The environmental requirements for cleanrooms have become stricter as manufacturing processes need more stringent environmental conditions. The National Environmental Balancing Bureau (NEBB) developed and issued the first edition of Procedural Standards for Certified Testing of Cleanrooms (CPT) in October 1988. Since the standard’s first edition, there were two subsequent revisions: The second edition was issued in April 1996, and the third edition was issued in October 2009. Presently, NEBB is collaborating with the American National Standard Institute (ANSI) to issue a fourth edition of the CPT as an ANSI standard. The CPT standard committee is presently three years into the standard revision process. The following includes why testing standards are periodically updated, ANSI’s requirements for developing a standard, who would make a good standard committee member, what the current testing procedures entail, and the proposed changes to CPT.

Why Are Testing Standards Periodically Updated?

Technology and industry requirements are ever-changing. It’s common for testing standards to be revised on a periodic basis. Some reasons a standard is updated include:

1.         Improvements in test equipment sensitivity and accuracy;

2.         Improvements in testing procedure efficiency and accuracy;

3.         Address changes in industry and regulatory requirements;

4.         Synchronize with similar testing standards from other standard committees; and

5.         Provide guidance to ensure more consistent testing procedures.

What Are ANSI’s Requirements for Developing Standards?

The ANSI standard development philosophy is due process and inclusivity. Any party (technical society, company, government agency, or individual) with a direct and material interest has a right to participate. The ANSI due process includes:

Who Would Make a Good Standards Committee Member?

Per ANSI’s due process requirements for participants from diverse interests (provider, user, interested party) and a three- to five-year commitment by standard committee members, it is important, as a committee member, to have the necessary skills, experience, and attributes. Having prior committee membership experiences, I acknowledge the following skills, experience, and attributes as excellent traits for standards committee members:

1. Passion — The work performed is not just a job but a mission. Passionate members are always striving to improve themselves and the world around them.

2. Experience — Have experience working on projects and facilities that utilize these standard on a regular basis. Understand the value of the standard, where it could use additional clarifications, and where it could use updating.

3. Open-Mindedness — Understand your experience and perspective may not necessarily match what other committee members possess. See differences of opinion as an opportunity to learn.

4. Collaboration — Standards committee members are all equals and must be willing to work as part of a team.  

5. Consensus — Most standard committee decisions will be unanimous. There are decisions where there are different perspectives. The ability to compromise and develop a consensus is needed to develop a final resolution.

6. Time — The unfortunate reality is committee members are typically in high demand and don’t have much spare time. Have an understanding of the required time commitment and schedule accordingly.

7. Articulate — Individuals must be able to express ideas, concepts, and thoughts in a way that can be easily understood in a way that is not condescending. It is also important to express yourself without feeling inhibited.

Current Testing Procedures and the Proposed Changes

The CPT committee is evaluating the existing test procedures and examining any potential additional test procedures. This article provides what the existing CPT testing procedures are, any potential testing procedure changes being evaluated, and potential testing procedures to be added to the CPT. It's important to understand these potential changes to the CPT have not been formally approved by the CPT committee and must also be approved by the NEBB board of directors. This article is a perspective of one CPT committee member and not endorsed by the CPT committee.

The following outlines the existing CPT standard test procedures and lists any potential changes to the test procedure.

• Global Change No. 1 — The CPT standard is to be reformatted and reorganized to meet the ANSI standard requirement.

• Global Change No. 2 — The existing test procedures are split into two categories: primary and secondary. Depending upon the industry cleanroom being tested, a number of the secondary tests are critical and considered primary. The CPT committee is evaluating whether to combine the primary and secondary test procedures into one group with each test procedure having equal weight.  

• Global Change No. 3 — The inclusion of a table that recommends specific test procedures that are normally utilized by a specific industry. This guidance document will help personnel understand which test procedures are normally performed for their industries.

• Global Change No. 4 — The test procedures for Sections 10.2 to Section 10.9 go back and forth between unidirectional and non-unidirectional zones. It is being evaluated whether creating separate test categories (unidirectional, non-unidirectional) would make it easier to follow the test procedures.

