Technical considerations for selecting air filter products in the powder injection preparation industry

The selection requirements for air filters in the powder injection preparation industry (sterile packaged powder injection and freeze-dried powder injection) are one of the most stringent areas among all pharmaceutical formulations. The core challenge lies in controlling the risk of dust explosions and cross contamination, while ensuring a sterile environment, and also dealing with complex working conditions caused by special processes such as freeze-drying and compressed air.
Based on the latest industry practices and GMP standards, the selection of air filters in the powder injection preparation industry needs to focus on the following five technical issues:

• 1. End filter grade: The A-level area (packaging area, freeze-drying machine feeding area) in contact with the product must use H14 high-efficiency filters (with MPPS efficiency ≥ 99.995%) to ensure absolute interception of particles ≥ 0.3 μ m. H13 level can be used for B/C level background areas, but downgrade configuration is not recommended for A level.
• 2. Anti static and explosion-proof design: This is the most easily overlooked but also the most critical safety concern. Powder injections (such as penicillin, cephalosporins, hormones) are prone to static electricity during airflow transportation.
• 2.1 . Requirement: Filters used for packaging and weighing rooms (whether they are return air filters or equipment built-in filters) must have conductive layers/anti-static functions (surface resistance ≤ 1 × 10 ⁹ Ω), and the filter frame and installation frame must be reliably grounded.
• 2.2 Reason: Static electricity accumulation not only causes powder adsorption to clog the filter element, but more seriously, it may also trigger dust explosion. In areas involving organic solvents (such as for cleaning or processes), filters and housings must comply with ATEX or NFPA explosion-proof certification.

Powder injection preparations not only require a clean environment, but also the gases that come into direct contact with the process (such as compressed air and nitrogen) must meet sterile and dust-free standards.

• 1. Compressed air system: The compressed air that comes into direct contact with the powder or is used to blow the inner wall of the bottle must not contain oil or water.
• Selection configuration: It is necessary to configure a three-level precision filtration combination (such as T-grade removing 1 μ m particles → A-grade removing 0.1 μ m particles → H-grade removing 0.01 μ m particles), and ensure that the compressed air after end filtration has an oil content of ≤ 0.001ppm (H-grade standard) and less than 1 microorganism/m ³.
• 2. Nitrogen system: Nitrogen used for air breaking or nitrogen protection in freeze-drying machines. In addition to achieving the above filtration accuracy, the purity also needs to meet the process requirements.

The daily routine of the powder injection workshop involves high-intensity disinfection and sterilization (VHP vaporized hydrogen peroxide, alcohol wiping, wet heat sterilization), and the physical and chemical tolerance of the filter is the foundation for long-term stable operation.

• 1. Outer frame material: 304 or 316L stainless steel frame must be selected, and galvanized frame or paper frame is strictly prohibited. Stainless steel is resistant to disinfectant corrosion,

Avoid rust and particle contamination.

• 2. Sealing structure:
• 2.1 Liquid tank seal: For the terminal high-efficiency filter installed in the A/B level area, it is recommended to use the liquid tank seal (gel seal) or stainless steel frame+corrosion resistant silicone gasket to ensure that there is no side leakage even under the pressure fluctuation.
• 2.2 BIBO (bag in bag out): For highly allergenic powder injection varieties (such as penicillin), the high-efficiency exhaust filter must adopt BIBO structure to ensure zero contact between operators and toxic dust during replacement.

In the powder injection preparation industry, selection is just the beginning, and it is more important to ensure that the selected products can pass validation and achieve data traceability.

• 1. Factory requirements: Each high-efficiency filter must be scanned and leak checked one by one before leaving the factory, and must be accompanied by a unique number and factory inspection report to facilitate GMP traceability.
• 2. Verification after installation:
• 2.1 PAO leak detection: After installation, PAO (poly alpha olefin) aerosol scanning leak detection must be carried out, and the leakage rate standard is usually ≤ 0.01% (i.e. transmittance of one ten thousandth).
• 2.2 Wind speed and flow direction: The A-level area needs to verify that the average wind speed of one-way flow is between 0.36-0.54m/s, and the streamline is parallel.
• 2.3 Online monitoring interface: When selecting, consideration should be given to whether the filter reserves a differential pressure sensor interface for connection to the BMS/EMS system, to achieve real-time differential pressure monitoring and automatic alarm (such as alarm when the resistance reaches twice the initial resistance value or 450Pa), and to avoid overdue operation.

• 1. Freeze dryer: During sterilization, a large amount of wet and hot steam is generated in the freeze dryer.
• Requirements: The air filter and vacuum pump exhaust filter used for freeze-drying machine venting must be able to withstand pure steam or dry heat at 121 ℃ or even 135 ℃, and the filter material must have hydrophobicity and high temperature resistance (such as PTFE film).
• 2. High viscosity/moisture absorbing dust: For powder needle varieties that are prone to moisture absorption or have high viscosity, if return air is used in the packaging room, it is recommended to use PTFE coated filter material for the return air filter. The surface is smooth, the powder is not easy to adhere, and it is convenient for pulse back blowing to clean the dust, avoiding resistance surge.

summary suggestions
The selection of filters in the powder injection preparation industry can follow the following principles:

• 1. A-level zone: H14 stainless steel frame+anti-static filter material+liquid tank seal, paying attention to VHP corrosion resistance.
• 2. Process gas: three-stage filtration+zero grade oil-free standard, focusing on microbial retention capacity.
• 3. Highly sensitive/hazardous areas: BIBO structure+explosion-proof certification, pay attention to occupational protection.
• 4. General requirements: Scan one by one, perform PAO leak detection, and monitor pressure difference online, paying attention to data integrity.