Talk about being everywhere – from the gas in your tank to the perfume on your dresser. Flammable liquids are truly ubiquitous in our lives, making them one of the most common hazardous chemicals we encounter daily. Just think about it: gasoline, industrial solvents like toluene, your favorite cosmetics, or even that high-proof liquor at home all fall squarely into this group, posing a hidden fire risk if not handled right.

To ensure everyone's on the same page, the internationally recognized GHS system precisely defines these liquids as having a flash point not exceeding 93°C, meticulously categorizing them into four distinct groups based on their specific flash point and initial boiling point data. Understanding these classifications is absolutely key to safely navigating a world where these potent liquids are constantly present.

Category 4 Flammable Liquids: A Brief Overview

Category 4 flammable liquids are those with closed-cup flash points above 60 °C (140 °F) and at or below 93 °C (199.4 °F). They present a combustible hazard—not the same as more volatile Category 1–3 flammables—and are subject to specific labeling, handling, storage, and regulatory requirements to manage their fire risk safely.

1. Definition and Classification

Under the Globally Harmonized System (GHS) and U.S. OSHA’s HazCom standard (29 CFR 1910.106):

  • Category 4: liquids with flash point > 60 °C (140 °F) and ≤ 93 °C (199.4 °F).
  • Flash points are measured via standard closed-cup methods (e.g., ASTM D93).
Category Flash Point Initial Boiling Point
1< 23 °C (73 °F)≤ 35 °C (95 °F)
2< 23 °C (73 °F)> 35 °C (95 °F)
3≥ 23 °C (73 °F) and ≤ 60 °C (140 °F)-
4> 60 °C (140 °F) and ≤ 93 °C (199.4 °F)-

Note: Liquids with flash points above 93 °C are not classified as flammable under GHS.

Examples of Category 4 liquids include diesel fuel, fuel oils with moderate flash points, and some lubricating oils.

2. Labelling Requirements

  • Signal word: Warning
  • Pictogram: Not required for Category 4
  • Hazard statement: “Combustible liquid” (H227)
  • Precautionary statements: Keep away from heat, sparks, open flames, and hot surfaces.

3. Hazards and Controls

Category 4 liquids generate combustible vapors near their flash points. When heated within 16.7 °C (30 °F) of their flash point, they must be handled like Category 3 flammables.

Engineering Controls and PPE

  • Use general/local exhaust ventilation to keep vapor below 25% of the LFL.
  • Closed transfer systems, grounding and bonding.
  • Store in NFPA 30-rated fire-resistant cabinets or rooms.
  • Wear flame-resistant lab coats, chemical-resistant gloves, and safety goggles or face shields.

4. Storage Requirements

4.1 OSHA 29 CFR 1910.106 (General Industry)

  • Incidental storage: up to 120 gal per fire area.
  • Portable tanks (≤ 660 gal): max 120 gal per tank.
  • Cabinets: max 120 gal per cabinet; max 3 cabinets per fire area without fire suppression.
  • Inside storage rooms must follow NFPA 30 standards.

4.2 NFPA 30 (Combustible Liquids Code)

  • One cabinet may contain up to 120 gal of Class IIIB (GHS Cat 4).
  • Separate from oxidizers by 25 ft or fire-rated partition.

5. Handling Practices

  • Minimize heating near flash point; apply Category 3 controls if within 30 °F.
  • Use spark-proof equipment and wiring.
  • Transfer via closed systems, self-closing valves, or approved cans.
  • No compressed air transfers.
  • Clean spills immediately. Store containers closed and upright.
  • Post “No Smoking” signage. Prohibit ignition sources nearby.

6. Regulatory Context

  • OSHA HazCom: aligns with GHS for flammables ≤ 93 °C.
  • DOT (49 CFR 173.120): defines liquids < 60 °C flash point as flammable; Category 4 as “combustible.”
  • EU CLP: does not adopt GHS Category 4. Liquids > 60 °C flash point not classified as flammable.

7. Summary of Key Limits

Requirement Category 4 Liquids
Flash point range> 60 °C and ≤ 93 °C
Label hazard statement“Combustible liquid”
Signal wordWarning
Max in storage cabinet120 gal
Incidental storage (outside)120 gal per fire area
Portable tank limit120 gal per portable tank (≤ 660 gal capacity)
Separation from oxidizers≥ 25 ft or fire-rated partition

Conclusion

Effectively minimizing fire risks hinges on understanding the characteristics and regulatory framework of Category 4 flammable liquids. Implementing the following is imperative:

  • Proper labeling
  • Controlled storage environments
  • Robust ventilation systems
  • Strict adherence to safe handling protocols

Substances like diesel and lubricating oils, when exposed to elevated temperatures, pose significant risks. Strict compliance not only meets regulations but also ensures workplace safety—preventing catastrophic fires and explosions.