One Reason To Do Validation
This exercise is an insurance policy. Users conduct validation to prove that their normal cleaning test is currently valid (hasn't been “fooled”). But, because validation represents additional work, it isn't justified for every operation. Usually, when a cleaning test is “fooled”, unexpected types of contamination are involved. Table 1 lists some examples.
A Second Reason To Do Validation
A frustrating situation, in which validation is essential, occurs when there is no flaw in the cleaning test. Yet performance in the next step of use fails due to a cause unrelated to the cleanliness of the parts. Often, the defect is incorrectly attributed to the cleaning process. Effort is wasted in troubleshooting a process which is performing flawlessly while the true cause of failure remains undetected.
What is Not Validation
A quotation attributed to philosopher George Santayana is “fanaticism is the practice of redoubling your efforts when you have forgotten your aim.” Validation does not mean that the normal test should be rerun many times under increased scrutiny.
More, of similar data, adds no new insight. More eyes looking in the wrong direction won't see approaching disaster. More thought with the same point of view won't produce inspiration. One validates a result by examining it from another point of view. This means something different must be done.
I often recommend a “total cleanliness” approach to validation of cleanliness tests.
Others call this approach “brute force.” Instead of measuring NVR, TOC, using an OSEE instrument, or counting particles, do all of the following:
- Boil a part in a suitable solvent(s) to extract everything which contaminates its surface
- Heat another part to a suitable temperature to vaporize everything which contaminates its surface.
- Clean another part in the normal manner, and weigh it again.
A Specific Approach Toward Validation
Consider an approach toward validation focused on the nature of the cleaning test under scrutiny. Measure the parameter being measured in the normal cleaning test using another approach sensitive to the same parameter.
An excellent way to do this is to use ASTM standards as validation tests. Good ones are: (1) ASTM E21.05, “Standard Method for Measurement of Nonvolatile Residue (NVR) on Surfaces,” (2) D903-98(2004) Standard Test Method for Peel or Stripping Strength of Adhesive Bonds for particulates and surface films.
Validation by another cleaning test should substitute for the normal cleaning test.
Depending upon results and required certainty, the validation test might replace the normal test every 5% to 20% of cleanliness tests.
While validation of cleanliness testing is not justified for every cleaning operation, considering use of it for every operation is justified.
John Durkee is an independent consultant specializing in critical cleaning for contamination control. Contact him at PO Box 847, Hunt, TX 78024 or 122 Ridge Rd. West, Hunt, TX 78024; 830-238-7610; Fax 612-677-3170; or email@example.com