What are the 3 W questions used to guide an accident investigation?

The three W questions used to guide an accident investigation are: "What happened?" which focuses on the details and circumstances of the incident; "Why did it happen?" which seeks to identify the root causes and contributing factors; and "What can be done to prevent it from happening again?" which aims to develop recommendations and improvements to enhance safety and prevent future incidents. These questions help create a comprehensive understanding of the accident and inform effective corrective actions.