Abstract
Major industrial accidents such as Bhopal (India, 1984), Seveso (Italy, 1976), and Mexico City (Mexico, 1984) not only claimed thousands of lives but also revealed the critical importance of a structured, preventive system for managing major hazards in the chemical industry. This article, drawing on the practical guide of the ILO, UNEP, and WHO, examines the key components of major hazard control and provides a framework for risk reduction in such facilities.
1. Introduction
The chemical industry is one of the most important industrial infrastructures in any country. At the same time, due to the handling of hazardous materials (flammable, toxic, explosive), the potential for major industrial accidents is very high. Controlling such hazards requires a preventive, systematic, and multi-layered approach that begins with accurate hazard identification and extends to community-level emergency preparedness.
According to the ILO/UNEP/WHO guide, the three key pillars of major hazard management are:
Major Hazard Installation (MHI) Identification
Systematic Risk Assessment
Design and Implementation of Control Systems and Emergency Planning
2. Major Hazard Installation (MHI) Identification
2.1. MHI Identification Criteria
A facility is considered a Major Hazard Installation (MHI) when:
It stores hazardous chemicals above defined threshold quantities (according to SEVESO III or EPA RMP).
Its chemical processes are prone to explosive, thermal, or toxic reactions.
2.2. Real-World Examples of MHIs
Refineries and Petrochemical Plants: Storing thousands of tons of LPG or benzene.
Chlorine Production Plants: Risk of release of asphyxiating gas with acute respiratory effects.
Fertilizer Industries: Such as ammonia and ammonium nitrate plants.
Case Study: Beirut Port Explosion (2020)
Long-term, unmonitored storage of ammonium nitrate led to an explosion equivalent to 1.1 kilotons of TNT. This incident is an example of failure in MHI identification and control.
3. Risk Assessment in Chemical Facilities
Risk assessment in MHIs must be multi-layered, precise, and reviewable. International guidelines emphasize the combined use of qualitative and quantitative methods.
3.1. Risk Analysis Methods
HAZOP: Process deviation analysis – Identifies unexpected scenarios
FTA: Root cause analysis – Aids in designing protective systems
QRA (Quantitative Risk Assessment): Quantitative analysis of probability and consequences – Defensible before regulatory authorities
Case Study: MIC Unit in Bhopal
The lack of a valid QRA led to the risk of a massive MIC release during non-standard maintenance being overlooked.
3.2. Surrounding Environmental Risk Assessment
Mapping populated areas around the facility
Modeling the effects of substance release (using software such as PHAST or ALOHA)
Identifying critical centers (hospitals, schools) within the impact zone
4. Control Systems and Safety Engineering
Control systems must begin at the design stage and be updated throughout the facility’s lifecycle.
4.1. Types of Controls
Engineering Controls:
Emergency Shutdown (ESD) systems
Safety valves, blast walls, vented tanks
Administrative Controls:
Employee training
Management of Change (MOC)
Periodic audits
Failure in change management was the main cause of the Flixborough accident.
4.2. Tracking and Early Warning
Gas and temperature sensors
SCADA and PLC systems
Real-time monitoring through cameras and audio alarms
5. Emergency Planning and Preparedness
Emergency plans play a vital role in mitigating the consequences of accidents.
5.1. On-Site Plans
Automatic fire alarm and suppression systems
Evacuation routes and safe assembly points
Training on roles and responsibilities of employees
5.2. Off-Site Plans
Public warning systems (e.g., SMS or regional sirens)
Coordination with fire departments, emergency services, and police
Developing response scenarios and conducting joint drills with municipal bodies
In the Seveso accident, failure to promptly inform residents exacerbated the effects of dioxin exposure.
6. Recommendations and Conclusion
The ILO/UNEP/WHO guide is a practical reference for developing countries that lack modern PSM infrastructure. It simplifies the risk management path without requiring overly complex standards.
6.1. Practical Suggestions for Iranian Industries
Establish a national database of hazardous facilities.
Mandate annual risk assessments and registration in a system supervised by the Environmental Protection Organization and the National Standards Organization.
Conduct emergency drills with the participation of city management and rapid response organizations.
Design a dedicated process safety unit in all chemical complexes.
6.2. Conclusion
Major hazard management is an ethical, social, environmental, and economic responsibility. By learning from past disasters, a safer future can be achieved for the chemical industry.
Key Point: Major hazard control is not only a legal requirement but also an ethical responsibility of industries toward society.
Prepared by: Dr. Majid Alizadeh
WSO Office in Iran
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