Chemical Safety Board: "Safety Pays Off: The Value of Vigilance" [5min video]
youtube.com
youtube.com
With a budget of just $14M it regularly investigates accidents causing $100M+ of property damage, not to mention the casualties and environmental impact.
This video gives overview of what the agency does and why they believe it's well paying for itself.
I have no stake in this, I'm not from US. I've long watched their work as they provide really excellent investigation reports.