10 CFR 708.6: Reasonable fear of serious injury.

Participation in an activity, policy, or practice may cause an employee to have a reasonable fear of serious injury that justifies a refusal to participate if:

(a) A reasonable person, under the circumstances that confronted the employee, would conclude there is a substantial risk of a serious accident, injury, or impairment of health or safety resulting from participation in the activity, policy, or practice; or

(b) An employee, because of the nature of his employment responsibilities, does not have the training or skills needed to participate safely in the activity or practice.