Part 112 min

1.2 Who decides a chemical is hazardous

Before a label can say “Danger” and before a safety data sheet can list a hazard statement, somebody has to decide what the chemical actually does. That decision is called classification, and under 1910.1200 it is not the employer's job — unless the employer chooses to make it so. Understanding who classifies, against what criteria, and what happens to hazards that fit no box, explains most of what you will later see printed on a container.

1 Who classifies, and who may rely on it

Paragraph (d)(1) puts the duty in one place: chemical manufacturers and importers shall evaluate chemicals produced in their workplaces or imported by them to classify the chemicals in accordance with this section. Then it releases everyone else: employers are not required to classify chemicals unless they choose not to rely on the classification performed by the chemical manufacturer or importer.

That sentence is the reason a receiving clerk can accept a drum and a foreman can hand out a product without either of them running a hazard assessment. The classification arrived with the shipment, printed on the label and expanded on the safety data sheet. Your job is to use it, not to reproduce it.

For each chemical, the manufacturer or importer determines the hazard classes and, where appropriate, the category within each class. Class is the kind of hazard — flammable liquid, skin corrosion, acute toxicity. Category is the severity inside that class, and it runs the counter-intuitive way: Category 1 is the most severe. A Category 1 flammable liquid is worse than a Category 4. People who grew up with 0-to-4 rating systems get this backwards constantly.

On the job: when two suppliers' sheets for “the same” product disagree on hazard category, you are not obliged to referee. Use the sheet for the product you actually bought, from the supplier who shipped it. If the difference matters to your controls, ask that supplier — and keep the answer with the sheet.

2 What gets considered, and what does not have to happen

Paragraph (d)(2) sets the evidence rule: those classifying shall identify and consider the full range of available scientific literature and other evidence concerning the potential hazards. It then adds a sentence that surprises people: there is no requirement to test the chemical to determine how to classify its hazards.

Classification is an evaluation of existing evidence, not a testing program. The same paragraph names where the criteria live: Appendix A to 1910.1200 for health hazards and Appendix B for physical hazards. Both are mandatory appendices, and both are long — Appendix A works through acute toxicity, skin corrosion and irritation, serious eye damage, respiratory and skin sensitization, germ cell mutagenicity, carcinogenicity, reproductive toxicity, specific target organ toxicity from single and repeated exposure, and aspiration hazard. Appendix B covers the physical families: explosives, flammable gases, aerosols, oxidizing gases, gases under pressure, flammable liquids and solids, self-reactive substances, pyrophoric liquids and solids, self-heating substances, substances which emit flammable gases in contact with water, oxidizing liquids and solids, organic peroxides, corrosive to metals, and desensitized explosives.

Paragraph (d)(1) also requires the classification to include hazards associated with the chemical's intrinsic properties, including a change in the chemical's physical form and chemical reaction products associated with known or reasonably anticipated uses or applications. That is the paragraph that reaches the dust generated when a solid is ground, and the fume produced when a coating is heated.

3 Mixtures

Almost nothing on a jobsite is a pure substance. Paragraph (d)(3)(i) sends mixtures to the same two appendices: those evaluating chemicals shall follow the procedures in Appendices A and B to classify the hazards, including determinations about when mixtures of classified chemicals are covered by the section.

Paragraph (d)(3)(ii) then allows a practical shortcut. When classifying mixtures they produce or import, manufacturers and importers may rely on the information provided on the current safety data sheets of the individual ingredients — except where they know, or in the exercise of reasonable diligence should know, that a sheet misstates or omits required information. Reasonable diligence is the limit on the shortcut: a supplier cannot build a mixture sheet on an ingredient sheet they have good reason to distrust.

