Keeping The Cleanroom Clean
Last month we talked about why the cleanroom was created – to prevent contamination in research or manufacturing environments. We looked at the history and development of cleanrooms as a concept, and we explored some of the different industries that utilize cleanroom technology. This month we’re going to take a look at how cleanrooms actually stay clean and offer some advice as to why, and how, to maintain your own.
A “Clean” Room by Design:
There are many different sources of contamination that must be controlled in order to keep a pollutant free environment. Some of the common ways to contaminate a room is through the airflow, which is why the HEPA filter was originally designed – to keep dust, pollen, and other airborne pollutants out. The second most common and controllable source of contamination of a cleanroom is the people that physically work in the room. The combination of strong air filter systems designed both for workflow and air flow help to control these sources. Humans emit an estimated 100,000 particles per minute when just standing still so it’s important to ensure that physical work processes are as efficient as possible. As such, in cleanrooms it’s best to contain similar activities to certain areas of the room, which aids in preventing unnecessary movements.
To help deal with incoming air particles the airflow in every cleanroom is designed to move in one of two patterns. The first uses a Laminar Air Flow Hood to ensure that air flows in a straight, unimpeded path, commonly known as a laminar flow. In a cleanroom this is also known as Single Pass Design; where the air runs through a HEPA Filter, is pumped into the room, and then purged from the environment without being recycled. This is ideal for use in environments that require less precise controls for temperature or humidity as well as smaller working spaces.
The second type of airflow is primarily utilized in environments that need to control temperature and humidity with extreme precision. In these rooms air does not typically flow in one particular direction. These conditions are best suited for a Recirculating System. The idea behind a Recirculating design is that instead of continuously sucking in air only to purge it out immediately the air systems intake air then recirculates it, as demonstrated by the image below. This system uses a laminar flow hood in combination with other nonspecific velocity filters to ensure that the movement of the air is not in a specific direction. The Recirculating design is also much more effective at handling large amounts of air than the Single Pass system, so this design is commonly found in larger cleanroom environments.
The last step in well-rounded cleanroom design is the gowning room, or the changing area for a cleanrooms staff. Keeping cleanroom garments in an isolated area is an essential step in reducing the level of exposure to outside contaminants that they may normally see. As such, it is best practice to enter a gowning room in a series of steps.
First, the employee will use a shoe cleaner to loosen and remove any particulates, and then they’ll walk over an adhesive shoe mat to ensure that their shoes aren’t tracking anything else in. Before ever entering the gowning room they’ll pass through a HEPA filtered air jet, also known as an air shower, to remove any loose contaminants. Then, they’ll proceed to the hand washing station, which is generally a no-touch hand sink to make sure their hands aren’t spreading any particles as they put on their suits. At this point employees begin donning the ‘cleanroom outfit’. Our general rule at Your Cleanroom Supplier for procedure this is pretty simple. Start with your head and work your way down. Shoe covers should be applied last, right before entering the final air shower, which leads to the workspace. Exiting the workspace is also a controlled process, though much less of a degree. The worker will exit through another air shower and then discard all disposable garments, like gloves, masks, or booties. All other garments, like lab coats that are not disposable will be returned to their storage areas. It’s absolutely imperative that no aspect of the cleanroom ensemble leaves the gowning room as this could be a major source of contamination for the future.
Managing the Human Element
Despite the safe guards put in place by all of the cleanroom equipment, humans are still the largest source of contamination within a room for a variety of reasons. Skin flakes, oil, sweat, and spittle are some of the most natural ways for humans to infect a room – not to mention sneezing or coughing. Hair, both from the face as well as head can also be seen as an issue. To control this, it’s recommended to use a beard cover when necessary in combination with a hair net when appropriate. Most lab suits also include a hood to further prevent contamination.
Another potential source of human based contamination includes any cosmetics or perfumes that employees wear in to work that day. It should be established as a ground rule not to wear any sort of cosmetics in the cleanroom. No make up of any kind, any aerosol, after shaves, or perfumes.
As mentioned earlier, standing still can result in the shedding and spread of over 100,000 particles per minute. That’s just standing still! Walking at a gentle speed of 2 mph can raise that number by a huge amount – up to 5,000,000 ppm! The volume only goes up from there. In fact, horseplay like these guys:
could put an entire workplace at risk of contamination and as such employees should be trained to avoid a few basic actions. Employees should be explicitly trained to avoid erratic movements, leaning on any surfaces, writing on any garments, and to never, under absolutely any circumstance, should they remove any items brought into the cleanroom from underneath their garments. These sort of actions can be considered reckless and as points of contamination.
Rodger McFadden, the Senior Scientist for Staples, INC, wrote the definitive guide on how to handle the human element within a cleanroom. These 17 points have been reproduced in their entirety, and can be Downloaded Here. It should not be used as a replacement for any pre-existing guidelines in your cleanroom, but it is a set of solid recommendations that will assist in keeping your cleanroom as clean as it can be.
As you can see, the way you behave is just as important as the equipment itself. Knowing the appropriate way to walk and interact with your environment will ensure to reduce any potential contaminants from being further introduced to the workspace, but it’s only part of proper cleanroom operations. Designing for work flow and air flow make up another part, but as we will talk about next month, when we take a look at the art and process proper of cleanroom maintenance, there is still a lot left to keep in mind.
Images sourced from Wikipedia