Every company has a organizational chart - a ladder of power, but how this structure functions during a crisis must be clarified with all the stakeholders in the company; particularly the communications department. A crisis can hit at any time, and the company needs to determine secondary command structures in case key decision-makers are unavailable at the time.
Not only is it important for those to know who need to spring to action (and how those people are contacted) - it is equally important that everyone else in the organization knows they can not speak on behalf of the company or to the press. Something that is best handled in a company employee handbook.
Organizations also need to decide which situations warrant which spokes person, and plan accordingly.
Most importantly, the spokes people need to be media trained in advance. Effective spokes people should receive professional media training and should be well versed on how to deal with the press. An organization's spokes person need not necessarily be the most senior staffers. For example, in some cases, the CEO is not the most efficient spokes person due to experience, knowledge or geographical location.