Where each classification decision is made
Decision	Made by	Criteria in
Is this a hazardous chemical at all?	Manufacturer or importer	Definition of “hazardous chemical”, (c)
Which health hazard classes and categories?	Manufacturer or importer	Appendix A (mandatory)
Which physical hazard classes and categories?	Manufacturer or importer	Appendix B (mandatory)
Which label elements follow from that?	Manufacturer or importer	Appendix C (mandatory)
What goes on the safety data sheet?	Manufacturer or importer	Appendix D (mandatory)
What does my crew need to be told and trained on?	You, the employer	Paragraphs (e), (f)(6)-(11) and (h)

4 Hazards not otherwise classified, and the ones OSHA added

The GHS boxes do not catch everything. A chemical can present a real physical or health hazard that fits no class or category in Appendices A or B. The standard calls that a hazard not otherwise classified, abbreviated HNOC, and it does not let the hazard disappear: an HNOC must be conveyed on the safety data sheet, in section 2, even though paragraph (f)(1) states that hazards not otherwise classified do not have to be addressed on the shipped container label.

Appendix C, paragraph C.2.3.3, allows the exclamation mark pictogram to be used for HNOCs — permitted, not required — as long as the words “Hazard Not Otherwise Classified” or the letters “HNOC” appear below the pictogram.

Two more hazards deserve naming because OSHA carries them beyond the base GHS: combustible dust, defined in paragraph (c) as finely divided solid particulates of a substance or mixture that pose a flash-fire or explosion hazard when dispersed in air or other oxidizing media; and simple asphyxiants. Both appear in the required training content at (h)(3)(ii), alongside pyrophoric gases and hazards not otherwise classified. If your process makes dust from a solid, that (d)(1)(i) “change in physical form” clause and the combustible dust definition are talking about you.

Common mistake: assuming that because a hazard is not on the label, it is not on the sheet. Hazards not otherwise classified are deliberately kept off the shipped label by (f)(1) and deliberately kept on the safety data sheet. Reading only labels loses them.

5 Reading a classification without becoming a toxicologist

You do not need Appendix A to use a classification. You need three habits.

1
Read the class, not just the pictogram. The flame means flammable; whether it is a Category 1 flammable liquid with a flash point below 73 °F or a Category 4 that barely qualifies changes how you store it. Section 2 of the safety data sheet names the class and category in words.
2
Remember that 1 is worst. Every GHS category numbering runs from most severe to least. Nothing about the label tells you this, so it has to be taught — and it is exactly the kind of thing (h)(3)(iv) means when it asks training to explain the labels employees receive.
3
Look for what the classification cannot tell you. A classification describes the product as supplied. It does not know that you will heat it, spray it, grind it or mix it with the product on the next shelf. Section 10 of the sheet, stability and reactivity, is where those interactions get named — you will work through it in Part 3.

6 Trade secrets: the limit on what a sheet must reveal

Paragraph (i) allows a manufacturer, importer or employer to withhold the specific chemical identity — the chemical name, other specific identification, and the exact percentage or concentration range — from section 3 of the safety data sheet, on conditions. The claim must be supportable; the sheet must still disclose the properties and effects; the sheet must state that the identity or concentration is withheld as a trade secret; and where a concentration range is claimed, the sheet must give the concentration as one of the prescribed ranges listed in (i)(1)(iv)(A) through (M), using the narrowest range possible.

The protection is not absolute. Paragraph (i) goes on to require disclosure of a withheld identity to a treating physician or nurse in a medical emergency, and to health professionals, employees and their designated representatives in non-emergency situations under stated conditions. Trade secrecy limits what is printed; it does not survive a medical emergency.

Key takeaways

Manufacturers and importers classify; employers may rely on that classification and are not required to redo it.
Class is the kind of hazard, category is the severity — and Category 1 is the most severe, not the least.
Classification considers the full range of available evidence; there is no requirement to test the chemical.
Appendix A holds the health hazard criteria, Appendix B the physical; both are mandatory.
Hazards not otherwise classified stay off the shipped label but must appear on the safety data sheet.
A trade secret may hide a chemical identity on the sheet, never from a physician in a medical emergency.

Free educational content — not OSHA-authorized training, no certificate or card issued. Follow your employer's program and the standards cited.