What happened

Medupi Unit 4's generator exploded at about 10:50 p.m. while the unit was on a short-term maintenance outage and workers were purging hydrogen to investigate an external leak. Eskom's preliminary investigation found that air had been introduced while enough hydrogen remained to form an explosive mixture and that the approved purging procedure appeared not to have been followed. The blast caused extensive damage to the generator, exciter, auxiliaries, fire systems and nearby structures. No physical injuries or fatalities were reported, although seven employees were treated for shock. Nine employees were later suspended during investigations into procedural non-compliance and management failures. A 2022 estimate put repairs at about R2.5 billion. The loss of the unit materially tightened an already constrained national power system; after extensive repairs using a refurbished generator stator, Eskom returned Unit 4 to service on 6 July 2025.

When cited sources give different casualty, damage or spill figures for this event, they’re reported side by side above rather than merged into one number. See how confidence levels work.