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hazard categories

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Hazard categories under OSHA’s Hazard Communication Standard

Hazard categories are the severity levels used within OSHA’s Hazard Communication Standard (HazCom), 29 CFR 1910.1200, to describe how dangerous a chemical is within a specific hazard class. In practice, hazard categories power key HazCom requirements—like container labels, Safety Data Sheets (SDSs), and employee training—by standardizing how hazards are classified and communicated.

OSHA HazCom aligns with the Globally Harmonized System (GHS). Under GHS-style classification, you’ll generally see hazards described in three layers:

  • Hazard group (e.g., Physical hazards, Health hazards)
  • Hazard class (e.g., Flammable liquids, Skin corrosion/irritation)
  • Hazard category (e.g., Category 1 vs. Category 4, where lower numbers often indicate greater severity)

Because SDSs and labels can come from multiple manufacturers and jurisdictions, having consistent hazard categories is essential for clarity—especially when you’re managing large chemical inventories. A centralized SDS platform like SwiftSDS helps teams keep classifications, SDS revisions, and workplace chemical lists organized so that hazard information stays accurate and accessible.

Hazard categories vs. hazard classifications (and why it matters)

People often use “hazard categories” and “hazard classifications” interchangeably, but they are not the same.

  • Hazard classification is the overall process of determining whether a chemical is hazardous and assigning its hazard classes and categories (OSHA calls this hazard classification in 29 CFR 1910.1200(d)).
  • Hazard categories are the specific category assignments within a hazard class (e.g., “Flammable Liquid Category 2”).

This distinction matters because HazCom compliance depends on correct classification. Under 29 CFR 1910.1200(f) (labels) and 29 CFR 1910.1200(g) (SDS), the label elements and SDS content must reflect the hazards determined by classification.

Where hazard categories appear on an SDS

Hazard categories are usually listed in Section 2: Hazard(s) identification, alongside:

  • Signal word (Danger/Warning)
  • Hazard statement(s)
  • Pictogram(s)
  • Precautionary statement(s)

They may also show up in other sections (e.g., Section 9 physical/chemical properties, Section 10 stability/reactivity) depending on the hazard.

Important: OSHA requires employers to maintain SDSs and make them readily accessible to employees (29 CFR 1910.1200(g)(8)). A cloud-based system like SwiftSDS supports fast retrieval on any device—especially useful during spills, exposures, or emergency response.

How many hazard classifications are there?

A common question is: how many hazard classifications are there under HazCom?

There isn’t a single fixed number that fits every workplace because:

  • OSHA recognizes multiple hazard classes across physical and health hazards (and “simple asphyxiants” and “combustible dust” are addressed in HazCom in specific ways).
  • Each hazard class can include multiple hazard categories (severity levels).

So, instead of thinking in one total count, it’s more accurate to think of a framework:

  1. Determine whether the chemical is hazardous.
  2. Assign the applicable hazard classes (physical and/or health).
  3. Assign the corresponding hazard categories for each class.

If your goal is workplace compliance, the practical question becomes: Which hazard classes and categories apply to the chemicals we actually use? Maintaining that mapping across every product, supplier change, and SDS revision is exactly where SDS management gets difficult—and where SwiftSDS can reduce risk by keeping an up-to-date SDS library tied to your chemical inventory.

Hazardous materials classification: physical vs. health hazards

OSHA’s hazardous materials classification approach under HazCom generally covers physical hazards and health hazards (29 CFR 1910.1200(c) definitions and 1910.1200(d) classification requirements).

Physical hazards (overview)

Physical hazards describe how a chemical can ignite, explode, react, or accelerate combustion. These are the hazards most tied to fires, explosions, and reactive incidents.

Health hazards (overview)

Health hazards describe how a chemical can harm the body—immediately or over time—through inhalation, skin contact, ingestion, or eye contact.

