What is the difference between being combustible and flammable?

In industrial safety, understanding the properties of materials is paramount for preventing accidents and ensuring safe handling. Two frequently used terms in this context are “combustible” and “flammable.” These terms are often used interchangeably in everyday language, but they have distinct meanings and implications, particularly in safety and regulatory contexts.

Definitions of combustible and flammable

According to Wikipedia, a combustible material is a material that can burn (i.e., sustain a flame) in the air under certain conditions. A material is flammable if it ignites easily at ambient temperatures. In other words, a combustible material ignites with some effort and a flammable material catches fire immediately on exposure to flame

Combustible materials are those that can catch fire and burn. The term broadly refers to any substance that can undergo combustion, which is a chemical reaction involving oxygen that produces heat and light. Scientifically, combustible materials are defined by their flash points. The flash point is the lowest temperature at which a liquid can form an ignitable mixture in air. For a material to be classified as combustible, its flash point is typically above 60 degrees Celsius (140 degrees Fahrenheit) but below 93.3 degrees Celsius (200 degrees Fahrenheit).

Flammable materials are those that can easily catch fire and burn rapidly. These substances require lower temperatures to ignite compared to combustible materials. Flammable materials are characterized by having flashpoints below 37.8 degrees Celsius (100 degrees Fahrenheit). This lower flash point means that flammable substances can ignite at lower temperatures, making them more hazardous in many situations.

Non-combustible material

A non-combustible material is a substance that does not ignite, burn, support combustion, or release flammable vapors when subject to fire or heat, in the form in which it is used and under conditions anticipated. Any solid substance complying with either of two sets of passing criteria listed in Section 8 of ASTM E 136 when the substance is tested in accordance with the procedure specified in ASTM E 136 is considered to be non-combustible.

Chemical structure influencing flammability and combustibility

The chemical structure of a substance plays a significant role in determining its flammability or combustibility. Molecules with specific functional groups, such as hydrocarbons, are more likely to be flammable or combustible. For example, alkanes, alkenes, and aromatic hydrocarbons are typically flammable due to their ability to easily vaporize and mix with air, creating an ignitable mixture.

The physical state (solid, liquid, gas)

The physical state of a material also influences its flammability and combustibility:

• Solids: Combustible solids, like wood or paper, require sufficient heat to reach their ignition temperature. They generally burn slower compared to liquids and gases.
• Liquids: The volatility of liquids, which is how easily they evaporate, plays a crucial role. Highly volatile liquids, like gasoline, are flammable because they can easily form vapors that ignite.
• Gases: Gases can be highly flammable if they mix with air in the right proportions. Natural gas, propane, and hydrogen are examples of flammable gases.

Examples of common combustible and flammable materials

Some examples of common combustible and flammable materials:

• Combustible solids: Wood, paper, cloth, plastics, coal, charcoal, leaves, wax, rubber, lubricants, oil-based paint, straw, and cleaning solvents
• Combustible liquids: Engine oil, diesel, kerosene, linseed oil, benzaldehyde, and dichlorobenzene
• Flammable materials: Gasoline, ethanol, acetone, natural gas, rubbing alcohol, nail polish remover, hand sanitizer, wart remover, aerosols, mattresses, and dryer lint

Examples of ignition sources, regarding combustible and flammable materials include: 

• Pilot lights
• Stoves
• Welding equipment
• Blow torches
• Soldering irons
• Electric motors
• Bearings
• Pulleys
• Cable breaks
• Arc welding
• Lightning
• Static Electricity
• Cigarettes
• Forklift Forks
• Metal Chain Sparks
• Fasteners, Screws, and Nails
• Metal Tools

Description of combustible dust testing parameters

Combustible dust testing is typically completed following ASTM E1226: Standard Test Method for Explosibility of Dust Clouds and ASTM E1515: Standard Test Method for Minimum Explosible Concentration of Combustible Dusts or other equivalent international test methods.

• Go/No Go Explosion Screening will indicate if the material you or your client are processing is an explosion hazard.
• Maximum Pressure (PMax) and Maximum Rate of Pressure Rise (KSt) are typically used in the design of explosion protection systems such as venting and suppression.
• Explosion prevention parameters such as Minimum Ignition Energy (MIE), Minimum Explosible Concentration (MEC), Minimum Ignition Temperature (MIT), and Limiting Oxygen Concentration (LOC) are used to design safety concepts to prevent explosions from occurring.
• Flammability parameters such as Burn Rate, Layer Ignition Temperature (LIT), Auto Ignition Screening (Grewer), and others characterize the combustion and burning behavior of the material.

