Special rules for working in a cleanroom (Restricted activities)

Special rules for working in a cleanroom (Restricted activities) 

Since the major goal of this section is to describe the techniques needed to work as a minimally contaminating employee, you might guess that there are some activities that are forbidden because they cause too much contamination. This subsection will follow the same format as the earlier subsection on restricted materials. We will begin with a list, and then explain why these activities are restricted.

Gowning for class 10,000 cleanrooms

Many of these restricted activities are not very natural.  In fact, we commonly perform these restricted activities. You must develop the habit of not engaging in these very natural, everyday activities while in the cleanroom. Furthermore, you must also help remind/inform your coworkers to minimize their activities also.

No fast motions
No sitting or leaning on equipment
No writing on equipment or cleanroom garments  (Asymtek, VPI)
No removing items from under cleanroom garments  (cell phones, keys)
No wearing of cleanroom garments outside the cleanroom and adjacent gowning area
No wearing of soiled or torn garments
No touching or scratching of exposed hair or skin
No coughing or sneezing over work areas
Don't wear contaminated gloves (gloves should be changed outside the main facility, except under emergency situations)

Read more:

What is one allowed to wear under a cleanroom garment?

The basics of working in a cleanroom

Fast motions are not allowed in a cleanroom. This can be difficult, all projects are behind schedule, everything is needed yesterday, and if you needed something later you would not be going to get it now. The rationale for this restriction comes from studies of how people disturb the air flow in a cleanroom.

When movements (walking, moving arms, etc.) are slow enough the air flow in the cleanroom is only minimally disturbed, and the flow quickly returns to its pre-agitated state. When rapid movements are executed turbulence is produced. This can cause large scale motions of particles and can take a long time to relax back to the non-turbulent state.

The turbulence that is produced by rapid motion generally include vortices that sweep up particles and then deposit them on surfaces, often the substrates that are being worked on. The best advice that can be given in this area is to just move along slowly and calmly, and perform all operations as if it were the hottest summer day. The work must be completed, but rushing can produce more problems than it solves.

While in a cleanroom you should not sit or lean on equipment. This too is very unnatural. How often do we place a hand on a table and lean on it, or how often do we lean against a wall or a kitchen countertop. In informal settings it is not uncommon for people to sit on desks or tables. Thus, for most of us this is a standard mode of behavior which must be suppressed. Furthermore, it is not uncommon for operators to spend hours in the cleanroom and really want to take a load off of ones feet.

Once more, the rationale for this rule is to minimize contamination. By leaning or sitting on equipment you can easily remove contamination such as settled particles from the equipment as well as your cleanroom garment. Furthermore, you might catch part of your garment on a protuberance and rip the garment leading to more widespread contamination.

Lastly, such behavior might upset the alignment of some of the equipment and lead to further problems.  Cleanroom stools are present for sitting, but care must be taken when using them.  Do not spin on these chairs or zoom across the floor, both activities which would result in severe air disturbance in the room.  Also, the stool seats are slippery to cleanroom garments.  Care must be taken when sitting down to avoid having the stools slip out from under you, causing you to land on the floor.

Writing on equipment or garments is prohibited for a number of reasons. However, once more this can be difficult to avoid. Suppose a piece of equipment has just been adjusted, and the numbers or procedure needs to written down.

The time taken to go get a cleanroom notebook, or paper may seem to be too excessive  because the numbers are only needed for that piece of equipment.  Why not have them where you need them? Suppose a supervisor tells you to remember to get or do something later. You don't want to forget so why not write it on a glove or a garment sleeve where you can not forget?

All of these rationalizations for not following the rules seem reasonable; however, they ignore the potential contamination that can occur by writing on equipment or garments. This rule exists because the writing on equipment may not stay and it may well then become so much particle contamination. Furthermore, the writing may rub contamination off the equipment, but provide nothing to pick it up. Similarly writing on garments or gloves generally will produce some contamination, remove some contamination, and worst of all possibly tear or rip these important contaminant reducing clothes.

