What is Hazardous Material?

Which code or standard applies to hazardous materials? How much of a particular hazardous material can be stored or used? What floor of the building can that hazardous material be stored or used on? These are all questions some are faced with daily. There is an assumption that people, such as facility managers, building owners, engineers, and first responders, just inherently know when a material is a hazardous material. And, that once they know it is a hazardous material, they know how to deal with that material properly and safely. We have seen the potential impacts of materials that are improperly stored or used such as in the 2013 fire and explosion at West Fertilizer Company in Texas. How can we prevent incidents like this from happening? The first step is knowing how to identify a hazardous material.

Part of the challenge when it comes to determining and classifying hazardous materials is that there is not one consistent definition of “hazardous material” nor is there one consistent approach to the classification of hazardous materials. Therefore, when looking at Safety Data Sheets (SDS) or literature provided by the manufacturer, it is imperative to know and understand which hazardous material classification system is being used. NFPA 400, Hazardous Materials Code, has its own definition and classification method that consists of 14 different categories. The U.S. DOT uses a 9-category classification system. OSHA has its own definitions established in 29 CFR, which has been revised to align with the Globally Harmonized System of Classification and Labelling of Chemicals (GHS).  While there has been an effort to coordinate between the groups, differences do still exist. Information on SDS is often based on the GHS system and not the system in NFPA 400.

Defining Hazardous Material

The approach I like to take is to assume materials are hazardous, until I have proven that a particular material is not. As we will discuss there are a number of different definitions and triggers that could lead to a material being considered hazardous. Therefore, I would not want to rely on an initial assumption that a material is not hazardous. When determining if a material is to be considered hazardous, the first step is to identify for what purpose you are evaluating the material for. If you are transporting the material in the United States then the DOT’s definition is what you would need to use, whereas if you are storing or using the material, then you would need to use the definition found in the applicable building code or fire code.

GHS does not define the term “hazardous material”, but the DOT defines a hazardous material as “means a substance or material that the Secretary of Transportation has determined is capable of posing an unreasonable risk to health, safety, and property when transported in commerce, and has designated as hazardous under section 5103 of Federal hazardous materials transportation law (49 U.S.C. 5103). The term includes hazardous substances, hazardous wastes, marine pollutants, elevated temperature materials, materials designated as hazardous in the Hazardous Materials Table (see 49 CFR 172.101), and materials that meet the defining criteria for hazard classes and divisions in part 173 of this subchapter.”

NFPA 1, Fire Code, NFPA 101, Life Safety Code, and NFPA 5000, Building Construction and Safety Code, all use the definition from NFPA 400 for hazardous material. NFPA 400 defines a hazardous material as:

A chemical or substance that is classified as a physical hazard material or a health hazard material, whether the chemical or substance is in usable or waste condition. 

The definitions of physical hazard material and health hazard material are integral in understanding and properly applying this definition. A physical hazard material per NFPA 400 is a substance that is classified as any one of the following:

  • Explosive
  • Flammable cryogen
  • Flammable gas
  • Flammable solid
  • Ignitible (flammable or combustible) liquid
  • Organic peroxide
  • Oxidizer
  • Oxidizing cryogen
  • Pyrophoric
  • Unstable (reactive)
  • Water-reactive material

A health hazard material per NFPA 400 is a chemical or substance that is classified as any one of the following:

  • Toxic
  • Highly toxic
  • Corrosive material

Many of these terms are defined within NFPA 400 to further help in defining what a hazardous material is.

It is also worth noting that other NFPA codes and standards may use a different definition for “hazardous material”. That is why it is essential to understand for what purpose (e.g., offsite transportation, storage, use, etc.) you need to determine whether something is a hazardous material or not and then consult the appropriate document to determine if it meets the definition. There is not one universally accepted definition. One example of a document that defines hazardous material differently is NFPA 30, Flammable and Combustible Liquids Code. NFPA 30 defines hazardous material or hazardous chemical as a “material presenting dangers beyond the fire problems relating to flash point and boiling point.” The annex material goes on to explain that the other dangers could include things like toxicity, reactivity, instability, or corrosivity. However, that is not intended to be an exhaustive list.  While this may seem to conflict with NFPA 400, when you consider the scope of NFPA 400 the definition from NFPA 30 actually aligns with how NFPA 400 is applied. Although a flammable and combustible liquid that has no other physical or health hazards would be considered a hazardous material per NFPA 400, it is excluded from the scope of the document. I’ll talk more about this in a future blog where we will look in detail at the scope and applicability of NFPA 400. 

Classifying Hazardous Materials

As I mentioned earlier, different organizations have different ways of classifying hazardous materials. The DOT uses a 9-system classification method while NFPA 400 uses a 14-system category method. Some of the DOT classifications are further broken into divisions, while some of the NFPA 400 categories are broken into subclassifications.

The 9 classes used by the DOT are:

  • Class 1: Explosives
  • Class 2: Gases
  • Class 3: Flammable Liquid and Combustible Liquid
  • Class 4: Flammable Solid, Spontaneously Combustible, and Dangerous When Wet
  • Class 5: Oxidizer and Organic Peroxide
  • Class 6: Poison (Toxic) and Poison Inhalation Hazard
  • Class 7: Radioactive
  • Class 8: Corrosive
  • Class 9: Miscellaneous

The 14 categories of hazardous materials used in NFPA 400 are:

  1. Corrosive solids, liquids, or gases
  2. Flammable solids
  3. Flammable gases
  4. Flammable cryogenic fluids
  5. Inert cryogenic fluids
  6. Inert gases
  7. Organic peroxide formulations
  8. Oxidizer solids or liquids
  9. Oxidizing gases
  10. Oxidizing cryogenic fluids
  11. Pyrophoric solids, liquids, or gases
  12. Toxic or highly toxic solids, liquids, or gases
  13. Unstable (reactive) solids, liquids, or gases
  14. Water-reactive solids or liquids

Compounding the challenge associated with determining and classifying hazardous materials, is the fact that between the two systems many of the categories use similar verbiage but may have different thresholds that trigger that particular classification.  One example is flammable liquid. DOT defines flammable liquid as “a liquid having a flash point of not more than 60 °C (140 °F), or any material in a liquid phase with a flash point at or above 37.8 °C (100 °F) that is intentionally heated and offered for transportation or transported at or above its flash point in a bulk packaging”. NFPA 400 states that a flammable liquid is an ignitible liquid that is classified as a Class I liquid. There are three subclassifications of a Class I liquid. The table below summarizes the specific thresholds for the subclassifications.


Flash point

Boiling point

Class IA Liquid

Below 73 OF (22.8C)

Below 100 OF (37.8C)

Class IB Liquid

Below 73 OF (22.8C)

At or above 100 OF (37.8OC)

Class IC Liquid

At or above 73F (22.8C) but below 100O F (37.8O C


These discrepancies mean that when determining the category of hazardous material you have, you need to know what system was used to provide a classification, such as the one found on a Safety Data Sheet, or you need the actual test data so the classification can be determined based on the definitions.

In summary, although there is agreement that hazardous materials are physical or health hazard materials, there is not one standard definition or approach to determining if a material should be considered hazardous or not. NFPA 400 defines hazardous material as any chemical or substance that is a physical hazard material or a health hazard material. Hazardous materials are then categorized based on the physical or health hazard they present. There are 14 different categories in NFPA 400 and a material may fall into one or more of those categories. Be on the lookout for my future blogs which will take a deeper dive into NFPA 400, covering topics like applicability of NFPA 400, maximum allowable quantities (MAQs), and more.

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Valerie Ziavras
Technical Services Engineer, supporting product and content development throughout the association.

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