the inside and outside of the chamber should be recorded during the dry heat sterilization process.

(3)FDA Aseptic Manufacturing Guidance

The integrity of the high-efficiency filter should be guaranteed to ensure a sterile environment, and the leakage test of the high-efficiency filter should be carried out at the time of installation to detect leakage around the sealing ring, around the frame or on the filter medium. Therefore, leak testing of HEPA filters on sterile operating facilities should be performed regularly. For example, such tests in sterile operating rooms should be performed twice a year; additional tests can be performed when the air quality is not ideal. Equipment renewal may result in the destruction of ceiling or wall structures, or in the simulation of culture medium filling tests or the destruction of sterility of drug products. Filters, including those installed in tunnel ovens and dry heat sterilizers used for depyrogenation of glass bottles, should also be leak tested. HEPA filters in heated areas such as these tunnel ovens can be inspected in other ways when there is a good reason.

(4)EMA Sterility Addendum

Clean room, air, and equipment should be reconfirmed regularly according to the established procedures. The maximum time interval for reconfirmation in Class A and B areas is 6 months, and the longest interval for reconfirmation in Class C/D areas is 12 months.
The reliability of BI (biological indicator) is of the utmost importance. It’s need to comfirmed by supplier. And transport and storage conditions should be controlled to prevent the quality of biological indicators from being compromised. Before each use of a new batch of biological indicators, the quantity and identification of the batch of indicator organisms should be checked. Generally, batch certification information provided by a confirmed supplier can be used.
Dry heat sterilization tunnels should be configured to ensure airflow through the tunnel from higher-level areas to lower-level areas, thereby protecting the integrity and performance of the Class A sterile field. Gas flow directions are visualized and linked to temperature studies. The effects of all airflow changes should be assessed to ensure that the warming profile is maintained. All air fed to the tunnel oven should pass through at least a HEPA filter; and be tested regularly. To demonstrate air filter integrity (at least semi-annually), tunnel components in contact with sterile components should be properly sterilized or disinfected.
On the whole, different countries have different descriptions of the understanding and regulations of dry heat sterilization, but the overall requirements are basically the same: if the sterilization process needs to be verified, the re-verification period is one year, and major changes in equipment should be re-verified, and the sterilization process should be re-verified, the bacteria should have records, and the sterilization records should be used as one of the release basis.

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