| Feature | SIRAC (IEC 62061) | ISO 13849-1 Graph | HRN / Matrix Methods | | :--- | :--- | :--- | :--- | | | Low (4 variables) | Medium (5 variables including training) | High (arithmetic scoring) | | Output | SIL / PLr | PLr | Risk Score (e.g., 12/25) | | Best For | Functional safety of control systems | Mechanical & pneumatic systems | General risk inventories | | Auditability | Excellent (clear logic) | Excellent | Poor (subjective numbers) |

"It’s just a calculator," Henderson argued. "It’s a simplified tool. It doesn't know the real world."