An employee of the municipal electrical utility marked an area of a construction site as "safe to dig." Later, an employee of one of the construction firms working on-site was preparing to dig a trench with a mechanical digger. A site foreman, hired to manage the project by the site owner, asked him if he wanted the job site power to be cut for a period of time. The worker replied that his work area was safe, and proceeded to dig the trench. Severing a live cable, the worker was seriously injured. Discuss the issues of proximate cause raised by these facts.