FAULT TREE ANALYSIS OF FLY-OUTS IN METAL LATHE MACHINE OPERATIONS
The most probable accident in lathe machining has been identified to be fly-outs. This study aim at determining the causal factors leading to fly-out accidents during lathe machining operations and subsequently determine the probability of occurrence of fly-out accident. Fault tree analysis (FTA) was used to identify risk factors. Boolean algebra equations were used to analyse the probability of fault occurrence. Monte Carlo simulation was carried out using OpenFTA software and the output of 1000 iterations was compared with the output of Boolean algebra. Safety intervention alternatives were evaluated by comparative analysis of before and after implementation of safety measures. Twenty four (24) minimum cut sets comprising of 21 basic events and 3 undeveloped events were identified. The top event has probability of 0.748 signifying high likelihood for fly-out. Monte Carlo simulation gave lower and upper bounds probabilities of 0.725 and 0.773, respectively. The event of the chuck key not pulled out of the chuck before machining begins was however noted to have the highest contribution to the occurrence of fly-out accident. The result of safety intervention alternatives revealed that the probability of fly-out becomes 0.192 with a safety benefit of N27, 800 after the first tier implementation. Other tiers of safety interventions will see the probability of fly-out go further down. By this, safety engineer has a scale for effectiveness of respective safety intervention programmes. Key words: fly-out, accident, safety, intervention, lathe, machine, operation