API RP 505-2025 PDF

Full title and description

API RP 505:2025 — Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Zone 0, Zone 1, and Zone 2. This edition provides updated guidance for identifying and documenting hazardous (classified) locations at petroleum production, processing, storage, and handling facilities to support safe selection and installation of electrical equipment.

Abstract

The recommended practice gives procedures and criteria for classifying areas where flammable gases or vapors may be present in quantities sufficient to produce explosive atmospheres (Class I — Zone 0, Zone 1, Zone 2). It covers definitions, release source evaluation, extent and duration considerations, ventilation effects, special circumstances (enclosed spaces, piping, vents), use of gas detection, and documentation needed to support electrical equipment selection and installation. The 2025 edition updates and consolidates material from the prior (2018) edition.

General information

• Status: Current.
• Publication date: January 6, 2025.
• Publisher: American Petroleum Institute (API).
• ICS / categories: 29 — Electrical engineering (notably 29.020 electrical engineering in general and 29.260 electrical equipment for working in special conditions / explosive atmospheres).
• Edition / version: 3rd edition (2025).
• Number of pages: 192 pages.

Scope

Applies to petroleum facilities where flammable liquids, gases or vapors are produced, processed, stored or otherwise handled and where electrical equipment selection and installation must account for classified locations. The RP provides methods to determine the degree and extent of Class I Zone 0, Zone 1 and Zone 2 locations, including consideration of release sources, duration and frequency of release, dispersion and ventilation, and special facility layouts (buildings, compartments, vessels, piping). It is intended to be used with applicable electrical installation codes and standards such as the NEC/NFPA 70, CSA C22.1, and IEC guidance where referenced.

Key topics and requirements

• Definitions and terminology for Zone-based hazardous-area classification.
• Methodology to identify and evaluate release sources (operational, equipment failure, vents, openings) and determine extent of classified areas.
• Criteria for duration and frequency of flammable atmospheres to distinguish Zone 0, Zone 1 and Zone 2.
• Ventilation and dispersion considerations, including how natural and mechanical ventilation affect classification.
• Use of gas detection and monitoring to influence classification decisions.
• Documentation, drawings, and labeling requirements for classified-area determinations.
• Guidance for interfacing with electrical installation codes and equipment selection (eg, explosion-protected equipment types and installation practices).

Typical use and users

Primary users include electrical and process engineers, facility designers, safety and reliability engineers, inspectors, operations and maintenance personnel, electrical contractors working in petrochemical and oil & gas facilities, and regulatory authorities responsible for permitting and enforcement. The RP is used when preparing area classification drawings, specifying explosion-protected electrical equipment, performing hazard analyses, or updating documentation for inspections and audits.

Related standards

Commonly used together with API RP 500 (for Division-based classification), API RP 14FZ (offshore electrical systems), NFPA 70 (NEC), CSA C22.1, and IEC/EN standards for explosive atmospheres (for example IEC 60079 series, including IEC 60079-10-1 on area classification). Users should apply the RP in coordination with national/local electrical codes and other API standards where referenced.

Keywords

hazardous area; classified locations; Zone 0; Zone 1; Zone 2; petroleum facilities; electrical installations; area classification; gas release; ventilation; explosion protection; API RP 505; 2025 edition.

FAQ

Q: What is this standard?

A: API RP 505:2025 is an API recommended practice that provides guidance for classifying hazardous (explosive) locations at petroleum facilities for the purpose of selecting and installing electrical equipment.

Q: What does it cover?

A: It covers methods to identify potential sources of flammable gas or vapor releases, criteria for assigning Class I Zone 0/1/2 designations, effects of ventilation and enclosure, documentation and labeling, and considerations for equipment selection in accordance with applicable electrical codes.

Q: Who typically uses it?

A: Electrical engineers, process engineers, facility designers, safety professionals, inspectors, operations staff, and electrical contractors in the oil, gas and petrochemical sectors.

Q: Is it current or superseded?

A: The 2018 edition has been superseded by the 2025 edition. The API RP 505:2025 publication is the current edition (published January 2025) and replaces the prior 2018 edition.

Q: Is it part of a series?

A: Yes. API RP 505 is part of API’s hazardous-area classification guidance and is used alongside related API RPs such as RP 500 (Division-based classifications) and RP 14FZ (offshore electrical systems), as well as national and international electrical codes and IEC explosion-protection standards.

Q: What are the key keywords?

A: Zone classification, hazardous area, Class I, Zone 0, Zone 1, Zone 2, petroleum facilities, electrical equipment selection, ventilation, gas detection, area classification documentation.