A hidden danger beneath our streets

Photograph by the Ministry of Defence

I don’t wish to alarm people in these sobering times, but there is another threat to the people of Sheffield, and it lies beneath our feet.

It’s almost eighty years since German bombers dropped around 355 tonnes of high explosives and 16,000 incendiary canisters on Sheffield during the Blitz of 1940. The bombers targeted residential and industrial areas and the city centre received incredible damage, with The Moor, Angel Street and King Street almost obliterated.

While death and destruction were immense, Sheffield’s citizens might have been forgiven that one of our nastiest periods had been consigned to history.

Alas, we are still likely to suffer the consequences for years to come.

Photograph by Sheffield Star

According to experts, Sheffield is a ‘high risk’ area for unexploded bombs, those that fell from the sky, failed to detonate, and buried themselves deep underground.

Bombs often failed to explode because they were ‘dud’ – casualties of fast, furious and error-prone wartime manufacturing.

But why didn’t the authorities deal with them?

At terminal velocity, a bomb would have penetrated 3-4 storeys before detonating. If it failed, its downward motion sent it deep underground, leaving destruction behind and almost impossible for watchers to determine the exact number and location.

The legacy is that we almost certainly have dozens of unexploded bombs hidden under the streets of Sheffield, as well as in other cities across Britain.

It is only now that some of these unexploded devices are returning to haunt us. Over the years, bombs have been discovered near Bramall Lane, Hillsborough, Don Valley, Owlerton and Burngreave. And it is just four years ago that four bombs were successively discovered in Matilda Street.

Most of these bombs have been found on construction sites, the Construction Industry Research and Information Association stating that in one two year period an estimated 15,000 military items were extracted from UK building sites. Now that buildings are getting taller, foundations dug deeper, we are starting to uncover devices , about five per cent of which are still live.

Worryingly, discoveries are still being made as original sites are being redeveloped for a second time after blocks thrown up in the post-war building boom reach the end of useful life.

The problem with unexploded bombs is their unpredictability, with Army Bomb Disposal Units (split between the Royal Engineers and Royal Logistic Corp Ammunition Technicians) having little information about how long it has been there and how it might have changed over time.

Photograph by The Independent

Most construction in the UK is now subject to risk assessment on the likelihood of unexploded bombs underground. These assessments may take the form of visual interpretation using historical photographs, as well as with geophysical and geothermic surveys. A similar set of processes was used when the site was cleared to make way for the construction of the Moor Market.

The situation is a lot worse in Germany where barely a week goes by without a new discovery. In 2014, a German digger driver was killed after accidentally striking an unexploded British device at Euskirchen, north of Frankfurt. And last year, a large explosion in a field near Ahlbach created a huge crater and turned out to be an undiscovered wartime bomb exploding after 75 years.

“According to the rule of thumb, if German ordnance hit the ground, it exploded, while Allied bombs were notoriously unreliable,” says Stephen Taylor, a period munitions expert.

Photograph by BBC News