The main purpose of a Cleanroom or Controlled Area is to isolate operations and processes from the external environment, which is considered uncontrolled and highly contaminating. However, the very dynamics of the operations and processes require continuous interaction with the outside, both for the entry of raw materials and materials into the Cleanroom and for the exit of finished products and waste from the Cleanroom to the outside. Continuous interaction with the outside or with other parts of the lower Grade within the Controlled Area is one of the main sources of contamination and a fundamental point to consider in the design of a Controlled Area.
Annex 1 GMP defines an Airlock as an enclosed space with interlocked doors, constructed to serve as a physical separation and to maintain air pressure control between adjacent rooms (usually with different air cleanliness standards). The purpose of an airlock is to prevent the entry of particulate contamination and micro-organisms from a less controlled area. Therefore, whenever there is a change of GMP Grade between rooms there must be an airlock.
Annex 1 also defines "Pass-through hatch", as a synonym for airlock, but usually smaller in size.
An airlock is generally considered to be a room, meaning an enclosure of sufficient size and access for a person to enter. A SAS (Safety Access System), also known as Pass-through Hatch or Transfer Hatch, is a smaller airlock, with internal size and door dimensions that physically prevent a person from entering.
As a general rule, material airlocks should be separate from personnel airlocks. When this is not physically possible, it must be justified and procedures implemented to prevent contamination. These procedures should aim to separate the use of the airlock for personnel and materials over time, ensuring the airlock is cleaned and decontaminated before switching its use.
Airlocks, regardless of their size, should be treated with active filtered air of sufficient quality to the grade they must maintain. Air from another room, even if classified, is not considered of sufficient quality if it has not passed through a filtration process before entering the airlock.
An airlock should have, at rest, the same grade as the room it leads to; hence any airlock needs filtered air to achieve the classification. Even a SAS connecting to a Grade D room should have Grade D at rest, thus requiring filtered air.
The interlock is an electromechanical or electromagnetic component that can lock and physically prevent a door from opening when the opposite door is open. Airlock and SAS doors leading to Grade A or B rooms should be interlocked to prevent their physical opening. For Grades C and D, a door opening control system with visual (traffic light) or audible (siren) devices is allowed.
When necessary, a delay in opening the access door may be established to ensure the airlock’s cleanliness conditions before opening the door to the more restrictive room.
The fundamental task of airlocks is to protect the room they access. The level of protection offered by the airlock should be proportional to the room's cleanliness grade.
Material airlocks do not need to maintain an ascending grade classification like personnel changing rooms. A material airlock can communicate an Unclassified Area with a Classified Area in a single passage (double door) provided that it provides sufficient protection, e.g. by ultra-filtered air, chemical decontamination, one-way direction etc...
The A/B area is the most critical within the aseptic process, with strictly low viable particle limits (microorganisms capable of growth). 0 cfu (colony-forming units) in Grade A and 10 cfu in air or 5 in sedimentation plates for Grade B.
Therefore, the transfer of materials to Areas A/B is one of the most critical activities in the aseptic process and can jeopardize the microbiological classification of Areas A/B.
In order to reduce the contamination risks, material airlocks in A/B areas should preferably be unidirectional, i.e. should be used in one direction only, either entry or exit.
Materials entering Grade A or B must be sterilised. This is achieved in steam autoclaves or dry heat sterilization ovens (depyrogenation). When sterilization is not possible because the materials could be damaged by heat, another system achieving the same goal of preventing contamination should be used. Essentially, a double-door airlock with a chemical disinfection system to reduce the bioburden.
When materials cannot be sterilized upon entry (autoclave or oven), they should be supplied sterile, protected by double or triple hermetic bags. In this case, the airlock must ensure the biological decontamination of the bag's exterior.
The number of bags should be at least equal to the number of different grade steps the material must pass through. The final passage to the A-B area should be by chemical decontamination or by a process, usually automatic, that allows the removal of the outer bag while avoiding contamination of the sterile inner bag. The decontamination, or sterility of the transfer process must be validated.
For materials exiting Areas A or B, no decontamination process is necessary, but the airlock chamber must recover the Grade B classification after the exit process.
If the same airlock is used for entry and exit, a time separation must be established between entry and exit, applying decontamination controls to ensure protection of the Grade A-B area at all times, especially when the airlock is reused for sterile material entry. Cleaning and decontamination processes, whether automatic or manual, must be defined and validated, implemented after use for exit and before use for entry.
Material airlocks do not require a stepwise grade transition; a material airlock can connect Area A/B with Grade D or even unclassified areas, provided that appropriate cleaning and decontamination procedures are defined and validated based on the risk.
Material access to Areas C and D should also use airlocks, with characteristics defined based on a risk analysis of the area they access. Requirements are not as strict as those for airlocks for Areas A/B but must include at least door opening indicators and active filtered air inside. Other processes, such as automatic or manual disinfection, can be incorporated based on the risk analysis and Contamination Control Strategy (CCS).
