Chloride Usage On Airport Runways: Safety And Maintenance

Airports use a variety of methods to keep their runways clear of snow and ice. While common salt, or sodium chloride, is often used on roads, it is not suitable for use on runways as it can damage the aluminium skin and structure of planes by encouraging rust. Instead, airports use a combination of physical and chemical methods to keep their runways clear. Physical methods include plowing, brushing, and blowing snow and ice off the runway, while chemical methods include applying de-icing fluids such as urea, potassium acetate, and glycol.

Airports don't use sodium chloride due to its corrosive effects on aircraft

Airports do not use sodium chloride to de-ice their runways due to its corrosive effects on aircraft. While sodium chloride is commonly used on highways and tracks to reduce icing, it is prohibited on airport runways as it can damage the aluminium skin and structure of aeroplanes by acting as a catalyst for rust.

Aluminium is widely used in aircraft because of its low density and ability to resist corrosion. However, when it comes into contact with sodium chloride, or salt, the protective oxide layer on the aluminium's surface is disrupted, making it more susceptible to corrosion. This corrosion can weaken the structural integrity of an aircraft over time, increasing the risk of accidents and endangering the safety of passengers and crew.

Instead of sodium chloride, airports use alternative methods and chemicals to keep their runways clear of snow and ice. These include mechanical methods such as large plows, blowers, and other snow machines, as well as de-icing fluids like glycol, urea, and potassium acetate. These methods effectively remove or prevent the formation of ice without causing damage to aircraft.

Additionally, some airports have implemented heated runways, which use underground heating systems to melt snow and ice buildup. While this technology is not yet widely adopted due to the high energy costs and maintenance issues associated with built-in heating equipment, it offers a potential solution for improving runway operations during harsh weather conditions.

By avoiding the use of sodium chloride and employing alternative de-icing strategies, airports prioritise the safety and structural integrity of aircraft, ensuring that flights can depart and arrive without corrosion-related delays or incidents.

They use potassium acetate, urea, or glycol-based de-icers instead

While chloride is a common de-icing chemical, it is not used on airport runways as it can damage the aluminium skin and structure of aeroplanes by catalysing rust. Instead, airports use a combination of physical and chemical methods to keep their runways clear of ice and snow.

Physical methods include grooving, snow plowing, and air blasters, which remove snow and ice build-up. When it comes to chemical methods, airports use de-icing fluids that are designed to prevent ice from accumulating. These include urea, potassium acetate, and glycol-based de-icers.

Urea is a solid granulated de-icer that is often used in conjunction with plowing and brushing. It is less corrosive than sodium chloride and is considered safer for use around aircraft. Potassium acetate is another popular de-icer, used in places like Denver International Airport. It is a liquid de-icer that is often applied before or after snow has been cleared from the runway.

Glycol-based de-icers are also used on runways. They can be in the form of an antifreeze, such as ethylene glycol, which is heated and sprayed onto the wings and fuselage of aircraft. This creates a barrier that prevents ice from sticking. Additionally, glycol is used in some automated runway de-icing systems. These systems dispense glycol along the runway to prevent ice from forming. However, glycol is poisonous to animals and can make the runway slippery, so it is not widely used.

De-icers are applied in solid or liquid form

Solid de-icers include sand and granulated urea, while liquid de-icers include ethylene/propylene glycol-based fluids, potassium acetate, and potassium formate. The use of liquid de-icers has been associated with damage to carbon brakes and corrosion of cadmium-plated airframe components. As a result, there has been a move towards alkali-metal-salt-based products, which are less likely to cause these issues. However, these products can create wet and mixed contamination, reducing friction until the frozen contaminant is fully melted. They can also form "black ice" when the water from melted snow and ice dilutes the liquid de-icing agent.

The application of de-icers in either solid or liquid form is just one part of the process of maintaining runway safety in cold weather conditions. Airports also use mechanical methods such as plows, blowers, and other snow machines to clear runways and taxiways. Heated runways, which use electric copper heating cables or underground heating systems, are also employed at some airports, especially those located in colder climates.

Heated runways are expensive to run and maintain

Chloride-based de-icing chemicals, such as sodium chloride (common salt), cannot be used on airport runways as they are corrosive to the aluminium skin and structure of airplanes. Other de-icing methods are therefore used, such as plowing, blowers, snow machines, and de-icing fluids.

Heated runways are not common at airports due to the high costs of installing and operating the systems required to heat such large areas. For example, it has been estimated that heating a 9000x150 foot runway would cost around $28,500 per use. This would require an enormous amount of energy, with one estimate suggesting that Chicago O'Hare airport would need 600,000 kWh of power to melt the snow on its runways during an hour of a snowstorm, costing at least $100,000.

In addition to the high energy costs, there are other challenges associated with heated runways. The warm air above the heated areas could cause turbulence, affecting the landing of planes. There are also concerns about the durability of the pavement warming system under the repeated landings of heavy aircraft. Furthermore, if the heating system fails or cannot keep up with very cold temperatures, the melted snow could refreeze and form ice, which is more difficult to deal with than snow.

While heated runways could potentially reduce snow removal time and minimize travel disruptions, the high costs and technical challenges mean that most airports rely on conventional de-icing techniques and snow removal methods. However, some airports are experimenting with innovative technologies, such as geothermal heating systems and temperature sensors, to address this issue.

Airports use a combination of physical and chemical methods to keep runways clear

De-icing chemicals are used to prevent the formation of ice on the runway surface, as it is more challenging to melt it once it has formed. These chemicals, often referred to as Pavement De-icing Products (PDP) or Runway De-icing Fluids (RDF), work by lowering the freezing point of water, causing any precipitation on the runway to melt quickly. This makes it easier for aircraft to take off and land and prevents the formation of a thick layer of ice.

Some commonly used de-icing chemicals include Ethylene/Propylene Glycol-based fluids, Potassium Acetate, and Potassium Formate. However, these chemicals can be environmentally hazardous, so there has been a shift towards using alkali-metal-salt-based products. It is important to note that sodium chloride (common salt) is not used on runways as it can damage the aluminum skin and structure of airplanes. Instead, airports may use other chemical agents such as urea, glycol, or magnesium chloride, which create a 'brine' that prevents water droplets from freezing and sticking to the runway surface.

In addition to chemical methods, some airports utilize specially designed heated runways. These runways have electric copper heating cables or underground heating systems that pump hot water or glycol (a type of antifreeze) through tubes beneath the runway to melt snow and ice. Heated runways may also be equipped with melted snow collection systems to ensure that airport drainage systems are not disrupted.

Overall, keeping runways clear of snow and ice is crucial for maintaining safe and efficient aviation operations. By employing a combination of physical and chemical methods, airports can effectively manage snowfall and ice accumulation, ensuring smooth flight operations even during harsh weather conditions.

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