Incident energy at the wrong working distance.

§1Facts of the loss

The Erie East Lake Road foundry — a 1,200 ton/year ductile-iron casting operation serving primarily the automotive and rail-rolling-stock supply chain — operates a 4,000 A 480Y/277 V main switchboard feeding seven motor-control centers and the foundry’s induction-furnace controls. The switchboard, manufactured by Eaton Cutler-Hammer in 2007 and last refurbished in 2019, bears arc-flash labels generated by a 2019 IEEE 1584-2002 study reporting 8.4 cal/cm² at 18 inches working distance on the bus side of the line-side cubicle.

On the morning of 23 October 2025, a senior electrician — referred to in the sealed report as Worker M.K., the parties to the matter being well-known to the bar — was conducting a scheduled infrared thermal scan of the switchboard interior through the open cubicle door. The IR scan was authorized under the foundry’s electrical safety program with the worker in Category-2 arc-rated PPE: an 8 cal/cm² ATPV outer jacket and pants, an 8 cal/cm² ATPV face shield, voltage-rated gloves, and dielectric boots. The arc-rating selection was made against the installed 8.4 cal/cm² label and the labeled 18-inch working distance.

At 09:48:12 EDT, the worker observed an unexpected reading on the FLIR camera and adjusted position to obtain a clearer thermal image. At approximately 09:48:28, an arc initiated at the phase-A line-side connection of the cubicle, propagated to the adjacent phase-B over a 95 ms duration before the upstream 1600 A breaker (Eaton ND-frame, Series C) cleared the fault. The worker sustained Category-2 burns to the dorsal right hand (between the glove cuff and the jacket sleeve) and to the right forearm (where the jacket sleeve had ridden up at the shoulder joint).

§2Reconstruction

The available short-circuit current at the failure terminal was re-derived from FirstEnergy / Penelec’s 2024 utility-supplied secondary-side report and the as-built switchboard impedance values. The result — 38.2 kA bolted three-phase at the cubicle terminal — matched the 2019 study within instrument resolution. The 2019 arc-flash label correctly reflected the available short-circuit current at the time the label was generated.

The arc duration was reconstructed from the Eaton ND-frame breaker’s logged event (recovered from the trip unit’s onboard log via Eaton’s ProField PT300 interface — the trip unit logged the operation at 09:48:28.367 with a clearing time of 95 ms / 5.7 cycles at 60 Hz). The 95 ms clearing matched the 2019 study’s assumed 6-cycle clearing assumption within one half-cycle; no discrepancy in the upstream protection’s behavior.

The incident-energy calculation was then re-run under IEEE 1584-2018 (the current edition; the 2019 study had used the 2002 edition). At 18 inches working distance, the 2018 calculation gave 9.7 cal/cm² — 15% higher than the 8.4 cal/cm² 2002-edition label. The label had not been refreshed when the 2018 edition became applicable, which was the practice across most of the Lake Erie corridor in 2019–2020.

§3The twelve-inch question

The dispositive question on the matter was not the incident energy itself but the working distance at which it was sustained. The 2019 installed label reported 8.4 cal/cm² at 18 inches. The 2018-edition recalculation gave 9.7 cal/cm² at 18 inches. Both values exceeded the worker’s 8 cal/cm² clothing system. Plaintiff’s theory was straightforward: the installed label undercalculated the hazard; the worker selected PPE against the label; the resulting injury was the foreseeable consequence of the labeling defect.

The defense theory required reconstructing the worker’s actual standing position. We obtained the foundry’s overhead surveillance camera footage from the cubicle door — the camera was installed in 2022 as part of a broader process-control upgrade and had captured the worker continuously from 09:46 through the arc event. Frame-by-frame analysis between 09:48:00 and 09:48:28 showed the worker repositioning his feet at 09:48:18 — adjusting position from approximately 18 inches from the bus stab to approximately 30 inches from the bus stab to obtain a better FLIR angle on the upper bus connections.

At 30 inches working distance, the incident energy on the 2018 recalculation drops to 4.4 cal/cm². The worker’s 8 cal/cm² clothing system was at this distance materially over-rated for the actual hazard. The Category-2 burn the worker actually sustained was inconsistent with thermal exposure on an under-rated clothing system at 30 inches and consistent with a different mechanism — examination of the worker’s glove showed evidence of polymer-coating residue on the outer surface, transferred from the FLIR camera’s zinc-selenide IR window during the scan and ignited by radiant flux from the arc.

§4PPE analysis

The worker’s arc-rated jacket was sent to Intertek’s Cortland, NY garment-testing laboratory for ASTM F1959 examination. The jacket showed thermal exposure consistent with 4.0–4.5 cal/cm² incident energy at the chest area — well below its 8 cal/cm² ATPV. The jacket did not break open; the labels stitched in remained intact. The clothing system performed as designed at the actual incident energy.

The voltage-rated glove that the worker had been wearing on the right hand was sent to UL Solutions in Northbrook for chemical-residue analysis. The glove’s outer leather surface bore visible evidence of a polymer coating consistent with the FLIR camera’s ZnSe lens-cleaning solvent residue. The worker had handled the FLIR’s lens cap moments before initiating the scan; the contaminant had transferred to the glove and ignited at the radiant flux levels present during the 95 ms arc duration. The burn pattern on the worker’s right hand and forearm — concentrated where the glove cuff met the jacket sleeve, with no other thermal exposure to the worker’s body — was consistent with contaminant ignition rather than with garment breakdown.

§5Finding & resolution

The worker’s injury at the Erie East Lake Road foundry on 23 October 2025 was not caused by inadequate arc-flash labeling or by an under-rated clothing system. At the worker’s actual standing position (approximately 30 inches from the phase-A bus stab, reconstructed from cubicle surveillance footage), the 2018-edition incident-energy calculation gives 4.4 cal/cm², well below the worker’s 8 cal/cm² ATPV system. The injury was caused by ignition of a polymer-coating residue on the worker’s glove outer surface, transferred from the FLIR camera’s ZnSe-lens cleaning solvent prior to the scan, at the radiant flux levels present during the 95 ms arc duration. Sealed PE report · 11 April 2026 · Theron O. Adekunle, PE

The finding shifted the matter’s exposure substantially. The foundry’s defense team obtained dismissal of the claim against the foundry and against the labeling contractor in April 2026; the matter against the FLIR camera manufacturer settled separately for an undisclosed amount in May 2026. The arc-rated clothing system manufacturer was dismissed at the same time as the foundry; the clothing system was found to have performed as warranted.

This Case File is the firm’s most-cited recent R-02 matter on the question of working-distance reconstruction from physical evidence. Defense engineers who have not reconstructed the worker’s actual standing position — relying solely on the labeled working distance and the installed label’s incident-energy value — have missed the question of the matter in three of the four arc-flash matters the firm has reviewed for outside counsel since the publication of this case.

§6References