What Is Flash Point
Flash point is the lowest temperature at which a liquid produces enough vapor to ignite when exposed to an ignition source. It's measured in degrees Fahrenheit or Celsius and appears on every Safety Data Sheet (SDS) for flammable and combustible liquids.
This matters because flash point determines how a substance must be stored, transported, and handled. A liquid with a flash point of 100°F behaves very differently from one at 200°F, and OSHA enforces different safety requirements for each. The flash point is not the temperature at which a liquid burns on its own, that's the autoignition temperature, which is always higher.
OSHA Classifications Based on Flash Point
OSHA and the EPA use flash point to classify liquids into specific hazard categories:
- Flammable liquids: Flash point below 100°F (37.8°C). Examples include gasoline, acetone, and mineral spirits. These require Class IB or IC cabinets and strict ventilation.
- Combustible liquids: Flash point between 100°F and 200°F (37.8°C to 93.3°C). Diesel fuel and kerosene fall here. Storage rules are less stringent but still regulated.
- Non-flammable: Flash point above 200°F. Water-based products typically fall here and have minimal restrictions.
Practical Workplace Application
In a manufacturing or maintenance setting, flash point directly impacts your emergency preparedness and safety audit compliance. If you store lacquer thinner (flash point 41°F), you need flame arresters on ventilation, grounding equipment during transfer, and storage at least 35 feet from exits. A material with a flash point of 180°F requires none of these controls.
During a safety audit, inspectors will verify that stored chemicals match their SDS flash point classifications. Improper storage of a high-risk chemical by flash point can result in citations ranging from $10,816 to $161,232 per violation under OSHA standards 1910.106 and 1910.107.
Home Safety Context
Homeowners encounter flash point concerns with paint thinners, turpentine, gasoline storage, and some cleaning products. Storing these materials in an unheated garage where winter temperatures drop below the flash point creates a false sense of safety, but the hazard still exists during warmer months or near heat sources like water heaters and furnaces. A single 5-gallon can of paint thinner stored improperly has caused house fires.
Common Questions
- Does flash point change over time? No. Flash point is a fixed chemical property for a given substance. However, if a liquid evaporates or mixes with other substances, its effective flash point may change, which is why you never combine chemicals without consulting their individual SDS documents.
- Can you store two flammable liquids together if one has a higher flash point? OSHA requires all flammable liquids with flash points below 100°F to be stored in the same approved cabinet, regardless of minor flash point differences. The lowest flash point in the group determines storage requirements.
- Is flash point the same as volatility? No. Flash point is the ignition threshold temperature. Volatility describes how quickly a substance evaporates. Acetone has a low flash point (0°F) and high volatility, while some oils have higher flash points but still evaporate slowly.