API 500 Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Division 1 and Division 2

API 500

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

1. Scope:

The purpose of this recommended practice is to provide guidelines for classifying locations Class I, Division 1 and Class I, Division 2 at petroleum facilities for the selection and installation of electrical equipment Basic definitions given in the 1996 edition of NFPA 70, the National Electrical Code (NEC), have been followed in developing this recommended practice. This publication is only a guide and requires the application of sound engineering judgment.

Electrical installation in areas where flammable liquids, gases, or vapors are produced, processed, stored or otherwise handled can be suitably designed if the locations of potential sources of release and accumulation are clearly defined. Once a location has been classified, requirements for electrical equipment and associated wiring should be determined from applicable publications. Applicable publication may include NFPA 70 (NEC) or API RP 14F. Reference Section 2 for publications for other possible applications.

This document applies to the classification of locations for both temporarily and permanently installed electrical equipment. It is intended to be applied where there may be a risk of ignition due to the presence of flammable gas or vapor, mixed with air, under normal atmospheric conditions. Normal atmospheric conditions are defined as conditions that vary above and below reference levels of 101.3kPa and 20 °C provided that the variations have a negligible effect on the explosion properties of the flammable materials.

The following items are beyond the scope of this document:

1. Piping systems used for odorized natural gas used as fuel for cooking, heating, air conditioning, laundry and similar appliances;
2. Catastrophes such as well blowouts or process vessel rupture. Such extreme conditions require emergency measures at the time of occurrence;
3. The suitability of locations for the placement of non-electrical equipment; and
4. Classification of locations containing combustible dust, ignitable fibers, or flyings.

Recommendations for determining the degree and extent of classified locations for specific examples of situations commonly encountered in petroleum facilities are given in Section 8 through 14. While it is important for area classifications at refineries, production and drilling facilities, and pipeline facilities to agree to some extent, there are differences in production, drilling, transportation and refining facilities. Some differences include the process conditions, types and quantities of products handled, the physical size of typical facilities, and varying housing and sheltering practices.

Section 8 includes applications that are common to several of the facility types described in Section 9 through 14.

Section 9 is applicable to locations in which flammable petroleum gases and vapors and volatile flammable liquids are processed stored, loaded, unloaded, or otherwise handled in petroleum refineries.

Section 10 is applicable to locations surrounding oil and gas drilling and workover rigs and production facilities on land and on marine fixed (bottom-founded, non-floating) platforms where flammable petroleum gas and volatile liquids are produced, processed (for example, compressed), stored, transferred (for example, pumped), or otherwise handled prior to entering the transportation facilities.

Section 11 is applicable to locations on Mobile Offshore Drilling Units (MODUs).

Section 12 is applicable to locations surrounding oil and gas drilling and workover rigs and production units (FPUs) such as, but not limited to, tension leg platforms (TLPs), floating production systems (FPSs), floating production systems with off-loading (FPSOs), single anchor leg mooring buoys (SALMs), caisson structures, spars, and other floating structures where flammable petroleum gas and volatile liquids are produced, processed (for example, compressed), stored, transferred (for example, pumped) or otherwise handled prior to entering the transportation facilities.

Section 13 is reserved for future use.

Section 14 is applicable to onshore and offshore facilities handling the delivery of flammable or combustible petroleum liquids or flammable gases. Pipeline facilities may include pump and compressor stations, storage facilities, manifold areas, valve sites and pipeline right-of-way areas.

2. Contents:

1 Scope
1.1 Purpose
1.2 Scope
2 References
2.1 Industry codes, guides and standards
3 Acronyms and abbreviated definitions
3.1 Acronyms
3.2 Definitions
4 Basic conditions for a fire or explosion
5 Flammable and combustible liquids, gases and vapors
5.1 General
5.2 Flammable and combustible liquids
5.3 Flammable highly volatile liquids
5.4 Flammable lighter-than-air-gases
5.5 National electrical code grouping of atmospheric mixtures
6 Classification criteria
6.1 General
6.2 National electrical code criteria
6.3 Ventilation
6.4 Adjacent areas
6.5 Use of combustible gas detection equipment
7 Extent of a classified location
7.1 General
7.2 Outdoor locations
7.3 Enclosed locations
8 Recommendations for determining degree and extent of classified locations – common applications
8.1 General
8.2 Recommendations for areas surrounding specific equipment
9 Recommendations for determining degree and extent of classified locations in petroleum refineries
9.1 Introduction
9.2 Recommendations
10 Recommendations for determining degree and extent of classified locations at drilling rigs and production facilities on land and on marine fixed platforms
10.1 General
10.2 Drilling areas
10.3 Production facilities
10.4 Drilling wells
10.5 Producing oil and gas wells
10.6 Oil and gas processing and storage equipment
10.7 Automatic custody transfer (ACT) units
10.8 Flammable gas-blanketed equipment and produced/processed water handling equipment
10.9 Compressor or pump handling flammable liquids, gases or vapors
10.10 Drip pans
10.11 Instruments
10.12 Sumps
10.13 Drains
10.14 Reserved for future use
10.15 Screwed connections, flanges, valves and valve operators
10.16 Control panels containing instrumentation utilizing or measuring flammable liquids, gases or vapors
11 Recommendations for determining degree and extent of classified locations on mobile offshore drilling units (MODUS)
11.1 General
11.2 Definitions specific to MODUS
11.3 Reserved for future use
11.4 Classified locations on mobile Offshore drilling units (MODUS)
11.5 Basis for area classification
11.6 Classification of hazardous (classified) locations
11.7 Drill floor and derrick areas
11.8 Substructure or moonpool areas
11.9 Mud system processing equipment overview
11.10 Mud tanks (After discharge of final degasser)
11.11 Mud ditches or troughs
11.12 Mud pumps
11.13 Mud processing equipment (between the bell nipple and mud discharge of final degasser)
11.14 Desander or desilter (between mud discharge of final degasser and the mud pit)
11.15 Vents
11.16 Diverter line outlet
11.17 Blowout preventer (BOP)
11.18 Well test equipment areas
11.19 Rooms used to store paint (paint lockers)
11.20 Battery rooms
11.21 Reserved for future use
11.22 Helicopter fuel storage areas
11.23 Classification of adjacent spaces
12 Recommendations for determining degree and extent of classified locations at drilling rigs and production facilities on floating production units
12.1 General
12.2 Floating production storage and offloading units (FPSOs)
12.3 Tension leg platforms (TLPs)
12.4 Spars, caissons and similar units
12.5 Classification of adjacent spaces
13 Reserved for future use
14 Recommendations for determining degree and extent of classified locations at petroleum pipeline transportation facilities
14.1 General
14.2 Use of figures
14.3 Figures
Appendix A – Sample calculation to achieve adequate ventilation of an enclosed area by natural means using equations 1 and 2
Appendix B – Calculation of minimum air introduction rate to achieve adequate ventilation using fugitive emissions
Appendix C – Development of ventilation criteria
Appendix D – Informative annex – an alternate method for area classification
Appendix E – Procedure for classifying locations
Appendix F – Preferred symbols for denoting class I, division 1 and division 2 hazardous (classified) locations
Figures
Tables

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