As you may know I work with many medical volunteers, both in the MRC system and some who curiously are trying to organize on their own. Every state has different laws and levels of coverage for their medical volunteers. I am lucky (so are my volunteers) in that if they are in an organized unit and registered as emergency workers they are immune from suit as are their regular employer, and place of employment.
Not so much in other states, this is the reason we need a national law to provide protection for all volunteers. This article is written by lawyers and describes the problem and the need
Volunteer Protection under the law
Worth a read and if you don't know what your laws and protections are for your volunteers take some time and do a little research; being able to quote the law will make your recruiting easier if they don't have to worry about suit.