HAZARD AND OPERABILITY REVIEW ON BHOPAL TRAGEDYItemStudy NodeProcess ParameterDeviation(Guide Words)Possible CausesPossible ConsequencesAction Required

1AN2 flowFlowNo1.Control valve fails closed1. 2. Controller fails& closed valve

1.May be fatal2. Flammable liquid1. Select valve to fail to open2. Place controller on critical instrumentation list

1BHigh1.Control valve fails open1. MIC tank could not pressurised & slow initial reaction1. Instruct operators and update procedures

1CTemperatureLow1.Low water supply1. None-controller handles1. None

1DHigh1.High water supply1. cooling system capacity limited1. Install high flow alarm/cooling water high temperature alarm

2AGas StreamFlowNo1. Control valve fails closed

2. Controller fails and closes valve

3. Air pressure fails lead to closing valve due to small amount of MIC in storage tank (less gas produced)

1. Clogging of gas in pipeline cause explosion occur in MIC storage tank

2. As above

3. As above

1. Check and repair control valveSelect valve to fail open2. Place controller on critical instrumentation list

3. Clean the cloggingInstall filter with maintenance procedureInstall gas flow meter and low flow alarm

2BHigh1. Control valve fails open

2. Controller fails and opens valve1. possible runaway on heating and lead to explosion

2. The rupture disk is stimulated to burst

1. Instruct operators and update procedures.

2. See 1A.2

2CLow1. Partially plugged gas flow route

2. Control valve fails to respond 1. Diminished cooling, possible runaway and can lead to explosion due overheating

2. As above 1. See 1A.3

2. See 1A.2

2DAs well as1. Backflow of water to MIC storage tank1. Possible runaway reaction with the MIC component1. Install water indicator2. Do schedule checking and monitoring

2EPart of1. Covered under 1C

2FReverse1. Backflow of gas due to high back pressure1. Loss of cooling, possible runaway of heating2. Contamination of MIC component1. Install check valve

2GOther than1. Not considered possible

2HSooner than1. Cooling normally started early1. None

1. Carry out inspection frequently.

2ILater than1. Operator error1. Temperature rises, possible runaway1. Interlocking between gas flow and reactor feed (MIC)

2JTemperatureLow1. Low MIC temperature 1. None1. None

2KHigh1. High MIC temperature1. Temperature rise and boiling process occurs which can lead to explosion if temperature too high1. Install high flow alarm or MIC high temperature alarm

2LPressureHigh1.Cover under 1B

2MLow1.Cover under 1C

3ACooling StreamFlowNo1.Circulation of pump failed to operate2. Refrigerant service failure1. Loss of cooling, possible runaway

1. Reinstall pump with consistent maintenance procedure.

3BHigh 1.Controller fails and valve open1.Loss of cooling, possible runaway1. Check and monitor the reliability of refrigerant

3CLow1. control valve fails to respond1. Liquid MIC cannot be cooled as usual1.Instruct the operator and update the procedure for the control valve

3DAs well as4. Contamination of Freon supply

4. Possible chemical reaction with MIC component

1.Do schedule checking and monitoring

3EReverse3. Backflow due to high back pressure3. Loss of cooling, possible runaway 1. Install check valve

3FOther than3. Not considered possible.

3G

Part of1. Covered under deviation on low

3HSooner than1. Cooling normally started early

3ILater than1. Operator error1. Temperature may increases2. Route of water, possible runaway

3JWhere elseNot considered possible

3KTemperature

HighHigh pressure, increases the water supply temperature1. Cooling system become limited, temperature increases1.Install alarm high flow alarm/cooling water high temperature alarm

3LLowNo flow, lower the water supply temperature 1. None-controller handle the situation 1. None

4AStorage TankPressure

High1. Drain line filter blockedValve leak1. Water pass through header1.Unblock filter at drain lineChange controller

4BLow1. Insufficient Pressure to make water flow 1. MIC tank could not be pressurised causes tank PVC failed to open1.Control tank pressure (Tank was designed for only 70psig(4bar)

4CTemperatureHigh1. Overheated1. Water leak into tank that contains E610 gases causing runaway heat and producing reaction1. Supervise temperature sensor

2. Turn on the refrigeration system (Freon refrigeration system was shutdown to save money)

4DLow2.

5AMixing Eductor

AgitationNo1. Power Breakdown

2. Motor malfunction 1. No mixing, possible accumulation of unreacted product.

1. Feed valve must fail closed on power breakdown.

1. Install agitation speed indicator and agitation speed alarm. Schedule preventive maintenance of motor.

5BMore1. Motor controller fails, motor turn at higher speed

1. Higher reaction rate, causing higher temperature and pressure, possible runaway. 1. See 2A. 2

5CLess1. Power supply low 1. Lower reaction rate, accumulation of unreacted material. 1. See 2A.2

5DReverse1. Not considerable possible

5EFaster /slower1. Not considerable possible