Cleanrooms are used anywhere a clean environment is required, ranging from satellite production in the space industry to spray painting cars in the automotive industry, to medical device production. Because of this diversity of use cases, permanent or modular clean rooms vary in size and complexity. However, one common factor is the need for proper standards and procedures put into place to maintain strict levels of cleanliness.
Standards
“Classification to ISO Standard 14644-1:2015 is based on the area of the cleanroom which is divided into grid squares,” explains Andy Worsick, sales executive, EMS Particle Solutions. “We take a measurement with particle counters at each location and see how many particles there are, and we carry out follow-up measurements every 6-12 months.”
The ISO Standard classifies cleanrooms into nine categories, which are graded on the number of particles of certain sizes or greater that are measured per m3. ISO Class 1 is the most stringent, only allowing a maximum of ten 0.1 micron (μm) sized particles per m3. Class 9 is the least stringent. Worsick explains: “Semiconductor facilities are typically ISO Class 3 or 4, and the heart of an aseptic pharmaceutical manufacturing process equates to 5, I’ve hardly ever come across a 1 or 2.”
Some cleanrooms feature isolators or restricted access barrier systems (RABS). An isolator is a decontaminated unit supplied with EU GMP Grade A air quality that provides uncompromised, continuous isolation of its interior from the external environment (for example, surrounding cleanroom air and personnel). A RABS provides an enclosed, but not closed, environment meeting defined cleanroom conditions using a rigid-wall enclosure and air overspill to separate its interior from the surrounding environment.
Furniture
Layout plays a significant role in maintaining cleanroom standards because every piece of furniture or equipment can interrupt air flow and cause contamination. “It’s really important to understand the process and where the process is happening,” explains Joe Murphy, BIM manager, Connect2Cleanrooms (pictured, right). “We use computational fluid dynamics (CFD) software for our high-end rooms to demonstrate that air-flow patterns do not present a contamination risk.
“There are always challenges when trying to ensure an even distribution of airflow within a cleanroom. There are natural areas where you get turbulence and stagnant air pockets, due to the air coming in from above and being obstructed by personnel, equipment, and furniture,” he continues. “The correct selection of furniture can make a big difference. For example, workbenches with perforated holes in the top can reduce turbulence and improve the airflow.”
For dirty processes like injection moulding, it’s important to remove as much of the particulates produced at source. This can be achieved with an extraction arm.
Air monitoring
Depending on the type of work being conducted within the cleanroom, the number of air changes per hour are considered.
Murphy adds: “According to our calculations, if you want to meet ISO Class 9, you’re looking at five full air changes per hour. At ISO Class 6 you’re probably looking at between 70 and 100 depending on process and occupancy levels.”
HVAC control is also important in cleanrooms. Processes could be sensitive to changes in temperature and humidity and – if parameters are unstable – they can affect the way particles move within a room. Often within a cleanroom there’s a lot of equipment and it’s necessary to understand how the heat generated by each piece of equipment affects the section of the cleanroom it sits in or even the whole cleanroom.
However, both Murphy and Worsick say workers are the largest contamination source in a cleanroom.
Particle size
Human hair has a diameter of about 70-100μm; the naked eye can see particles of around 30-50μm, and bacteria tends to be between 5-10μm. Air particle counters, used in measuring and monitoring the cleanliness of cleanrooms, typically measure for particles between 0.1-0.5μm up to 25μm.
There are two types of particles measured in cleanrooms: viable and non-viable. Viable particles are living, either micro-organisms, moulds or spores measuring between 0.2-30μm. Non-viable particles are non-biological.
“Measuring non-viable particles with a handheld portable counter is our bread and butter,” says Worsick. He adds that checking for viable particles is a little more complex. Rather than a photodetector, the particles in the air are impacted on to a contact plate or petri dish containing agar jelly, using an active air sampler (example pictured above). This dish is then sent off to a lab where it is incubated and monitored for micro-organisms forming on it.
In additional to air samplers, cleanroom viable monitoring is also performed using four-hour settle plates, contact plates and/or swabs.
Connect2Cleanrooms produces an owner manual with a schedule for when filters should be checked or changed.
Murphy says: “There’s a sense with some people that a cleanroom should remain clean itself. But processes and people naturally shed particles that need to be removed from the environment. Cleaning will remove non-viable particles, but organisations concerned with viable particles – typically healthcare and pharmaceutical applications – will need to disinfect cleanrooms too.”
“There should be a regular clean,” he adds. “For example, wiping all surfaces down with a suitable agent, such as alcohol, but cleaning and disinfection procedures should be based on the individual cleanroom’s product and processes. Rubbish and waste should be removed from the cleanroom at least daily. People should gown following the correct procedure. We offer CPD-certified training on how to mitigate risk by implementing correct behaviours, such as cleaning, gowning, and transfer procedures, it’s a good education for the cleanroom industry.”
He adds that, in terms of a fan filter, connections should be checked to make sure it’s operating correctly. These checks should be made bi-weekly, with filter checks every six months. The HVAC plant should also be monitored, in line with the manufacturer’s guidance. This is usually around every six months.
Working with a cleanroom manufacturer will ensure your room is built to the correct cleanroom standards. An experienced design team should present options to optimise the clean space and ensure a facility is meeting any regulatory requirements, while minimising any contamination that could potentially affect product quality.