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Fatal Unchahar power plant blast in India ascribed to mistake by senior staff

24 July 2018

The explosion on 1 November 2017 that killed 45 workers at the Unchahar power plant in Uttar Pradesh was the result of an “error in judgment” by some of the plant’s most experienced operators, according to an internal investigation into the state-run electricity producer’s biggest disaster.

Unchahar power plant - Image: NTPC
Unchahar power plant - Image: NTPC

The plant’s Head of Operation, Head of Ash Handling Maintenance and Head of Boiler Maintenance - each with 28 years of experience - made a decision not to shut down a 500-megawatt (MW) boiler at Unchahar to clear a buildup of ash prior to an overpressurisation in the unit that caused the gas release, according to a Reuters report.

“The shut down of the boiler much before the incident would have been prudent,” the investigation report concluded. It was written by an internal committee of senior National Thermal Power Corporation figures. 

The three experienced engineers died in the accident, alongside 42 contract workers. Many others were injured in the explosion.

The plant operators were aware of an ash buildup in the Unit-6 boiler and had reduced the unit’s load to 300 MW while workers cleared the ash from the furnace bottom in the hours leading up the accident, the report said.

The ash buildup, however, caused a boiler tube carrying steam to leak, leading to a high pressure buildup and subsequent burning of flammable substances, the report said.

That led to a build up of steam pressure in the unit that caused it to “trip”, or involuntarily shut down, following which hot ash and gases were released at high speeds that killed and injured the workers, according to the summary.

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