An aerosol can is a sealed metal container designed to dispense a product using a pressurized gas, known as a propellant. This system contains both the liquid product and the propellant, held in a balance of pressure and temperature. Aerosol cans can freeze, but the exact temperature required varies widely. This freezing threshold depends entirely on the specific chemical formulation inside the container, particularly the active product ingredients.
The Unique Physics of Aerosol Freezing
The contents of an aerosol can are a complex mixture, generally consisting of the active product and a liquefied gas propellant. While the propellant, often a hydrocarbon like propane or butane, has an extremely low freezing point, the product itself is the most vulnerable component. Many aerosol products, such as air fresheners, cleaners, or personal care items, are formulated with water or alcohol as a primary solvent base.
Water-based products typically begin to solidify near the freezing point of water, \(32^\circ\)F (\(0^\circ\)C). The presence of other chemicals, like alcohol or the propellant, lowers this temperature through a process called freezing point depression. This means the overall mixture must be cooled below the freezing point of its main solvent before it turns completely solid.
If the can is exposed to sub-zero temperatures, the liquid product may become thick or turn into a slushy state while the propellant remains stable. Even if the active ingredient mixture is frozen, the can still contains high-pressure liquefied gas, which is key to dispensing the product. Partial freezing can lead to blocked internal dip tubes and valve systems, making the can unusable until it is warmed.
Pressure Changes and Can Integrity
The primary hazard associated with a frozen aerosol can is the structural stress placed on the metal container. When liquid water freezes, it expands in volume by about 9%, a property that applies to any water-based product inside the can. This expansion exerts immense outward pressure on the rigid walls of the can.
Aerosol cans are constructed to withstand high internal pressure from the propellant, but they are not designed to handle the outward, physical expansion force of a solidifying substance. This volume increase can deform the can, often causing the top or bottom seams to bulge. Once the can’s structure is compromised by this expansion, its ability to safely contain the propellant is permanently weakened.
A frozen can presents a danger when it begins to thaw. As the temperature rises, the liquefied propellant returns to its gaseous state, and the internal pressure increases significantly. If freezing has already created microfractures or weakened the can’s seams, the subsequent pressure increase during thawing can exceed the container’s structural limits, potentially leading to a dangerous leak or rapid rupture.
Safe Thawing and Storage Practices
The key to preventing freezing is proper storage, which means keeping aerosol cans within a manufacturer-recommended temperature range. Most manufacturers suggest storing cans at ambient room temperature, ideally between \(60^\circ\)F and \(90^\circ\)F (\(15^\circ\)C to \(32^\circ\)C). They should be kept in a cool, dry, and well-ventilated area, safely away from any risk of freezing.
If a can has already been exposed to freezing temperatures, it must be thawed slowly and carefully to mitigate safety risks. The can should be moved to an indoor area with a stable ambient temperature, allowing it to warm up gradually. Never use external heat sources, such as direct sunlight, hot water, or a space heater, as this rapid temperature increase will accelerate the internal pressure.
A can that has frozen and thawed should be carefully inspected before use. If the can shows visible signs of damage, such as a bulging seam, a leak, rust, or a crack, it should be considered compromised and discarded according to local hazardous waste regulations. Even if the can appears structurally sound after thawing, its performance may be permanently affected due to internal component damage or changes in the product formulation.