The confusion often arises because both standards share a singular objective: Hazardous Area Classification (HAC). Ultimately, the goal is to determine the appropriate Electrical Equipment Protection required for installation in these sensitive environments.
The fundamental difference lies not in the type of gas, but in the Methodology of Classification.
API 500: The Division System
API 500 represents the classic North American approach, widely utilized for decades. It categorizes hazards into two primary tiers:
- Division 1: Locations where ignitable concentrations of flammable gases are present under normal operating conditions (Continuous or frequent hazard).
- Division 2: Locations where flammable gases are handled but are only expected to be present under abnormal conditions, such as a leak or equipment failure (Occasional or accidental hazard).
While this system is practical and straightforward, it is often considered "broad," as it groups varying degrees of risk into only two categories.
API 505: The Zone System
API 505 is the American alignment with the International Electrotechnical Commission (IEC) standards. It was developed to provide a higher level of precision and to assist global companies in unifying their safety engineering standards.
This system offers a more "granular" philosophy, dividing risk into three distinct levels:
- Zone 0: Ignitable concentrations are present continuously or for long periods.
- Zone 1: Ignitable concentrations are likely to exist under normal operating conditions.
- Zone 2: Ignitable concentrations are not likely to occur in normal operation, and if they do, they persist for a short period only.
The Bottom Line: By introducing Zone 1, the API 505 system bridge the gap between Division 1 and Division 2. This allows for a more precise selection of electrical equipment and offers potential cost optimization without compromising safety.