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I NTRODUCT I ON HAZARDOUS LOCATION DATA

It is also important to consider the boundaries between hazardous areas. Zone 2 or Division 2 locations normally exist adjacent to Zone 1 or Division 1 locations (unless separated by an impervious barrier or partition). If the area classification depends on artificial ventilation, a failure of the system would allow the flammable material to migrate into lower classified or even unclassified locations. TYPE OR GRADE OF RELEASE ZONE FLAMMABLE MIXTURE PRESENT Continuous 0 1000 hours per year or more (10%)

The key difference between the two systems is that the Zone system looks at the areas with the highest level of risk. Over 1000 hours per year is identified as “Zone 0”, and 10 to 1000 hours per year as “Zone 1”. The Class I, Division 1 higher risk areas are the combination of Zones 0 and 1. The criteria used to identify the lower risk areas of Zone 2 and Division 2 is virtually identical. The table below provides a comparison between the “Class/Division” System and the “Zone” System. CLASS I DIVISION SYSTEM ZONE SYSTEM NOTES:

Between 10 and 1000 hours per year or more (0.1% to 10%) Less than 10 hours per year (0.01% to 0.1%) Less than 1 hour per year (Less than 0.01%)*

Primary

1

Zone 0 locations are a typically less than 1% of hazardous locations in a facility. While the wiring practices and acceptable products differ, Zone 1 encompasses most of Class I, Division 1. Zone 2 and Class I, Division 2 are essentially the same

Zone 0

Secondary

2

Division 1

Gases and Vapors

Unclassified

Zone 1

The above is a combination of Tables 2 and 3 from API RP505 *Some controversy surrounds the 1 hour per year figure. The IEC does not define hours per year. The illustrations below compare the similarities and differences between the Division System and the Zone System. Essentially, the greater the amount of material involved or longer the time it is present, the higher the risk.

Division 2

Zone 2

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