Hazardous Area Classification
The following describes PetroRisk’s approach to Hazardous Area Classification, based upon IP-15.
The purpose of HAC is to determine the extent of the hazardous areas expected to be created by equipment in the proposed facilities.
The area classification will be utilised to develop the hazardous area layouts for the facility and define the basis for correct selection & location of fixed electrical / instrumentation equipment items.
Grade of Release
For the purpose of area classification, a source of release is defined as a point from which a flammable gas, vapour or liquid may be released into the atmosphere.
Three grades of release are defined in terms of their likely frequently and duration.
- Continuous grade of release – A release that is continuous or nearly so or that occurs frequently and for short periods (IP part 15)
- Primary grade release – A release is likely to occur periodically or occasionally in normal operation (between 10 and 1000 hours per year)
- Secondary grade release – A release that is unlikely to occur in normal operation and, in any event, will do so only infrequently and for short periods (IP part 15)
For Area Classification in Petroleum Installation, the classification of fluid is done in two steps, first in Classes and then in Categories.
The class of fluid relates to their flash point and handling temperature.
Table 1 – Fluid Class (As per Table A1 of IP-15 3rd Ed “Petroleum Classes”)
|Class 0||Liquefied petroleum gases (LPG)|
|Class I||Liquids that have flash points below 21°C|
|Class II(1)||Liquids that have flash points from 21°C up to and including 55°C, handled below flash point|
|Class II(2)||Liquids that have flash points from 21°C up to and including 55°C, handled at above flash point|
|Class III(1)||Liquids that have flash points above 55°C up to and including 100°C, handled below flash point|
|Class III(2)||Liquids that have flash points above 55°C up to and including 100°C, handled at above flash point|
|Unclassified||Liquids that have flash points above 100°C|
The category is derived from class and indicates to which extent a fluid on release can form a flammable mixture with air. This is a determining factor in the calculation of hazardous radius. For the same flammable fluid, at various stages of its processing or handling, there can be a different fluid category depending upon temperature and pressure at the specific points of release.
Table 2 – Fluid Category (As per Table 1.2 of IP-15 3rd Ed “Fluid Categories”)
|A||A flammable liquid that, on release, would vaporize rapidly and substantially. This category includes:
(a) Any liquefied petroleum gas or lighter flammable liquid
(b) Any flammable liquid at a temperature sufficient to produce, on release, more than 40% vol. vaporization with no heat input other than from the surroundings.
|B||A flammable liquid, not in category A, but at a temperature sufficient for boiling to occur on release.|
|C||A flammable liquid, not in categories A or B, but which can, on release, be at a temperature above its flash point, or form a flammable mist or spray.|
|G(i)||A typical methane-rich natural gas|
Hazardous Zone Classification
Area classification is the assessed division of a facility into hazardous areas and non-hazardous, and the subdivision of the hazardous areas into zones.
A hazardous area is defined as a three-dimensional space in which a flammable atmosphere may be expected to be present at such frequencies as to require special precautions for the use of electrical apparatus. All other areas are referred to as non-hazardous in this context though they may, in part or whole, form part of wider restricted area within the FACILITY in which all WORK is carried out under control.
Hazardous areas are subdivided into three zones as follows:
- Zone 0: The flammable atmosphere is continuously present or present for long periods
- Zone 1: The flammable atmosphere is likely to occur in normal operation
- Zone 2: The flammable atmosphere is not likely to occur in normal operation, and if it occurs, will exist only for a short period
Non-hazardous areas: Areas that do not fall into any of the above are non-hazardous.
The ‘Zone’ for a release is determined based on the grade of release, area of release and ventilation in the area.