Will Alcohol Left in a Car Spontaneously Combust?
4 Answers
Alcohol left in a car can spontaneously combust. Take the commonly used 75% medical alcohol as an example, its ignition point is 20 degrees Celsius. During summer, the outdoor temperature at noon can reach over 40 degrees Celsius. If a car is parked outside under the sun for a period of time, the temperature inside the car can rise to more than 50 degrees Celsius, which can easily trigger spontaneous combustion and explosion of alcohol. Here are some precautions regarding the storage of alcohol: Storage: It is best not to leave alcohol in the car. If disinfection is needed, you can find an open area to wipe the car interior with alcohol for disinfection, while ensuring proper ventilation inside the car for some time. Flammable and explosive items: Besides disinfectant alcohol, perfumes containing alcohol can also spontaneously combust when reaching a certain ignition point. Therefore, flammable and explosive items should not be stored in the car.
Having driven for twenty years, I believe keeping alcohol in the car poses significant risks. Although alcohol has a high auto-ignition point, and summer car temperatures only reach around 60-70°C—far below what's needed for spontaneous combustion—alcohol is highly volatile. If the bottle isn't tightly sealed, the gas can accumulate inside the car. In this scenario, encountering an electrostatic spark—like the one that jumps when plugging or unplugging a charger—can be dangerous. A colleague at my auto repair shop mentioned that alcohol vapor can also corrode plastic components and wiring in the car. It's advisable not to store alcohol bottles on the dashboard or door pockets where they're exposed to direct sunlight; instead, keep them in a sealed container in the trunk. If spilled, immediately open the windows for ventilation and clean it up thoroughly.
As a mom who shuttles kids every day, I pay special attention to in-car safety. Alcohol itself requires extremely high temperatures to spontaneously combust, which even the hottest car interior can't reach. However, during summer, the car interior can become a high-temperature enclosed space. When the concentration of evaporated alcohol gas reaches above 3%, it may explode upon contact with sparks from the cigarette lighter or charger. Last time in the parent group chat, I saw someone left an alcohol spray on the passenger seat, and the bottle burst under sunlight exposure. I've now switched to small sealed alcohol swabs and make sure to take them out after use. It's safer to keep anti-static wipes in the car at all times—after all, children's safety is not something to be careless about.
Last time, bringing alcohol to work almost caused trouble. Although the online rumors about spontaneous combustion are false—alcohol requires over 400 degrees to ignite on its own, and my tests showed the highest temperature inside a car after three hours of direct sunlight was 78 degrees—the real danger lies in the evaporating fumes. My alcohol bottle leaked due to bumps, and I smelled a strong odor when opening the car door. When the concentration exceeds safe levels, even the electrical sparks from the air conditioning fan motor could ignite it. Now, if I must bring alcohol, I limit it to two hours in the trunk, using a lab-grade sealed bottle wrapped in an insulated bag. Leaving the windows slightly open for ventilation is also crucial to prevent gas buildup.