How often do you reach into a pocket to remove something; for instance a billfold from a back pocket? During the winter, or when wearing a raincoat, it is common to reach inside one garment to get something out of another. This is so common we usually don't think of it in the terms just described.

Now suppose you want to do the same thing while in a cleanroom wearing a cleanroom garment. You must undo the garment, get what you want, and then redo the garment. While doing all of this, what happens? Contamination from your clothes and the inside of your garment gets spread all over.

Then what ever was under the garment, which has not been in a clean environment will add its own contamination to the mix. The only acceptable place to open a cleanroom garment and get something from under it is in the gowning area. Furthermore, objects should be removed only at the correct step of gowning or degowning. To open a cleanroom garment while in a cleanroom is the same as not dressing for the cleanroom at all.

One should not wear a coverall/gown outside the cleanroom or gowning area. Once more, this is not natural. How often do we run outside without a coat, because it will only be for a few moments? It takes time to put on and take off the cleanroom apparel, and I will only be outside for 5 seconds.

Why can't I run out and run in? 

The rationale for this rule goes back to why we dress for the cleanroom in the first place. Recall that we dress in the special cleanroom apparel to protect the product we are making from us. This is the exact reverse of why we wear clothes, shoes and coats, which is to protect ourselves from external elements.

Once a cleanroom garment has been worn outside a cleanroom (or the adjacent gowning area) it has become contaminated. To bring it back into the cleanroom is to bring that contamination into the cleanroom, and to some extent contaminate the cleanroom. This violates the reason for the cleanroom in the first place.

The rule to not wear soiled or torn garments follows from the cardinal rule to not bring anything into a cleanroom that is not absolutely necessary. A soiled garment brings in the materials on the garment.

These can easily contaminate the cleanroom environment. Similarly, a torn garment fails to protect the products from the employee so it is useless. In this area it is important to remember that people rarely put torn garments on except by accident. If you notice a coworker wearing a torn garment (usually in back where it can not be seen) you should tell them about the tear immediately, or if a part of the garment is being worn improperly..

The rule to not touch or scratch exposed hair or skin seems obvious enough. However, in practice it is not so easy. It is very common to push ones hair over while talking, wipe ones brow, or scratch an arm during everyday activities.

Recently, someone observed that the best way to get an itchy nose is to put a face mask on. So once more you are being asked to avoid performing a common, everyday activity. The rationale behind this rule is that scratching exposed skin, hair, or even a cleanroom garment puts a large number of contaminants into the air.

When hair and skin are scratched, bacteria, skin flakes and other particulate matter are removed from ones skin and randomly put into the air. Furthermore, how do you slowly scratch? Scratching through a cleanroom garment may dislodge particles and other contaminants that may be on the outside of the suit.

The no coughing or sneezing over work areas is obvious once it is mentioned, but many people do not think about it until it is mentioned. Sneezing or coughing puts particles and aerosols into the air. These can easily contaminate a work piece.

Obviously, you are not expected to not sneeze or cough; however, you should turn away from the work area when you sneeze, cough, or talk to another person. The talking rule is mentioned here for the same reason.  Even exhaling or working directly over a work piece should be avoided during critical operations, particularly wet coating steps.

Lastly, one should not continue to use contaminated gloves. Suppose one turns away from a workbench and sneezes into a glove. The aerosols and particles from the sneeze are now not only in the air, but also on your glove. At this point you are probably somewhat tempted to wipe your hand on the outside of your cleanroom garment.

This is poor practice, and you know why. You could get a cleanroom wipe and wipe your hands. This is clearly significantly better than the first option. However, upon reflection, the best thing to do is to get a new glove (or pair of gloves). This will minimize further contamination of work pieces. When gloves become very contaminated with chemicals or other materials, they should also be thrown out and replaced with clean gloves. A pair of cleanroom gloves is substantially less expensive then producing many defective displays.