From NPR: An Opera Singer's Guide to Protecting the Voice

This might be beneficial to choral directors:

NPR's Description:

An Opera Singer's Advice for Saving Your Voice
by Rob Sachs

Weekend Edition, March 29, 2008 · When your stock in trade is your voice, the slightest tickle in the back of your throat is scary. An opera singer gives advice about how to preserve and protect your voice.