Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified ...

How to Apply Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Division 1 and Division 2

Mastering the principles outlined in API Recommended Practice 500 (RP 500) is paramount for ensuring the safety and compliance of electrical installations in hazardous petroleum facility environments. A thorough understanding and correct application of its classification methodology directly impact personnel safety, prevent catastrophic incidents, and uphold regulatory standards. This guide will equip you with the practical steps to confidently implement RP 500's requirements, enhancing your expertise in hazardous area classification and solidifying your role as a critical safety asset.

Before You Begin

Prerequisites:

• • Knowledge: A foundational understanding of electrical systems, principles of hazardous area classification (including concepts like flammability limits and ignition sources), and common operations within petroleum facilities (e.g., refining, processing, storage). Familiarity with relevant national electrical codes is beneficial.
• • Tools/Resources: Access to API RP 500 (Third Edition, December 2012, with Errata, January 2014), plant or facility layout drawings, process flow diagrams (PFDs), piping and instrumentation diagrams (P&IDs), and information regarding the properties of materials handled at the facility (e.g., Material Safety Data Sheets - MSDS).
• • Time Required: Approximately 2-4 hours for initial familiarization and area walk-through, with ongoing effort for detailed analysis and documentation.

Step-by-Step Implementation

Step 1: Define the Scope and Objective

Clearly establish the specific area or facility section you are classifying. Understand the purpose of the classification—whether it’s for new installations, modifications, or periodic re-evaluation. This step ensures you are focusing your efforts correctly and aligns with the overall safety management system.

Step 2: Identify Potential Sources of Flammable Materials

Systematically review P&IDs, PFDs, and operational procedures to pinpoint all points where flammable liquids, gases, or vapors could be present. Consider normal operation, maintenance activities, and potential upset conditions, as these can significantly influence the presence and concentration of hazardous substances.

Step 3: Characterize Flammable Materials and Conditions

Determine the specific flammable materials involved (e.g., crude oil, natural gas, specific hydrocarbons). Gather data on their properties, such as flash point, autoignition temperature, and vapor density. Understand the typical operating temperatures and pressures, as these affect volatility and the likelihood of release.

Step 4: Analyze Ventilation and Potential for Gas Accumulation

Evaluate the natural and mechanical ventilation characteristics of the area. Consider how airflow patterns might affect the dispersion of flammable vapors. Areas with poor ventilation are more prone to the accumulation of hazardous concentrations, influencing the extent of classified zones.

Step 5: Determine Classification Criteria (Division 1 vs. Division 2)

Apply the criteria outlined in RP 500 to assign Division 1 or Division 2 classifications.

• • Division 1 areas are those where a flammable atmosphere is expected to exist under normal operating conditions, or where ignitable concentrations can occur frequently due to maintenance or operations.
• • Division 2 areas are those where ignitable concentrations are not expected to exist under normal operating conditions but may exist intermittently due to abnormal operations, or where leaks or spills are unlikely but not impossible.

Step 6: Delineate the Boundaries of Classified Locations

Based on the identified sources, material properties, and ventilation, draw the boundaries for each classified zone on your facility drawings. Consider the potential extent of flammable vapor clouds from leaks or releases, accounting for prevailing wind conditions and potential obstructions.

Step 7: Document and Review Classification

Thoroughly document the entire classification process, including the rationale for each decision