With the recent cold weather, Fred Tongue went to Cheshire to see how the salt that keeps Britain’s roads frost-free is harvested, and observed the granular detail needed to plan for winter demand.
The fact that our roads are frost free when the temperature drops can often go unnoticed. You wake up, de-ice the car and are able to drive to work, even if the temperature is well below zero. Behind each salted roadway is a serious logistical exercise in manufacturing and planning, planning that has been conspicuously poor in the past.
In the winter of 2009/10 there was a prolonged period of nationwide cold weather on the back of a cold winter the year before. The country found itself with very limited stocks of salt, with implications for the road system that became crystal clear.
Roads closed and the RSA Insurance Group reported that the inactivity was costing the UK £690m a day. Things needed to change. Once the cold spell had passed, a report into what had gone wrong – the Quarmby Report – was published.
The main lesson to be learned, according to Philip Burgess, director general of the Salt Association, is, “the need to further improve winter resilience with respect to safeguarding salt supplies for the treatment of our road network, in order to keep the country moving during periods of ice and snow.”
He added, “We all remember the consecutive severe winters of 2008/9 and 2009/10, during which salt supplies were stretched to the limit. We must continue to urge local highways authorities to be well prepared and to avoid complacency by moving away from a ‘just-in-time’ supply approach”.
Since 2010 there has been a much greater emphasis on building up a strategic reserve of brown salt to help keep the country on the move, and part of this approach has been to ensure local councils stock up over the summer to avoid a similar situation happening again.
Burgess said that, “In the UK, we are pretty much self-sufficient when it comes to salt production,” reinforcing the point that when icy roads go untreated, it’s down to stock mismanagement, not supply.
The mining industry began production of ‘brown salt’ in the 1860s, and originally produced salt for animal feed and cowlicks – there were of course no cars on roads to worry about back then.
Brown salt for de-icing:
- After chemical engineering, de-icing is the next biggest consumer of the mined chemical, sodium chloride – ‘salt’
- ‘Brown salt’ gets its colour from the presence of small amounts of (claylike) marl
- Road de-icing is not ‘gritting’, which is simply the scattering of small stones or chippings. To help keep roads safe, scattered salt mixes with water to form brine, lowering the freezing point of the mixture by at least 10ºC
- The Salt Association quotes research which estimates that for every £1 expended on winter road maintenance, about £8 is saved in the economy as a whole.
With the arrival of motorways a century later, the national demand for salt kicked in, and brown salt started to be used at a national level for de-icing. The country now uses anywhere from three quarters of a million to two million tonnes of salt every year on the roads, depending on how the weather behaves.
To gain a better insight into the world of brown salt production, I went to Winsford, Cheshire to visit an active salt mine and see exactly what goes into keeping our roads safe in the winter.
Compass Minerals sits on the Cheshire salt plain, which stretches from Northern Ireland all the way across to Boulby in North Yorkshire. The mine is spread out over 12 square miles and reaches depths of 300m across two levels.
Chris Heywood, head of sales and logistics showed me around, and started by explaining some of the technological changes that have been seen across the industry. “If you notice how irregular they [the mine’s walls] are,” he told me, “you will see lots of jagged edges. That’s because when we were mining in these old areas we were using a method called drilling and blasting – dynamite blasting.”
Nowadays, it’s common practice to use huge boring machines, which bite into the rock and leave a much cleaner, more uniform finish to the mine. In order for the boring machines to cut through the rock along the correct path, laser-positioning equipment helps keep them on course, because, as Burgess explained, “The salt sea moves, it undulates as it works its way through Cheshire.
“Surveyors take samples to track the salt’s location and we use this information to orient the lasers. The driver follows the laser and keeps the borer on track to where the salt lies.”
The world of salt production is certainly very different to when it first began, and thankfully there is now legislation in place to ensure that the supplychains and roads of the UK will be safeguarded against the shortages we have experienced. We’ve learnt the hard way what happens if we’re caught short of salt, so there’s no excuse for running out of this vital mineral in the future.