A chemical base is a substance that increases the concentration of hydroxide ions when dissolved in water, which is why basic solutions are also called alkaline. Bases are characterized by a pH value greater than 7 and are known as proton acceptors. People often mistakenly assume flammability is the primary hazard of bases, confusing intense chemical reactions with fire. Most common bases cannot ignite or burn, but understanding the exceptions and other dangers is important.
Defining Flammability and Reactivity
Flammability describes a material’s ability to ignite and sustain combustion—a rapid reaction with oxygen that releases heat and light. To be flammable, a substance must possess carbon and hydrogen atoms to serve as fuel. For liquids, the flash point is the lowest temperature at which the liquid produces enough vapor to form an ignitable mixture. The vapor catches fire, not the liquid itself; a lower flash point indicates higher flammability risk.
Flammability is distinct from chemical reactivity, which describes a substance’s tendency to undergo any chemical change. Bases are highly reactive, especially when mixed with acids or water, leading to vigorous, heat-releasing (exothermic) reactions. This heat generation can be mistaken for combustion, but it results from chemical changes like neutralization or dissolution, not burning. A substance can be hazardous due to its reactivity without posing a fire hazard.
The Chemistry of Non-Flammability in Common Bases
The most familiar bases, known as inorganic bases, are non-flammable due to their chemical structure. Compounds like sodium hydroxide or potassium hydroxide are ionic salts, held together by strong electrical attractions, unlike the covalent bonds found in fuels. These inorganic compounds lack the carbon and hydrogen framework necessary to support a sustained combustion reaction.
These compounds are also already in a highly oxidized state, having reacted with oxygen to form hydroxide ions. Since combustion is rapid oxidation, a substance that is already oxidized has no capacity to burn further. Additionally, many industrial bases are sold as aqueous solutions. The large volume of water acts as an effective flame retardant, requiring a sustained heat source to boil off the water before ignition could occur.
The Flammable Exceptions: Organic Bases
The rule that bases are non-flammable has exceptions among organic bases. These compounds contain carbon and hydrogen atoms, making them structurally similar to organic fuels. Organic bases, such as amines like triethylamine or pyridine, contain a nitrogen atom that accepts a proton, qualifying them as bases. Their carbon-hydrogen chains provide the necessary fuel for fire.
Due to their organic structure and high volatility, many organic bases have low flash points and are classified as flammable liquids. For example, triethylamine, used in resin manufacturing, has a flash point of approximately \(-8.9\,^{\circ}\text{C}\) (\(16\,^{\circ}\text{F}\)). Pyridine, a solvent and precursor for agricultural chemicals, has a flash point of about \(20\,^{\circ}\text{C}\) (\(68\,^{\circ}\text{F}\)), posing a fire risk near room temperature. In these cases, the flammability hazard results directly from their organic composition, not their basic nature.
Primary Hazards of Bases
Since fire is not the main hazard, the primary danger associated with strong bases is their intense corrosivity, or causticity. Strong bases cause severe chemical burns by reacting with organic tissue through saponification, the breakdown of fats. This reaction turns the fatty components of skin and cell membranes into soap, allowing the base to penetrate deeper and cause extensive damage.
Alkaline burns are insidious because they may not cause immediate pain, leading to longer exposure and more profound injury before a person realizes contact has occurred. Strong bases also pose a reactivity hazard when mixed with water or acids, instantly releasing a large amount of heat. This exothermic reaction can cause the solution to boil and splatter violently, spreading corrosive material and causing both thermal and chemical burns. Handling strong bases requires specific safety measures, including proper ventilation, gloves, and eye protection, with immediate and prolonged rinsing being the standard first aid for skin contact.