Assignment Information:

Given the following fault tree on the next page and its associated probabilities, please develop the minimal cut sets and given those minimal cut sets, calculate the probability that the top event will occur. In addition, for each cut set, calculate the relative importance to the top event's total probability. Include in your work, an executive summary, the fault tree you developed and all calculations and analytical work.

• Basic event # 1 involved an operator making a calculation error as she read a gauge on a process parameter that was required to be X 12% (the calculation was done in the operator's head and not on a piece of paper;

• Basic event # 2 involved an operator changing the position of a valve and there was no feedback or indication of what the valve position was (fully closed, fully open, halfway open, etc.);

• Basic event #3 involved the potential for an error on a two-person job of talking about the control card for a computer-controlled piece of equipment (the task is done so that each operator checks the work of the other before the equipment is placed back in service;

• Basic event #4 involved an operator activating the wrong piece of equipment since the incorrect activation switch was similar in size, shape and color to the desired activation switch. The two switches were positioned such that the desired switch was aligned with the wrong piece of equipment and the wrong switch was aligned with the desired piece of equipment.

• Basic event # 5 involved a general omission from a passive or walk around inspection.

Deliverables:

• Executive Summary
• Analysis | Results
• Completed Fig. X
• FTA Calculations
• Top event probability
• Importance measures

(Highest) (Lowest) 10 10" 10"2 1d" 16\" to" 106 1int tln'lo 1in100 Selection at . Upper limit to Missening large switch dissimilar "05'5""! manual valves "1 shape 0' location (no status indication 1 \"99"\": 5mm" except open or closed) .Two-man team . . (one do; one check Crew reaction Missettlng large then reverse roles) during air disaster . . manual valves Technician "seeing' an (controlled by procedure out of calibration keys, chaining, etc-) instrument as \"in tolerance" O 0 Simulated military General error of emergency omission for items . embedded in procedure Passive Inspections (general walk-arounds) . Selection of key operated . General error at switch rather than nonkey omission (no control room display) switch (does 0 not include Monitorilnspector error at decision) tails to recognize . initial error by operator General errors oi commission, e.g., misread label and selected . wrong switch Simple arithmetic errors (without re-dolng calculation on separate paper) Figure 12-2 Estimates of human performance error rates. (Source: SSDC course handouts. Data points were compiled from various government studies.) A D Z 3 C 4 5