Understanding the Four Categories of Flammable Liquids (OSHA 1910.106)
Knowing how to handle flammable liquids is critical. The Occupational Safety and Health Administration (OSHA) has clear guidelines in 29 CFR 1910.106 that classify flammable liquids into four categories based on their physical properties. Understanding these categories helps reduce fire hazards and keeps employees safe.
What Is a Flammable Liquid?
According to OSHA, a flammable liquid is any liquid having a flash point at or below 199.4°F (93°C).
🔥 Flash point is the lowest temperature at which a liquid gives off enough vapor to ignite in air. So, just because a liquid is in a closed container and looks harmless doesn’t mean it’s safe. If its vapors can catch fire under normal working conditions, it's flammable.
What are the 4 Categories of Flammable Liquids?
OSHA classifies flammable liquids into Categories 1 through 4.
These categories are based on the liquid’s flash point and boiling point.
🔹 Category 1:
Flashpoint: Below 73.4°F (23°C)
Boiling point: ≤ 95°F (35°C)
Examples: Diethyl ether, some gasoline blends
This type ignites easily even at room temperature. They also evaporate quickly, creating dangerous vapor clouds.
🔹 Category 2:
Flashpoint: Below 73.4°F (23°C)
Boiling point: Above 95°F (35°C)
Examples: Acetone, Toluene
Still very dangerous - these vapors can travel and ignite at a distance.
🔹 Category 3:
Flashpoint: Between 73.4°F (23°C) and 140°F (60°C)
Examples: Paint thinners, mineral spirits
Common in many workplaces, these liquids may not ignite as easily but still pose a significant risk.
🔹 Category 4: Combustible (Still Considered Flammable by OSHA)
Flashpoint: Between 140°F (60°C) and 199.4°F (93°C)
Examples: Diesel fuel, motor oil
Often overlooked, but these can still ignite under the right conditions.
OSHA Flammable Liquid Categories (29 CFR 1910.106)
How To Store and Handle Flammable Liquids
Under 1910.106(d), OSHA provides strict rules about storing flammable liquids:
Use approved containers (e.g., safety cans) clearly labeled with the liquid name and hazard.
Limit quantities in work areas - typically no more than 25 gallons of Category 1 liquids outside of a storage cabinet.
Store in flammable liquid cabinets that are fire-resistant and labeled "Flammable - Keep Fire Away."
Ground and bond containers when transferring flammable liquids to prevent static sparks.
Key Safety Tips for Flammable Liquids
Ventilation matters: Vapors can travel and find ignition sources far away.
No open flames or sparks: Especially near Categories 1 & 2.
Personal Protective Equipment (PPE): Chemical-resistant gloves, goggles (and face shield if there is the possibility for a splash), and a chemical-resistant apron
Employee training: Workers must understand labeling, handling, and emergency response.
Bottom Line
Flammable liquids are everywhere, and OSHA’s four-category system helps you evaluate and control the risks. Understanding these categories isn’t just about compliance; it’s about preventing injuries, fires, and even explosions. If your facility uses or stores flammable liquids, a proper safety program, employee training, and routine inspections go a long way in protecting people and property.
Need Help complying with OSHA’s flammable liquids regulation?
This blog was written by Brandy Zadoorian, CSP, and Triangle Safety Consulting LLC's Owner and Principal Consultant.
She offers audits, expertise, resources, and guidance to help manufacturing facilities improve compliance with OSHA Requirements, minimize injuries and illnesses, and reduce risk!
She is a Certified Safety Professional (CSP) under the Board of Certified Safety Professionals.
