Contaminant leakage in cleanrooms can compromise the controlled environment, leading to product defects in industries such as pharmaceuticals, electronics and biotechnology, and food contamination in production facilities.
With most contaminants coming from those working in the cleanroom, we must look at the essential measures to take in identifying and avoiding contaminant leakage in cleanrooms.
In this article, we discuss how to implement a comprehensive simulation technique to analyse and predict the behaviour of fluids, including airflow, heat transfer, and the distribution of contaminants in a given environment.
We also consider the control of contributory external factors, such as humidity, temperature, and air pressure differentials as well as the human factor.
The clean environment
Numerous manufacturing or research procedures require contaminant-free controlled environments in which dust and dirt are limited or even eradicated.
Medical instrument manufacturing and packaging, electronics and computer manufacturing, food preparation and some military applications all have strict requirements for maintaining a clean environment.
Cleanrooms are measured for particulate count at three different levels: As Built, At Rest and Operational. As Built refers to the cleanroom as it is when it is built, empty of any equipment, materials or workers.
Cleanrooms are typically certified by the manufacturer as to their level of cleanliness at the As Built level. At Rest refers to the cleanroom once equipment, machinery, furniture and products have been moved in, before the workers.
These elements can be sources of contamination, therefore a change in particulate count should be expected. Finally, there is the Operational level.
This refers to the cleanroom when all the equipment and materials are moved in and there are people performing tasks. With additional potential sources of contaminants, a further change in particulate count is normal.
Identify contaminants
Any process that involves friction or movement is going to cause particulation.
To prevent a drastic increase in contamination at the operational level it is important to adhere to proper protocol and procedures—such as gowning, cleaning and workflow.
If the process involves machinery, then it may be necessary to further isolate that machine within the cleanroom to prevent it from contaminating the rest of the operation.
Metal shavings, gases and oil mist from pneumatic machinery are all sources of contamination. A common solution to avoid this issue is to build a cleanroom within a cleanroom using partitions or curtains, to isolate the machine.
Venting that area separately from the rest of the room may also be necessary.
Contributory issues
While you may have identified your current operation and allowed for or dealt with the current level of contaminants, there is future usage to be aware of too.
The operation might begin with three workers in the cleanroom, and then increase to five or six. Additional extra body heat, as well as any heat-producing machinery in your clean area, and the cleanroom starts to get hot and uncomfortable. Therefore, air conditioning is essential.
This is where you get into the difference between single-pass and recirculating rooms. A single-pass room is a simple design in which the air enters the room through HEPA Fan Filters and exits near the vents at the floor.
A recirculating design uses a double-ceiling system
A recirculating design uses a double-ceiling system (the space between the ceilings is called a plenum), a double wall (the space in the walls is called an air chase), or a combination of these two.
Clean air is introduced through the HEPA filters, and exits through air chases that will typically have a louvered grille with a prefilter returning the air back up into the plenum space.
Once back in the plenum area, the recirculated air will mix with the new conditioned air and the process of passing through the HEPA fan filter will begin again.
Most cleanrooms, easily more than 90%, are positive-pressure rooms—designed to keep contaminants from entering the room.
Air is introduced into the cleanroom, typically at the ceiling level, after passing through a fan-powered HEPA filter that removes particles as small as 0.5 microns.
Most cleanrooms, easily more than 90%, are positive-pressure rooms
This creates a pressurised room in which the air pressure in the room is greater than outside the room.
The air, and the contaminants in the air, are pushed down towards the floor and ultimately pushed out vents in the lower portions of the walls of the room.
Negative-pressure rooms are designed to keep contaminants from leaving the room.
A negative pressure room is used in instances of infectious diseases and pathogens, bio-contaminants and some hazardous processes using chemicals, flammables and potentially explosive liquids and powders.
The concern here is not what gets into the room, but what might get out!
In a negative pressure room, air is pulled out of the enclosure through reversed HEPA filters, creating a negative pressure inside the room (which prevents contaminants from leaving the room), while air is constantly being drawn in through venting and other openings.
The force of the air entering the room prevents contaminants from escaping.
Simulation
Implementing a comprehensive simulation technique to analyse and predict the behaviours of fluids, airflow, heat transfer, and the distribution of contaminants in a cleanroom environment involves several key steps.
A simulation approach is crucial for identifying potential contaminant leakage points and understanding how external factors, such as humidity, temperature, and air pressure differentials, as well as human factors, can impact the cleanroom environment.
