13 Jun Hazardous Area Classification
Manufacturing can develop or use explosive gases or dusts in their processes. These areas must be documented as potentially explosive for several reasons. The need for this documentation is referenced by safety organizations such as the IECEx system or the USA National Fire Protection Association (NFPA) 70 Code. The term used for identifying potentially explosive atmospheres is “Hazardous Area Classification”.
Hazardous Area Classification (HAC) is addressed in the following:
IEC 60079-14:2013 Standard
Clause 4.2 Documentation:
area classification documents (see IEC 60079-10-1 and IEC 60079-10-2) with plans showing the classification and extent of the hazardous areas including the zoning (and maximum permissible dust layer thickness if the hazard is due to dust);
NFPA 70 (NEC) USA:
(A) Documentation. All areas designated as hazardous (classified) locations shall be properly documented. This documentation shall be available to those authorized to design, install, inspect, maintain, or operate electrical equipment at the location.
There are two basic routes for developing HAC documents, they are:
- The Simplified method as per IEC 60079-10-1 clause 5.4:
Where it is not practicable to make required assessments from individual sources of release, a simplified method may be used.
Simplified methods shall identify sources for each of the zone types, zone 0, 1 and 2 that are suitably conservative to allow for potential sources of release without individual detail. The judgement is best made by reference to a set of criteria based on industry experience and appropriate to the particular plant.
It is not necessary to carry out a detailed assessment of all items in a plant where an assessment for one item or condition would be adequate to provide a conservative classification for all other similar items or conditions on the plant.
A conservative Hazardous Area Classification may result in classifying the entire room as hazardous whereas CFD visualization may results in a reduction of the area classification.
- Computational Fluid Dynamics (CFD) modelling in conjunction with the application of Standards to develop the Hazardous Area Classification.
From NFPA 497:
5.5.3 The size of a building and its design could influence considerably the classification of the enclosed volume. In the case of a small, inadequately ventilated room, it could be appropriate to classify the entire room as Class I, Division 1, or Class I, Zone 1.
However, by utilizing CFD, room ventilation may reveal that the hazardous area is smaller than predicted, resulting in cost-savings for the company. If an area is not classified as hazardous, then equipment marked as safe for hazardous locations is not required. Several factors must be considered if using CFD for an HAC. Below is a visualization of a well-ventilated room as noted by the air movement and exhaust from the building:
Design Engineering professionals’ reference HACs extensively when designing or placing electrical equipment in an area classified as hazardous. Join us in the upcoming CompEx Ex12 Course for additional discussion on this important topic.