• Section 10.2, “Cleanroom/Filter Airflow Velocity and Uniformity Tests” — This test determines the average filter face velocity and uniformity and/or the average room airflow velocity and uniformity within the cleanroom. This test procedure would be part of the unidirectional zone category. The filter face airflow velocity reading distance from the filter face is adjusted to the devices used for maintaining the velocity distance reading from the filter face. For space airflow velocity, the measuring location was adjusted from 36 inches above the floor to the actual work surface.

• Section 10.3, “Airflow Velocity and Uniformity Test - Filter Face Airflow Velocity” — This test documents the average airflow velocity and uniformity. The test procedure would be part of the unidirectional zone category. Beyond the unidirectional zone categorization, there are no test procedure modifications being evaluated.

• Section 10.4, “Airflow Velocity and Uniformity Test - Filter Face Airflow Velocity - Non-Unidirectional (Volume Method)” — This test determines airflow via an airflow hood. The test procedure would be part of the non-unidirectional zone category and is very similar to Section 10.8, “Airflow Volume and Uniformity Test - Flowhood Method.” This test is being evaluated for a change to air velocity measurement at a minimum of 6 inches from the filter face and calculating the air volume.

• Section 10.5, “Airflow Velocity and Uniformity Test – Filter Face Airflow Velocity – Non-Unidirectional (Velocity Method)” — This test determines the average airflow velocity and uniformity of the filter face. The test procedure would be part of the non-unidirectional zone category. Beyond non-unidirectional zone categorization, there are no test procedure modifications being evaluated.

• Section 10.6, “Airflow Velocity and Uniformity Test - Average Room Airflow Velocity” — This test determines the average room airflow velocity and uniformity at the specified work surface. The test procedure would be part of the unidirectional zone category. Beyond unidirectional zone categorization, no test procedure modifications are being evaluated.

• Section 10.7, “Airflow Volume and Uniformity Test” — This is the measurement of airflow quantity. No test procedure modifications are being evaluated.

• Section 10.8, “Airflow Volume and Uniformity Test Flowhood Method” — This section is in regards to utilizing a flow hood for directly measuring airflow volume. No test procedure modifications are being evaluated.

• Section 10.9, “Airflow Volume and Uniformity Test - Traverse Method” — This section is utilized to measure airflow volume when a flow hood cannot be used. No test procedure modifications are being evaluated.

• Section 10.11, “Filter Installation Leak Tests - Aerosol Photometer Test Method” — This section covers filter leak testing utilizing the photometer test method. The proposed changes include expansion on test instrumentation guidance, adjustments on aerosol concentration, and expanded guidance on filter repair.

• Section 10.12, “Filter Installation Leak Tests - Discrete Particle Counter Test Method” — This portion covers filter leak testing utilizing the particle counter test method. The proposed changes include expansion on test instrumentation guidance, adjustments on aerosol concentration, and expanded guidance on filter repair.

• Section 10.13, “Filter Installation Leak Tests - Total Aerosol Penetration Test Method” — This section covers filter leak testing utilizing the total aerosol test method. The proposed changes include expansion on test instrumentation guidance, adjustments on aerosol concentration, revised testing procedures, and expanded guidance on filter repair.

• Section 10.14, “Airborne Particle Count Cleanliness Classification Test – ISO 14644” — This determines the actual particle count level in cleanrooms and clean zones for the particular occupancy state (i.e., as-built, at-rest, operational). The section title will be changed to “Airborne Particle Count Cleanliness Classification Test.” The proposed changes expand the guidance on occupancy state, instrumentation, and procedure.

• Section 10.16, “Room Pressurization Tests” — This section verifies the completed cleanroom installation’s capability of maintaining the specific pressure difference between the specific cleanroom and adjoining spaces. The proposed changes expand the guidance on room pressurization testing.

• Section 11.2, “Airflow Parallelism Tests” — This shows the actual vertical airflow pattern inside a unidirectional cleanroom. The proposed test modifications include test conditions (i.e., as-built, at-rest, in-operation), and additional test procedure guidance.

• Section 11.3, “Recovery Tests” — This determines the ability of the installation to reduce the concentration of airborne particles by dilution. The proposed test modifications include extensive guidance on test equipment and test procedures.

• Section 11.4, “Lighting Level and Uniformity Tests” — This verifies the installed lighting levels and lighting uniformity meet specified requirements. No test procedure modifications are being evaluated.

