Determining Hazardous Classified Areas in Industrial Plants
When installing new equipment in a plant—whether it’s a new construction or an existing facility—it’s critical to determine the hazardous classified areas to ensure safety and compliance. These classifications help define where explosive or flammable atmospheres may exist, guiding the selection and installation of appropriate equipment.
This post outlines the steps to determine hazardous classified areas and provides guidance for ensuring proper equipment installation.
1. What Is a Hazardous Classified Area?
A hazardous classified area is a location where flammable gases, vapors, liquids, dust, or fibers are likely to be present in sufficient quantities to pose a risk of fire or explosion. Classifications help identify the level and frequency of these risks.
Common Standards for Classification
- NFPA 70 (NEC): Defines classifications in the United States.
- IEC 60079 (ATEX): International standards for explosive atmospheres.
2. Why Hazardous Classification Is Essential
- Ensures compliance with safety standards and regulations.
- Helps select equipment designed to operate safely in hazardous environments.
- Protects personnel, equipment, and the facility from risks of fire and explosion.
3. Steps to Determine Hazardous Classified Areas
Step 1: Understand the Process and Materials
- Identify Hazardous Substances:
- Review the materials used in the process (e.g., gases, liquids, or dust).
- Obtain Material Safety Data Sheets (MSDS) to understand their flammability and explosion characteristics.
- Key Parameters to Consider:
- Flashpoint, ignition temperature, and flammability limits.
- Material behavior under different conditions (e.g., temperature and pressure).
Step 2: Conduct a Site Survey
- Evaluate the Area:
- Analyze the plant layout, process units, and ventilation systems.
- Identify potential sources of release (e.g., valves, pumps, tanks, or vents).
- Assess Ventilation:
- Determine whether natural or mechanical ventilation can dilute hazardous materials below explosive limits.
- Poorly ventilated areas are more likely to be classified as hazardous.
Step 3: Define the Source of Release
- Determine Release Types:
- Continuous Release: Materials are constantly released (e.g., open vents).
- Primary Release: Expected under normal operating conditions (e.g., pump seals or flanges).
- Secondary Release: Only occurs during malfunctions or maintenance activities.
- Example:
- A vent from a storage tank with flammable liquid creates a primary source of release.
Step 4: Classify the Area Based on Zones or Divisions
- For Flammable Gases or Vapors:
- Division 1 (NEC) / Zone 1 (IEC): Hazardous materials are present during normal operations.
- Division 2 (NEC) / Zone 2 (IEC): Hazardous materials are present only during abnormal conditions.
- Zone 0 (IEC): Continuous hazardous presence (e.g., inside a tank or confined space).
- For Combustible Dust:
- Class II, Division 1 (NEC) / Zone 20 or 21 (IEC): Dust is present during normal operations.
- Class II, Division 2 (NEC) / Zone 22 (IEC): Dust is present only under abnormal conditions.
Step 5: Determine the Extent of the Hazardous Area
- Use industry standards like API RP 500 or IEC 60079-10 for guidance.
- Calculate the area around the source of release based on:
- Volume and type of material released.
- Ventilation rate.
- Temperature and pressure conditions.
- Example:
- A pump seal releasing flammable vapors may create a hazardous area extending a few meters, depending on ventilation.
Step 6: Document and Verify the Classification
- Create Hazardous Area Drawings:
- Use plant layout diagrams to map hazardous zones or divisions.
- Review and Approve:
- Have the classification verified by qualified personnel (e.g., a Hazardous Area Classification Specialist or Certified Electrical Engineer).
4. Installing Equipment in Hazardous Areas
Step 1: Select Appropriate Equipment
- Explosion-Proof: Contains explosions within the equipment housing (e.g., Class I, Div. 1/Zone 1 areas).
- Intrinsically Safe: Limits energy to prevent ignition in hazardous environments.
- Pressurized or Purged Enclosures: Prevent flammable atmospheres from entering the equipment housing.
Step 2: Follow Installation Standards
- Adhere to standards such as NEC 500/505 or IEC 60079 for electrical equipment installation.
- Ensure proper sealing of conduit and cable glands to prevent gas ingress.
Step 3: Inspect and Test
- Verify that the equipment meets hazardous area requirements.
- Conduct regular inspections to ensure seals, enclosures, and equipment remain intact.
5. Common Challenges and How to Overcome Them
| Challenge | Solution |
|---|---|
| Incomplete Process Information | Collaborate with process engineers to understand material properties and release points. |
| Poor Ventilation | Enhance ventilation systems or redesign the process layout. |
| Equipment Compatibility | Consult manufacturers for certified equipment suitable for the classified area. |
6. Tips for Managing Hazardous Area Classification
- Engage Experts: Work with qualified hazardous area specialists or consultants for accurate classification.
- Use Software Tools: Leverage tools like PIPENET or PHAST for dispersion modeling and area classification.
- Regular Updates: Reevaluate classifications when equipment, processes, or materials change.
- Employee Training: Train personnel on hazardous area standards and the safe use of equipment.
7. Conclusion
Determining hazardous classified areas is a critical step when installing new equipment in industrial plants. By following a systematic approach—understanding materials, assessing site conditions, and adhering to classification standards—you can ensure the safe and compliant installation of equipment.
With proper documentation, collaboration, and regular reviews, plants can minimize risks and maintain safe operations, whether working with new installations or existing systems.