Director, Thermadyne Pvt. Ltd., Faridabad
Rashmi Nagabhushan is an M.Tech from IIT Delhi and has over 20 years experience in various capacities in group companies of Continental Device India Ltd. She has been associated with Thermadyne Pvt. Ltd., the complete clean room company, for the last 13 years.
Lakhs of Rupees spent in installing a clean room can go down the drain if cleanliness levels are not maintained on a continuous basis. Personnel training and discipline are the key factors. Sustenance guide lines should be followed both in letter and spirit. Clean room discipline can make a success or a failure of a clean facility. People must be motivated and trained to achieve cleanwork habits and follow timely maintenance practices.Indoor air quality is of paramount importance for human comfort and health. Similarly, indoor air quality of manufacturing facilities plays a vital role in the yield and quality of many products.
There has been a great deal of advancement in building clean rooms suitable for different applications. Many individual national standards and now international ISO standards are available which define cleanliness classes and measuring procedures for their compliance. Guide lines are also available on the cleanliness levels required for various manufacturing facilities. Expertise now exists to achieve even Class 10 and Class 1. But little is said as to how to sustain the built cleanliness. In fact, by and large, the contract between the customer and contractor is on satisfying the ‘as built’ or ‘at rest’ requirements. And in most cases it is found that cleanliness levels in operational conditions are considerably poorer and some times may lead to conflicts between the two parties. First and foremost, many factors are required to be taken into consideration before designing and installing clean rooms to ensure achievement and sustenance of clean room conditions. Some of the important ones are listed below
Factors to be Considered at the Design Stage
- Type of industry (to determine class of cleanliness).
- Contamination generation by process, abrasion or by constructional materials.
- Occupancy and physical activity level.
- Contamination level in the surrounding areas.
- Presence of heated surfaces.
- Equipment lay-out in the room.
- Process exhausts.
- Future expansion plan.
- Statutory requirements
The reasons sound very trivial, but their impact is unbelievable. The unhappy situation can be largely attributed to lack of personnel discipline which results in many short comings and ultimately in the failure of the clean room. If however the following practices are followed we can save the situation.
Steps to be Taken after Clean Room Installation
- Personnel training.
- Proper maintenance of air conditioning systems and other clean air systems to ensure that required air quantity is supplied on a continuous basis.
- Timely cleaning / changing of filters, again to ensure that designed clean air quantity is maintained.
- Proper and continued use of change room entry equipment.
- Proper gowning.
- Clean room discipline.
- Scheduled cleaning of clean rooms.
- Strict observance of equipment maintenance practices for clean rooms.
- Regular monitoring of clean room conditions.
Being a clean-room company, installing and validating clean rooms, we have first hand experiences on the main culprits which lead to problems of sustenance of air cleanliness. To give you an insight into some of the problems, a few case studies are listed below.
CASE STUDY - 1A class 10,000 facility was successfully installed. On revalidation after 6 months, particle counts were found to be in the range of 2 to 3 lakhs. It was observed that clean-room gowning procedures were not being followed properly, specially in terms of shoes. The surrounding area of the building also had rubble and people were bringing in a lot of dirt. The situation was worsened by the constant movement of people inside the clean area.
A thorough cleaning-up of the area, proper gowning and proper changing of clean room slippers brought back the clean conditions. See Table 1.
|Table 1 – See case study 1|
|Designed Class - 10,000
0.5μ and above particle count (Average)
|Number of Hepa filters - 16|
||Within specified limits|
|After 6 months||210,000||350,000||Dirty shoes inside change room.
Gowning improper. Air shower not
used properly. Sleepers washed once in
a month. Water tap inside change room.
|After one year||170,000||294,000||Shoes outside change room.
Rest same as above.
|After 1.5 years||81,000||140,000||Dresses in garment storage cabinet,
new dresses. Three times floor
cleaning (wet). Worker discipline better.
|After 2 years||14,000||34,000||Air curtain at change room entrance.
|After 2.5 years
After 3 years
|Filters not changed.|
CASE STUDY - 2In another case filters choked unevenly due to dampers not being provided independently for each filter. The choked filters i.e. four out of twelve were replaced. This resulted in most of the air coming through the new filters resulting in pockets of unclean area and also, generally a higher count due to turbulence caused by high velocity through clean filters. See Figure 1.