• Section 11.5, “Sound Level Tests” — This section is focused on sound levels. The existing CPT document sound testing procedure references the NEBB procedure standards for the measurement of sound and vibration. The CPT standard does provide information on required instrumentation and equipment, preliminary test procedures, test procedures, acceptance criteria, and reporting. To keep the CPT document current with the latest edition of the NEBB sound and vibration testing procedures, the CPT standard document will refer to the NEBB sound and vibration testing standard procedures.

• Section 11.6, “Vibration Level Tests” — This refers to vibration levels. As with the sound level test, the CPT standard document will refer to the NEBB sound and vibration testing standard procedures.

• Section 11.7, “Temperature and Humidity Uniformity Tests” — This section examines the measurement of temperature and humidity. The section defines general temperature and humidity (11.8) measurement for occupant comfort and the comprehensive temperature (11.9) measurement for both occupant comfort and process requirements. Changes are proposed regarding the temperature and humidity uniformity testing titles to “Environmental Comfort Temperature and Relative Humidity Testing” and “Process-Driven Temperature and Relative Humidity Testing.”  

• Section 11.8, “General Temperature and Humidity Uniformity Tests” — This section refers to the measurement of temperature and humidity for occupant comfort. Beyond changing the test section title to “Environmental Comfort Temperature and Relative Humidity Testing,” the temperature testing will include temperature uniformity testing and temperature stability testing. The relative humidity testing will include relative humidity range testing and relative humidity stability testing.

• Section 11.9, “Comprehensive Temperature and Humidity Uniformity Tests” — This section covers the measurement of temperature and humidity for process. Beyond changing the test section title to “Process-Driven Temperature and Relative Humidity Testing,” the temperature testing will include temperature uniformity, temperature stability, and temperature spatial variation testing. The relative humidity testing will include relative humidity range testing and relative humidity stability testing.  

• Section 11.10, “Electrostatic Tests” — This section examines the benchmarks regarding the level of electrostatic charge, resistance properties of surfaces, and the effectiveness of the ionizer charge neutralizing systems. No test procedure modifications are being evaluated.

• Section 11.11, “Conductivity Tests” — This section measures the resistance between specified points on the floor covering and from the floor covering to the building ground. No test procedure modifications are being evaluated.

• Section 11.12, “Electromagnetic Interference (EMI) Test” — This section aims to determine if there is AC and DC extremely low-frequency electromagnetic interference emitted by a magnetic field source. It is being proposed the test procedure be modified to measure at 1 meter above the floor, provide guidance on what equipment should be tested, and expand the acceptable acceptance criteria.

• Section 11.13, “Air Change (ACH) Test” — This is a calculation to determine the cleanroom air change rate. It is being proposed to group the air change rate with the airflow sections 10.2 to 10.9 to form section 10.10. These sections deal directly with airflow measurements and placing the air change calculation in this section provides better testing organization.

• Section 11.14, “Bench Scan Filter Leak Tests” — This section determines the integrity of HEPA filters before installation. No test procedure modifications are being evaluated.

1.     Additional Potential Test Procedures

There are a number of additional new tests being evaluated for inclusion into the CPT standard. It is expected a couple of the proposed new testing standards will be approved. The potential new test includes the following:

a. Segregation — A procedure to assess the separation effectiveness in terms of a protective index achieved by a specific airflow.

b. Microbial — A procedure for obtaining surface samples for potential microbial contamination.

c. AMC/SMC — A procedure for obtaining surface samples for potential surface molecular contamination.

d. Volatile Hydrocarbons — A procedure for obtaining samples for potential volatile hydrocarbon contamination.

e. Airflow Visualization — A testing procedure to create visualized airflow and to record for future observations.

f. Fan Energy — Testing to determine fan energy usage on a watts per cfm basis.

g. Cleanroom Stability in Variable Airflow — Testing determines the minimum supply and return airflows, space pressurization stability during airflow modulation, and tuning supply and return airflow modulation rates to maintain space pressurization stability.

The CPT standard committee has extensive and broad experience in pharmaceutical, electronic, aerospace, health care, and other technology industries. The standard review deliberations are very engaging, and each member has thoughtfully shared his or her knowledge. If you have any suggestions that could contribute toward making the CPT standard better, please send me an email at bsme82@comcast.net.