Petroleum ether is an extremely flammable liquid, classified as a highly dangerous fire risk due to its physical properties. This solvent is widely used in laboratories and industry as a non-polar solvent for extraction and chromatography applications. Despite its name, petroleum ether is not a true ether, meaning it does not contain the oxygen atom bonded to two carbon groups characteristic of compounds like diethyl ether. Serious consideration must be given to its handling and storage due to its high flammability.
Chemical Identity and Volatility
The solvent is a mixture of light, saturated aliphatic hydrocarbons, primarily consisting of pentane and hexane fractions. It is a distillate of petroleum, often known by other names like petroleum spirits or benzine. The specific components determine the product’s boiling range, which can vary from 30–60°C to 90°C or higher, depending on the grade. Petroleum ether’s high volatility is the main source of its fire risk, driven by its low boiling point range. This low boiling point causes the liquid to evaporate rapidly, releasing large volumes of hydrocarbon vapor into the surrounding air, which is what ignites.
Defining the Specific Flammability Hazard
The degree of flammability is quantified by several metrics that place petroleum ether in the highest hazard category. Its flash point (FP) is the lowest temperature at which it produces enough vapor to form an ignitable mixture with air, often ranging from -50°C to -18°C. This extremely low flash point classifies it as a Class IA or IB flammable liquid, meaning it presents a severe fire risk at ordinary room temperatures. Its physical properties mandate that it receives a flammability rating of 4, the highest possible, under standards like NFPA 704.
The risk is amplified by its flammability limits, known as the Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL). The LEL is the minimum concentration of vapor in air required for ignition, typically around 1.1%, while the UEL is the maximum concentration, often near 5.9% to 8.3%. This relatively wide explosive range means a small amount of vapor release can quickly create a flammable atmosphere easily ignited by a spark or flame. The autoignition temperature, the minimum temperature required to ignite the vapor without an external spark, is relatively high, usually between 240°C and 288°C, but can still be reached by hot surfaces in a laboratory setting.
Safe Handling and Storage Protocols
Controlling the vapor is the primary focus of safe handling protocols to prevent fire hazards. Mandatory ventilation, particularly the use of a certified chemical fume hood, is required when working with petroleum ether to keep vapor concentrations below the LEL. All sources of ignition must be strictly eliminated from the work area, including open flames, sparks from electrical equipment, and static discharge.
Static electricity is a significant ignition source because the liquid is a poor electrical conductor, allowing static charges to build up rapidly during transfer or pouring. To counteract this, grounding and bonding procedures are necessary, involving physically connecting the dispensing and receiving containers with a conductive wire before and during liquid transfer. Containers must be kept tightly closed when not in use and stored in a cool, dry, well-ventilated area specifically designated for flammable liquids.
Emergency Response to Petroleum Ether Fires
In the event of a petroleum ether fire, the correct choice of extinguishing agent is paramount because water is largely ineffective and potentially dangerous. Since the solvent is less dense than water and insoluble, applying a water stream can cause the burning liquid to float and spread the fire. The recommended extinguishing agents work by smothering the fire, cutting off the oxygen supply, and include carbon dioxide (CO2) extinguishers, dry chemical powder extinguishers, or alcohol-resistant foam. Firefighters must wear full protective gear and self-contained breathing apparatus due to the toxic fumes produced by the combustion of petroleum products.