What distinguishes a "Tier 1" accident from a "Tier 2" accident?

A "Tier 1" accident is characterized by the involvement of an ambulance and the need for medical treatment, which indicates a higher severity level and necessitates immediate medical attention for those injured. This tier often reflects serious incidents requiring thorough analysis and response protocols to mitigate risks and ensure safety in the workplace. The involvement of medical treatment is a clear indicator of the accident's impact on individuals' health and safety, making it a critical factor in differentiating between various accident severities.

In contrast, the other options do not adequately capture the essential factors that define the tier classifications. The location of the incident, number of witnesses present, and time of day may contribute context to the accident but do not inherently classify an accident's severity in the same way that medical treatment requirements do. Thus, the distinction between Tier 1 and Tier 2 accidents is primarily informed by the nature of injuries and medical responses involved.