What is the difference between flammable and combustible

What is the difference between flammable and combustible? Both flammable and combustible substances can catch fire easily. These two substances differ from each other based on the flash point range to which they must be exposed to catch fire. The flash point is the lowest temperature at which the material given off flammable vapours could ignite when mixed with air to form a flammable mixture.

Many workplaces use flammable and combustible liquids, and to keep the workplace safe and manage risks effectively, the difference between flammable and combustible must be understood.

This blog (muniriyathse) discusses the main difference between flammable and combustible substances, including their flash points. We will explain the risks and show how these substances should be handled and stored to ensure a safe and compliant work environment.

Key point what is the difference between flammable and combustible?

Flammable materials ignite easily and burn quickly, while combustible materials require more heat to ignite and burn more slowly. Flammable liquids have a flash point less than 100°F (37.8°C), while combustible liquids have a flash point equal to or greater than 100°F (37.8°C).

Flashpoints of liquids Flash point
Petrol gasoline*	-43 ºC	Diesel fuel*	52 ºC to 82 ºC
Ethanol	16.6 ºC	Phenol	79 ºC
Acetone	-20 ºC	Kerosene*	38 ºC -72 ºC
Methanol	12 ºC	Formaldehyde	64 ºC
Propylene oxide	-37 ºC	Hydrazine	52 ºC
Ethyl chloride	-50 ºC	Paint thinner*	40 ºC
Benzene	-11 ºC	Naphthalene	78.89 ºC

In addition, some materials become spontaneously inflamed and can release flammable or toxic gases when they come into contact with humid air or water called pyrophoric. This is the case of Calcium Carbide, Magnesium Powders and Sodium Hydride.

The volatility of the material is an important factor that determines the level of combustibility of the air. This depends on its vapour pressure, and this vapour pressure is related to temperature.

If the surface area of the material increases, the amount of vapour also increases, forming a fog. For example, a small piece of paper catches fire easily, while an oak desk made of wood-like paper is more difficult to burn or ignite.

Proper storage and handling of flammable, combustible and pyrophoric materials is essential to preventing fires and ensuring safety in various environments.

Flammable vs. Combustible: Why You Need to Know the Difference

Once started, a fire can devastate a building in a matter of minutes, destroying material, damaging facilities beyond repair, and claiming lives. To stay safe, business owners should know the properties of all materials or liquids in their facility that could start or accelerate a fire.

Some materials are more easily flammable than others. This makes them more dangerous to work with. It also presents challenges in storing them safely. Developing effective fire safety procedures means knowing the difference between flammable and combustible materials and liquids.

Flammable and combustible liquids are primarily regulated at the federal level by OSHA under 29 CFR 1910.106 (general industry) and 29 CFR1926.152 (construction).

Additionally, the National Fire Protection Association (NFPA) establishes consensus codes and standards for flammable and combustible liquids under NFPA 30: Flammable and Combustible Liquids, which are generally enforceable under OSHA and many state and local regulations.

It is important to note that both flammable and combustible materials can pose a fire and explosion hazard. It is important to handle these materials with care and to take precautions to prevent fires.

Here is a table that summarizes the key differences between flammable and combustible materials:

Feature	Flammable	Combustible
Flash point	Below 100°F (37.8°C)	100°F (37.8°C) to 200°F (93.3°C)
Ignition	Easily ignites at low temperatures	Requires more heat or an ignition source to burn
Examples	Gasoline, alcohol, propane	Wood, paper, cloth
Definition	Flammable materials are those that can easily ignite and burn at relatively low temperatures.	Combustible materials are those that can burn, but they require more heat or an ignition source to do so.
classification	There are three classes of flammable liquids: IA (ligroin, diethyl ether, and pentane), IB (benzene, ethanol, acetone, and cyclohexane) and IC (p-xylene).	There are three classes of combustible liquids: II (engine oil, diesel fuel, cleaning solvents, kerosene), III-A (oil-based paints, mineral oil, linseed oil), and III-B (doughnut oil, oil-based paints).

Flammable

Flammable substances ignite and continue to burn in contact with any ignition source.  Most flammable liquids are volatile. They evaporate and give off vapour at lower temperatures that mix with nearby air to form a flammable mixture.

Factors such as flash point, flammability limits, and autoignition temperature determine the flammability of a material. Vapours that mix with air in adequate quantities in the presence of an ignition source can cause an explosion.

The proper amount is called the flammable range or explosive range. The lowest quantity of flammable mixer which is capable of flash of fire is called lower explosive limit (LEL). The explosive or flammable range includes any concentration of flammable gas or vapor in the air in which a flame will travel or a flash of fire will occur if the mixture can catch fire.

Plants that use, store, or display flammable substances are more likely to experience hazards than other plants. Flammable substances will be stored away from stairs, exits and public areas. It will be stored in closed containers or tanks. Flammable liquids should be stored safely with appropriate fire control devices such as portable fire extinguishers or small hoses.