This type of airlock is connected to the HVAC system and can therefore maintain a GMP rating and differential pressure. This airlock is able to maintain a certain interior rating, however, opening the door on the 'dirty' side affects the rating of the airlock so a system is desirable to ensure that the interior of the airlock has regained the specified rating before opening the door on the "clean” side. This effect can be achieved by completing the interlocking system with a delay that prevents the door from opening until the airlock has recovered the required classification grade. A recovery test conducted during the validation phase will indicate the necessary delay time.
Another issue with this type of airlock is the potential for personnel to enter its interior. As a general rule, material airlocks must not be used for personnel access. The fundamental difference between personnel airlocks and material airlocks, besides their dedicated use, is that the personnel airlock consists of several consecutive stages in ascending grades (D-C-B) since personnel move themselves from one stage to the next. However, the material airlock consists of a single stage because the material must be moved by people, and these individuals should not cross consecutive stages involving a grade change without changing their clothing. Therefore, the general process of material transfer in an airlock involves two people positioned at either end of the airlock: one person introduces the material from the lower classified side (the “dirty” side), entering the airlock as little as possible, and another person removes the material from the higher classified side (the “clean” side), also entering the airlock as little as possible. Due to the interlocking doors, both individuals cannot be inside the airlock simultaneously.
In some cases, HEPA air filtration in the airlock is insufficient, for example, for the entry of materials into Grade A/B areas where a reduction in bioburden is required. This reduction is typically achieved through fumigation with a sanitising agent such as hydrogen peroxide, peracetic acid, glutaraldehyde, etc.
Hermetic Door with Ramp
Airlock Door with Pneumatic Seal
In this case, the SAS must be complemented by a range of accessories to enable effective and safe sanitisation:
Also known as Pass-through Hatch. This is the simplest type of airlock. Its effectiveness is based on the interposition of two or more interlocked or signalised doors with alternative opening, without interior air treatment.
This type of airlock is not permitted by Annex 1 GMP for transferring materials to classified rooms as it lacks active air, a fundamental characteristic that Annex 1 requires for all airlocks connecting to GMP classified areas (Grades A to D).
To meet the specifications of Annex 1 GMP, SAS must be flushed with ultrafiltered air. This type of SAS is often referred to as a dynamic SAS and can take various configurations.
Essentially a miniature cleanroom, it features a HEPA filter at the top of the chamber connected to the HVAC supply network and a low-level or floor return grille connected to the HVAC return system. It operates continuously as an integral part of the HVAC system. This type of SAS cannot perform any decontamination process, either automatic or manual, because the fumigating product would be dispersed by the HVAC system to other rooms.
It is also often referred to as "self-ventilated". It consists of a fan and a HEPA filter operating in a closed circuit over the SAS chamber. This system classifies the chamber to the required grade but, being a closed circuit, it cannot act on the internal pressure of the chamber to maintain a pressure differential between the "dirty" and "clean" rooms. However, SAS doors are highly hermetic, so a pressure gradient system is not as necessary.
The SAS ventilation system draws air from one of the rooms (usually the "dirty" room), filters it through HEPA, and returns it to the "dirty" room via a lower grille. This system achieves the required cleanliness grade in the chamber and maintains the SAS at a higher pressure than the "dirty" room, but there is an open communication between the SAS chamber and the "dirty" room through the air return grille. When the "clean" door is opened, there is direct communication between the "clean" and "dirty" areas through the chamber and the return grille, even if the "dirty" door is closed and interlocked. With the ventilation system running continuously, the clean air flow would prevent contamination from entering the "clean" area from the "dirty" area, but stopping the ventilation system could allow contamination.
In some cases, the recirculation system is complemented with a small air intake from the "dirty" area before the HEPA filter, helping to overpressurise the SAS chamber. This is similar to the previous case; while the system is running, the pressure regime and airflow prevent contamination from the "dirty" area to the "clean" area, but stopping the ventilation system could allow contamination.
In this case, the ventilation system is entirely independent of the rooms. It takes air from a technical area through a pre-filter and introduces it into the chamber via a fan and a HEPA filter. Air is extracted from the chamber through another HEPA filter and another fan and expelled outside. By controlling the fan speeds, the internal chamber pressure can be balanced to a specified value. The extraction HEPA filter, although theoretically unnecessary, is highly recommended to prevent external contamination from entering the chamber through the extraction duct and grille when the fans are stopped.
The independent ventilation system allows the fans to be off when the SAS is not in use and only activated during transfer operations. It also ensures that during the opening of the "dirty" door, the extraction fan is stopped, so all clean air pushed into the chamber exits towards the "dirty" area, preventing dirty air from entering the chamber. Similarly, during the opening of the "clean" door, the extraction fan remains active, so air from the chamber does not exit to the "clean" area.
In any case, whatever the ventilation model, this type of SAS requires PLC automation to control the interaction between fans, door interlocks, timings, etc. It should even be able to discriminate between an inlet cycle to the "clean" area and an outlet cycle to the "dirty" area.
This type of SAS or airlock requires an independent open-cycle ventilation system, as closed-cycle recirculation does not facilitate ventilation to remove the biocide after disinfection, and closed-cycle systems with air intake would allow the nebulised biocide to escape to occupied areas. The most suitable system is independent open-cycle ventilation with HEPA supply and HEPA extraction.
