Dry-heat tunnels

Glass vials are received from the warehouse and enter the washing area. The vials are washed in a validated vial washer, using deionized water and water for injection with sterile compressed air. The vials are depyrogenated in a validated laminar flow dry heat tunnel and unloaded into the sterile filling room under laminar flow. 

The dry heat tunnel is connected directly after the washing machine. Starting at this point, the vials will be processed under class 100 laminar flow areas. First, the washed vials are loaded directly to the preheating zone of the tunnel, which is covered by HEPA filtered laminar flow. The vials are heated and dried properly before passing to the second stage, sterilization and depyrogenation zones. Finally, the vials will be cooled down to room temperature at the cooling zone. 

The two types of processes currently used in dry-heat sterilization include 1) dry-heat batch sterilization/ oven sterilization and 2) dry-heat tunnel sterilization. Process 1 is the type of dry heat unit widely used in the pharmaceutical industry it uses the principle of convective heat transfer to heat the load. Process 2 is only found in large-scale processes, and the main application of this process is in the sterilization and depyrogenation of glass.f ... 

Dry-heat tunnel sterilization is a continuous conduction process in contrast to the batch processes in ovens. A continuous conduction process is one in which a predetermined quantity of items is subject to a continuous conduction cycle at a predetermined rate to effect sterilization and/or depyrogenation. ... 

Air Drying Equipment. Tunnel kiln dryers (70) are long furnaces comprised of several zones of different temperature, humidity, and air flow through which the ware travels on a moving car or belt. These kilns afford continuous processing. Periodic kiln cross-circulation dryers (70) are box furnaces in which ware is stacked on permanent racks or on a car that can be shuttled in and out of the furnace. Fans or jets are used to circulate heat uniformly through the ware. The process is not continuous, but production rates can be enhanced by shuttling multiple cars. 

Recent sterilizer developments have led to the use of dry-heat sterilizing tunnels where heat transfer is achieved by infra-red irradiation or by forced convection in filtered laminar airflow tunnels. Items to be sterilized are placed on a conveyer belt and pass through a high-temperature zone (250 - 300 + °C) over a period of several minutes. 

Dry heat is used to sterihze and depyrogenate components and drug products. The definition of dry heat sterilization is 170 °C for at least 2 hours and a depyrogenation cycle at 250 °C for more than 30 minutes. Typical equipment includes tunnel sterilizers (force convection, infrared, fiame) and microwave sterilizers. An important aspect is the need to ensure air supply is filtered through HEPA filters. Biological indicators such as Bacillus subtilis can be used to gauge the performance of sterilization. 

Depyrogenatton process. A dry heat laminar how tunnel is used at ABC Pharmaceutical Industries for the sterilization and depyrogenation of vials used in aseptic processing. The following system description applies to... 

Dry heat sterilization validation. The tunnel operations conform to the master validation plan employed at ABC Pharmaceutical Industries. The sterilizing tunnel has undergone installation qualification, operational qualification, and performance qualification. The sterilizing tunnel is revalidated on an annual basis. The sterilization/depyrogenation cycle revalidation data for the tunnel are provided in validation archives. Sterilization validation reports are provided in validation archives. 

Two types of dry-heat sterilization systems are utilized in the pharmaceutical industry today. They are the conventional hot air oven and the tunnel system. The major difference between the two systems, as far as validation is concerned, is the belt or line speed variable with the tunnel system. 

As with any sterilization process, the first step in dry-heat sterilizer validation involves qualification of all the equipment and instrumentation used. This step includes examination and documentation of all utilities, ductwork, filters, and control valves or switches for the oven or tunnel unit, and the calibration of the instrumentation used in validating and monitoring the process. The instruments used are as follows ... 

A suggested step-by-step sequence in the microbial validation of a dry-heat process for sterilizing and depyrogenating large-volume glass containers by a convection batch oven is presented. Procedures for the validation of a tunnel sterilization process have been reported by Wegel [25] and Akers et al. [26],... 

Fig. 10 Flow diagram of LAF continuous-belt tunnel for dry heat sterilization and depyrogenization. (From Ref. courtesy of Kluwer.)...

The products are dried in tunnel dryers to a moisture content less than 2%H20 and fired at 1300 — 1450 °C in tunnel kilns heated with gaseous or liquid fuels. The firing brings about physical changes (densification, strenghtening) as well as chemical ones, which change the phase composition. 

The manufacture of silica refractories consists in the grinding of the previously crushed quartzite in a wet pan, the addition of the slaked lime and the molding of the prepared mixture by hand, in sanded steel molds. The pieces are then dried in tunnels and fired in down-draft kilns for about 9 days, carrying the temperature to the softening point of cones 16 to 18. The cooling requires from 5 to 7 days. The tunnel-car kiln is used in at least one plant, with a maximum heat treatment equivalent to cone 12 to 14. 

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