Previous and IEC Ed.3.0 method 

1. Previous method 

   The hazardous areas were used to be determined according to the sample figures shown below based on API RP500, or 505 and NFPA497.
   
   

   API 500	NFPA 497

2. IEC Ed.3.0 method

   Compared to the previous method, the method of determination of hazardous area had drastically changed. What used to be a sample figures as published by the NFPA and API had been changed to a method of individually risk assessment by quantifying the amount of leakage and the degree of diffusion. Previously, since the sample figures described above was used, if it is a flammable dangerous substance, the dangerous zone is set almost uniformly, not limited to the evaluation of its vapor pressure, molecular weight, and possibility of leakage. Therefore, the entire section with plant equipment was often set as a hazardous area.
   
   
   IEC Ed 3.0 presents criteria for evaluating risk (suggested values of ventilation level such as leak size and wind), evaluates risk for each case, and determines whether it is a hazardous or a non-hazardous area. This has made it possible, and as a result, the range of non-hazardous areas has often increased. If it is determined to be a hazardous area, the range (hazardous distance) can also be read from the graph.   
   
   

 Comparison of Hazardous Areas between Previous and IEC Ed3.0 methods 

1. Outdoor facilities
   

   【Previous method】
   Regardless of the substances handled or operating conditions, the entire facility is uniformly designated as a hazardous area.
   
   【IEC Ed3.0 method】
   By conducting detailed risk assessment for each individual case,  it becomes possible to determine whether an area is hazardous areas or non-hazardous.  As a result, the range of non-hazardous areas has often expanded.
   Comparing the area classification diagrams of the previous  and IEC Ed3.0 method reveals the following points.
   
   ・For vents in the primary grade of release, some hazardous areas remain for highly volatile substances (such as gasoline in the diagram below).  However, for kerosene or diesel oil, some vents no longer create hazardous areas.
   
   ・For secondary grade of release, hazardous areas remain around valves, pumps, and other components in gasoline piping lines. However, these areas are confined within the surrounding hazard distances, and the entire oil containment dike is not set as a hazardous area. A large non-hazardous area is secured.
   
   ・Some hazardous areas remain at the jetty area and loading/unloading area, they have been reduced compared to the previous method.
   
   
   

2. Indoor facilities

【Previous method】
The entire area is a hazardous area.


【IEC Ed3.0 method】
By conducting detailed risk assessment for each individual case, it becomes possible to determine whether an area is hazardous areas or non-hazardous. As a result, the range of non-hazardous areas has often expanded.
Ventilation Improvement
Unlike outdoors, indoor spaces allow for the installation of ventilation equipment, enabling the enhancement of its capacity and the increase of ventilation rates. This makes it possible to reduce the range of remaining hazardous areas and even designate the entire indoor space as a non-hazardous area.

Installation of local exhaust ventilation
When the hazardous area is localized, it is possible to make it a non-hazardous area by installing local exhaust ventilation around the area and increasing the ventilation rate locally.

 Key points for non-hazardous areas 

•Chemical properties of substances
Most areas can be classified as non-hazardous areas depending on the fluid handled (e.g. kerosene), since calculations are based on material property data.

•Within oil dike of oil terminals and refuelling facilities
Most areas within the dike become non-hazardous areas, except for limited areas around fittings, vents and pits.

•Adoption of equipment designed to prevent leakage
By employing of leak-proof equipment such as canned pumps and bellows-type valves, they can be excluded from sources of release, thereby ensuring a non-hazardous area.

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