Light My Fire: Ranking Flammable Liquids

Posted on 2/13/2023 by Lion Technology Inc.

US DOT and OSHA each impose regulations that apply to flammable and/or combustible liquids. But the two agencies "regulate" these liquids differently, and for different reasons. Each views the hazards and risks of flammable liquids through the lens of a specialized mandate from Congress—OSHA to protect workers in the workplace.and US DOT to ensure safe transportation of hazardous materials (among other goals). 

In the business of moving goods from one place to another, these two mandates overlap. You can see how OSHA and DOT categorize flammable liquids below. When you recognize the similarities and consider each agency’s regulatory goals, you can limit confusion about what rules apply to your activities or materials at any moment.

OSHA and US DOT both use flash point and boiling point to “rank” regulated flammable liquids.

Flash point is the lowest temperature at which an ignition source near the liquid “flashes” back and ignites the vapors. You can see details about how a flash point test works here.

Boiling point is what it sounds like; the temperature at which a liquid starts boiling. To be more specific, boiling point is the temperature at which the vapor pressure of the liquid equals the atmospheric pressure—in other words, when the liquid starts to turn to vapor of fumes.* 

Light My Fire: Ranking Flammable Liquids

OSHA Hazard Communication for Flammable Liquids 

OSHA groups flammable liquids into four categories, with criteria laid out in Appendix B to the Hazard Communication Standard or HCS (29 CFR 1910.1200). 

The HCS exists to make sure that employees are informed and trained about the hazards of chemicals in their workplace. OSHA's categories for flammable liquids make employers and workers aware of the severity of the hazard, so that they can take appropriate steps to limit the risk of handling and working around the material.  

Table B.6.1 - Criteria for Flammable Liquids (29 CFR 1910.1200, Appendix B)

Category Criteria
Flash point < 23°C (73.4°F), 
Initial boiling point ≤ 35°C (95°F).

Flash point < 23°C (73.4°F), 
Initial boiling point > 35°C (95°F).
Flash point ≥ 23°C (73.4°F) and ≤ 60°C (140°F).
Flash point > 60°C (140°F) and ≤ 93°C (200°F)

* The ASTM test method for boiling point that OSHA approves in the HCS utilizes a distillation unit to slowly heat a liquid. The initial boiling point is the temperature at which the first drop of condensate is obtained rising off of the liquid.

US DOT Hazardous Materials Regulations for Flammable Liquids

While OSHA is concerned with flammable liquids in the workplace, US DOT's mandate—through its sub-agency the Pipeline and Hazardous Materials Safety Administration (PHMSA)—kicks in when those materials enter the cycle of transportation. The categories of flammable liquids in the Hazardous Materials Regulations (HMR), called "packing groups," are used by shippers to determine the type and strength of packaging needed to contain the material. 

When a material has more than one hazard, the packing group ("PG" for short) sometimes contributes to the material's "ranking" against other hazmat when determining precedence of hazard.  

DOT/PHMSA Packing Group Assignments for Flammable Liquids (49 CFR 173.121) 

Category Criteria
Initial boiling point ≤ 35°C (95°F);
Flash point < 23°C (73.4°F)
Initial boiling point > 35°C (95°F)

Flash point ≥ 23°C, ≤ 60°C (≥ 73°F, ≤ 140°F)
Initial boiling point > 35°C (95°F)
"Combustible"         Flash point ≥ 60°C, ≤ 93°C (≥ 140°F, ≤ 199.4°F)

The criteria for categories 1 through 3 are essentially identical in OSHA and DOT. regulations. DOT rounds 93° Celsius to "200°F" in its fourth category, while OSHA uses the more exact 199.4°F. That fourth category, which OSHA considers "Category 4" can be classed as "combustible liquids" in transportation (under certain conditions), qualifying for some reliefs from the HMR. (More: 3 Combustibles Shipping Examples).

Upcoming DOT Hazmat Training in Dallas, Houston, Chicago, and...

Join Lion for engaging, lively in-person training and develop the expertise you need to classify and name hazardous materials, package hazmat, mark and label packages, fill out shipping papers, and comply with DOT security plan and security training requirements for hazmat employees.  

Hazmat Ground Shipper Certification (DOT) Workshop

Dallas, TX March 2–3
Houston, TX March 20–21
Chicago, IL April 20–21
Cincinnati, OH         April 26–27
St. Louis, MO May 3–4
Ontario, CA May 10–11
San Diego, CA May 17–18        

The 2023 Training Schedule of hazmat shipper workshops and webinars is available now.

Find a Post

Compliance Archives

Lion - Quotes

We have a very busy work schedule and using Lion enables us to take the course at our own time. It makes it easy for me to schedule my employees' training.

Timothy Mertes

Hazmat Shipping Professional

Well designed and thorough program. Excellent summary of requirements with references. Inclusion of regulations in hard copy form, as well as full electronic with state pertinent regulations included is a great bonus!

Oscar Fisher

EHS Manager

I had a positive experience utilizing this educational program. It was very informative, convenient, and rewarding from a career perspective.

John Gratacos

Logistics Manager

The instructor clearly enjoys his job and transmits that enthusiasm. He made a dry subject very interesting and fun.

Teresa Arellanes

EHS Manager

The training was impressive. I am not a fan of online training but this was put together very well. I would recommend Lion to others.

Donnie James

Quality Manager

The instructor was very very informative, helpful, understandable and pleasant. This course answered many questions I had, being new to this industry.

Frances Mona

Shipping Manager

I like Lion's workshops the best because they really dig into the information you need to have when you leave the workshop.

Tom Bush, Jr.

EHS Manager

Amazing instructor; real-life examples. Lion training gets better every year!

Frank Papandrea

Environmental Manager

The instructor was very knowledgeable and provided pertinent information above and beyond the questions that were asked.

Johnny Barton

Logistics Coordinator

My experience with Lion classes has always been good. Lion Technology always covers the EPA requirements I must follow.

Steven Erlandson

Environmental Coordinator

Download Our Latest Whitepaper

In most cases, injuries that occur at work are work-related and must be recorded to maintain compliance with OSHA regulations. This report shows you the 9 types of injuries you don’t record.

Latest Whitepaper

By submitting your phone number, you agree to receive recurring marketing and training text messages. Consent to receive text messages is not required for any purchases. Text STOP at any time to cancel. Message and data rates may apply. View our Terms & Conditions and Privacy Policy.