Rubbing alcohol is a common household product primarily used as a topical antiseptic and disinfectant. It is typically a mixture of Isopropyl Alcohol (IPA), or isopropanol, and water, most often sold in a 70% concentration. Burning this substance is highly inadvisable and poses significant dangers to health and property safety, especially indoors. The risks stem from its chemical makeup, which promotes incomplete combustion, producing toxic byproducts and creating an extreme fire hazard due to its low ignition temperature.
The Chemical Composition and Combustion Profile
Rubbing alcohol is a solution containing Isopropyl Alcohol (IPA). The most common variety is 70% IPA, meaning 30% of the liquid is water. This substantial water content makes burning rubbing alcohol inefficient and dangerous, as the water absorbs heat and interferes with the combustion process.
When fuel burns, it ideally undergoes complete combustion, reacting with oxygen to produce only carbon dioxide and water vapor. However, the water in rubbing alcohol cools the flame, preventing the fuel from reaching the high temperatures necessary for a clean burn. This cooling results in incomplete combustion, which breaks the alcohol’s carbon chain down into hazardous compounds.
This incomplete process yields a sooty, less energetic flame unsuitable for clean heat or light. The remaining carbon atoms are not fully oxidized, instead forming particulate matter and other carbon-containing gases. This chemical profile is the root cause of the inhalation dangers.
Inhalation Dangers from Toxic Byproducts
The primary health risk of burning rubbing alcohol is the inhalation of toxic gases and fine particles released during incomplete combustion. The cooled flame generates a significant amount of Carbon Monoxide (\(\text{CO}\)). This colorless, odorless gas is dangerous because it binds to hemoglobin in the bloodstream, displacing oxygen and leading to Carbon Monoxide poisoning, which can cause confusion, loss of coordination, and death.
Another significant byproduct is formaldehyde, a volatile organic compound (VOC). Formaldehyde is a known irritant that can trigger respiratory issues, eye irritation, and headaches even at low concentrations. Exposure to its fumes can exacerbate conditions like asthma and contribute to serious long-term health concerns.
The incomplete burn also creates soot, which is fine black carbon particulate matter. These tiny particles can penetrate deep into the lungs, causing irritation and inflammation of the respiratory system. Inhaling this soot contributes to chronic lung conditions, especially if burning is attempted indoors without proper ventilation.
Physical Hazards: Flashpoint and Vapor Risk
Beyond the toxic fumes, the physical properties of isopropyl alcohol create an extreme fire and explosion risk. The flashpoint is the lowest temperature at which a liquid produces enough flammable vapor to ignite. Rubbing alcohol has an extremely low flashpoint; for 70% IPA, this temperature can be as low as \(18.3^{\circ}\text{C}\) (\(64.9^{\circ}\text{F}\)).
This means rubbing alcohol generates flammable vapor even at typical room temperatures, making it a constant fire risk. The vapor is heavier than air, allowing it to travel along floors and surfaces away from the liquid source. If this invisible vapor trail reaches an open flame or spark, it can instantly ignite and cause a rapid flashback to the container, resulting in a dangerous flash fire or explosion.
The risk of “flame jetting” is present when attempting to refuel a container that is still hot or burning. Adding a low flashpoint liquid to a warm container instantly vaporizes the liquid, creating a sudden, uncontrolled burst of flame. This hazard requires all flammable liquids, including rubbing alcohol, to be stored away from heat and handled with extreme caution in approved, sealed containers.
Safer Alternatives for Fuel and Heat
For applications requiring a clean-burning fuel, consumers should select products specifically engineered for that purpose rather than relying on rubbing alcohol. Safer alternatives minimize both the physical fire hazard and the risk of inhaling noxious fumes.
The most widely recommended alternatives include:
- Denatured alcohol, often sold as methylated spirits. This fuel is predominantly ethanol, which burns much cleaner than isopropyl alcohol, producing fewer toxic compounds and minimal soot.
- Specialized camp fuel or lamp oil, which are formulated for safe and efficient combustion in approved devices. These fuels are designed to burn steadily and cleanly, reducing the risk of incomplete combustion byproducts like carbon monoxide and formaldehyde.
- High-proof grain alcohol, such as 190-proof ethanol, which can also be used and burns cleanly, though it is often more costly.
When using any flammable liquid for heat or light, ensure the device is purpose-built for that fuel type. All burning should take place in a well-ventilated area to prevent the accumulation of combustion byproducts.