Part 1 of this blog series introduced the concept of intrinsic safety. Part 2 describes the characterization of hazardous environments with respect to intrinsically safe electronic devices.
Internationally, the International Electrotechnical Commission (IEC) is considered to be a benchmark in the definition of explosive atmospheres and certification of electrical equipment for explosive atmospheres via its IECEx standards. Additionally, various countries impose their own standards and requirements in defining explosive atmospheres. The ATEX (ATmosphere EXplosibles) standard is applicable to thirteen countries within the European Union.
In the US, regulatory bodies such as the Occupational Safety and Health Administration (OSHA) and National Electrical Code (NEC) have established definitions that classify locations which exhibit potentially dangerous conditions to the degree of hazard presented. In hazardous locations, specially designed equipment and special installation techniques must be used to protect against the explosive and flammable potential of these substances. Similarly, in Canada, the Canadian Electrical Code (CEC) defines hazardous areas.
Each standard/classification has slightly different requirements, which makes it critical to identify all required environments and geographies prior to design. Although these standards are harmonized, it is possible to design a product that does not meet the intended use environment without a major redesign.
Characteristics of the environment include the specific explosive materials in the atmosphere (gases, vapors, and dust), the likelihood those explosives exist and in what concentrations, ignition temperature, and more. Each standard specifies the rating of explosive atmospheres differently. Typical labeling for an explosive environment based on the ATEX and IECEx standards might resemble:
ATEX II 2G (Zone 1) Ex ib IIC T4 Gb
This alphabet soup of letters and numbers encode specific atmospheric characteristics that together ultimately affect the protection method and design choices for a device developer. It is critical that the developer properly map the needed hazardous environment specification to the IS design details, so the optimal total solution can be implemented.
While largely harmonized, each explosive atmosphere standard defines atmospheric characteristics somewhat differently. Seemingly small differences in environment definition standards can greatly impact the product implementation approach to enable usage in both environments For example, a product meeting ATEX II 2G (Zone 1) Ex ib IIC T4 Gb typically cannot be used in the United States Division 1 environments without a major redesign.
With the hazardous environment location understood and product requirements set, the intrinsically safe device can be designed. Once the device has achieved certification, it can be manufactured. Part 3 of this blog series describes considerations for the production of intrinsically safe electronic devices.