History of Snow Removal
According to the National Snow and Ice Data Center, early snow control attempts involved citizens leveling drifts of snow to ease sleigh traffic in the 1700s. Several cities had ordinances requiring homeowners to clear their sidewalks, but streets were not cleared on a city-wide basis. Travel and the exchanging of goods, therefore, depended on individuals clearing the streets themselves. Wintertime travel in the early 1800s was mostly on foot as a result. With increased industrialization in the mid 1800s came the first snow plow, drawn by horses, and enabling transportation to recover quickly following winter storms. The snow plow created the basis for municipal responsibility in snow removal but new problems were also created, as merchants complained about the removed mounds of snow blocking their storefronts and sidewalks.
Sleigh drivers also disapproved of the ruts and uneven surface of the streets following plowing. Some cities responded by hiring shovelers to work in conjunction with the plows to haul the snow away and dump into rivers. Salt was used in a few cities but was strongly protested because it ruined the streets for sleighing and damaged the clothes and shoes of pedestrians. Following the blizzard in 1888, cities recognized the need for more organized and efficient snow removal. Rather than waiting until the storm was nearly over, city officials began to plow as the storm began, giving better results and more rapidly cleared roads. By dividing cities into sections and hiring more drivers, streets were cleared with greater efficiency.
With the advent of motorization, snow removal was revolutionized in the 20th century. Motorized plows and dump trucks arrived as early as 1913. Many cities abandoned horse-drawn carts and motorized their snow removal fleets. Caterpillar tractors equipped with plow blades were utilized, along with trucks, for plowing, while steam shovels, cranes and railway flatcars were used to haul snow away. Snow loaders also came into use in the early 1900s. As more cars took to the road, though, new problems ensued, as public safety demanded removal of even light snowfalls. Furthermore, residential streets, as well as main streets, needed clearing. Plowing left behind a slick layer of ice on the road so city officials began spreading salt by the ton. No longer concerned with protests, motorized salt spreaders became an essential tool. Later complaints of damage to vegetation and automobiles by salt led to improved salt spreaders with more efficient gauges. With so many cars on the road, shopping centers and office buildings began to see a need to clear their parking lots for employees and customers, thereby creating a specialized market. Smaller plows and snow blowers were in demand and many of these companies turned to private snow removal contractors to clear their lots.
While the introduction of motorized vehicles and subsequent technological advancements has made snow management and plowing faster, the basic process of plowing today is not much different than it was 75 years ago. Although the refinement of weather forecasting has allowed professionals to better predict and prepare for a storm, we still have to wait for the snow to fall, at which point we push it out of the way.
Why the need for snow removal?
While falling snow can be a majestic site, a parking lot, street or sidewalk of snow is hazardous and troublesome to those determined to not let a snowfall alter their day. With so many people out and about, the potential for motor vehicle accidents increases, as well as personal injury from wet and icy parking lots and sidewalks. As 90% of slips and falls occur in less than an inch of snow, it is important for businesses to manage winter conditions properly to reduce their liability. The protection of concrete and/or asphalt is an added benefit of removing snow from your property.
Liability issues The National Safety Council estimates there are approximately 300,000 injuries and more than 1,500 deaths per year as a result of wintertime weather. Premise liability laws concern a building owner’s responsibility to remove potentially dangerous conditions around their property to prevent injury to guests. This is the category of law under which accidents from ice and snow fall. Building owners are given a window of time following the end of the storm in which to clear their parking lots and sidewalks of snow and ice and to take measures preventing ice from forming in the future.
This often involves monitoring outside temperatures, if not pavement surface temperatures, and requires some form of surface treatment to aid in the prevention of ice. While many building owners hire outside companies to manage snow conditions, liability for injury is not necessarily transferred to their snow management contractors. It is important, therefore, to understand your snow removal options, research potential snow removal companies and formulate a plan that will protect you, your property, your employees and your customers. These recent verdicts against building owners and managers indicate how serious slip and fall claims can be and underscore the importance of managing snow and ice on your property in a conscientious way:
- $475,000 awarded to a New York woman who slipped and fell on a flea market parking lot. The defendant claimed that the flea market owner and the owner of an adjoining lot were negligent in clearing their lots from a snowstorm the previous day.
