Combining sterile product protection and operator safety
When processing sterile, potent active pharmaceutical powders, the same design question comes up regularly: should an isolator operate under negative or positive pressure?
It looks like a choice between two conflicting objectives. Negative pressure prevents hazardous powder particles from escaping to the environment, while positive pressure is usually associated with protecting sterile products from external influences.
In reality, a manufacturer does not necessarily have to choose between these two objectives. With a well-designed isolator concept, product protection and operator safety can be achieved at the same time. The key lies in combining pressure control, HEPA filtration, airflow, background classification and controlled material transfer.
Why negative pressure matters with potent active ingredients
With potent active ingredients (APIs), operator protection is central. Depending on the toxicity of the product, very low airborne concentrations can already cause unwanted exposure. The required containment is therefore determined based on, among other things, the Occupational Exposure Limit (OEL) and the corresponding Occupational Exposure Band (OEB).
An isolator operating at negative pressure relative to the surrounding room helps prevent product particles from escaping in the event of a leak. Under a pressure difference, air in principle flows from the higher-pressure space to the lower-pressure space. With a suitable negative pressure cascade, air is therefore drawn towards the isolator instead of potent powder escaping uncontrolled into the production environment.
How do you protect the sterile product at the same time?
Negative pressure alone is not enough to protect a sterile process. Additional measures are needed:
- HEPA-filtered supply air.
- Suitable airflow patterns inside the isolator.
- An appropriately classified background room.
- Control of air leakage and pressure differences.
- Monitoring of critical process parameters.
- Validated cleaning and disinfection procedures.
The air quality and the required classification of the background room must be determined based on the type of isolator, the process and the applicable GMP requirements. EU GMP Annex 1 distinguishes between different isolator concepts and the associated protective measures.
A sterile product therefore does not have to be protected by positive pressure in the isolator alone. The quality, direction and control of the airflow are also decisive.
Designing a pressure cascade that controls both risks
One possible solution is a pressure cascade in which the process chamber is at negative pressure relative to the background room, while the supply of HEPA-filtered air supports the required product protection. Another option is a design with separate process and transfer zones, where material transfer, waste removal and cleaning are treated as separate containment questions.
The right configuration depends on the risk assessment and the requirements for both product and operator. It is important that the installation responds safely to loss of pressure difference, filter problems or a damaged glove. Think of alarms, interlocks and predefined process actions.
The weakest points are often at the transfer
The isolator wall itself is usually not the only factor that determines containment. In practice, risks arise mainly during process operations where connections are opened or material is transferred. Think of:
- Feeding raw materials via Rapid Transfer Ports (RTP).
- Powder transfer via split butterfly valves.
- Glove changes.
- Removal of waste and used liners.
- Sampling during production.
- Cleaning and maintenance.
These operations must be part of the containment design. A closed docking connection, for example, can help limit exposure when filling or emptying a container.
The removal of potent product residue also deserves specific attention. A sterilisation cycle with, for example, hydrogen peroxide (H₂O₂) does not automatically replace validated removal of chemical product residues. Sterility and product decontamination are different objectives.
How do you demonstrate that the isolator actually works?
A technically well-designed isolator must also demonstrably meet the required containment performance. SMEPAC testing can be used for this: Standardized Measurement of Equipment Particulate Airborne Concentration. Using a suitable test surrogate, exposure is measured during representative process operations.
It is important that the test does not take place only under ideal conditions. Include critical operations as well, such as:
- Loading and unloading material.
- Glove changes.
- Waste removal.
- Cleaning operations.
- Changing containers.
In addition, glove integrity, leak tightness, pressure control and filter performance must be checked according to the validated test and maintenance programme.
The right isolator starts with a process risk assessment
At Hecht Technology we approach containment as an integral part of powder processing. The choice of isolator should not be based solely on the required OEB classification. Product sterility, material transfer, cleaning strategy and the process environment also determine the final design.
By combining these factors from the start, you get an installation that protects operators and supports the required product quality.
Conclusion
Negative pressure and sterile product protection do not have to be mutually exclusive. With a well-designed isolator, HEPA-filtered air, controlled airflow and an appropriate background classification, both objectives can be combined. The greatest attention should go to material transfer, glove integrity, waste removal and validated containment performance.