I work with test equipment on a daily basis. I do not believe that there are a large number of what we would call false positives, or the machine alarming for non-dangerous chemicals.

There may be some, and in the initial roll out of the technology there were likely many. However, what we are calling "false positives" are more than likely from one of three sources:

1. Cross-contamination from poor handling practices for the TSO's
   
2. Improper preparation or cleaning of the machine following testing of a known sample for calibration and the subsequent cross contamination
   
3. Random alarms (if they will do it for the WTMD and Scanners, they will do it for the ETD.)

I have observed the first, but I only suspect the other two and I could be wrong.

The testing process they use is very well tested in a variety of situations. It is successfully used across multiple industries and processes. However, it still requires thoughtful preparation of the sample, meticulous cleanliness and avoidance of any source of potential cross contamination. The CP is not conducive to any of these and "false positives" are inevitable. A more correct term for "false positive" would be "alarm from unknown source." That is a lot more words but is more accurate.

If I were doing this testing in industry, let's just suppose it is to check a machine before maintenance, the absolute first-before-anything-else-thing I would do is run another test while verifying that all the the testing parameters were properly done before accepting the result of the test. We would never tear down a machine for repairs based on a single test without verification. Yet that is what they do when they proceed directly to an invasive search without verifying the integrity of the sampling.

But, that testing is done by highly skilled technicians, many with specific certifications in the processes, and the cost of failure can be significant. However, at the CP, the testing is done by... er.... uh.... TSO's, and the cost is ours, not theirs..