Section 3(e)(4)(A) of FLSA and 29 CFR §§ 553.101 through 553.106 states that individuals are volunteers and not employees of a public agency when they meet the following criteria:

• Perform hours of service for civic, charitable or humanitarian reasons without promise, expectation, or receipt of compensation for the services rendered (§ 553.101(a)). Volunteers can receive no compensation. Volunteers may be paid expenses, reasonable benefits or a nominal fee to perform such services (§ 553.106(a));
• Offer their services freely and without any pressure or coercion, direct or implied, from the employer (§ 553.101(c));
• Are not employed by the same public agency to perform the same services as those for which they propose to volunteer (§ 553.101(d)). For example, a park’s department worker can serve as a volunteer firefighter for the same agency (§ 553.103(c)).