Ireland, like most countries in Europe, has to depend on rock salt to cope with such winters, writes RONAN McGREEVY
IT IS ONE of the mysteries of the prolonged freeze that an abundant substance such as salt has suddenly become one of the most precious.
There are billions of tonnes in the seas around this island, but, to paraphrase the Ancient Mariner, there is salt, salt everywhere and not a grain to spare.
Sea salt is processed for commercial purposes by evaporating the salt in the hot sun, a practice that could never be economic in Ireland.
Even if it was available, it does not have the necessary salinity to be effective, Minister for the Environment John Gormley said in a briefing yesterday. Instead, Ireland, like most countries in Europe, has to depend on rock salt.
Rock salt occurs as the result of the drying of ancient inland sea beds. In central Europe, particularly in Germany, Poland and Denmark, there are huge mines.
There are only three in Britain and Ireland.
The only one in Ireland is the Irish Salt Mining and Exploration company near Carrickfergus, Co Antrim, which employs 55 to 60 people a year. It produces rock salt solely for deicing and operates on a contract basis with local authorities, mostly in the UK.
Mining occurs all year around and clients start stocking up from May. Spokesman David Lee said: “We’ve had four weeks of this weather. We can only keep so much in stock and councils can only keep so much in stock.”
He said those who thought the current salt shortage was unique had short memories. There was a similar critical shortage in Britain during a cold snap last February.
Salt does not solely operate by melting the snow as is commonly perceived, but by lowering the temperature at which water freezes. Salt water starts to freeze at about -2 degrees.
The higher the concentration of salt, the lower the temperature at which the ice will freeze on roads.
Although in theory salt is effective up to -21 degrees, in fact it only operates up to road temperatures of -7 degrees and is useless during heavy falls of snow.
Salt is ordered by local authorities and stored in salt barns because it is an extremely corrosive substance.
Retired former National Roads Authority regional engineer Michael Cahill said it would be “silly” for local authorities to store up vast quantities on the off-chance of a once-in-a-generation winter like this one.
The alternative to salt is grit, but the two terms are used interchangeably to cause confusion.
What most people understand to mean gritting is often the salting of roads. “It is like saying that all ballpoint pens are Biros,” he said.
Unlike rock salt, there is no shortage of grit in Ireland. Every quarry has tonnes of it, but it is of limited use. “The purpose of putting the grit out on the road is to give you some purchase,” Mr Cahill added. Because it is cheaper and more abundant, grit is used on secondary roads.