High School Logic, Chapter #4 - You Can't Prove a Negative

In testing for the presence of any substance, it is useful to try and remember an important lesson from our high school logic class, e.g. you can't prove a negative. For example: you can't prove that there is no lead in a house. You can test 1,000 samples of paint and find them to be lead free, but sample #1,001 might still contain lead.

As related to issues like: lead, (asbestos, oil tank leaks etc.), this means that:

  1. You should test for a suspected material in the most likely place(s) where the material might be found. For example: lead paint is much more likely to exist on painted old woodwork than on plaster walls.
  2. You should test for lead in the material most likely to contaminate the area in which pregnant women and small children might be exposed. For example: painted woodwork in a child's room or painted material which is being disturbed during a construction process.
  3. Don't assume that all look alike material has the same chemical content. For example: lead containing and lead free solder and paint can look alike. The installer may have run out of a product during the work and continued with a matching product with a different chemical content.
  4. Disclosure laws may require a party to reveal knowledge of a condition or the likelihood of a condition. Such laws may require a party to reveal that a material was tested for a hazardous material and was found to contain such material. Such laws may also require a party to reveal the possibility that a hazardous material may exist. (If you are in doubt about the law, check with your attorney.) But there is no way to prove that something does not exist.

Lead in the Home