Advanced simulation techniques can be utilised to proactively identify and address potential contaminant leakage issues, ensuring the controlled environment is maintained at the desired level of cleanliness.
Some widely used software tools include Computational Fluid Dynamics (CFD) software like ANSYS Fluent, COMSOL Multiphysics, or OpenFOAM
Firstly the simulation objectives need to be defined. Identifying the specific contaminants to be analysed, while considering the cleanroom layout and critical parameters for your industry, such as airflow patterns, temperature ranges, and acceptable contaminant levels, need to be fully understood, as do the boundary conditions for the simulation, including airflow rates, temperature settings, and pressure differentials.
A reliable and validated simulation software that specialises in fluid dynamics, heat transfer, and contaminant dispersion needs to be selected.
Some widely used software tools include Computational Fluid Dynamics (CFD) software like ANSYS Fluent, COMSOL Multiphysics, or OpenFOAM.
CFD modelling assists in designing efficient technology solutions for new and legacy data centre environments by providing predictive results that bridge high-performance computer server operations with the critical mechanical system. Subzero Engineering includes CFD services for Simplex cleanrooms.
Human factor models needed to be included in the simulation to account for the impact of personnel movement, activities and potential sources of contamination.
Gowning procedures, movement patterns and the release of contaminants from personnel need to be considered. Every cleanroom ISO Class 7 or cleaner should have an anteroom for gowning, set off from the larger cleanroom.
This keeps street dirt from getting into the clean area. Interior isolation is also important in food processing and pharmaceuticals to prevent cross-contamination.
Once the simulation has been run, the results should identify potential contaminant leakage points, areas of stagnant airflow, and other critical factors affecting cleanliness.
These results need to be compared against industry standards and cleanroom classification requirements.
Modifications and management
Based on the simulation results, the cleanroom design, ventilation systems, and operational procedures need to be optimised to minimise the risk of contaminant leakage.
Consider modifications to the layout, airflow patterns, or personnel protocols, and implement continuous improvement measures based on feedback from simulations and actual cleanroom performance.
Measures to be undertaken should include:
1. Personnel training and gowning procedures: Training personnel and emphasising the proper gowning procedures and protocols of hygiene to minimise the introduction of contaminants.
2. Regular audits and inspections: Conduct regular audits and inspections of cleanroom facilities to identify potential sources of contamination with a systematic checklist to ensure compliance with cleanliness standards.
3. Airflow monitoring: Install airflow monitoring systems to detect variations and potential disruptions in the airflow patterns. Regularly calibrate and maintain airflow monitoring devices to ensure accurate readings.
4. HEPA filter maintenance: Regularly inspect and replace HEPA filters to maintain the effectiveness of air filtration systems. Ensure proper sealing and installation of filters to prevent bypass and leakage.
5. Controlled ingress and egress: Establish designated entry and exit points for personnel. Implement airlocks to minimise the transfer of contaminants.
6. Material and equipment handling protocols: Implement procedures for transferring items into the cleanroom, including proper packaging and decontamination processes.
7. Real-time environmental monitoring: Utilise real-time environmental monitoring systems to track and analyse factors such as temperature, humidity and particle counts with alarms for immediate notification of deviations from specified conditions.
8. Training on contaminant sources: Educate personnel about common sources of contaminants, such as skin flakes, hair, and clothing fibres.
9. Material compatibility assessment: Evaluate the compatibility of materials and equipment used in the cleanroom to ensure they do not contribute to contamination. Choose materials with low particle shedding and easy cleanability.
10. Continuous improvement: Establish a continuous improvement program based on feedback from audits, inspections and environmental monitoring. Regularly review and update procedures to incorporate industry best practices and emerging technologies.
11. Emergency response plan: Develop an emergency response plan for quick containment and resolution in case of accidental contaminant release. Conduct periodic drills.
12. Documentation and record keeping: Maintain comprehensive documentation of cleanroom protocols, maintenance activities, and training records. Use historical data for trend analysis and to identify areas for improvement.
By implementing these measures, cleanroom operators can significantly reduce the risk of contaminant leakage and maintain the integrity of the controlled environment.
Regular training, monitoring, and continuous improvement are key components of a successful contamination control strategy.
Subzero Engineering specialises in the design and construction of modular cleanrooms, which are constructed of pre-built components.
A modular cleanroom can easily be enlarged, reconfigured, or taken down and moved elsewhere to be reconstructed in a new location.
