|For many of us in northern
climates, working or playing on the frozen surface of a river or
lake is part of winter. Knowing how to do so safely can be a
matter of life or death. This handout presents general,
common-sense precautionary measures that should be followed when
you plan to be on a floating freshwater ice cover. Since it cannot
cover every ice condition you may encounter, your judgement is
critical. Remember: Only you are responsible for your own safety!
There are four things to focus on when planning an outing on the
ice: your physical condition, your clothing, your equipment, and
Anyone who goes out on the ice should be in reasonably good
condition and be able to sustain periods of intense exertion if an
emergency arises—either falling through the ice themselves or
rescuing someone who does. Being able to swim, or at least being
comfortable staying afloat, is important in an emergency and can
reduce the chances for panic.
Naturally you should choose clothing that provides protection from
low air temperatures, wind, and precipitation while at the same
time allowing you mobility. But in addition, when you select
clothing, keep in mind the possibility of falling through the ice.
Clothing that would severely restrict your ability to swim or to
stay afloat is not a good choice. Hip boots or waders should never
be worn, as they can fill with water and restrict movement while
adding weight. A personal flotation device (PFD) should be worn.
This can be a vest or jacket, either inflatable or aturally
Include items for testing and measuring the ice thickness, as well
as items for rescue or self-rescue. In the first category are a
heavy ice chisel, an ice drill or auger (manual or powered), a
measuring tape or stick that can be hooked under the bottom edge
of the ice in an auger hole, and possibly a perforated ladle for
cleaning ice out of the auger holes. In addition to the PFD, bring
a rope or rescue throw bag containing a rope that floats. Ice
rescue picks sold for ice fishermen are an excellent idea. They
thread through your jacket sleeves like children's mittens and are
immediately available in an emergency for pulling yourself out of
the water onto the ice.
- Never go out on an ice
cover alone, and never go out on the ice if there is any
question of its safety.
- While you are planning
the outing, obtain the record of air temperature for the past
several days and continue observing air temperatures while the
ice will be used to support loads.
- Always let someone know
of your plans and when you will return.
- When you arrive at the
water's edge, visually survey the ice. Look for open water
areas, and look for signs of recent changes in water levels: ice
sloping down from the bank because the water dropped, or wet
areas on the ice because the water rose and flooded areas of the
ice that couldn't float because it was frozen to the bottom or
the banks. (If the ice is snow-covered, look for wet areas in
- Listen for loud cracks or
booms coming from the ice. In a river this can mean the ice is
about to break up or move; on a lake larger than several acres
such noises may be harmless responses to thermal expansion and
- Look for an easy point of
access to the ice, free of cracks or piled, broken ice.
- If you are taking a
vehicle or other equipment on the ice, go out on foot first.
Vigorously probe ahead of yourself with the ice chisel. If the
chisel ever goes through, carefully turn around and retrace your
steps back to shore, and try again some other day.
- Near shore, listen for
hollow sounds while probing. Ice sloping down from the bank may
have air space underneath. This is not safe; ice must be
floating on the water to support loads.
- After getting on the ice,
others in the group should follow in the leader's steps, but
stay at least 10 feet apart.
- Only after you have
learned the characteristics of the ice cover should any vehicle
be taken on the ice.
WHAT YOU NEED TO KNOW ABOUT
Once on the ice it is time to begin more systematic observations
of the ice sheet you want to use to support a load. There may be
many variations in the structure, thickness, temperature, and
strength of a floating freshwater ice sheet.
How thick is the ice?
This is determined by drilling holes with the drill or ice auger.
The technique is to drill a hole and check the ice thickness every
150 feet or so along the intended path. This should be done more
frequently if the ice thickness is quite variable. Note whether
the ice in each hole is clear (sometimes called black ice) or
white (due to air bubbles—sometimes called snow ice). Measure the
thickness of both kinds.
