1. To be unpaid, an internship must be similar to the training provided in an academic or vocational setting. (workersxzcompxzkit)
2. Unpaid interns must not displace regular paid workers.
3. An employer must not receive an “immediate advantage” from an unpaid intern’s work.
WC Calculator: http://www.reduceyourworkerscomp.com/calculator.php
Do not use this information without independent verification. All state laws vary. You should consult with your insurance broker or agent about workers' comp issues.