Snow Hardening Products for the
Preparation of Race Surfaces for
Alpine Skiing
UNDERSTANDING THE BASICS...
How They Work & Considerations for Their Use
A Review of Current Information
Prepared for the North American FIS TD Updates
Calgary AB & Lake Placid NY, October 2011
Doug Campbell
#1019
Sources of
Information:
Print Resources
Manufacturer’s
Instructions
Practical Experience
Scientific Research
What do we actually know about this?
Snow Surface
Preparation
Alpine Ski Racing
requires a hard, durable
snow surface and subsurface to promote
safety and fairness.
Proper Mechanical
Working Procedures
are the primary method
to prepare a suitable
race surface.
Snow Surface
Preparation
Water Treatment of
snow surfaces may be
necessary to increase
snow strength to
suitable levels when
this cannot be
accomplished by
mechanical methods
alone.
Snow density and
physical connections
between snow crystals
may be increased with
the addition of water
 Snow Hardening Products Most
Snow Surface
Preparation
Snow Hardening
Products are the only
method to increase
snow strength when the
temperature is above
the freezing point of
water.
However, the use of
snow hardening
products may be
minimized, even during
melting temperatures,
when snow surfaces
have otherwise been
properly prepared by
mechanical means or by
the addition of water.
Commonly Used in North
America


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Sodium Chloride - NaCl
Urea - CO(NH2)2
Ammonium Nitrate - NH4NO3
Snow Hardening Products
Sources of Information
PRINT RESOURCES
Sources of
Information
Print Resources
Sources of
Information
Print Resources
Sources of
Information
Print Resources
Sources of
Information
Print Resources
Sources of
Information
Print Resources
Sources of
Information
Print Resources
Snow Hardening Products
Sources of Information
MANUFACTURER’S
INSTRUCTIONS
Sources of
Information
Manufacturer’s
Instructions
Gerema PTX 311 is an
Ammonium Nitrate
Product
Sources of
Information
Manufacturer’s
Instructions
Sources of
Information
Practical Experience
Hand broadcast of snow
hardener.
Sources of
Information
Practical Experience
Rows of boot packers
Followed by hand
broadcast of product
Followed by application
of water
Followed by ski
steppers
Sources of
Information
Practical Experience
Application of Water
Sources of
Information
Manufacturer’s
Instructions
Gerema PTX 312Speedy is 100% Sodium
Chloride
Snow Hardening Products
HOW DO THEY WORK?
Snow
Hardening
Products
How Do They Work?
 Snow hardening by the
application of chemicals is
primarily the effect of melting
point depression
 The dissolution of “salts” in water
will depress the melting point.
 Snow grains or ice in contact with
the solute may melt.
 This change of phase from solid to
liquid requires heat, which is
withdrawn from the surrounding
snow causing a net cooling effect.
Snow
Hardening
Products
How Do They Work?
This simple diagram
illustrates how:
(a) Is at equilibrium with
the number of water
molecules freezing to the
ice, equal to the number
of frozen water molecules
melting.
(b) With the introduction
of a solute, is now out of
equilibrium with fewer
water molecules available
to freeze to the ice
relative to the number of
water molecules melting.
Kurschner, P; Maki-Marttunen, T; Vestergaard, S; Wandl, S., Modelling & Simulation of Ice/Snow Melting, 2008
Snow
Hardening
Products
How Do They Work?
The animated model at
this web-link better
illustrates melting point
depression.
Snow
Hardening
Products
How Do They Work?
This may be modeled
mathematically...and is
only slightly more
complex than a race
points calculation
If people do not believe
that mathematics is
simple, it is only
because they do not
realize how
complicated life
is. ~John Louis von
Neumann
Kurschner, P; Maki-Marttunen, T; Vestergaard, S; Wandl, S., Modelling & Simulation of Ice/Snow Melting, 2008
Snow
Hardening
Products
How Do They Work?
 The dissolution of salts also
consumes energy to break bonds
between the ions of the salt
molecule.
