chemical form where appropriate. The application rates given for liquid
chemicals are the equivalent dry chemical rates.
Comments and notes are given in each table where appropriate to further
guide the maintenance field personnel in their anti-icing operations.
Black ice. Popular term for a very thin coating of clear, bubble-free, homo-
genous ice that forms on a pavement with a temperature at or slightly above 32F
when the temperature of the air in contact with the ground is below the freezing
point of water and small slightly supercooled water droplets deposit on the sur-
face and coalesce (flow together) before freezing.
. Supercooled droplets
of liquid precipitation falling
surface whose temperature is below or slightly above freezing, resulting in a
hard, slick, generally thick coating of ice commonly called glaze or clear ice.
Non-supercooled raindrops falling on a surface whose temperature is well below
freezing will also result in glaze.
Frost. Also called hoarfrost. Ice crystals in the form of scales, needles,
feathers, or fans deposited on surfaces cooled by radiation or by other processes.
The deposit may be composed of drops of dew frozen after deposition and of ice
formed directly from water vapor at a temperature below 32F (sublimation).
Light snow. Snow falling at the rate of less than half an inch per hour;
visibility is not affected adversely.
Liquid chemical. A chemical solution; the weight of the dry chemical in
solution applied per lane mile is the chemical application rate used in this guide.
Moderate or heavy snow. Snow falling at a rate of half an inch per hour or
greater; visibility may be reduced.
Sleet. A mixture of rain and snow that has been partially melted by falling
through an atmosphere with a temperature slightly above freezing.
Slush. Accumulation of snow that lies on an impervious base and is saturated
with water in excess of its freely drained capacity. It will not support any weight
when stepped or driven on but will "squish" until the base support is reached.
lb/ln-mi. Pounds per lane mile of roadway.