The sudden, loud pop from a freezer followed by a sticky, frozen mess is a common domestic disaster. This phenomenon, where a soda can turns into a pressurized projectile, is a demonstration of fundamental physics, not a manufacturing defect. The aluminum can is no match for the immense force generated by a liquid changing its state inside a sealed container. This explosive failure lies entirely in the unusual behavior of water when it transitions into ice.
The Anomalous Expansion of Water
The primary component of any soda is water, which exhibits a rare physical property unlike almost any other substance. Most liquids contract as they cool and solidify, meaning their solid form is denser than their liquid form. Water, however, reaches its maximum density at about 4 degrees Celsius, just above its freezing point.
As the temperature drops toward 0 degrees Celsius, water molecules arrange themselves into an ordered structure. This arrangement is driven by hydrogen bonds, which force the molecules into a fixed, open hexagonal crystal lattice. This cage-like structure creates empty space between the molecules, making the solid form of ice less dense than the liquid water.
This structural rearrangement causes a significant volume increase upon freezing. When water turns into ice, its volume expands by approximately 9 percent. This substantial increase in volume is the mechanical force that overwhelms the structural integrity of the can.
Internal Pressure Dynamics and Can Failure
A sealed soda can is already a highly pressurized environment. The carbonation process introduces dissolved carbon dioxide gas, creating an internal pressure that typically ranges from 17 to 30 pounds per square inch (psi) when refrigerated. This pre-existing pressure gives the thin aluminum shell its structural rigidity, allowing it to resist crushing and stacking forces.
However, the can is a fixed-volume container with no flexibility to accommodate the 9 percent expansion of its contents. Once the liquid begins to solidify, the growing ice exerts a rapidly increasing hydraulic pressure against the can walls. This expansion pressure quickly adds to the existing carbonation pressure, pushing the total internal force past the can’s design limits.
Standard aluminum cans are engineered to safely withstand pressures up to 80 or 90 psi before the ends or seams begin to fail. Since the expansion of ice can generate forces reaching thousands of pounds per square inch in a confined space, the can’s failure is inevitable. The can bursts at its weakest point, releasing the contents in a high-velocity explosion of ice and sticky syrup.
How to Prevent Freezer Explosions
Avoiding this messy outcome requires using rapid cooling methods that prevent the liquid from reaching its freezing point. The most effective technique is to utilize a chilled bath instead of relying on the freezer’s slow air circulation. Submerging the can in a mixture of ice, water, and salt can chill the beverage in just a few minutes.
Adding salt lowers the freezing point of the water in the bath, allowing the mixture to reach a temperature below 0 degrees Celsius without freezing. This colder solution transfers heat away from the can much faster than cold air. If a freezer must be used, wrapping the can tightly in a wet paper towel before placing it inside will help speed up the cooling process. The evaporation of water from the towel assists in drawing heat away, but a timer should be set for no more than 15 to 20 minutes to prevent freezing.