Mind the ice

Chuck Kuhn

Winter temperatures will be climbing over the next few days, and we know that some Fermilab folks enjoy skating on the pond in front of Wilson Hall after it ices over.

It’s fine to skate on the ice, but be safe when doing so. Here are some tips to help you judge whether or not an iced over pond near you is safe for recreational activity.

The safety of ice depends on a combination of factors, not on one factor alone. Asses the following factors together:

  • Appearance of the ice – its color, texture and features
  • Thickness of the ice – there are recommended thicknesses for different uses. See below
  • External temperature over a period of time and on the day
  • Snow coverage
  • Depth of water under the ice
  • Size of the body of water
  • Chemical composition of water — saltwater or fresh water
  • Local climate fluctuations
  • The length of time the ice has existed.

Know your ice color. Do not rely on color alone. But as an approximation, you can use these guidelines:

  • Light gray to dark black: Melting ice, which occurs even if air temperature is below 32 degrees Fahrenheit (0 degrees Celsius). Ice of this color is not safe. Its weak density can’t hold a load. Stay off it.
  • White to opaque: This indicates water-saturated snow freezing on top of ice, forming another thin ice layer. Most times it’s weak due to being porous from air pockets.
  • Blue to clear: This indicates a high-density, very strong, safe ice to be on if it is thick enough. If it is less than 4 inches (10 centimeters) thick, stay off it.
  • Mottled and slushy or “rotten” ice. Ice of this texture (texture more so than color) is thawing and slushy. It is deceptive: It may seem thick at the top but it is rotting away at the center and base. Most prevalent in spring, it may show signs of browns from plant tannins, dirt and other natural materials that are resurfacing from thawing. This ice is not suitable, for even one footstep.

Remember not to rely solely on color. For instance, ice of any color is subjected to a running water force underneath will be weaker than ice not subject to that pressure.

The thickness of ice must be taken into consideration. According to the Minnesota Department of Natural Resources,

  • If the ice is 2 inches thick or less, stay off it.
  • Ice that is between 2 and 4 inches thick is suitable for ice fishing or other activities on foot.
  • Ice that is between 5 and 7 inches thick is suitable for a snowmobile or ATV.
  • Ice that is between 8 and 12 inches thick can hold a car.
  • Ice that is between 12 and 15 inches thick can support a medium-size truck.

White ice or “snow ice” is only about half as strong as new clear ice. Double the above thickness guidelines when traveling on white ice.

Chuck Kuhn is the Fermilab fire chief.