(a) In this section, "volunteer" means a person who:
(1) renders services for or on behalf of the department under the supervision of a department employee; and
(2) does not receive compensation that exceeds the authorized expenses the person incurs in performing those services.
(b) A department employee or an authorized volunteer who performs a department duty or responsibility under this subchapter is immune from civil or criminal liability for any act or omission that relates to the duty or responsibility if the person acted in good faith and within the scope of the person's authority.