I would suggest your getting a hold of Paisley S. Cato's
"Institution-Wide Policy for Sampling" which appeared in Collection
Forum, Volume 9, Number 1, pages 27-39.  She provides an analysis of the
problem of preserving yet using natural history materials.  The Appendix
consists of an excerpt of her museum's (Virginia Museum of Natural
History) Collection Policy that concerns destructive or consumptive sampling.
Good luck.
-- Ann Pinzl
   Nevada State Museum
P.S. I might add that those of you who are concerned with the use and
preservation of natural history (anthropological, biological, geological)
collections should know about 9maybe even join?) the Society for the
Preservation of Natural History Collections (SPNHC) - if you are
interested, you can contact me, [log in to unmask]