Understanding Arc Flash Hazards and Safer Infrared Inspections
The role of an electrical thermographer is critical in modern industry. These professionals perform infrared inspections to detect hidden problems in electrical distribution systems before they result in failures or unplanned shutdowns. The challenge? Thermographers must work with energized equipment under load, and infrared cameras cannot “see” through closed metal panel covers.
Traditionally, this meant removing covers to scan energized equipment, a practice that introduces serious safety hazards, particularly the risk of arc flash events. The safer solution is the installation of permanent infrared (IR) access points, which allow inspections without exposing workers to live conductors.
Why Keep the Covers Closed?
Leaving panel covers in place during inspections provides multiple benefits:
- Increased Safety: Eliminates direct exposure to energized components.
- Improved Accuracy: Reduces background reflection and interference, making thermal readings more consistent and repeatable.
- Regulatory Compliance: Aligns with NFPA 70E and OSHA requirements for minimizing arc flash exposure.
To achieve this, facilities now use purpose-built infrared access points such as ports, panes, and windows.
Infrared Access Points: Ports, Panes, and Windows
Infrared access devices allow thermographers to scan equipment without removing covers. There are three main types:
Infrared Port
A simple hole or series of holes in the panel. While it provides access for thermal scanning, it offers no protection in the event of an arc fault.
Infrared Pane
A thin polymer optic that permits infrared radiation to pass through. While it limits direct human contact, it cannot withstand high heat and may melt during an arc flash, offering little real protection.
Infrared Window
A robust crystal optic designed to act as a permanent inspection window. Unlike ports or panes, properly designed IR windows can withstand high temperatures and pressures, providing both visibility and a barrier against arc flash energy.
How Infrared Windows Enhance Safety
IR windows are designed to:
- Provide a physical barrier between thermographers and live conductors.
- Reduce arc flash trigger risks while enabling on-load inspections.
- Withstand extreme temperatures and pressures associated with arc flash events.
- Allow multiple inspection methods – including infrared thermography, visual checks, and even corona inspection.
Unlike polymer optics, crystal windows remain stable under stress and can be engineered to be arc-resistant. Many feature locking security covers, ensuring only trained personnel perform inspections while also protecting the optic material from impacts and environmental wear.
Regional Standards and Testing Requirements
Electrical inspection devices must be certified to meet regional safety standards. The complexity lies in the fact that standards differ significantly across regions:
- ANSI C37.20.7 (North America)
- EEMACS G14-1 (Canada)
- IEC 62271 (Europe)
These standards are not interchangeable. For example, equipment tested under IEC 62271 cannot automatically be considered compliant with ANSI or EEMACS standards.
In North America, IR windows are classified as industrial electrical components and must be recognized by a Nationally Recognized Testing Laboratory (NRTL) such as UL. Relevant codes include:
- UL 746C (polymer materials in electrical equipment)
- UL 50 / NEMA ratings (environmental and enclosure integrity)
Matching the component’s rating to the host panel’s classification is essential to maintain environmental integrity and compliance.
Choosing the Right Optic Material
Not all materials that transmit infrared radiation are suitable for permanent installation in electrical equipment.
- Thin film polymers: Low cost, common in security devices, but unsuitable for high-energy environments. They cannot withstand arc flash temperatures and may become molten projectiles.
- Mesh/polymer composites: Inconsistent transmission, prone to reflection and deflection errors, and not suitable for quantitative inspection.
- Crystal optics: The preferred material. Properly coated crystal IR windows maintain IR transmission, withstand arc flash conditions, and allow accurate thermal imaging.
Advantages of Crystal Optics
- Maintain camera flexibility across a wide spectral range.
- Allow both infrared and visual inspections.
- Support corona detection.
- Offer true arc resistance.
Understanding Transmission and Measurement Errors
No IR window is 100% transmissive. Thermographers must account for reflection and absorption when interpreting readings. The rule is:
Reflection + Absorption + Transmission = 1
For crystal optics, transmission errors are consistent and can be corrected with proper calibration. However, polymer/mesh optics create inconsistent transmission paths, leading to vignetting, deflection, and unreliable readings. This makes them unsuitable for accurate, repeatable inspections.
Arc-Resistant Infrared Windows
Modern crystal IR windows are engineered to withstand the conditions of an arc fault. Given that up to 77% of electrical injuries are caused by arc flash, selecting arc-resistant optics is not optional, it’s essential.
Arc flash events can occur even with covers closed. Contrary to the myth that “99.99% of arc flash events occur with the cover removed,” data shows nearly 1 in 5 failures happen during normal equipment operation. This is why arc-resistant switchgear and arc-rated IR windows are critical for thermographers.
NFPA 70E and Workplace Safety
The NFPA 70E standard is the globally recognized benchmark for electrical safety. It requires:
- Performing arc flash hazard analysis.
- Establishing shock and flash protection boundaries.
- Specifying PPE levels for live work.
- Labeling equipment with hazard warnings.
By using IR windows, facilities can reduce exposure, minimize PPE requirements, and improve worker safety without compromising inspection accuracy.
Key Takeaways
- Thermographers face serious risks when inspecting live equipment.
- Infrared windows provide safe, repeatable access for on-load inspections.
- Crystal optics are the preferred choice for arc flash protection and accurate imaging.
- Compliance with NFPA 70E, ANSI, UL, and NEMA standards is essential.
- Properly designed IR windows reduce hazards, protect equipment integrity, and extend the life of electrical assets.
Conclusion
Infrared thermography is one of the most effective tools for preventing unplanned electrical outages, but it must be performed safely. By equipping switchgear and electrical panels with arc-resistant IR windows, facilities can empower thermographers to work safely, efficiently, and in compliance with modern safety standards.
At JM Test Systems, we provide electrical safety testing equipment, calibration services, and IR window solutions designed to protect technicians while delivering reliable inspection results.
Call 1-800-353-3411 to learn more about our infrared inspection tools and electrical safety services.
