ENGI 9121 Advanced Safety, Risk and Reliability Engineering Assignment 3 Winter 2025 | MU

Important points: 

• You can make appropriate assumptions about the data you believe is missing as long as the assumptions are clearly stated. 
• Assignment due date: Monday, March 03, 2025, at 11:59 PM NST 

Questions: 

Case 1: Consider the flash distillation problem as illustrated below. The liquid and vapour under consideration are flammable. A high level of liquid in the vessel may result in over-pressurisation of the vessel. 

The following basic process control systems are implemented in the process: 

• Transmitter L1 measures the level and manipulates the outlet flow valve (valve V1) to maintain the level.
• Transmitters F4 and P1 measure the overhead line flow and pressure, respectively, and manipulate the overhead outlet flow valve (valve V2) to maintain the flow and pressure 

A high-pressure alarm (not shown in the diagram) is also implemented to alert the operator to take appropriate action. 

If the operator fails to respond, a pressure relief valve is installed (not shown in the diagram) to release the materials in the vessel to the atmosphere and thus prevent the vessel's failure. 

The management specifies the safety target level as the "probability of release to the atmosphere to be not greater than 10-4per year". The release into the atmosphere can cause serious permanent injury to one or more persons and can result in the death of one person, as well as causing temporary damage to the environment. The vessel is not isolated, and plant personnel are always exposed to possible accidents. There are no other measures in place to avoid or minimise the exposure of plant personnel. The frequency of the occurrence of release can be considered low. 

• Part 1: Use the risk graph method to determine the SIL requirement for the flash distillation process.
• Part 2: Use the 3-Dimensional risk matrix method to determine the SIL requirement and compare it with that from the risk graph method.
• Part 3: Draw an event tree to determine whether the existing safety systems meet the safety requirement of 'probability of release to the atmosphere to be not greater than 10-4 per year'.
• Part 4: Draw an event tree with an additional SIS with SIL obtained using the risk graph or risk matrix method to determine whether the modified process will meet the safety requirement.
• Part 5: Comment on whether a dike will be helpful to meet the safety requirement