CASE STUDY - 3One small company asked us to do their clean-room validation. We found the particle counts to be high. On investigating we found that out of four terminal Hepa filters two were replaced by fine filters after choking. Since the air discharge from the filters was through perforated grilles it took us some time to figure out the problem.
CASE STUDY - 4Filters were choked and sufficient air quantity was not reaching the area, resulting in negative pressure inside the area. Each time the entry door was opened, dirty air was coming in. The problem was accentuated as an additional exhaust was fixed for a new process machine which was not taken into consideration in the initial design.
CASE STUDY - 5An otherwise satisfactory facility failed miserably on start-up. It was found that machines were crowding the clean room very badly and not allowing proper air flow.
Besides, unclean compressed air was being used freely, resulting in a total collapse of the clean area.
CASE STUDY - 6Window air conditioners were added subsequently to supplement cooling of an existing clean facility. Installation was done very poorly leaving gaps between the air conditioner and the window cut out. Also some unfiltered fresh air was getting added through the window air conditioner.
CASE STUDY - 7In another case a good clean room (Class 10,000) deteriorated badly due to influx of additional people and machinery to cope with the sudden increase in production capacity.
CASE STUDY - 8One laboratory which was near a railway line developed cracks in the ceiling due to vibration and resulted in high particle count. A patch up did help but ultimately the laboratory had to be shifted to another location.
CASE STUDY - 9A satisfactory clean facility detiorated within six months. A thorough investigation revealed that the fan used in the air handling unit did not have the desired static pressure capability. Inadequate clean air supply resulted in negative pressure and ruining of the facility.
- In some cases cracking and detaching of sealing compound in Hepa filters with time was found to be a major reason of failure.
- In a number of cases, damaged Hepa filters were found to be in use in spite of the concerned people being aware that this would cause problems.
- While choked filters are replaced, their installation does not get adequate attention due to inadequate training of maintenance staff. Thus we get either dirty clean rooms or quickly choked Hepa filters.
- Validation is not done at regular intervals. If you don’t monitor the clean room, you can sit pretty without any warning till you collect losses due to rejection of products.
- In many cases even at the first validation, initial results are poor. But a through cleaning of the area invariably results in the designed class of cleanliness.
Recommendations for Maintaining Existing Clean Room Conditions in the Clean Room Area
- Only authorised personnel should enter the clean rooms. • No body should be allowed into the clean room without wearing clean room garments including cap and clean room shoes/chappals properly.
- Always stay in the “air shower” for a specified time before entering clean rooms.
- After the use of garments and shoes, these should be kept at a proper place. Never go into “nonclean” areas from change room with garments or shoes.
- Do not walk into a clean room unless necessary.
- Smoking in the clean room and change room is prohibited.
- Do not take contamination producing material like tobacco, food, match boxes, purses, cosmetics, card boards and unnecessary papers inside the clean areas. Also do not apply cosmetics in the clean area.
- Do not sharpen pencils in the clean room and use a ball point pen only. • Wear gloves and finger cots whenever required.
- Do not touch contaminated articles or surfaces after wearing finger cots/ gloves.
- Do not scratch your head or rub your nails inside the clean room or change room and keep finger nails clean.
- Do not take personal items into clean room, keep them in lockers provided.
- Keep your work table clean.
- Clean / change filters in the air conditioning system as and when required.
- Never sweep the clean room floor, vacuum them or wet mop them as per frequency specified.
- Clean walls, ceilings and furniture as per frequency specified with wet mop.
- Garments should be washed as per frequency specified.
- Clean all furniture, equipment and raw material packages etc. properly before taking into clean room.
- Do minimum maintenance of equipment inside the clean room. Take the equipment outside the clean room for maintenance.
- Unpacking of the machinery required for the clean areas should be done outside the clean room.
Clean room discipline which covers all the points listed earlier and above can make a success or a failure of a clean facility. People must be motivated and trained to achieve clean work habits and follow timely maintenance practices