Heinrich's Safety Triangle: Why 300 Near-Misses Predict 1 Fatality

The Original 1:29:300 Model

In 1931, Herbert William Heinrich published Industrial Accident Prevention: A Scientific Approach, introducing what would become the most cited model in workplace safety. Based on analysis of thousands of industrial accidents, Heinrich proposed a ratio:

The model suggests that these events share common root causes, and that by addressing the high-volume, low-severity events at the base of the triangle, you can prevent the rare but catastrophic events at the top.

Modern Research and Updates

Heinrich's original research has been refined and validated by subsequent studies:

While the exact ratios vary, the fundamental principle holds across all studies: the base of the triangle is always much larger than the top, and reducing the base reduces the top.

Practical Application

The Safety Triangle gives organizations a clear strategy:

1. Make the base visible. Most near-misses and unsafe conditions go unreported. The first priority is creating systems that capture them.
2. Analyze patterns. Individual near-misses are data points. Patterns across many near-misses reveal systemic failures.
3. Fix root causes, not symptoms. If the same near-miss keeps happening, the intervention needs to be deeper — redesign the process, retrain the team, or engineer the hazard out.
4. Track the ratio. As your reporting culture matures, you should see near-miss volume increase (more reporting) while injuries decrease (more prevention). That's the triangle shrinking from the top.

Common Misunderstandings

• "The ratio is exact." It's not. The 1:29:300 ratio is an approximation. The principle — that many small events predict few large ones — is what matters.
• "Every near-miss will eventually cause a fatality." Not every near-miss escalates. But without investigation, you can't know which ones will.
• "Zero near-miss reports means zero risk." The opposite is true. Zero reports means zero visibility. The hazards are still there; you just can't see them.
• "The triangle means we should only focus on near-misses." You should address all levels. The triangle just tells you where the highest-volume intervention opportunity is.

Using the Triangle Today

Modern organizations apply the Safety Triangle by:

• Deploying anonymous reporting to maximize the visibility of the triangle's base
• Measuring leading indicators (near-miss volume, hazard resolution time) alongside lagging indicators (injuries, fatalities)
• Setting targets for reporting volume rather than just injury reduction
• Celebrating near-miss reports as evidence of a healthy safety culture