System and discipline management requirements for clean workshops

People in the clean room are an important source of indoor pollution in the clean room. The pollution caused and spread by the activities of people in the clean room must be reduced as much as possible to ensure the cleanliness of the room and reduce maintenance costs. 

The purpose of formulating the discipline of the clean room is to minimize the risk of product contamination. When formulating the discipline of the clean room, the operation management personnel of the clean room should first formulate strict disciplines to regulate the activities of the personnel working in the clean room and the internal operation staff of the clean room, including maintenance personnel and service personnel; secondly, it should be noted that the products produced in the clean room have different sensitivities to pollution, and the discipline formulated for the clean room should reflect this.

1. Strictly control the personnel entering the clean room

When people walk, they can generate about one million particles with a diameter of 20.5um per minute. The more people in the clean room, the more particles are emitted. Therefore, managers should try to control the number of people in the clean room, that is, only necessary personnel are allowed to Enter the clean room. 

In addition, the number of visitors to the clean room should be minimized. Since visitors have not received training on clean room work, they can only enter the clean room under the management of supervisors. The ideal solution is to design an observation window for visitors to use in the clean room, so that visitors do not have to enter the room, thus reducing the probability of causing pollution.

1.1 Basic requirements for clean room staff

Compared with staff in general places, clean room staff should try to reduce the pollution emitted by the human body. Clean room operation managers should formulate detailed requirements in order to control the pollution caused by indoor staff within an acceptable range.

a. Basic requirements for the physical condition of clean room staff

Clean room staff should maintain good health. People with the following physical conditions may produce a large number of polluted particles. Therefore, it is not advisable to enter the clean room to work until the symptoms are completely eliminated.

• Suffering from certain skin diseases

Especially dermatitis, skin burns, excessive dandruff, etc., because the skin may spread a large number of skin cells, it is not advisable to work in the clean room.

• Suffering from respiratory diseases

For example, colds, chronic lung diseases, etc., are prone to excessive coughing or sneezing and emitting a large number of droplets. It is not advisable to work in the clean room before recovery.

• People with allergies

People with allergies are prone to sneezing, itching, runny nose and other symptoms, and are generally not suitable for working in clean workshops.

• People who may carry certain microorganisms and germs

In biological clean workshops, it is sometimes necessary to separate people from products to prevent the microorganisms and germs that people may carry from growing on products, thereby damaging products or causing diseases. The question of whether these people are suitable for the work they are doing should be considered together with the sensitivity of the product to the growth of a specific type of microorganism on it.

(Figure 1: Personal health of clean room workers)

b. Basic requirements for the hygiene habits of clean workshop staff

Clean workshop staff should maintain good personal living and hygiene habits. Bad habits can also cause potential pollution sources in clean workshops. The following hygiene habits require clean workshop staff to pay attention to them in daily life.

• People should have good personal hygiene habits

Take a bath regularly to remove dandruff. Wash your hair after each haircut to prevent hair dandruff from falling on the product. People with dry skin should use skin cream instead of skin care oil to moisturize the skin to reduce the spread of dandruff.

• Generally, it is not allowed to use cosmetics when working in A Clean Room.

All kinds of cosmetics, talcum powder, hair care products, hair styling glue, nail polish, etc. are not suitable for use. Clean rooms usually regard all foreign objects on the human body as pollutants. Cosmetics will cause pollution to clean rooms, because when using cosmetics, a large number of particles (20.5um particles are up to 109) will be deposited on the skin, and some of these particles may be released into the clean room.

• Generally, it is not allowed to use watches and jewelry in clean rooms, such as earrings, necklaces, bracelets, rings, etc. If jewelry is used, it must be placed inside clothing and gloves. Under the ring may be a place where dirt and filth are hidden. Some people may not want to take off their wedding rings or engagement rings for emotional reasons. If the ring and the skin under the ring finger can be washed, it is also allowed to carry the ring. However, the place on the ring that may pierce the gloves should be wrapped with tape.

• Do not smoke directly within a few hours before entering the clean room. Smokers can release more particles from their mouths than ordinary people, and their bodies will also release certain chemical gases. Therefore, some clean workshops require personnel to not smoke a few hours before entering the clean workshop.

c. Restrictions on personal belongings of clean workshop staff

The general principle is that any items not required for production shall not be brought into the clean workshop. Specific regulations can be determined by the management of the clean workshop based on what items will cause pollution to the product. Generally speaking, the following items should be prohibited from being brought into the clean workshop: food, wine, candy, chewing gum; canned or bottled drinks; cigarettes, matches, lighters; self-use medicines, potions, ointments; radios, record players, pocket tape recorders, mobile phones, pagers; newspapers, magazines, books, handkerchiefs, facial tissues; pencils, erasers, pens; coins, wallets, cosmetics, handbags, etc.

