Read the case study Business in Bhopal.

(10 marks) Make a list of ten factors that caused this accident and explain the role of these factors in the accident.

Give yourself one mark for any ten of the following factors. If you have the factor, but not the explanation of why it is a factor, you will only receive 0.5 marks. Only mark the first 10 factors. (There may be other acceptible factors than these listed here.)

• graveyard shift causing fatigue due to shiftwork
• low frequency of events causing boredom
• deteriorating conditions of equipment in the plant meant nothing worked right and operators could not anticipate failures in the plant
• low morale meaning operators felt they couldn’t change things
• budget cuts meaning things went unrepaired, layoffs of maintenance people
• writing in English meant operators did not make complete logs
• poor training and turnover meant maintenance people had little experience
• no historical pressure trace meant operator did not know past pressure values
• lack of MIC sensors outside meant personnel were exposed to the gas
• tank pressure display could not read past 55psig meaning operators had no reading past this level
• no temperature sensor for the tank in the control room meant operators were unaware of this information
• outdoor valving controls meant operators had to work near explosive area with MIC burning their eyes and lungs
• valves were too weak, meaning they blew and the tank could not be isolated
• safety system (refrigeration, also flare tower) was offline and not workable
• vent gas scrubber and water curtain (another safety system) was undersized for the situation and couldn’t contain the accident

(5 marks) What are the system characteristics of the Bhopal plant that made this accident likely?

The system had complex interactions that the operators did not understand (1 mark). An example of this was that MIC could not be mixed with water (1 mark). The act of flushing the MIC lines created an interaction that should not have been there, bring the components of water and MIC into proximity (1 mark). The water/MIC reaction was not reversible and occurred rapidly, indicating that this new system was tightly coupled (1 mark). The failure of the valves to isolate the MIC tank is another piece of evidence that this was a tightly coupled system (1 mark).

No other characteristics will earn marks.

(3 marks) If you could pin this accident down to one cause, what would it be?

The overall cause of this accident is a lack of safety culture on the part of management (3 marks, no other solution will get marks on this question).

(22 marks) Create a fault tree, showing how the accident occurred.

How marks are awarded:

1 mark for each element, 1 mark for each AND gate.

Note: you must start from the right event. Be very specific about what is the last event in the accident. You may draw AND gates if you wish.

See fault tree file.