40 years on from the Bhopal disaster – What happened and what have we learnt?

Posted

29.11.2024

Site: Sevin pesticide manufacturing facility in Bhopal, India owned by Union Carbide India Limited (UCIL).

Incident: Methyl isocyanate (MIC) gas leak which spread over Bhopal.

Fatalities: 10,000 fatalities in the first 3 days with approx. 15,000-20,000 premature fatalities over the following four decades.

Consequences: Multiple members of the public lost their lives and more than 120,000 people still suffer from ailments (including blindness, extreme difficulty in breathing and gynaecological disorders) caused by the accident and the subsequent pollution at the plant site and surrounding areas.

What happened?

On 2nd – 3rd December 1984, at the Union Carbide chemical plant, a highly toxic gas leak of methyl isocyanate (MIC) occurred over the city of Bhopal. There were approx. 10,000 fatalities in the first 3 days with approx. 15,000-20,000 premature deaths in the decades which followed. The methyl isocyanate had leaked from the E610 storage tank due to contamination with water which had caused the contents to react creating a runaway reaction and allowing the toxic gas to be released from the tank (approx. 30 tonnes in the first 60 minutes which increased to 40 tonnes within 2 hours). The toxic gases (understood to be a mixture of methyl isocyanate, chloroform, dichloromethane, hydrogen chloride and carbon dioxide) were carried in a Southeast direction over Bhopal. This all happened in the early hours of 3^rd December 1984. At 12:50 am an employee triggered the alarm as the concentration of the gas around the plant was difficult to tolerate. This triggered two siren alarms – one for inside the plant and one for the public for the Bhopal area. Unfortunately, the public alarm had been muted instantly to avoid panicking the public and the plant itself was evacuated. The worst of the gas leak emitted from the tank was approx. 2am and 2.15am, the plant public siren was eventually sounded to alert the general public but this was too late since the majority of people ended up exiting their houses into the cloud of gas instead of sheltering in place which meant a lot of people were exposed (estimates of over 500,000 people). The initial effects of exposure were coughing, eye irritation, suffocation, burning in the respiratory tract, breathlessness, stomach pains and vomiting. This had led to thousands of people dying by the following morning due to choking, reflexogenic circulatory collapse and pulmonary oedema.

Figure 1: Sevin pesticide plant in Bhopal. Reference: The Bhopal Gas Disaster – THE BHOPAL MEDICAL APPEAL

Why did it happen?

The Bhopal disaster occurred due to a combination of technical failures, inadequate safety measures and systemic management neglect. The failures are highlighted below:

The initial leak of MIC was likely due to emergency relief vent bursting open due to the runaway exothermic reaction over pressurising the tank which allowed a large quantity of MIC to leak into the atmosphere forming the vapour cloud. The direct atmospheric venting should have been prevented by at least 4 safety devices which had either malfunctioned or were not in use. These were (see Figure 2):
- A refrigeration system which was meant to cool the MIC tanks had been shut down in January 1982 and the Freon removed in June 1984. The high temperature alarm had also been disconnected and the tank storage temperatures ranged from 15-40 ^o
- A flare tower to burn the MIC gas as it escaped but a connecting pipe was removed for maintenance, but it would have been inadequately sized for the quantity of gas produced from the storage tank.
- A vent gas scrubber which had been deactivated at the time and was on ‘standby’ mode and therefore couldn’t scrub any of the gases released. It was also assumed it didn’t have the capacity to scrub the quantity of gases released from the storage tank.
- Water curtain to suppress the gas was not operational and designed with inadequate height.

The facility did not have adequate safety mechanisms to detect gas leaks or contain the initial leak which allowed the gas leak to spread. The plant was in a state of shutdown which meant a lot of the safety equipment had been turned off/idle. The site also had long-standing history of safety issues with frequent leaks reported and equipment malfunctions.
The 2 siren alarms (one for the plant and one for the public) had also become independent from one another which meant the public alarm could be switched off when there was a critical incident like on the day. This meant when it was reactivated it was too late to allow people to either evacuate or shelter in place. The lack of training of the community lead to a lot of confusion for people who left their houses instead of sheltering in place which could have saved some lives.
The facility was situated in a highly populated area which placed thousands of residents around the hazardous site and put them at increased risk. The zoning regulations were limited 40 years ago.
Insufficient emergency response to the incident lead to more lives being lost and due to lack of contingency plans and infrastructure the evacuation and medical assistance were not effective since the hospitals were not equipped or trained to handle exposure to toxic gases.

Figure 2: Explanation of why the Bhopal disaster occurred. Reference: What Happened – THE BHOPAL MEDICAL APPEAL

What can We Learn 40 years on?

The 40^th anniversary of the Bhopal disaster serves as a reminder of the catastrophic consequences which can occur if neglecting process safety in chemical operations. The lessons learned emphasise not only operational and cultural improvements but also specific physical measures that can prevent similar disasters. Here are key elements for companies to implement at their sites:

Robust Containment Systems

Lesson Learned: In Bhopal, the lack of robust containment allowed toxic methyl isocyanate (MIC) to escape into the environment.
Key Actions:
- Install secondary containment systems (e.g., bunds, double-walled tanks) to prevent leaks from spreading.
- Use inert gas blanketing to suppress reactions in volatile or reactive chemicals (always check the compatibility of chemicals with inert gases).
- Ensure storage tanks and pipelines are built with corrosion-resistant materials and regularly inspected.