(Figure 2: Clean room)

1.2 Basic requirements for clean workshop maintenance personnel and service personnel

People who enter the clean workshop to repair equipment or provide services may also pollute the clean workshop environment due to lack of training and supervision. If maintenance technicians are not informed in advance, they may use the same maintenance methods used outside the clean workshop to repair equipment, and the consequences may be serious. Service personnel from outside companies may not have received any training on cleanroom pollution control methods. For this reason, the following are a series of relevant regulations that maintenance personnel and service personnel entering the cleanroom should know:

a. Entry with permission

Maintenance personnel and service personnel can enter the cleanroom only after obtaining permission from the cleanroom manager.

b. Training and supervision

Maintenance personnel and service personnel should be trained in cleanroom technology. In addition, their work in the cleanroom should be under the close supervision of the cleanroom manager. The time of entering and leaving the cleanroom and the working conditions should be recorded and filed.

c. Wearing clean clothes

Maintenance personnel and service personnel must wear clean clothes that are the same or equivalent to those of cleanroom workers. When they enter and exit the cleanroom, they should change clothes in the same way as the cleanroom staff. Whether it is weekends or other off-duty time, it is not allowed to enter the cleanroom without wearing clean clothes. Maintenance personnel and service personnel must take off their original work clothes before entering the cleanroom, and wash their hands carefully before changing clean clothes.

d. Special tools for cleanrooms

The tools used for maintenance in cleanrooms are only for use in cleanrooms and must be kept clean. If maintenance personnel, service personnel or contractors from outside units need to bring their necessary tools into the clean room, these tools should be cleaned before they can be brought into the clean room.

e. Entry of text, drawings and other materials

Text or drawings written on non-clean room special paper shall not be brought into the clean room. They can be copied on clean room special paper, or covered with plastic film, or placed in a clean room special plastic bag before they can be brought into the clean room.

f. Dust-generating operations need to be isolated

Some operations that generate particles, such as drilling holes, repairing ceilings and floors, should be isolated from the rest of the clean room by taking corresponding measures. At the same time, local exhaust or vacuum cleaners should be used to remove the generated particles.

g. Cleaning after maintenance work

Maintenance personnel and service personnel must clean the site according to the requirements of the clean room after completing the work, and ensure that the area is cleaned according to the "clean room cleaning method" by personnel with professional knowledge. Only cleaning agents, cleaning materials and cleaning equipment approved for use in clean rooms can be used during cleaning.

2. Disciplines to be observed in cleanrooms

To ensure that products are not contaminated, staff in cleanrooms must abide by relevant codes of conduct. Cleanroom managers must formulate a set of rules and regulations that are consistent with the product requirements of their cleanrooms, and publicize them during staff training. These rules and regulations should be posted in the dressing area or production area. The following are the contents that are suitable for the generally adopted rules and regulations.

2.1 Preventing reverse airflow along the corridor from increasing pollution

To prevent air from flowing from high-pollution areas to low-pollution areas, and from the corridor outside the cleanroom to the production workshop, staff should abide by the following disciplines:

a. Personnel must enter and exit the cleanroom through the dressing area

The dressing area is not only used for changing clothes, it is also a buffer zone between the external contaminated corridor and the clean production area. Unless there are special circumstances, staff shall not use direct exits such as emergency exits between the production area and the corridor, because this will allow pollution to enter the production area directly, and their clothes will also be contaminated.

(Figure 3: Cleanroom clean clothes)

b. All doors in the clean room should be closed (except for those that maintain positive pressure)

If the door is open, the air between two adjacent areas will flow in reverse due to turbulence and regional temperature differences.

c. Manual door closing and opening should be slow

If the door is opened and closed quickly, the air will be induced due to the fast rotation of the door leaf, causing the air to flow in reverse to the clean room. For positive pressure clean rooms, the door is generally opened inward, that is, to the production room. 

The higher air pressure in the room makes the door close more tightly. Some doors are opened outward to facilitate the exit of people holding items in their hands. Door closers should be installed on the door to keep the door closed at ordinary times, and the door closer should control the door to rotate slowly when opening and closing the door to reduce the reverse flow of air caused by the induction effect. Outward-opening doors generally do not have handles, which helps to avoid contamination caused by gloves.

d. Points to note when passing through the airlock room (air shower)

Make sure to pass through the second door after the first door is closed. An indicator light can be used to show whether the door is in a closed state. Usually, this can be achieved by using Electronic interlocking devices on both sides of the door. The usage of the transfer element is similar to this. However, it should be noted that when a fire occurs, it must be ensured that the airlock will not be dangerous. In other words, when a fire alarm occurs, the electronic interlock of the airlock door should be released.