 The larger and more complex the
salt molecule, the more energy is
consumed to dissolve it.
 Research indicates; however, that
the net cooling effect of this process
is insignificant relative to that of
melting point depression.
 However, this process plays a
significant role in how different
snow hardening products work.
Snow
Hardening
Products
Scientific Research
Researchers at the
Swiss Federal Institute
for Snow and Avalanche
Research have
published valuable
information on this
specialized area of
interest, including this
2002 handbook.
Fauve, M.; Rhyner, H.; Schneebeli,
M., 2002: Preparation and
maintenance of pistes. Handbook for
practitioners. Davos, Swiss Federal
Institute for Snow and Avalanche
Research
Snow
Hardening
Products
Scientific Research
Researchers at the same
Institute provided an
overview for TD’s,
ROCs and Coaches that
was shared at the North
American FIS TD
Update in 2008
Snow
Hardening
Products
Scientific Research
 The same group of researchers at
the Swiss Federal Institute has
completed additional valuable
research that was circulated as a
draft manuscript in 2010 with the
possible title, Effects of Snow
Hardeners on the Snow Cover of
Ski Runs
 The following slides contain an
overview of some interesting
information contained in the draft
document.
Comparison of Ammonium Nitrate to NaCl
Rixen, C; Schneebeli, M., Effects of snow hardeners on the snow cover of ski runs, 2010
Both Products are NaCl
The Difference is Grain Size
Rixen, C; Schneebeli, M., Effects of snow hardeners on the snow cover of ski runs, 2010
Snow Strength
....and so it’s not all about how cold how fast?
Rixen, C; Schneebeli, M., Effects of snow hardeners on the snow cover of ski runs, 2010
Snow
Hardening
Products
Scientific Research
Model illustrating the
dissolution of the salt
(SH), the increasing
and infiltrating solute
concentration (SC), the
withdrawal of heat
represented by the
black arrows, and the
temperature at depth
represented by (T)
Rixen, C; Schneebeli, M., Effects of snow hardeners on the snow cover of ski runs, 2010
Snow
Hardening
Products
Scientific Research
A more detailed model
of the same process.
Rixen, C; Schneebeli, M., Effects of snow hardeners on the snow cover of ski runs, 2010
Snow
Hardening
Products
Some Observations and
Considerations
 Relative grain size of the product
influences the rate of reaction. The
smaller the grain size, the more
immediate the reaction and vice versa.
 NaCl causes a faster and deeper heat
withdrawal than Ammonium Nitrate as
the dissolution of NaCl is more
spontaneous. This; however, causes a
relatively increased solute
concentration and infiltration which
damages snow structure and results in
relatively lower snow strength
 On the other hand, the spontaneous
dissolution of NaCl quickly produces its
own water and therefore requires less
snow humidity to react than
Ammonium Nitrate.
Snow
Hardening
Products
Some Observations and
Considerations
Continued...
 Ammonium Nitrate application can
result in higher snow strength
relative to NaCl
 Although Ammonium Nitrate
requires more humidity than NaCl to
produce a comparable accelerated
cooling effect, it appears that the
addition of water results in overall
reduced snow strength.
 The lower solute concentration and
slower infiltration rate of
Ammonium Nitrate can result in
greater snow strength.
Snow
Hardening
Products
Some Observations and
Considerations
Continued...
 Increased temperature will
increase the rate of dissolution
and subsequently increase the
rate of reaction and reduce the
duration of the hardening effect.
 NaCl is corrosive and may kill
vegetation while nitrogen based
fertilizers such as urea and
ammonium nitrate, if not over
applied, may promote vegetation
growth.
Snow
Hardening
Products
 General Considerations and
Leading Practices

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Local experience is an asset
Experiment with test patches, not the
race.
Respect the environment and area
regulations
These products are corrosive and
hygroscopic and will burn skin. Wear
appropriate personal protective
equipment.
Snow
Hardening
Products
References
Snow Hardening Products
QUESTIONS?