Another essential requirement for these SAS and airlocks is the presence of fully sealed doors to prevent biocide escape into occupied areas, both in the "clean" and "dirty" areas. In the case of SAS, door tightness can be achieved through continuous pressure seals (static seals) or inflatable seals with compressed air (dynamic seals).
Typical Cycles of a Decontamination SAS:
Pre-treatment: Depending on the type of biocide to be injected, prior conditioning of the chamber may be necessary to reach temperature and humidity conditions that ensure optimal biocide performance.
Injection: During this stage, the biocide is injected for a specified time to achieve the required concentration.
Contact: Once injection is complete, the chamber is maintained with the biocide concentration in the environment for a specified time.
Aeration: In this stage, the chamber is ventilated by injecting and extracting ultrafiltered air until the biocide concentration is reduced below safety limits to protect personnel unloading the SAS or airlock (e.g., for hydrogen peroxide, this limit is below 1 ppm).
A PLC control system is essential for managing the phases of the cycle and timing, as well as for establishing protections to prevent malfunctions, such as starting injection with an open door, opening doors during any stage, managing cycle aborts, and emergency stops.
Managing cycle aborts is also crucial, as an aborted cycle after biocide injection requires a complete aeration stage before allowing the "dirty" area door to be opened. In no case should the "clean" area door be opened since decontamination has not been completed.
In personnel airlocks, clothing changes occur, both when entering and removing when exiting. These operations, especially removing clothing, are highly contaminating with viable particles. Therefore, it is discouraged.
4.11 The transfer of materials, equipment, and components to Grade A or B areas must be conducted via a unidirectional process. Whenever possible, items should be sterilised and transferred into these areas through double-ended sterilisers (e.g., a double-door autoclave or a depyrogenation oven/tunnel) sealed in the wall. When sterilisation during the transfer of items is not possible, a validated procedure that achieves the same objective of preventing contamination must be applied (e.g., effective disinfection during transfer, rapid transfer systems for isolators, or a bacteria-retentive filter for gaseous or liquid materials). The removal of items from Grade A and B areas (e.g., materials, waste, environmental samples) must be performed via a separate unidirectional process. If this is not possible, temporal separation of movements (incoming/outgoing materials) should be considered and controls applied to prevent potential contamination of incoming items.
4.12 Airlocks must be designed and used to provide physical separation and minimise microbial and particulate contamination between different areas, and must be used for both materials and personnel moving between different grades. Where possible, airlocks used for personnel movement should be separated from those used for material movement. When this is not practical, temporal separation of movements (personnel/material) should be considered by procedure. Airlocks must be effectively treated with filtered air to ensure the cleanliness grade is maintained. The final stage of the airlock should, in the "at rest" state, be of the same cleanliness grade (both viable and total particles) as the cleanroom it leads into. Separate changing rooms for entry and exit to Grade B areas are desirable. When this is not practical, temporal separation of activities (entry/exit) should be considered by procedure. When the CCS indicates a high risk of contamination, separate changing rooms should be used for entering and exiting production areas. Airlocks must be designed as follows: Airlocks should be designed as follows:
4.13 For pass-through hatches and airlocks (for both material and personnel), the entry and exit doors must not be opened simultaneously. For airlocks leading to Grade A and Grade B areas, an interlocking system must be used. For airlocks leading to Grade C and Grade D areas, a minimum of a visual and/or audible warning system must be operational. When necessary to maintain area segregation, a delay between closing and opening interlocked doors must be established.
8.46 When necessary, materials, equipment, and components should be sterilised using validated methods appropriate for the specific material. Adequate protection must be provided after sterilisation to prevent recontamination. If sterilised items are not used immediately after sterilisation, they should be stored using appropriately sealed packaging and a maximum retention time should be established. When justified, components packaged with multiple layers of sterile packaging do not need to be stored in a cleanroom if the integrity and configuration of the sterile packaging allow the items to be easily disinfected during transfer by operators to Grade A (e.g., using multiple sterile covers that can be removed at each transfer from lower to higher grades). When protection is achieved through containment in sealed packaging, this packaging process should be carried out before sterilisation.
8.47 When materials, equipment, components, and ancillary items are sterilised in sealed packaging and then transferred to Grade A, this should be done using validated methods (e.g., airlocks or pass-through hatches) with corresponding disinfection of the sealed packaging exterior. The use of RTP (Rapid Transfer Ports) should also be considered. These methods must be demonstrated to effectively control the potential risk of contamination to Grade A and B areas, and similarly, the disinfection procedure must be proven to effectively reduce any contamination on the packaging to acceptable levels for entry into Grade B and A areas.
GLOSSARY
Airlock: A closed space with interlocked doors, constructed to maintain air pressure control between adjoining rooms (typically with different air cleanliness standards). The purpose of an airlock is to prevent the ingress of particles and microbial contamination from a less controlled area.
Pass-Through Hatch (SAS): Synonymous with airlock, but typically smaller in size.
Author:
Miguel Ruiz
GMP Consultant at Valtria