On rivers the ice thickness
and quality can change a lot in a short distance; be particularly
alert to variations in ice thickness due to bends, riffles or
shallows, junctions with tributaries, etc. For both rivers and
lakes, warm inflows from springs can create areas of thinner ice.
The ice near shores can either be thinner (due to warm groundwater
inflow or the insulating effect of drifted snow) or thicker (due
to the candle-dipping effect of variable water levels).
snow cover thickness on the ice cover; significant variations in
thickness may mean highly variable ice thicknesses.
How thick does it need to
be? A simple formula to estimate the minimum ice thickness
required to support a load is
where h is the ice thickness
in inches and P is the load, or gross weight, in tons. You can
also use the graph or table to determine the minimum thickness.
Remember that the load is
the total load in tons (not a vehicle's load capacity).
to support a load
The equation, graph, and
table are valid when the load (such as a person on foot, or a
wheeled or tracked vehicle) is distributed over a reasonable area
of a continuous ice sheet. The larger the load, the greater the
area it should cover for the calculation to remain valid. Neither
large loads that are concentrated in relatively smaller areas, nor
loads that are at or near the edge of a large opening in the ice,
are safely described by the equation, graph, or table.In such
cases, seek more advice.
The equation, graph and
table assume clear, sound ice. If white, bubble-filled ice makes
up part or all of the ice thickness, count it as only half as much
Any recent large snowstorm
creates a new load on the ice. If the new snow is heavy enough,
the ice sheet will sag and its top surface will be submerged below
the water level. Then water will flood the top of the ice sheet
through cracks, saturating the lower layers of the snow. Until
this slush is completely frozen, stay offthe ice sheet. When the
saturated snow becomes frozen, it is an added thickness of white
Contrary to what you would
expect, a rapid, large air temperature drop makes an ice sheet
brittle, and the ice may not be safe to use for 24 hours or more.
If the air temperature has
been abovefreezing for at least 6 of the past 24 hours, multiply
the load by 1.3 before you use the equation (or use the lower
dashed line on the graph), obtaining a larger minimum ice
thickness to account for any possible weakening. If the air
temperature stays above freezing for 24 hours or more, the ice
starts losing strength, and the equation, figure, and table no
longer represent safe conditions. Stay off the ice!
You are likely to encounter
cracks in the ice. Cracks are either wet or dry. If they are dry,
they do not penetrate the ice sheet and are not a concern. If they
are wet, multiply the load by 2, as shown on the graph, before you
use the equation to obtain the required minimum ice thickness.
If you plan to leave a load
on the ice for extended periods, usually more than two hours,
multiply the load by 2 (as shown by the upper dashed line in the
graph) before you use the equation to find the required minimum
SAFE OPERATIONS ON THE ICE
If using an enclosed vehicle, alwaysdrive with the windows or a
door open for quick escape.
If you drive across wet
cracks, your path should be as close to perpendicular to them as
possible, instead of parallel to them.
A load deflects the ice
slightly into a bowl shape. When you drive on floating ice, this
moving bowl generates waves in the water. If the speed of the
waves equals the vehicle speed, the ice-sheet deflection is
increased and the ice is much more likely to break. The problem is
more serious for thin ice and shallow water. In general you avoid
this danger by driving below 15 mph.
When there are two loads on
the ice, the safe distance between them is about 100 times the ice
thickness at the required minimum thickness. This is shown in the
third column of the table. When the two loads are different,
choose the spacing shown for the larger load. At ice thicknesses
greater than the required minimum, this spacing can be reduced.
A loaded ice sheet will
creep, or deform, over a long period of time, without any
additional load. If an ice sheet has to be loaded for a long
period, drill a hole near the load. If the water begins to flood
the ice through the hole, move the load immediately. Remember this
if your vehicle ever becomes disabled: if left for a few days, it
may break through the ice as a result of long-term creep.
Be sure you understand this information. Don't hesitate to seek
the advice of others whose experience you trust. Be safe out on