- $2 million awarded in Connecticut to a man who slipped on ice outside a hotel. The lawsuit claimed that the hotel managers were aware that the area got icy for several years but failed to correct the problem or warn pedestrians.
- $390,000 awarded to a Philadelphia man who slipped in an icy industrial parking lot. The man claimed the industrial park’s owner allowed rainwater to drain directly on the lot and did not salt, shovel or clear ice and snow from the lot.
- $942,000 awarded to an Omaha man who slipped on ice while stepping over a pile of snow outside a motel. The jury found that the motel’s parking lot was not sufficiently lit to reveal the icy surface.
Effects of snow on concrete and asphalt Although concrete may appear to be a completely solid object, it actually contains numerous microscopic passageways. These tunnels are formed during the initial crystallization process as concrete is transforming from a liquid to a solid state and the needles of interlocking cement paste crystals grow. When water freezes, its volume expands by about nine percent and any water that has entered these passages can break the needles of the interlocking paste crystals. Snow left on concrete will melt and enter the tunnels only to refreeze at night and, over time, will cause cracks and potholes on your lot. Removing snow from the surface of your lot will keep the water content of the concrete down and minimize freezing damage, thereby helping to preserve your investment.
Asphalt is a mixture of tar, oil byproducts, curative and aggregate gravel spread over compacted earth and gravel for drainage. Under heat and stress from traffic, asphalt eventually cracks leaving gaps for snow and water to enter. This water freezes during winter and the resulting expansion forces dirt and gravel out, leaving a hole when the water melts again. The thin asphalt layer over the hole is left weakened and eventually collapses causing a pothole. To help prevent this unsightly and potentially damaging hazard, snow must be consistently removed from the surface. While it is impossible to keep the asphalt completely dry during and following winter storms, removing snowfall will decrease the volume of water available to seep into the cracks and will minimize freeze damage to your lot.
How surface treatments work
Snow-melt products are designed to weaken the bond between ice/snow and the ground, not to completely melt all the ice and snow that accumulates. Chemical deicers in their solid state are unable to melt anything. When they come into contact with water, however, they dissolve into liquid brine and this salt solution lowers the freezing point of water and melts ice and snow on contact. The brine spreads out under the ice and breaks the bond between ice and pavement, allowing plows to separate the ice from a surface. The melting action will continue until the brine is so diluted that the freezing point of the solution reaches ground temperature. Some surface treatment chemicals also release heat when they dissolve in water, thereby melting snow more quickly. The efficiency of the various chemicals also depends on the temperature and whether the salt needs direct contact with moisture to dissolve or if it can absorb moisture from the air. All of these factors are important to consider when selecting the best deicer for your job.
Eutectic temperature The lowest possible temperature at which deicer brine can dissolve ice is called its eutectic temperature. The eutectic temperature, however, only applies to a specific concentration of the deicer in water and no deicer is capable of staying at this concentration for long, as it continually becomes more diluted as more ice and snow is melted. As the solution gradually becomes weaker, the freezing point gradually increases. Therefore, eutectic temperatures are significantly lower than the temperature at which a deicer can be effective. For example, the eutectic temperature of sodium chloride is -6ËšF but its effective temperature is only 15ËšF. The lowest effective temperature is a more meaningful number to consider when selecting a deicing product. Be sure to research a product’s ingredients and effective temperature, as deicer manufacturers will sometimes mislead consumers by advertising the eutectic temperature on packaging without making clear what it means.
Melting capacity As temperatures drop, salt becomes less effective at melting ice and more chemical is needed to get the job done. The table below demonstrates how temperature affects the melting capacity of sodium chloride and shows that, at colder temperatures, more salt is needed to melt ice. In colder environments, choosing a chemical with a lower effective temperature allows a larger amount of snow to be melted per pound of salt.
