In the pharmaceutical industry, a sterile tunnel device is used to depyrogenate injectable products. The sterile tunnel is located in the production lines of injectable vials before the filling machine to depyrogenate the bottles before filling. The tunnel can sterilize and depyrogenate vials, ampoules, etc. using one-way hot air up to a temperature of 300-350 degrees Celsius.
In the past, infrared quartz tubes were used to regulate the temperature inside the sterile tunnel. Particles were emitted from these tubes into the tunnel, which caused the air flow inside the tube to be unstable and had a negative effect on the pressure conditions and cleanliness inside the tunnel. This was one of the reasons why the sterile tunnel was equipped with a laminar flow with a slow flow of hot air, which includes air filters that improve the control of the air flow pattern inside the tunnel.
A conveyor belt is installed inside the tunnel, and adjusting the speed of the conveyor belt affects the durability of objects (vials, ampoules, containers, etc.) in the hot air zone.
The sterile tunnel consists of the following parts:
1. Infeed chamber: Infeed The vials washed by Vial Washing enter the sterile tunnel inlet chamber (Infeed) by means of a conveyor belt. At this stage, the vials are exposed to a uniform air flow with an air flow speed of 0.5 m/s. This air flow first passes through a Pre-Filter with an efficiency of 40% and enters a HEPA, H14 filter with an efficiency of 99.997%. This air flow causes drying and preheating of the vials. The pressure inside the Infeed chamber is instantaneously sensed and monitored by pressure gauges installed on the tunnel. If the pressure increases or decreases from the defined value, the system automatically alarms.
2. Heating chamber: In this section, the air is heated by electric elements, with a maximum temperature of 350°C in the sterilization chamber. The temperature tolerance for the sterilization tunnel is usually ±15°C, and the temperature is monitored instantaneously by sensors installed in the tunnel, and the system gives an alarm if the temperature drops.
The heated air passes through HEPA filters, which are High Temperature Filters (Class H14) with an efficiency of 99.99%, and particles in the air up to 0.3 microns in diameter are absorbed by these filters. It should be noted that the temperature inside the tunnel and the duration of the vials’ stay in the tunnel vary depending on the speed of the conveyor belt.
To store energy, this hot air remains in the Heating chamber in a closed cycle, and this hot air operates in a loop, and only a part of it is vacuumed by the Exhaust vapor suction and is sucked and discharged to the outside space by the duct and Exhaust of the Cooling section installed under the device. The pressure inside the chamber is controlled by a pressure gauge.
3. Cooling chamber: After passing through the Heating chamber, the vials enter the Cooling section by a conveyor belt until the temperature of the vials, which has reached 300 degrees in the Heating section, decreases and reaches a temperature of approximately 10-15 degrees Celsius. The ambient air is vacuumed by two fans, which first pass through the Pre-Filter and then through the HEPA filter, and this air is blown vertically and regularly onto the vials in a gentle stream. After cooling the vials and absorbing their heat, this gentle air is vacuumed by the Exhaust Fan installed in the lower part of the sterilization tunnel and transferred to the external environment of the production section through the outlet channel.
Description of the sterilization operation:
During sterilization, open containers are surrounded by a stream of hot air. The stream of hot air must penetrate into and out of the empty glass containers (vials, ampoules, and bottles) that are ready to be sterilized. The time required for pyrogen removal is equal to the time it takes for the temperature inside the containers to reach the defined temperature.
Sterile Tunnel Validation:
The sterile tunnel validation process includes validation of heat distribution, pressure distribution, heat penetration, filter leakage, and measurement of microbial load, pyrogen, and endotoxin levels. Most importantly, the repeatability of the sterilization process is such that the dry heat process can sterilize and depyrogenate materials continuously under constant conditions and maintaining the desired temperature. In addition, the components of the sterile tunnel must be able to perform the depyrogenation operation at a selected temperature. Therefore, the temperature of the tunnel components must be validated.
The first step in validating a sterile tunnel is to verify the installation quality (Installation Qualification) of the tunnel equipment. Each sterile tunnel includes the following parts:
.1 Fan
.2 Exhaust or suction
.3 Filter
.4 Heating elements
.5 Temperature sensors and displays
.6 Differential pressure gauges
.7 Conveyor belt
.8 Control system and alarm
After installing the sterile tunnel, quality assurance experts, along with technical engineers, check the tunnel and its components according to the prepared checklists to ensure that they are installed correctly and are physically sound and free from any damage, dents, or fractures. And also all the systems supplying electricity, air, light and security systems, alarms, control and computer systems (software and hardware) are checked. All the defects are noted and at the end of the final report is prepared and presented to the technical unit so that the defects are eliminated in the shortest possible time.
All the operational procedures for working with the device, cleaning, repairing and maintaining the sterile tunnel are prepared by the technical and engineering unit and are attached to the validation documents after the approval of the quality assurance unit.
