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Hazardous Area Classification

OBJECTIVES OF HAZARDOUS AREA CLASSIFICATION

Area classification is a method of analyzing and classifying the environment where explosive gas atmospheres may occur, to facilitate the proper selection, installation and operation of equipment to be used safely in that environment. The classification also considers the ignition characteristics of the gas or vapour such as ignition energy and ignition temperature. Area classification has two main objectives, the determination of the type of any hazardous zone, and the extent of the zone.

The hazardous area classification of sources will be determined using calculated hazard radii together with either the physical geometry (e.g. a pit) or the shape factors, a risk-based approach will be used. The risk-based approach methodology provides a means of adjusting release frequency and hence hazard radii, to fit specific process scenarios.

Generally, process plant will constitute a Zone 2 area inside plant boundaries, within which there may be local Zone 1 and, more rarely, Zone 0 areas. Refer Hazardous Area Classification Layouts for better understanding of boundaries with respect to Zones.

The intention is to reduce, to an acceptable level, the probability of coincident existence of a flammable / explosive atmosphere and sources of ignition. This approach is implemented through:

  1. Minimizing the possibility of existence of flammable/explosive atmosphere.
  2. Correct selection of electrical equipment to be installed in these hazardous areas. The electrical apparatus/instruments are one of the potential sources of ignition of flammable gases/vapours.
  3. Ensuring that sources of ignition including electrical equipment are segregated from sources of flammable gas in accordance with code requirements.

APPLICABILITY OF HAZARDOUS AREA CLASSIFICATION

  1. Oil and gas industries
  2. Offshore platforms
  3. Onshore platforms
  4. FPSO
  5. Oil/gas processing unit
  6. Refineries
  7. Gas/oil Pipelines and distribution points
  8. Petrochemical industries 
  9. Mining and storage areas
  10. Sewage treatment plants
  11. Sugar mills
  12. Grain handling and processing units

STANDARDS FOR HAZARDOUS AREA CLASSIFICATION 

  • API RP 500 – Recommended Practice for Classification of Locations for Electrical Installation at Petroleum Facilities Classified as Class I, Division 1 and Division 2.
  • API RP 505 – Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class 1, Zone 0, Zone 1, and Zone 2
  • EI 15 IP 15 Model Code of Safe Practice Part 15 Area Classification for Installations Handling Flammable Fluids 4th edition June 2015
  • SP-2311 Hazardous Area Classification & Ignition Control

HAC METHODOLOGY

HAC Flow chart with input activity and output representation

1.1       Technique for Area classification

The methodology adopted for Hazardous Area classification approach is based on below mentioned technique.

1.1.1   Point source approach

For installations or processes (due to variability of temperature, pressure, equipment and the degree and type of ventilation) the extent of flammable release that would occur may vary greatly making individual assessment necessary. This is known as the 'point source approach’.

The Point source method can be used for all situations, where the release hole size is known, the hazard radius used from the Hazard radius table (Annex C, Table C4 from EI-15 standard).

1.1.2   Risk Based approach

Where ‘Release Rate’ is unknown (hole size and pressure), the ‘Risk-based approach’ shall be used as outlined in Annex C, Part-2 EI-15. The Risk based approach methodology provides a means of adjusting release frequency and hence hazard radii, to fit specific process scenarios. Examples include failure of pump / compressor seals, leaks from valves and flanges, or operational error.

1.1.3   Direct Example approach

Generic industrial equipment handling common flammable materials may be classified directly from typical examples (Annex- D from EI-15). Examples include drilling, work over and wellhead sites, tank storage for both upstream and downstream.

HAC Drawing
HAC

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