Melting rate Melting rate is a measure of how fast melting occurs at different temperatures and, like melting capacity, the rate is influenced by temperature.
Deicing products can, alternatively, be spread before snow falls in an effort to prevent ice from building up. Sitting on a surface, rock salt will do nothing, but as the snow falls the resulting brine prevents any bond from forming and leaves a parking lot ready to be plowed. In addition to not having to wait for ice to be broken down, the plowed surface will be cleaner than if it is plowed after ice has a chance to bond. Anti-ice applications generally involve liquids and, once they are applied, can have residual effects for several days, i.e. they will remain on the pavement if the snowstorm doesn’t hit or shows up late. When the storm does hit, pre-treating a site will reduce service time and the amount of chemical spread. Temperature can be a factor, though, as using liquids in temperatures that are too warm can leave dangerous, slippery pavements. It is, therefore, important to work with a well-trained contractor who understands these processes.
Chloride brines vs. dry salts
At colder temperatures, application results can be slow and require a large amount of chemical. In extreme cold, the addition of liquid brine to rock salt can improve chemical performance. To some, the application of a liquid to pavement seems counterintuitive and causes apprehension, but there is no question that liquid deicers melt faster and last longer than traditional salt applications. Rock salt needs to form a brine solution that is 23% salt to melt ice. Adding moisture to the dry salt before you spread it means less moisture the salt needs to come into contact with in order to begin doing its job. Furthermore, the brine sticks to the surface better than dry salts, which can be scattered by bounce, traffic and wind. Spreading pre-wetted salts uses substantially less salt overall and decreases the time spent clearing your lot.
Sand is sometimes spread with salt to improve traction but after snow and ice have melted, sandy pavement has less traction than sand-free pavement. Tests conducted by the National Safety Council have determined that salt gives as much anti-skid protection as abrasives when applied at normal deicing rates. The proper use of deicers along with the removal of snow and ice should be sufficient and eliminate the need for sand.
Most environmental damage results not from the product itself, but from misapplication or improper use of the product. Many of the chemicals used for deicing are also used in agricultural applications and are not necessarily detrimental to vegetation. Danger from chemical deicers to the environment is posed when the concentration of the chemical rises to abnormally high levels in the soil. Just as fertilizers can cause die back and browning when over applied, care should be taken not to use more salt than is needed for breakup and removal of snow and ice. The best way to prevent damage is to avoid overuse and to select the most effective product for your situation. Using the most effective product means you will need less chemical to clear the same amount of ice and snow and minimize exposure to plants, trees and shrubs.
Most damage to concrete from chemical deicers is not from the chemicals themselves but from the effects of freezing and thawing. By lowering the freezing point of water, deicers can increase the number of freeze-thaw cycles and add to the problem. When temperatures fluctuate between 10ËšF and 20ËšF, plain water will remain frozen. A deicing brine of rock salt and water, however, will freeze when the temperature drops below 15ËšF and thaw when it rises above 15ËšF resulting in more freeze-thaw cycles than if no deicer had been applied. For this reason, it is important to consider the lowest effective temperature when selecting a chemical deicer. It is also important to remove the snow once the deicer has broken the bond with the pavement. Removing the snow leaves less water available to seep into holes of the concrete.
Calcium magnesium acetate (CMA) was developed in response to concerns of the effects of salt on vegetation and the concrete of structures such as bridges and parking lots. In the 1970s, the Federal Highway Administration identified CMA as the only low-corrosion chemical alternative to road salt. It is approximately as corrosive as tap water and is biodegradable in soil. CMA can increase soil permeability, may improve plant growth and is unlikely to reach groundwater but it does come at a price: it costs approximately 30 times more than rock salt. While some environmentally sensitive situations require the use of CMA, many of the traditional chemical deicers pose no threat when applied at proper rates.
