If a process unit has an unmitigated risk estimate of PLL = 0.4 and tolerable risk established at PLL = 0.001, what is the required risk reduction factor?

• A. 400
• B. 4000
• C. 0.001
• D. Cannot be calculated with given information

Answer: (A)

To determine the required risk reduction factor, you need to compare the unmitigated risk estimate (PLL = 0.4) with the tolerable risk level (PLL = 0.001). The risk reduction factor is calculated by dividing the unmitigated risk by the tolerable risk.

The calculation follows this formula:

[

\text{Risk Reduction Factor} = \frac{\text{Unmitigated Risk}}{\text{Tolerable Risk}} = \frac{0.4}{0.001} = 400

]

This indicates that the unmitigated risk is 400 times greater than what is deemed tolerable. Therefore, to meet safety standards, a reduction of the risk by a factor of 400 is required to bring it down to an acceptable level.

Understanding this calculation is essential in functional safety, as it highlights the need to systematically evaluate risks and implement effective risk mitigation strategies to ensure safety within industrial processes.