Deicers are used to keep water wet at temperatures below the freeze point of water. An important factor to consider when calculating deicer application rates, therefore, is the water content in the snow and ice that must be melted. That amount varies depending on the air temperature at the time it is falling. Effective use of this data can result in labor and cost savings for the snow and ice professional.
The common answer is that one inch of newly fallen snow equals 1/10th of an inch of water depth when it melts. But as temperatures drop, you will notice that the snow is drier, which results in less water content.
Table 1 shows the amount of snowfall required within a temperature range to result in the water depth shown in the “Melt Water” column. For example, to get an inch of melt water at 28°F (-2.2°C) requires a 10-inch accumulation of freshly fallen snow. At 15°F (-9.4°C), it would require a total snowfall depth of 20 inches to get the same one inch of melt water.
Table 1 - Impact of temperature on melt water depth equivalent of snowfall
Cold weather performance
When temperatures drop, the amount of deicer required to make the surface wet increases, as does the time it takes for the deicer to work, regardless whether it is a liquid, solid or combination.
In Table 2, the column labeled “Number of Loads to a Wet Surface” represents the number of units of salt it takes to get to a wet surface under some depth of snow (water content) at the temperatures shown. In the column labeled “Number of Loads to a Wet Surface” the number “1” associated with 30°F (-1°C) assumes that one unit of salt (imagine a truckload) applied properly as a solid and at the correct application rate results in a wet surface. To achieve the same results, application rates increase as surface temperature drops.
Table 2 - Melting capacity of salt at different temperatures
The water content of ice is 109% of the depth. For example, using 1/1000th of an inch for ease of illustration, assume the ice measured 109/1000th of an inch in depth. In reality it would be 1/10th of an inch in depth due to expansion during freezing. Ice expands to a volume of 9% larger than when it was in liquid form.
From the data presented, it is easy to see why understanding how deicer chemicals work and the amount of water in freshly fallen snow are important when determining chemical application rates.
Dale Keep owns Ice & Snow Technologies, a training and consulting company based in Walla Walla, WA.