What Does
Freezing Point Mean?
The freezing point of a substance refers to the temperature at which it changes from a liquid state to a solid state.
A substance’s freezing point depends on the atmospheric pressure of its environment and whether the substance has been adulterated with another substance (e.g. salt lowering the freezing point of water to below 0℃/32°F).
Safeopedia Explains Freezing Point
Freezing points are an important consideration of occupational safety. A substance may become more or less hazardous if it is stored below its freezing point. Furthermore, the freezing point provides an important safety benchmark for considering the effects of worker exposure to cold environments.
The freezing point also comes into play when considering chemical substance safety. Chemical manufacturers and importers must indicate the freezing point of chemical substances on all safety data sheets (SDS) in all jurisdictions that comply with the Global Harmonized Standard (e.g., the European Union and the United States). The SDS is a mandatory aspect of chemical hazard communication under the GHS.
Knowledge of a chemical’s freezing point can be important to its safe handling. For example, acrylic acid freezes at 13°C and 55°F. The commercial variant of acrylic acid normally contains an inhibitor to prevent unintended reactions. Storing it below its freezing point will separate a portion of the acid from the inhibitor, and if the temperature of the chemical rises above the freezing point, the uninhibited portion of the acid may react violently. Organic peroxides dissolved in water or other solvents may solidify into unstable crystals if stored below their freezing points. These crystals can be very sensitive to shock and may pose an explosion hazard.
The freezing point of water (0℃/32°F) is an important benchmark for workers in cold environments. The Canadian Centre for Occupational Health and Safety advises that metal equipment handles should be designed with thermal insulating material to protect workers from potentially hazardous skin-to-metal contact if used in sub-freezing environments. Tools should also be operable with gloves and mittens. Furthermore, warming shelters should be available to workers and work should be paced to avoid excessive sweating. The cooling effect of sweat can exacerbate the exposure risk posed to workers and increase the risk of skin freezing to metal. The American Conference of Governmental Industrial Hygienists (ACGIH) recommends that temperatures be monitored every four hours in sub-freezing environments.