Marcegaglia steelworks video: Mystery of 'explosion' seen over Sheffield is solved as residents are reassured

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What people could see from miles across Sheffield is simply molten slag, created as part of the steel recycling process, glowing red before cooling

The mystery of an 'explosion' seen for miles across Sheffield, creating a spectacular orange and red glow above the city, has been solved.

A still from the video shared by Sheffield WeatherCam which shows molten slag created as part of the recycling process at the Marcegaglia melt shop in Tinsley, Sheffield, glowing red before cooling. The phenomenon can be seen across Sheffield, with some people saying it looks like an 'explosion', though Marcegaglia as assured the public it is part of the normal 'Green Steel' production at the site. Photo: Sheffield WeatherCam via X (formerly Twitter)A still from the video shared by Sheffield WeatherCam which shows molten slag created as part of the recycling process at the Marcegaglia melt shop in Tinsley, Sheffield, glowing red before cooling. The phenomenon can be seen across Sheffield, with some people saying it looks like an 'explosion', though Marcegaglia as assured the public it is part of the normal 'Green Steel' production at the site. Photo: Sheffield WeatherCam via X (formerly Twitter)
A still from the video shared by Sheffield WeatherCam which shows molten slag created as part of the recycling process at the Marcegaglia melt shop in Tinsley, Sheffield, glowing red before cooling. The phenomenon can be seen across Sheffield, with some people saying it looks like an 'explosion', though Marcegaglia as assured the public it is part of the normal 'Green Steel' production at the site. Photo: Sheffield WeatherCam via X (formerly Twitter) | Sheffield WeatherCam via X (formerly Twitter)

The Star shared footage earlier this month of what one reader described as a 'massive explosion' which had been recorded from Woodhouse Mill. It showed what looked like an orange fireball rising into the night sky before rapidly disappearing.

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Now new footage of the same phenomenon has been shared on X (formerly Twitter) by the Sheffield WeatherCam account, showing the source to be a steelworks in Tinsley, Sheffield.

Site in Tinsley can melt 250,000 tonnes of scrap a year

Sharing the video, Craig Thompson, who runs the account, said it showed a 'huge explosion of molten steel slag' at the old Outokumpu steelworks which was recently bought by the Italian firm Marcegaglia Stainless Ltd.

He told The Star the process is visible three or four times a night but looks more spectacular when it's raining as the molten steel slag hits the cold water and 'goes with a bang'.

The steel recycling process at the Marcegaglia melt shop in Tinsley can be seen for miles across Sheffield. Some people say the red glow from the molten steel slag looks like a huge explosion from a distance, especially in wet conditions when the effect is most spectacularThe steel recycling process at the Marcegaglia melt shop in Tinsley can be seen for miles across Sheffield. Some people say the red glow from the molten steel slag looks like a huge explosion from a distance, especially in wet conditions when the effect is most spectacular
The steel recycling process at the Marcegaglia melt shop in Tinsley can be seen for miles across Sheffield. Some people say the red glow from the molten steel slag looks like a huge explosion from a distance, especially in wet conditions when the effect is most spectacular | National World

The Star reported in April how Marcegaglia had bought three sites including the famous SMACC (Stainless Melting and Continuous Casting) meltshop in Tinsley, which is powered by electricity and can melt 250,000 tonnes of scrap a year.

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The company said at the time it was creating 40 jobs and 20 apprenticeships and was keen to ‘invest and increase volume’.

The SMACC site off Europa Link in Tinsley was previously owned British Steel Stainless, Avesta Sheffield and most recently the Finnish firm Outokumpu.

Strange glow over Sheffield explained by steel firm

Responding to the footage shared by the Sheffield WeatherCam account, a spokesperson for Marcegaglia said: "At the Marcegaglia Sheffield Stainless meltshop steel is produced using 90 per cent recycled content.

"As part of the process an inert product is produced, often referred to as slag. The slag as part of its recycling process, is tipped into specially created lagoons to cool and then further break up. This material is then recycled to roadstone.

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"Given that the slag is in a molten state it glows red before cooling. Under certain atmospheric conditions (mist, drizzle, low cloud), this colour is reflected by the water particles in the sky giving the glow that has been reported.

"Please be assured this is not the result of an explosion or an uncontrolled event, just part of the normal 'Green Steel' production here in Sheffield."

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