A vessel is used to store hexane, a combustible material. The level in the vessel is controlled by a level controller which operates a valve. If the vessel is overfilled, hexane will be released through a liquid vent and be contained within a dike. A hazard analysis was performed , and it was determined that the level controller might fail , liquid might be released outside of the dike , an ignition source might ignite the hexane , and there might be a possible fatality . The organization wanted to determine if the existing facility would meet their corporate risk criteria , or if any changes were required (such as adding a stand alone safety system ), how extensive the changes would need to be. Information given: a The organization established a yearly tolerable risk limit for a fire of 1E4 and 1E5 for a fatality. a The initiating event for this scenario would be a failure of the control system, which was estimated at lEl. a The only existing safety layer would be the dike , which had an estimated PFD of 1E2. a Alarms and operator action were not accounted for because , in this instance, the control system was the initiating event, therefore no alarms would be generated a The organization took a conservative view that if material was released outside of the dike, the likelihood of it finding an ignition source would be 100%. a However, the area was not always manned. The probability of someone being in the area was estimated at 50%. a The probability of someone in the area actually being killed by a fire, as opposed to merely injured, was estimated at 50%. 1. Draw the event tree diagram for the hazard . 2. Determine the probability of fire. Does it meet the corporate risk criterion for fire? What changes would require and what should be the extent of the change (i.e. risk reduction factor}? 3. Determine the probability of fatality. Does it meet the corporate risk criterion for fatality? What changes would require and what should be the extent of the change (i.e. risk reduction factor)? 4. Based on the above results, determine whether a safety function should be implemented. If yes, what will be the SIL requirement