A set of nonredundant (1oo1) safety equipment, with all component devices certified as having systematic capability SC 3, is used in a low-demand application. The longest DTI of the equipment set is 10 minutes. Demands are expected every 5 years. Proof testing takes 6 hours on average and is performed every two years while the plant is operational. After 20 years, the plant will be overhauled; therefore, the MT is 20 years. The proof test coverage is estimated at 94%. The SIF is not programmed to automatically shut down the process if a dangerous failure in the equipment is detected. However, all failures are annunciated to the plant maintenance center. MRTDD is 7 days;

MTRDU is also 7 days. All equipment can be completely tested after installation. The site safety index is presumed to be SSI 2. Failure rates for the equipment set are obtained for SSI 2. These are:

λDD = 950 FITS (9.5 • 10^-7 failures per hour)

λDU = 450 FITS (4.5 • 10^-7 failures per hour)

Considering all three verification barriers, to what SIL level does this design qualify?