2.2 Prevent improper actions of staff in the clean room from increasing pollution

To ensure that the actions of personnel will not cause excessive pollution in the clean room, the following relevant suggestions should be considered:

a. Staff are not allowed to have improper behavior

The amount of pollutants generated by personnel is proportional to the amount of activity. According to the test data of the Contamination Index (Contamination Index) published by Austin, RR., a famous American pioneer in clean technology, in 1965 in the American Association for Pollution Control (AACC), the amount of dust generated by personnel wearing clean clothes when performing different actions is listed in Table 1-1. 

As can be seen from the table, when a person is stationary, about 100,000 particles greater than or equal to 0.3um are generated per minute; when a person is active, the body, head, shoulders, etc. can generate about 1 million particles greater than or equal to 0.3um per minute; when a person walks at a speed of 3.6km/h, about 5 million particles greater than or equal to 0.3um are generated per minute. Therefore, all personnel in the clean room are required not to "act rashly", any movement should be cautious and carried out according to regulations, and too many useless movements are not allowed.

b. Operators should stand correctly

Relative to the product, the personnel should be in the correct position so that contaminants will not fall on the product. You should not lean over the product, otherwise the particles, fibers or particles with microorganisms scattered from your body will fall on the product.

c. How to move or pick up the product

You must consider how to move or pick up the product in advance. In order to prevent the gloved hands from contaminating the product, it is recommended to use the "non-contact" method to pick up the product. Although the personnel in the clean room wear gloves, the pollution will be less, but it may still become a source of pollution. This method is still used when the line width is large and a lower yield rate is still acceptable. 

An example of a "contactless" method is to use long clamps to move materials, which avoids contamination caused by holding materials by hand. People should not move materials by body. Although the clean clothes worn by people are much cleaner than ordinary clothes or work clothes, there are still particles and fibers on the clothes and they may be transferred to the items being moved due to improper operation. Therefore, operators should also be careful to prevent any items from being dragged over the top of the product.

(Figure 4: Clean room management)

d. People do not directly touch or lean on any surface in the clean room

Although the surface of the clean room is much cleaner than the outdoors, there are still particles, fibers and bacteria on the surface of indoor equipment. If people get contaminants from these surfaces, these contaminants may be transferred to the product. When you don't need to use your hands in the clean room, you should hold your hands tightly in front of you to help prevent your hands from accidentally touching the surface of the clean room equipment.

e. People should not talk while working

Talking, coughing, sneezing, etc. will cause saliva to spray out from the gap between the mask and the skin and contaminate the product. When coughing or sneezing, the head must be moved away from the product. Masks should generally be replaced after sneezing. Masks must be placed over the nose and not under the nose, because large particles will be released from the nose when breathing heavily.

f. Personal hands cannot be brought into the clean room

Private hands are obviously a source of contamination. They can bring particles (including particles with microorganisms) into the air and stick to gloves. Noses cannot be changed in the clean room. Nose changes can be done in the dressing area, and gloves must be changed afterwards. Staff should also avoid touching their own skin in the clean room. It is inappropriate to scratch or wipe any part of the skin.

2.3 Prevent improper use of materials in the clean room from increasing pollution

The following are suggestions for the use of materials in the clean room:

a. Use rags with low pollution levels in the clean room

The choice of which type of rag to use is determined by the maintenance cost budget of the clean room and what products the clean room produces. It is also necessary to determine the number of times the rag can be reused before it is discarded.

b. Minimize the movement of materials between clean rooms

Every time a product is taken out of the clean room, it may be contaminated in an area with poor cleanliness. When it enters the clean room again, it will bring this contamination into the room. It is best to store the product in a suitable clean area of the clean room, or in an adjacent clean area.

c. Prevent processed products from being contaminated

During the production stage, people generally pay great attention to not contaminating the product. Once a product is completed, it is easy to be forgotten in the clean room, and dust will gather on the product. Therefore, products that are susceptible to contamination should be placed in a sealed cabinet, or in a container, or in a one-way flow workbench, or in an isolation device. If the clean room is a one-way flow clean room. Products can be placed on storage racks through which airflow can pass. In addition, materials must not be placed on the floor.

d. Waste disposal

Waste should be collected regularly and placed in easily identifiable containers and removed from the clean room.

e. Keep the clean room clean and tidy

The clean room should be cleaned in the correct way, or disinfected when necessary, and the clean room should be kept neat and orderly. Only by using appropriate cleaning tools can the cleaning effect be guaranteed.