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Intrinsically Safe Product Design Part 4: Role of the Nationally Recognized Test Laboratory (NRTL)

Part 1 of this series introduced the concept of intrinsically safe design for explosive environments. Part 2 described considerations for the definition of explosive environments and how geographic regions for device use can impact both explosive atmosphere characterization and product implementation. Part 3 describes regulatory and quality requirements for ongoing production and sale of an intrinsically safe electronic device. This blog, the last in this series, describes the role of the Nationally Recognized Test Laboratory (NRTL) in the successful completion and certification of an intrinsically safe electronic product.

Integral to intrinsically safe design is review by a competent NRTL for compliance and identification of potential issues. The key for design success, with minimal iterations and therefore cost and schedule, is incorporation of best practices and phased reviews. It is far less expensive to resolve issues as early as possible within the design process than it is to correct mistakes identified after circuit and product implementation.

SECO USA’s experience has been that it is also far easier (and ultimately less expensive and much faster) to design a product from the outset with intrinsic safety compliance in mind than to take a designed product and make it compliant. This distinction is important, and to take full advantage of this process involves early involvement with an NRTL.

There are numerous competent NRTLs. Some tend to be US-based (such as Underwriter Labs (UL)). Others have international operations with labs in multiple countries. It is not necessary to have the same NRTL involved in the design as in the manufacturing audit, but it is important to have at least one involved in the early design process.

The NRTL has several roles in successful intrinsically safe product design and production, including the following:

  • Review of components, and their datasheets, for inherent non-conformances, such as capacitance and/or inductance exceeding limitations for the environment
  • Testing of components to characterize capacitance, inductance, thermal, current, voltage, and/or total power, when datasheet analysis is insufficient
  • Review of electrical schematics for general circuit operation and protective circuitry as needed
  • Review of printed circuit board routing for component, lead, and general metal spacing, placement of protective components, and more
  • Review of enclosure design for ruggedness, flammability, and general compatibility of the design with the intended environment
  • Testing of the final product
  • Auditing the product’s manufacturing facilities

Each of the above activities integrate across the phases of conventional electronic product design processes, starting with requirements definition and system design. With smart engagement of an NRTL throughout the design processes, early identification and mitigation of potential challenges saves valuable time and money while reducing design iteration.


This concludes SECO USA’s four-part series describing some of the non-technical details necessary in accomplishing a successful intrinsically safe product design. Key takeaways include:

  • Design from the outset for compliance.
  • Precisely define the usage environment, including the specifics of the atmosphere and the geographic location of usage.
  • Clearly understand and conform to the relevant documentation standards for the intrinsically safe product.
  • Identify/select the certificate holder and ensure QAN/QAR compliance. Prepare early for audits.
  • Involve an appropriate NRTL early in and throughout the design process.

The technical implementation is the next level of complexity for an intrinsically safe electronic device, adding further detail on top of the more business and production related aspects of manufacturing and selling an intrinsically safe product. The challenge can be daunting, especially if this is the such design for your organization.

Companies like SECO USA can assist in the design, development, and transition to production of an intrinsically safe product. Services range from helping bootstrap an organization new to development for the explosive environment market for longer term design and production capability, to being the go-to development and production company for intrinsically safe product. Contact SECO USA for an evaluation of your requirements.


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