Acetic acid, also known as ethanoic acid, is a simple organic compound. It is widely recognized as the substance that gives vinegar its sour taste and pungent odor. While the dilute form is a common household item, concentrated acetic acid is a major industrial chemical used in the production of plastics, pharmaceuticals, and various organic compounds. The direct answer to whether acetic acid is flammable is yes, but this hazard primarily applies to its high-concentration form at or above a specific temperature.
How Concentration Affects Ignition Risk
The risk of fire from acetic acid is almost entirely dependent on its concentration in water. Household vinegar typically contains only about 5% acetic acid, with the remaining 95% being water. This high water content effectively suppresses the production of flammable vapor and absorbs any heat, rendering dilute vinegar generally non-combustible under normal conditions.
Industrial-grade acetic acid, often referred to as “glacial acetic acid,” is nearly 100% pure. In this highly concentrated state, the substance is both corrosive and combustible. The concentrated acid can produce sufficient vapor at modestly elevated temperatures, presenting a genuine fire hazard that necessitates strict handling protocols.
Essential Ignition Metrics
Technical measurements exist to quantify the fire risk of concentrated acetic acid, which is crucial for safety management. The most important of these is the flash point, the lowest temperature at which a liquid produces enough vapor to ignite momentarily when an ignition source is present. Glacial acetic acid has a flash point typically reported around 39°C to 40°C (102°F to 104°F). This temperature is only slightly above standard room temperature, confirming that the concentrated acid poses a fire risk even without significant external heating.
For a fire or explosion to occur, the vapor concentration in the air must fall within a specific range, defined by the explosive limits. The Lower Explosive Limit (LEL) for acetic acid vapor is approximately 4.0% by volume in air. Below this concentration, the mixture is too lean to burn. The Upper Explosive Limit (UEL) is around 16.0% to 19.9% by volume. Above this concentration, the mixture is too rich in fuel and lacks the necessary oxygen for combustion.
Safety Protocols and Fire Response
Handling high-concentration acetic acid requires specific safety measures to mitigate both its corrosive and combustible properties.
Storage and Handling
Storage areas must be cool, dry, and well-ventilated to prevent the accumulation of flammable vapors. Containers should be tightly sealed and kept away from all ignition sources, including sparks and open flames. It is also important to separate acetic acid from incompatible materials, particularly strong oxidizers, as contact can cause a violent reaction and fire.
In the event of a spill of concentrated acid, ventilation must be maximized, and all ignition sources must be eliminated from the vicinity. The material should be contained and absorbed using non-combustible materials like dry earth or sand. Spills must be prevented from entering drains or sewers, as the material can cause environmental damage and vapor accumulation in confined spaces.
Fire Suppression
For fire suppression, appropriate extinguishing agents are required. The fire response team must avoid using a straight stream of water, which can spread the fire or cause the corrosive acid to splatter. Water fog or spray is acceptable, and it can be used safely to cool containers exposed to the fire to prevent a pressure rupture. All equipment used during cleanup and fire response should be non-sparking to avoid igniting any residual vapor.
- Dry chemical
- Carbon dioxide (CO2)
- Water spray
- Alcohol-resistant foam