Some other tests to determine whether a material is combustible or flammable:

• Flash Point Test: Measures the lowest temperature at which a liquid can form an ignitable mixture in air.
• Autoignition Temperature Test: Determines the temperature at which a substance will spontaneously ignite without an external source of ignition.
• Lower and Upper Explosive Limits (LEL and UEL): These tests measure the concentration range in which a vapor-air mixture is flammable.

ISO/IEC 17025 Certification and accredited laboratories for testing

ISO/IEC 17025 Certification, enables laboratories to demonstrate that they operate competently and generate valid results, thereby promoting confidence in their work both nationally and around the world. This certification also helps facilitate cooperation between laboratories and other bodies by generating wider acceptance of results between countries. Test reports and certificates can be accepted from one country to another without the need for further testing, which, in turn, improves international trade.

International safety standards and classifications

Various organizations provide classifications and standards for flammability and combustibility:

NFPA (National Fire Protection Association): The NFPA is a global nonprofit organization devoted to eliminating death, injury, property, and economic loss due to fire, electrical, and related hazards. One of the key contributions of the NFPA is its classification system for liquids based on their flammability and combustibility.

OSHA (Occupational Safety and Health Administration):  OSHA is a regulatory body in the United States that ensures safe and healthful working conditions by setting and enforcing standards. OSHA’s regulations for flammable and combustible materials are critical for workplace safety.

GHS (Globally Harmonized System of Classification and Labelling of Chemicals): The GHS is an internationally agreed-upon system, created by the United Nations, to standardize and harmonize the classification and labeling of chemicals.

Importance of standards regulatory compliance

These standards are crucial for ensuring safety in industrial and commercial settings. They provide guidelines for testing, handling, storing, and transporting hazardous materials, helping to prevent accidents and ensure compliance with regulatory requirements.

Role in risk assessment and safety planning

Understanding whether a material is combustible or flammable is vital for risk assessment and safety planning. This knowledge helps in:

• Identifying Hazardous Areas: Determining zones where flammable or combustible materials are used or stored.
• Implementing Control Measures: Using appropriate ventilation, temperature control, and ignition source control.
• Emergency Preparedness: Developing response plans for potential fire incidents.

Case studies highlighting accidents

Several industrial accidents underscore the importance of recognizing the differences between combustible and flammable materials:

• Buncefield Oil Depot Explosion (2005): A flammable vapor cloud explosion caused by a gasoline leak led to widespread damage and highlighted the risks associated with flammable liquids.
• Imperial Sugar Refinery Explosion (2008): Combustible sugar dust ignited, causing a catastrophic explosion and fire, demonstrating the dangers of combustible dust in industrial settings.

Best practices for handling materials

• Storage: Store flammable and combustible materials in appropriate containers, away from ignition sources.
• Labeling: Clearly label materials with their flammability or combustibility information.
• Training: Educate employees on the properties of the materials they handle and the associated risks.
• Monitoring: Regularly monitor and maintain equipment to prevent leaks and accidental releases.

Common misconceptions and confusions

• Myth: All flammable materials are highly explosive.
• Fact: While flammable materials can burn rapidly, not all are explosive. Explosion risk depends on the concentration of vapor and air and the presence of an ignition source.
• Myth: Combustible materials are safe to handle without precautions.
• Fact: Combustible materials can still pose significant fire hazards, especially in large quantities or in confined spaces.

Explanation of dangerous misconceptions

Misunderstanding the differences between combustible and flammable materials can lead to improper handling and storage, increasing the risk of accidents. For example, storing flammable liquids near heat sources can result in ignition and fire, while ignoring the risks of combustible dust can lead to catastrophic explosions.

Conclusion

Understanding the differences between combustible and flammable materials is essential for ensuring safety in everyday and industrial contexts. While both types of materials can catch fire, their distinct properties, such as flash points and ease of ignition, necessitate different handling and storage procedures.

Recognizing these differences helps in risk assessment, safety planning, and regulatory compliance, ultimately reducing the likelihood of accidents and enhancing overall safety. As we continue to work with a wide range of materials, ongoing education and adherence to safety practices remain crucial.

About Dust Safety Science

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