This practice involves loading snow into dump trucks and hauling it to another location and can be an important management tool for your business. Rather than plowing snow into huge piles in the middle of your parking lot, taking up valuable space in some instances, snow can be hauled away to another site to melt. Piles of dirty snow can be unattractive, hide business signs and storefronts and create hazardous trails of melted snow which then refreeze when the temperature drops. By removing snow off the lot, you can provide a safe, clear site, reduce obstructions and increase pavement areas.
Snow removal contractors
The Better Business Bureau provides these tips on hiring a snow removal contractor:
- Get several estimates and remember that the least expensive service is not necessarily the best.
- Be sure you understand the price options and are aware of any additional charges. Do they charge based on inches of snow fallen or a flat rate per season? How does the company determine the size of the snowfall? Are there sometimes additional charges during large storms?
- Find out what is included in the estimate, such as sidewalks, steps and the cost of salt? Will the area be cleared during the storm as well as after? Are there additional charges if the contractor has to come back?
- Ask for references and check them out.
- Check the BBB reliability report on the company you are planning on using.
- Make sure you get a written contract and the company provides proof that they are insured and bonded. Ask who you can contact regarding any damages, such as cracked driveways, and how you can terminate the agreement if necessary.
Deicing materials vary greatly and can range from the familiar rock salt to liquid chemicals. The type of material used depends on availability, environmental factors and effectiveness with regard to speed or temperature. No matter which chemical you use to manage snow, it takes time for it to go into solution and melt ice, regardless of how much is applied. Understanding the deicer you choose and its chemical properties can prevent over-applying, protecting your property and saving you money. While by no means exhaustive, here are some of the commonly used treatments:
Sodium chloride: Known as rock salt, this is the most commonly used product because of its low cost and effectiveness at moderately cold temperatures. It is easy to secure and requires no special handling or storing procedures. Sodium chloride requires heat in order to “go into solution,” which it absorbs from the air and the pavement, thus making it an effective ice-melting agent. One drawback to sodium chloride is that it must come into direct contact with moisture in order to dissolve so it does require more time to be effective than other chemicals, such as calcium chloride and magnesium chloride. The lowest effective temperature is 15F.
Calcium chloride: Calcium chloride is probably the second most commonly used deicer. It is exothermic, meaning it releases heat as it goes into solution, and therefore works more quickly than sodium chloride. Furthermore, instead of requiring direct contact with moisture to dissolve, calcium chloride readily attracts moisture from the air, enabling it to begin working more quickly. It is also effective at lower temperatures (as low as -20F) and is relatively harmless to plants and soil. The drawback to calcium chloride is that, because of its ability to attract moisture from the air, it requires special storage procedures to prevent it from reacting before it can be spread. Furthermore, calcium chloride can create wet pavements and slippery conditions when not applied properly.
Magnesium chloride: This salt is also exothermic but has less heat-release capability. It is, therefore, more efficient than sodium chloride, though not as effective as calcium chloride. It can be used in temperatures as low as 0F and is less toxic to plants and less corrosive than sodium chloride. However, like calcium chloride, it requires special storage procedures due to its ability to attract moisture. This compound is used in its crystal form for businesses and sidewalks but a number of highway departments have increased their use of liquid magnesium chloride as a deicer and an anti-icer. The liquid compound is spread on dry pavement before precipitation or on wet pavement before freezing temperatures to prevent snow and ice from bonding with the roadway.
Potassium acetate: A biodegradable liquid deicer that is less aggressive on soil and less corrosive. It is, therefore, preferred for airport runways but is not often used in other markets due to its high cost. Potassium acetate can be applied in temperatures as low as -15F making this compound effective at colder temperatures.
Calcium magnesium acetate: Developed as an environmentally friendly alternative to road salt, calcium magnesium acetate is the safest chemical for concrete and vegetation as it is approximately as corrosive as tap water. The cost, however, is about 30 times more than rock salt. The effective melting temperature is approximately 20F.
Potassium chloride, ammonium sulfate and urea: Commonly used as fertilizer, these three chemicals are occasionally used as deicers. All three are corrosive and have an effective temperature of 20F.
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