Effective Emergency Shutdown Systems

Lesson Learned: Critical safety systems like the refrigeration unit and flare towers at Bhopal were either non-functional or bypassed.
Key Actions:
- Deploy automated emergency shutdown systems (ESD) that can quickly isolate processes during emergencies.
- Ensure fail-safe designs for critical equipment, such as valves that default to a safe position during power failures.

Real-Time Monitoring and Detection

Lesson Learned: The disaster was exacerbated by the absence of real-time monitoring for toxic gas releases.
Key Actions:
- Install advanced gas detection systems to monitor for leaks and chemical concentrations continuously.
- Use pressure, temperature, and flow sensors integrated into SCADA (Supervisory Control and Data Acquisition) systems for proactive monitoring.
- Equip sites with early-warning alarms connected to community alert systems.

Controlled Inventory Levels

Lesson Learned: Large quantities of MIC were stored unnecessarily, amplifying the disaster.
Key Actions:
- Minimise on-site storage of hazardous chemicals by adopting a just-in-time inventory model.
- Use smaller, multiple storage tanks instead of a single large tank to reduce risk.
- Ensure chemicals are stored under appropriate conditions (e.g. refrigeration for volatile compounds).

Reliable Ventilation and Scrubbing Systems

Lesson Learned: The scrubbing system at the plant was under-designed and failed to neutralise the escaping gas and ensure these systems are kept online even if the plant is shut down to ensure reduced levels are emitted if there was to be an incident.
Key Actions:
- Install high-capacity scrubbers tailored to the chemicals being processed, which are capable of neutralising potential releases.
- Design ventilation systems to control the spread of airborne toxins in case of leaks.
- Regularly test and maintain these systems to ensure full functionality during an emergency.

Fire and Explosion Prevention

Lesson Learned: The reaction that led to the disaster involved a runaway exothermic reaction.
Key Actions:
- Implement active cooling systems to control exothermic reactions.
- Use pressure relief valves and rupture discs to safely release pressure build-ups and ensure they vent to safe areas and any toxic gases are sent to a scrubbing system to reduce the quantity released to the environment.
- Ensure all electrical and process equipment is rated for hazardous areas to prevent ignition sources and you have a completed Explosion Protection Document (EPD) which highlights the risks on a risk assessment, any ignition sources and hazardous area classification assessment to ensure you understand where the hazardous zones are.

Segregation and Zoning

Lesson Learned: Toxic chemical (MIC) processing was located dangerously close to residential areas.
Key Actions:
- Maintain safe distances between chemical storage/processing areas and nearby communities.
- Use zoning principles to separate incompatible processes or hazardous material storage areas.
- Establish buffer zones with barriers or vegetation to minimise offsite impact.

Comprehensive Maintenance Programmes

Lesson Learned: Corroded pipelines and poorly maintained equipment contributed to the disaster.
Key Actions:
- Implement predictive and preventive maintenance schedules for critical equipment especially key safety critical equipment.
- Use non-destructive testing (NDT) methods to detect early signs of wear or damage and if any damage/wear is identified then this is fixed immediately or if it cannot be fixed then upgraded equipment needs to be purchased and included in appropriate site budgets.
- Ensure any outdated equipment is replaced or upgraded to meet modern safety standards i.e. atmospheric storage tanks are designed to API 650 or BS EN 14015.

Secure Chemical Handling and Storage

Lesson Learned: Improper handling and storage procedures led to contamination and runaway reactions.
Key Actions:
- Implement strict operational procedures for handling reactive or toxic chemicals.
- Train personnel in safe loading and unloading protocols.
- Use maintained isolation valves to separate sections of pipelines during maintenance or emergencies.

Onsite Emergency Preparedness Infrastructure

Lesson Learned: Inadequate onsite response capability compounded the disaster’s effects.
Key Actions:
- Build dedicated emergency response centres with firefighting, medical, and neutralisation equipment.
- Store adequate emergency neutralising agents near critical processing areas.
- Equip facilities with evacuation shelters and clear escape routes.

Community and Environmental Protections

Lesson Learned: The proximity to unprotected residential areas magnified the disaster’s human death toll and people injured.
Key Actions:
- Conduct risk assessments to evaluate offsite impacts and adjust operations accordingly.
- Build containment barriers to limit chemical migration offsite.
- Regularly engage with local communities to prepare them for emergencies.

Adherence to Process Safety Standards

Lesson Learned: A lack of adherence to safety standards and inspections left the plant vulnerable.
Key Actions:
- Implement globally recognised process safety frameworks such as ISO 45001.
- Conduct periodic HAZOP (Hazard and Operability) studies and risk assessments or Process Hazard Revalidations (PHRs) to ensure any plant changes aren’t going to cause any process safety issues and are captured in a systematic way and all hazards and mitigations are captured.
- Ensure third-party audits of safety systems to identify and address gaps.

Conclusion

The Bhopal disaster serves as a powerful reminder of the catastrophic consequences when safety, accountability, and preparedness are neglected. By prioritising strict safety standards, corporate responsibility, community awareness, and regulatory oversight, industries worldwide can minimise the risks associated with hazardous materials and create safer environments for both workers and neighbouring communities.

Finch can help support our clients with hazardous substances storage tank systems ensuring the design is appropriate and technology is used well and ensure a disaster like Bhopal doesn’t happen at their sites.