Rock Salt Is Crucial To Preventing Hazards In Winter

Gritting lorries are out throughout winter, stopping ice from forming, but it is not as simple as just throwing rock salt on the street.

Rock salt prevents ice from forming and melts existing snow and ice. It is more effective, however, when it has been ground down by vehicles and pedestrians.

Known as grit to most people, rock salt acts to lower the freezing point on moisture, thereby causing ice to melt and preventing new ice from forming.

According to council members, its all about timing when it comes to laying rock salt. Road grit lands on dry roads but is blown away when people and vehicles pass.

On damp surfaces the gritting salt will stick. If you are too late, however, the surface will be frozen and drivers, pedestrians and workers will be in danger.

To find out when the roads need gritting, councils use sensors to measure the levels of dew, rain, salt and air and road temperatures. This data is used to decide when to send out the gritters.

In a city, going out to use rock salt in rush hour is a bad idea since the traffic will be stationary.

While roads use gritters, footpaths have rock salt put down by hand or by road-sweepers and cleaners.

The rock salt then has to be topped up several times in the day. Otherwise, it will get diluted to a point where it doesn't work any more.

Rock salt is sprayed out of the back of the gritters. This is usually done symmetrically, although drivers can alter width and angles of the delivery according to the road and the conditions.

Typically, it will spread 10g of salt per square metre. In more treacherous conditions, such as snowfall, it could be as much as 40g. This is because there is a substantial amount of melting required.

One problem with rock salt gritting is that less traffic means it can be less effective.

Rock salt is activated when it is driven over and ground down, mixing it with the moisture. It then becomes brine, a salty water, which is much more effective than rock salt on its own.

Rock salt is not used on every street. The priorities are the main road networks.

Then, after the main routes are covered in rock salt, schools and old people's homes are next.

Salt is activated quickly on the motorway. On streets, however, it can sit idly all night long and it is much harder to get a similar result.

However, it is still worth doing because it prevents large sheets of ice forming. Rock salt is the most preferable type of grit because it is looks clean on the street and in front of buildings from the car parks or entrance paths.

There are three salt mines in the UK, including one in Northern Ireland.

There are various types of rock salt including traditional brown rock salt for general de-icing, white rock salt, which provides a cleaner solution and newer products such as an industrial finer white salt, used purely for de-icing.