Probably the number one source of confusion in regard to height safety revolves around just what is deemed to be working at heights. There are a number of metric measures bandied about, and they are all wrong. Whenever it is possible to fall from one level to another the work should be considered working at heights.
Once you classify work in this way, and it is deemed to encompass working at height, a mandatory hierarchy of control must be applied.
While we generally think about the potential for a person to fall, consideration should also be given to falling objects such as tools and equipment, which pose a risk of injury to others working on a lower level.