Keeping the cleanroom free from contamination
Ensuring cleanrooms are free from contamination is essential for effective operation, and microbes, particulates and water vapour can all prove problematic
Ensuring cleanrooms are free from contamination is essential for effective operation, and microbes, particulates and water vapour can all prove problematic
Aseptic production requires stringent adherence to GMPs, and very careful design of clean areas to minimise the chances of contamination. Many areas need to be considered when designing a cleanroom, from airflows and air filtration systems through construction methods and materials, to operating and gowning procedures.
As Walter Greene explained at the recent ISPE Winter conference in Tampa, FL, US, the best place to start when designing a clean facility is a meeting that includes the staff who will actually be using it. But many other considerations have to be included early on, such as inventory policies, as space has to be allowed for operations such as the warehousing of empty vials.
Space utilisation is also important; labs, for example, take up a lot of space, especially equipment such as downflow booths, so this must be considered early in the planning process. Product flow also needs to be looked at, particularly in terms of pallet sizes and ensuring space and equipment can cope with these.
It is essential to identify gowning up procedures. 'This is not so simple,' he says. It necessitates running through current procedures, and plan what will be used in the future, particularly taking notice of how it will work in practice for the operators.
'Barrier technology was very popular,' he explained, 'but it fell out of popularity because a number of people had problems with it. But it is now coming back into fashion.' He also foresees a much greater use of robotics in this, in much the same way that high throughput screening has taken root in the discovery area. In addition, many future drug products will comprise very small amounts for delivery to the patient, and this will have a knock-on effect on manufacturing facilities.
With heating, ventilation and air conditioning (HVAC) systems, is it better to use 100% outside air or 85% return? Although the latter is cheaper, the trend is now towards the former, as this prevents cross-contamination. In addition, Czander's studies suggest that no more than four rooms should be included in one HVAC system.
One area that is often overlooked is sampling. It is no good merely having a curtained-off area, as the standards have to be as high as they are for the manufacturing operations. So a separate room is needed, and one that is large enough to handle all the required drums. Again, here, procedures must be established in advance so that the required amount of space is known: if every single drum is to be sampled, this will require more space to be available than if only one in six were being tested.
And, of course, when room layouts are being planned, then everything must be accounted for — not just the lyophiliser, but the people, control panels, pallets and so on. It must be large enough to be able to cope.
Perhaps the most notorious of the potential contaminants are microbes and spores. 'Design should be for the control of microbiological contamination in pharmacetuical cleanrooms — in other words, minimising it,' says James Walcroft, senior international analyst at Merck & Co.
The European regulations, in particular, give good guidance, he explained, including some 'real' numbers. Common contamination sources include:
Personnel is the most common source of contamination, with the billowing of gowns pumping microbes into the room. Poor operator technique is a particular hazard. It is important to know that the particle count in the room is negligible, but for pharmaceuticals, microbiology is more important. The two are not necessarily linked, as a rise in particulates need not be from the same source as any microbes present. 'You often do more damage than good by going in to monitor the cleanroom,' he says. 'Automated monitoring techniques are preferable.'
Passive monitoring involves looking at what lands on an agar plate within the room. This shows what will settle on surfaces, and so is an important test of the integrity of the cleanroom. However, laminar flow and the motion of operators have a big effect on the movement of microbes around a cleanroom.
Should you react to every single colony forming unit that is detective? Should there be an alert level? Or should action only be taken when failure levels are hit? Walcroft suggests that the alert level should be set sufficiently low to allow problems to be remedied before they become too big.
Four types of microorganism need to be considered:
Bacterial spores are a subset of Gram positive rods, and are important because they will persist through very harsh conditions, leading to the need to use autoclaves. The spore contains genetic material inside its hard shell, and can last through fairly extreme conditions, but when conditions the become right for the bacterium to exist again, it returns to the vegetative state. Spores require sporicidal cleaning agents to destroy them, such as Chlorox and hydrogen peroxide.
Essential in the effective operation of a cleanroom is air filtration, and this generally means the use of HEPA filters. As David Brande, principal and founder of Contamination Control Technologies explained, these date back to Germany during the second world war, and the technology was not released to the general public until the late 1950s. They have since found widespread use in the electronics and pharmaceutical sectors.
Originally, aluminium separators were used so the air could pass through. The filter is woven back and forth between the Al separators. The basic velocity ranges that are still used are based on this original design. The two sectors want good air filtration for very different reasons. With electronics, the important thing is to stop as much product being wasted as possible —a 35;40% cull rate is common. But in the pharmaceutical industry, the prime reason is to avoid injuring or killing people with contamination. Avoiding recalls is another important point.
HEPA filters are tested and graded into grades A;F at the factory. The pharmaceutical industry uses predominantly C grade filters. They are tested by machine and all hand-scanned, and it is a good idea to test the entire filter, including the frame. To make a HEPA filter, glass fibres are mixed into a slurry, sprayed onto the screens and then dried for final production. Water is sucked down from the screen and dried, in a process comparable to papermaking.
There are nine physical ways in which HEPA filters work, but the three shown in Fig. 2 are the most important: impaction, interception, and diffusion. Together, they account for 99% of all the particles picked up by the filter. As shown in Fig. 1, the diameter of the average human hair is 75µm, the average pollen particle 50µm, whereas the basis for ULPA filter testing is 0.12µm and the basis for cleanroom testing 0.5µm.
Impaction is the collection of particles that physically hit the screen, so generally relatively large matter. Interception is the attraction of particles to the filter's fibres by van der Waals forces. And diffusion is Brownian motion, where gas-sized molecules moving randomly run into filter accidentally. Minimum efficiency is at the lowest point of the ellipse of the graph in Fig 2, i.e. 0.3µm. This, however, is a theoretical figure only as it predates being able to test accurately. So HEPA filters are tested at 0.3µm because it was thought this was the most difficult size for the filter to collect. However, once testing procedures had moved on, it was found that the most penetrating particle size is actually 0.12µm.
It is not just the atmosphere that can carry in contamination, though. As Lee Emel of CRB Consulting Engineers explained, compressed air and gas systems are a potential source of contaminants. Compression is a process by which a compressible fluid is reducing in volume by means of a mechanical device. However, any contaminants that may be present will also be concentrated. Compressed gases, bought from a supplier in cylinders, are less of a problem than compressed air generated on site as they should be pure.
Water is one of the worst contaminants in compressed air; other potential contaminants include particulates, hydrocarbon vapours, or anything else that is drawn into the compressor.
There are two basic ways in which air can be dried: refrigeration and using a desiccant. Refrigeration uses a drop in temperature to condense water out, and a dewpoint of +2°C can be achieved using this method. As the temperature goes down, so does the moisture holding capacity. Desiccant dryers, however, use adsorption, and can remove water vapour to very low levels. Water molecules are attached to desiccant's surface by van der Waals forces, and dewpoints as low as ;73°C can be achieved. The method does have some limitations, as the desiccant can become overloaded with water.