A single negative sample does not always provide enough information to characterize an entire building material. Asbestos may not be distributed evenly throughout certain materials, and regulations and accepted sampling protocols may require multiple representative samples from homogeneous areas.
The appropriate number of samples depends on the type of material, size of the homogeneous area, project scope, and applicable sampling requirements.
Multiple samples reduce the chance that a small or nonrepresentative portion of material will determine the conclusion for a much larger area.
This is why MEC develops the sampling plan after inspecting the property rather than simply taking one sample of every material.