Is it appropriate to apply a safety factor to a NOEL? Is there a precedent for this? Are there scientific arguments against it?

Applying a safety factor to a NOEL is unusual and no precedent has been identified.

The NAS Committee acknowledges its recommendation “differs from the traditional approach.” (See page 15) Moreover, the NAS Committee does not provide supporting precedent to justify applying a safety factor to this kind of dose. In this instance, the NAS Committee recommends a reference dose more than 570 times lower than the dose it concludes does not cause adverse effects in humans.