Combustible

Combustible substances are substances that can easily burn or ignite in the air in contact with any ignition source. Combustible substances have a flash point of one hundred degrees Fahrenheit or higher.

In a workplace, Combustible liquids are of particular concern. Examples: Fuel Oils, Fuel, Diesel, Solvents, and Pyrophoric Liquid. It is also the material that ignites spontaneously in dry or humid air at or below 54 ºC. This is the case with Aluminum Alkyl and thorium Nitrate.

Combustible substances need three main conditions to burn or ignite: a combustible substance, a supporting substance for combustion and reaching the ignition temperature.

NFPA 30 flammable and combustible liquid code

The National Fire Protection Association (NFPA 30) defines the classes of flammable and combustible liquids

Combustible/flammable liquid classification by flash point according to NFPA
Class of liquid	Combustible	Class of liquid	Flammable
Class II	≥ 100°F (37.8 °C)	Class IA	< 100°F (37.8 °C)
Class III A	140°F (60 °C)	Class IB	≤ 100°F (37.8 °C)
Class III B	200°F (93 °C)	Class IC	73°F (22 °C)

Combustible/flammable liquid classification OSHA

The NFPA and OSHA differ in how they classify flammable liquids. In 2015, OSHA adopted the Globally Harmonized System (GHS) for the classification and labelling of chemicals. This change removed the term combustible from OSHA standard 29 CFR 1910.106. Thus, all liquids with a flashpoint lower than 199.4 F (93 C) are flammable.

Flammable liquid classification by flash point according to OSHA
Category 1	73°F (23 °C) and boiling point < 95°F (35 °C)
Category 2	73°F (23 °C) and boiling point >95°F (35 °C)
Category 3	>73°F (23 °C) and < 140°F (60 °C)
Category 4	>140°F (60 °C) and < 199.4°F (93 °C)

Which of the following is the best place to store flammable and combustible liquids

Whenever you work with flammable or combustible liquids, there is a risk of fire. Proper storage and handling is the first step in reducing those risks. Always use approved safety storage cabinets that meet OSHA and NFPA design and construction requirements. Look for cabinets certified by independent third-party testing agencies, such as FM Approvals, or UL. Here are some other things to keep in mind when storing flammable and combustible liquids:

• Keep it separate: Never store incompatible liquids near each other. This also means storing certain chemical groups away from other chemical groups, such as oxidizing and flammable. Justrite supplies shelf dividers to help organize chemicals within a safety cabinet.
• Ensure adequate ventilation: The vapours are invisible and denser than air. They can easily ignite in poorly ventilated areas, even at room temperature. All Justrite cabinets include dual vents with built-in flame arresters with plugs. While NFPA 30 does not require vented safety cabinets, it does state that the vent opening must be left sealed with the supplied plugs if the cabinet is not vented.
• Reduce the amount of materials your workplace contains: Your workplace should only contain the bare minimum necessary to keep the business running. Do not overstock, as this can worsen the consequences of an accident.
• Control the temperature of storage facilities: If you control the temperature of the area to limit vapours, be sure to monitor it closely. Note: If you vent the cabinet, consult your local fire marshal and/or code official to ensure local codes are met, and a professional engineer or EHS official to ensure fire resistance is not compromised.

Some general rules regarding flammable or combustible materials storage are:

• Don't store them near exits.
• Do not store them in direct sunlight, near electrical panels and heal sources.
• Keep flammable or combustible materials away from incompatible substances.
• Store them in sealed and labelled containers, preferably those supplied by the manufacturer.
• Store only the minimum required amount of flammable or combustible materials.
• Use personal protective equipment (PPE) when using flammable or combustible materials.
• Develop safe work procedures and ensure everyone follows them.
• Periodically carry out risk assessments.
• Provide employees with appropriate fire safety training.
• Keep the safety data sheet and NNFPA 704 diamond near a storage area.

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Conclusion

Flammable and combustible materials pose significant fire and explosion hazards, making proper handling and storage crucial for safety. Here's a summary of key safety measures:

• Identification and Classification: Understand the flashpoints of flammable and combustible materials.
• Handling and Storage: Store flammable and combustible materials in approved containers, such as safety cans or properly labelled cabinets. Avoid open flames, sparks, and electrical sources near flammable and combustible materials. Ground and bond all equipment to prevent static electricity buildup. Use appropriate personal protective equipment (PPE), such as gloves, goggles, and respiratory protection, when handling flammable and combustible materials.
• Ventilation: Use well-ventilated areas when handling flammable and combustible materials.
• Use fume hoods or other ventilation systems to remove flammable vapours from the work area.
• Spill Response: Have spill kits readily available. Contain spills immediately and prevent them from entering drains or waterways. Clean up spills promptly and properly dispose of contaminated materials.
• Emergency Procedures:
• Know the emergency contact number, assembly point and evacuation routes. Familiarize yourself with fire extinguisher operation and use the appropriate extinguisher for flammable and combustible material fires. Evacuate the area immediately in case of a fire or explosion.