Dry ice is the solid form of carbon dioxide, valued for its extremely cold temperature of approximately -78.5 degrees Celsius (-109.3 degrees Fahrenheit). Unlike water ice, it undergoes sublimation, turning straight into carbon dioxide gas rather than melting into a liquid. This unique property makes it highly effective as a refrigerant for shipping temperature-sensitive materials like perishables and medical specimens. It is also used in theatrical productions to create dense, low-lying fog.
Essential Safety Gear and Physical Handling
Direct contact with dry ice, even for a few seconds, can rapidly cause severe cold burns or frostbite due to its intense temperature. The extreme cold constricts blood vessels and freezes skin tissue, potentially leading to irreversible damage. Consequently, you must always wear appropriate personal protective equipment before handling the material.
The most important piece of gear is a pair of loose-fitting, insulated gloves, such as leather or specialized cryogenic gloves. Thin materials like cotton or standard nitrile gloves will not provide adequate thermal protection against the extreme cold. If insulated gloves are unavailable, use tongs, a scoop, or a thick cloth to move the material, ensuring a barrier between the dry ice and your bare skin. Eye protection, such as safety goggles or a face shield, is also recommended, particularly if the dry ice is being broken up.
Safe Storage and Transportation
The primary storage hazard comes from the continuous process of sublimation, which constantly releases large volumes of carbon dioxide gas. One pound of dry ice can generate around 250 liters of gas, and if this gas is trapped, the pressure buildup can cause an explosion or container rupture. For this reason, dry ice must never be stored in an airtight container, such as a sealed glass jar or a metal can with a tight lid.
Storage containers should be insulated, like a Styrofoam cooler, but must allow the gas to vent freely. Carbon dioxide gas is denser and heavier than ambient air, meaning it accumulates in low-lying, poorly ventilated areas. Storing dry ice in small, enclosed spaces, such as a basement or closet, can lead to a dangerous buildup of gas that displaces breathable oxygen. When transporting dry ice in a vehicle, ensure constant fresh airflow by cracking the windows or placing the container in the trunk, separate from the passenger compartment.
Recognizing and Treating Exposure
Improper handling or inadequate ventilation can lead to two main types of exposure: cryogenic burns and asphyxiation. Frostbite from skin contact initially presents as skin that appears waxy or white and feels hard or numb. To treat this cold injury, immediately remove any clothing not frozen to the skin and soak the affected area in warm water below 40 degrees Celsius (104 degrees Fahrenheit). Never rub the injured area or use dry heat, and seek medical attention immediately following initial first aid.
Exposure to high concentrations of sublimated carbon dioxide gas can lead to asphyxiation, which can occur without warning because the gas is odorless and colorless. Early symptoms of CO2 overexposure include headaches, dizziness, confusion, and a noticeable increase in breathing rate. If these signs appear, the person must be moved immediately to a location with ample fresh air. Carbon dioxide levels above 0.5% in the air can become hazardous, so prompt removal from the contaminated space is the only effective first-aid measure.
Proper Disposal Methods
The only safe method for disposing of excess dry ice is to allow it to fully sublime back into carbon dioxide gas. This process should take place in a secure, well-ventilated area, preferably outdoors, where the released gas can dissipate harmlessly. The dry ice should be placed in its original vented container on a non-damaging surface, such as Styrofoam or hard plastic, and kept away from children and pets.
Allow the material to evaporate completely until nothing remains. It is prohibited to dispose of dry ice by flushing it down a toilet, sink, or drain, as the extreme cold can instantly freeze and rupture plumbing. Placing it in a trash receptacle is also dangerous because the trapped gas can cause a sealed garbage bag or dumpster to explode. Depending on the size of the block, full sublimation can take up to 24 hours or longer.