Cleanrooms, Classes, and Control Charts

Sterile, Lab, Clean Room, Requirements, Standard


My question has to do with cleanroom monitoring, specifically particle counts. Using ISO 14644-1: 1999, (we are still transitioning to the new standard), we have 27 test sites in our cleanroom. Our Particle Counter takes 10 readings per minute and averages those readings into one value. This is the number we record at each of the 27 test sites. Since an ISO Class 8 Cleanroom can have no more than 3,520,000 particles greater than 0.5 micron in size per cubic meter, for the room, do you add all 27 results and compare to the acceptance criteria? Do you average all 27 results and compare to the acceptance criteria? or as long as each individual result is below the acceptance criteria we are in compliance? what makes me think you add all results together is that the acceptance criteria states: ISO Class 8 Cleanroom can have no more than 3,520,000 particles greater than 0.5 micron in size per cubic meter, for the room. Your input would be greatly appreciated!


The way for analyzing these data is very straightforward. Considering you have continuous data, the most appropriate way for accomplishing this is by using a control chart. Use the 27 readings for constructing the averages needed for a control chart. Identify control limits and respond to special cause variation only. You will know that you are in compliance as long as your control charts remain under control. If you ever find any points out of control, you may want to quarantine the product processed during that time and conduct the appropriate corrective actions. As your regular housekeeping, keep the cleanroom certification current. The same for the particle counter system calibration.

If you are new to control charts, the easiest/simplest reference I have ever found is Understanding Variation – The Key to Managing Chaos by Donald J. Wheeler.

Based on your data performance, you may also be able to identify areas within your cleanroom that perform better than class 8 (7 or better). Knowing where those areas are may be handy.


Aura Stewart

For more on this topic, please visit ASQ’s website.

Root Cause Analysis Samples

Q: I am looking for samples of a RCA.  I will be doing training on that topic and I would like to have some samples to use with the participants.

A: Thank you for contacting ASQ and the Quality Information Center.  I received your request for samples of root cause analysis.  Root cause analysis is defined as a “quality tool used to distinguish the source of defects or problems.  It is a structured approach that focuses on the decisive or original cause of a problem or condition” (from The Quality Improvement Glossary by Donald L. Siebels).

Root cause analysis figure

The image (right) is take from Root Cause Analysis: Simplified Tools and Techniques.

I found hundreds of RCA results on ASQ’s website (if you wish to browse through them all, here is the link to my original search results).  I thought you might be most interested in case studies which provide examples of how root cause analysis has been used.  I found more than 100 case studies which focus on root cause analysis and I’ve listed some case studies below which I thought would be helpful:

Abstract: Customer Complain investigations weren’t getting to root causes.  Logic trees proved more effective than fault trees in determining what actually went wrong.  After root cause analysis, complaint numbers dropped by half.  That and indirect benefits led to bottom-line results.

Abstract: The authors used Six Sigma to improve the process of manufacturing gear boxes for mechanical power transmission at a foundry in India. The goal was to improve product performance by reducing variation in the casting of components, thereby reducing defects. The analyze phase used root cause analysis and failure mode and effect analysis to identify several process variables, including pattern design and maintenance, worker training, and the proportions of scrap and coal inputted into the molds, that were increasing the frequency of the major defects.

Abstract: A root cause analysis project saved Clipper Windpower $1 million in lost revenue. By identifying the root causes of turbine failure during inclement weather, Clipper increased customer satisfaction through improved turbine availability. This project also supported a key supplier’s quality process, as Clipper’s team helped redesign and test an improved anemometer. Team members mastered quality tools and strategies, preparing them for future improvement projects.

Abstract: Cross-functional teams identified root causes of injuries and reduced accidents by 48 percent in one year while saving an estimated $714,000 in cost avoidance over a 24-month period. To compile data and identify root causes, team members used trend graphs, Pareto diagrams, bar charts, and fishbone diagrams. A key tool used in developing an action plan was the solution selection matrix, a systematic approach that allows for the best possible solutions to surface.

The following webcasts may also be helpful for those who are new to root cause analysis:

Root Cause Analysis for Beginners, Part 1” & “Root Cause Analysis for Beginners, Part 2

I hope that this information is helpful.  Please feel free to contact me with any questions or if you need additional assistance.

Best regards,

ASQ Research Librarian
Milwaukee, WI

Force Field Analysis

Force field analysis

Q: I am trying to get information on Force Field Analysis.  Can you please provide me more details on the subject?

A: Thank you for contacting ASQ.  I received your request for more information regarding force field analysis.

The Quality Improvement Glossary by Donald L. Siebels defines force field analysis as a “technique for analyzing the forces that aid or hinder an organization in reaching an objective.  An arrow pointing to an objective is drawn down the middle of a piece of paper.  The factors that will aid the objective’s achievement, called the driving forces, are listed on the left hand side of the arrow.  The factors that will hinder its achievement, called the restraining forces, are listed on the right side of the arrow.”

For more on this topic, please visit ASQ’s website.