The short answer is no, you cannot force employees to stay; however, both management and employees have certain obligations under OSHA. You must consider all possible emergency situations and develop an emergency action plan. The plan must include a description of conditions under which an evacuation would be necessary and conditions under which it may be better to shelter-in-place. The plan can consider how given situations might impact employees sheltering-in-place versus employees attempting to evacuate to safety; however, it cannot force employees to shelter-in-place. In some situations local officials may advise (or employees and the employer may decide) to evacuate to avoid situations they believe are potentially dangerous. It is your responsibility to train employees on the actions needed to be taken in an emergency, including the procedures to account for all employees and visitors during an emergency. In the situation we discussed, this means the employee must tell the person charged with worker accountability that they have decided to leave the workplace.