(77a) Hazardous Area Classification Methodology Comparison: NFPA, API, IEC

A critical element in the design and operation of facilities that process and produce flammable and combustible materials is the proper classification of hazardous areas (Hazardous Area Classification, or “HAC” for short) in order to understand where flammable and combustible materials may be present, and to ensure that proper controls are in place in these areas such that the potential for ignition is minimized. By understanding the areas where flammable and combustible materials are present within a facility, engineers and designers can make informed decisions on selecting equipment that are less likely to be a source of ignition, should a loss of containment event occur. This is essential as the time between the loss of containment occurring, and the cloud finding an ignition source, could mean the difference between life and death for personnel in the area. Hazardous Area Classification (HAC) is thus essential to protecting personnel and assets within these facilities and is required by OSHA as part of the National Electrical Code.

When performing a HAC analysis on a facility, there are various accepted guidelines, recommended practices, and standards that the analyst can choose from. Three of the main documents for classifying areas that contain flammable liquids and vapours are: (1) NFPA 497[1], API 500[2], and IEC 60079-10-1[3]. The overall objective of each document is the same, as the end goal is to appropriately classify regions around equipment that could be possible sources of flammable or combustible material, but each document has different methodologies and approaches to go about performing the analysis. Unless you are well-versed in each of the documents, an engineer might not know which document to apply to a given setup, or know the differences in approaches to classification between the documents. For example, if the engineer wants a more detailed approach to the classification of an internal room that contains a release source, IEC will provide a more specific approach to performing this analysis than NFPA or API, which might not be known if someone is only familiar with NFPA. Another important aspect of HAC is the understanding of the jurisdiction requirements and where a particular standard can be applied. There are nuances around the application of these standards as well as mixing them in certain applications.

This paper will seek to highlight the differences between the various approaches to performing an HAC study when using NFPA 497, API 500, and IEC 60079-10-1. Key differences in the approach and determination of HAC extent distances between the documents will be highlighted and discussed such that the engineer can be better informed in knowing what is contained in each document, and how it can be utilized for their operation.

[1] NFPA 497, “Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas,” 2024.

[2] API 500, “Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class 1, Division 1, and Division 2, 4th edition,” 2023.

[3] IEC 60079-10-1, “Explosive atmospheres – Part 10-1: Classification of area – Explosive gas atmospheres,” 2020.