The Chicago Fire Department says three workers were hurt while doing electrical work on a substation in downtown Chicago.
Fire officials say two workers were in critical condition at hospitals with serious burns after the Tuesday morning incident. A third worker was in good condition.
Officials say the workers were doing maintenance on a ComEd substation associated with the Chicago Transit Authority about 11 a.m. Tuesday when a panel from a transformer was blown, causing a flash fire.
ComEd says about 500 customers lost power. CTA service wasn't affected. The incident is under investigation.
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