Both types can apply to the same product. For example, a solvent might be a flammable liquid (physical hazard) and also cause skin irritation or narcotic effects (health hazards).

Physical hazard categories you should recognize

When people ask about physical hazard categories, they are usually referring to categories within common physical hazard classes. While the category numbering and criteria are technical, recognizing the major classes helps with label/SDS interpretation and training.

Common physical hazard classes under HazCom

Depending on the product, you may see categories assigned within these physical hazard classes:

  • Explosives
  • Flammable gases
  • Flammable aerosols
  • Oxidizing gases
  • Gases under pressure
  • Flammable liquids
  • Flammable solids
  • Self-reactive substances and mixtures
  • Pyrophoric liquids
  • Pyrophoric solids
  • Self-heating substances and mixtures
  • Substances and mixtures which, in contact with water, emit flammable gases
  • Oxidizing liquids
  • Oxidizing solids
  • Organic peroxides
  • Corrosive to metals

Each of these can include one or more hazard categories (for example, flammable liquids are categorized by flash point and boiling point criteria).

“Which of the following is not a physical hazard category?”

This is a frequent quiz or training question, and the trick is that many answer options are health hazards disguised as “hazard categories.” In general, physical hazard categories relate to fire, explosion, reactivity, or oxidation.

Examples that are not physical hazard categories (because they’re typically health hazards) include:

  • Carcinogenicity (e.g., “Carcinogen Category 1A/1B/2”)
  • Reproductive toxicity
  • Specific target organ toxicity (STOT)
  • Aspiration hazard
  • Skin sensitization

If you’re building training materials, it helps to teach employees to ask: “Is this about how the chemical behaves (physical) or how it affects the body (health)?”

Why hazard categories impact labels, training, and inventory controls

Hazard categories aren’t just technical details—they drive day-to-day compliance and controls.

Labels and workplace signs

Under 29 CFR 1910.1200(f), shipped container labels must include standardized elements tied to classification (including hazard statements that correspond to the category). Workplace labeling systems must also communicate key hazard information.

Employee information and training

Under 29 CFR 1910.1200(h), employers must train employees on hazardous chemicals in their work area at the time of initial assignment and whenever new hazards are introduced. When hazard categories change due to a revised SDS, training may need updating.

Chemical inventory decisions

If your inventory includes multiple products in the same hazard class but different categories (e.g., flammable liquid Category 2 vs. Category 4), storage, segregation, and quantity limits may differ based on your internal policy or fire code requirements.

SwiftSDS supports these workflows by combining:

  • A centralized SDS library with revision control
  • Chemical inventory management (locations, quantities, expiration dates)
  • Mobile access so workers can verify hazards on the spot

Common compliance pitfalls with hazard categories

Even strong safety programs can stumble on hazard categories due to document sprawl and frequent supplier updates.

Typical issues

  • Outdated SDSs with old classifications still circulating on shared drives
  • Mismatched label information vs. SDS Section 2
  • Incomplete chemical inventories (chemicals on-site without an SDS on file)
  • Training materials that don’t reflect current hazards

A practical way to reduce these gaps is to maintain one authoritative system of record. With SwiftSDS, businesses can store and organize SDSs centrally, standardize access across sites, and tie SDS availability directly to the active chemical inventory.

If an employee can’t quickly access the correct SDS during an emergency, hazard categories won’t help—accessibility and accuracy are part of compliance.

Take control of hazard categories with SwiftSDS

Hazard categories are the backbone of OSHA HazCom communication: they translate complex classification criteria into consistent label and SDS information workers can use. Keeping those categories accurate across every product and every location is challenging without a system designed for it.

SwiftSDS helps you stay organized and compliant by centralizing SDSs, supporting GHS-aligned hazard communication, and connecting SDS management to real-world chemical inventory tracking.

Ready to simplify hazard communication and SDS access? Explore SwiftSDS SDS Management and see how a centralized system can strengthen HazCom compliance across your workplace.