What factors should be considered when setting the air shower time for the air shower pass box?

The setting of the air shower time for the air shower transfer window needs to comprehensively consider multiple factors such as the characteristics of the items, the requirements of the clean environment, the performance of the equipment and industry standards, to ensure a balance between the purification effect and the operational efficiency. The following are the core influencing factors and their specific explanations:
I. Item Characteristics: Pollution Risk and Physical Properties
Pollution degree and source
High-contamination risk items (such as materials transferred from non-clean areas, laboratories or production workshops) need to extend the air shower time (usually ≥20 seconds) to thoroughly remove dust, microorganisms or particles adhering to the surface.
Low-contamination risk items (such as materials circulating in the clean area) can shorten the time (10 to 15 seconds).
Item list: Area and shape
Large surface area or complex structure (such as porous materials, equipment components, pallets) : The airflow is difficult to cover completely, and the time needs to be extended (25 to 40 seconds) to avoid residual dead corners.
For small items (such as reagent bottles and packaging boxes), the air shower time can be set at 10 to 20 seconds.
Material and dust generation
Dust-prone materials (such as paper packaging, plastic foam, fabric) : An additional 5 to 10 seconds of air shower time is required to prevent debris from falling off and contaminating the clean area.
Smooth surface items (such as metal and glass products) : The airflow is easy to blow, and the time can be appropriately shortened.
Ii. Cleanroom Grades and Process Requirements
Clean area level
High-grade cleanrooms (such as ISO Grade 5 / Class 100, used for sterile production of pharmaceuticals and electronic chip manufacturing) :
The number of particles must be strictly controlled. The air shower time is usually 20 to 40 seconds, and in some scenarios, it needs to be ≥30 seconds.
Medium and low-grade cleanrooms (such as ISO 7 to 8 / Class 10,000 to 100,000, used for food packaging and general laboratories) :
The air shower time can be set at 10 to 25 seconds, taking into account both efficiency and cost.
Industry standards and compliance
Pharmaceutical industry (GMP/FDA requirements) :
Aseptic transfer needs to verify the effect of the air shower time on the removal of microorganisms (such as a ≥99% decrease in colony count), which is usually set at 25 to 40 seconds.
Electronics industry (ESD control and dust sensitivity) :
Set the time according to the product precision (for example, semiconductor components need 20 to 30 seconds, and ordinary electronic accessories need 15 to 20 seconds).
Food industry (Microbial and Foreign Matter Control) :
The blowing time is generally 15 to 25 seconds, which should be combined with the sterilization requirements (such as in conjunction with ultraviolet lamps).
Iii. Equipment Performance and Operating Parameters
Airflow velocity and nozzle layout
Wind speed level:
The standard wind speed is 20 to 25m/s. If the wind speed is ≥25m/s, the time can be shortened by 5 to 10 seconds. If the wind speed is insufficient (such as < 18m/s), the time should be extended or the clogging of the filter should be checked.
Nozzle direction and quantity:
Double-sided/triple-sided air shower (with more comprehensive air flow coverage) : The time can be reduced by 20% to 30% (for example, 20 seconds for one side and only 15 seconds for both sides).
Single-sided air shower: The time should be extended to 20 to 30 seconds to ensure that the items are thoroughly blown clean after being turned over or rotated (if there is a rotating table).
Filter efficiency
Performance degradation of high-efficiency filters (HEPA)
If the filter has been in use for more than one year or its resistance increases, and the dust content in the airflow rises, the blowout time should be extended by 5 to 10 seconds, or the filter should be replaced promptly.
Interlocking logic and operation mode
Continuous transmission mode
When the same type of items are transferred frequently, a "memory time" (such as 25 seconds for the first transfer and 18 seconds for subsequent transfers) can be set to improve efficiency.
Double-door interlocking delay:
After the air shower is completed, it is necessary to ensure that the door interlocking delay is ≥5 seconds to prevent the backflow of external air. This time is not included in the duration of the air shower.
Iv. Operating Scenarios and Management Requirements
Transfer frequency and efficiency
High-frequency transmission (such as continuous feeding on the production line) :
To strike a balance between purification effect and production capacity, the "base time + incremental time" mode can be adopted (for example, 15 seconds by default and 10 seconds for large items).
Emergency transfer scenario:
Set the "Fast Mode" (such as 8 to 10 seconds), which is only for low-risk items and requires record-keeping and filing.
Personnel operation habits
Ensure that the operator places the items correctly (such as maintaining a distance of 10 to 15cm from the nozzle) to avoid incomplete air shower due to improper placement, which may indirectly affect the time setting.
Verification and Recording
Regularly verify the validity of the air shower time through dust particle detection or microbial sampling (such as once every quarter), and keep records (such as Excel spreadsheets or electronic ledgers) to meet the requirements of compliance audits.
V. Additional Considerations for Special Scenarios
Microbial control requirements
If the transfer window needs to control bacteria, spores and other microorganisms simultaneously, the ultraviolet lamp irradiation time (usually ≥30 seconds) can be combined, and the blow-off time should be increased by 10 to 15 seconds on this basis.
Temperature and humidity sensitive items
When transferring items sensitive to air flow temperature (such as biological reagents and precision instruments), the air shower time should be controlled to be no more than 20 seconds to avoid changes in the performance of the items caused by air flow temperature differences.
Energy conservation and environmental protection requirements
During non-peak production hours or in low-risk scenarios, the "energy-saving mode" (such as reducing wind speed by 30% and extending the time by 10 seconds) can be activated to reduce energy consumption while maintaining the purification effect.
Summary: The core logic of dynamic adjustment
The setting of air shower time is not a fixed value. It needs to be continuously adjusted through a closed-loop process of risk assessment → initial setting → verification testing → dynamic optimization. For example:
First setting: Based on the type of item and cleanliness level, refer to the default values of the industry (for example, set 30 seconds for pharmaceutical production and 18 seconds for electronic accessories).
Verification test: Use a particle counter to compare the number of particles before and after the air shower. If the removal rate of the target particles (such as ≥0.5μm) is ≥95%, the time is reasonable.
Continuous optimization: Every six months, re-evaluate the time parameters based on the equipment's operating status (such as filter resistance) and process changes (such as the introduction of new products).
By systematically considering the above factors, it can be ensured that the air shower transfer window not only meets the cleanliness requirements but also maximizes the material transfer efficiency.