Classifying hazardous area

Introduction

In workplaces worldwide, the presence of dangerous substances poses a significant risk not just to the integrity of operations but, more critically, to human life. The classification of hazardous areas is a fundamental aspect of process safety management, aimed at preventing and mitigating risks associated with explosive atmospheres.

The basics of flammable atmospheres

Flammable atmospheres form when air mixes with flammable gases, vapors, mists, or dusts in concentrations between the Lower Flammable Limit (LFL) and Upper Flammable Limit (UFL).

These can be generated by processes involving natural gas, solvents, or powdery materials like grain. Standards like the IEC 60079 series detail these hazardous conditions.

The presence of an ignition source in an environment with a flammable atmosphere can lead to fires or explosions. Common ignition sources include electrical equipment, hot surfaces, mechanical sparks, and static discharge.

Preventing explosions involves elimination or minimization of the hazardous material, controlling ignition sources, ensuring proper ventilation, and monitoring substance concentrations.

Standards and regulations for process safety

Ensuring safety in environments with flammable atmospheres requires strict adherence to a comprehensive set of standards and regulations. These guidelines are designed to protect workers, facilities, and the public from the risks associated with explosive atmospheres. Key standards and regulations include:

International standards

• IEC 60079 Series: Developed by the International Electrotechnical Commission, this series provides the foundation for classification, installation, and maintenance of equipment in explosive atmospheres. It emphasizes the importance of understanding the nature of hazardous areas to ensure appropriate protective measures are in place.

European Union Directives

• ATEX Directives: The EU’s ATEX Workplace Directive (1999/92/EC) and Equipment Directive (2014/34/EU) set essential safety requirements for workplaces and equipment in explosive atmospheres. They categorize hazardous areas into zones based on the risk level and dictate the standards for equipment and protective systems used in these areas.

United States Regulations

• NFPA 70 (National Electrical Code): Provides guidelines for electrical installations in hazardous locations, ensuring that electrical wiring and equipment do not ignite an explosive atmosphere.
• NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas: Provides guidance on classifying hazardous areas in chemical process settings.
• OSHA’s Process Safety Management (PSM) (29 CFR 1910.119): This regulation mandates comprehensive management of hazardous chemicals, including flammable gases and vapors. It outlines requirements for process safety information, process hazard analysis, and equipment integrity.

United Kingdom

• DSEAR (Dangerous Substances and Explosive Atmosphere Regulations 2002): Specific to the UK, DSEAR requires the assessment and control of risks from dangerous substances, including the classification of hazardous areas and the selection of appropriate equipment.
• BS EN 60079 Series: British standards based on the IEC 60079 series, addressing explosive atmospheres.
• BS EN 61241: Pertains to electrical apparatus for use in the presence of combustible dust, following the IEC 61241.

Hazardous area classification principles

Once the potential to generate a flammable atmosphere is realized, areas are given a classification based on the likelihood and duration of the explosive atmosphere’s presence.

Two primary systems are used globally for classifying hazardous areas: the Class/Division system (predominantly used in North America) and the Zone system (used in the European Union and other parts of the world).

• Class/Division System [NFPA 70] - Classifies areas into:
  • Hazardous Area Class: Defines the properties of the hazardous material which may or may not be in sufficient quantities to be ignitable.
    • Class I: locations with flammable gases
    • Class II: locations with combustible dusts
    • Class III: locations with ignitable fibers
  • Hazardous Area Division: The probability of the material producing a flammable atmosphere.
    • Division 1: where the material present has a high probability of producing an explosive atmosphere continuously, intermittently, or periodically under normal operation; and
    • Division 2: where explosive atmospheres are not likely to occur under normal operation or occur only for a short period during abnormal conditions.
  • Gas & Dust Group: The type of hazardous material
    • Groups A-D: Flammable gases (Class I only)
    • Groups E-G: Dusts/fibers (Class II or III)
• Zone System [IEC 60079] – Classifies areas into:
  • Gas:
    • Zone 0: Ignitable concentrations of flammable gases or vapors which are present continuously or for long periods of time.
    • Zone 1: Ignitable concentrations of flammable gases or vapors which are likely to occur under normal operating conditions.
    • Zone 2: Ignitable concentrations of flammable gases or vapors which are not likely to occur under normal operating conditions and do so only for a short period of time.
  • Dust/fibers:
    • Zone 20: An area where combustible dusts or ignitable fibers are present continuously or for long periods of time.
    • Zone 21: An area where combustible dusts or ignitable fibers are likely to occur under normal operating conditions.
    • Zone 22: An area where combustible dusts or ignitable fibers are not likely to occur under normal operating conditions and do so only for a short period of time.

Conducting a hazardous area classification

The process of classifying hazardous areas involves several key factors:

• Type of hazardous substance: Identifying the flammable substances present and their properties, such as the flash point and flammable limits for gases and vapors.
• Source of release: Determining how and where flammable substances could be released into the atmosphere.
• Concentration and ventilation: Assessing the potential concentration of flammable substances and the effectiveness of ventilation systems in reducing the concentration of an explosive atmosphere.
• Probability and duration: Evaluating the likelihood of an explosive atmosphere being present and the duration it is expected to last.

A critical part of the classification process is documenting the findings and decisions made during the assessment. This documentation should be regularly reviewed and updated to reflect any changes in the process, materials used, or layout of the area that could affect the classification.

Equipment selection and safety measures

Based on the classification, appropriate safety measures must be implemented to prevent ignition sources from coming into contact with the explosive atmosphere. This includes selecting suitable electrical equipment and protective systems and establishing safe working practices.

Conclusion

Classifying hazardous areas requires a deep understanding of the properties of flammable substances, potential sources of release, and the environmental conditions that could lead to an explosive atmosphere. Adhering to the principles of hazardous area classification ensures the safety of personnel and facilities by mitigating the risks associated with explosive atmospheres.

These principles, grounded in global safety standards such as NFPA 497 and the IEC 60079 series, provide a framework for identifying, assessing, and managing explosion risks in industrial settings.