GHS Revision 7 Converter: Every Hazard-Class Change in HCS 2024

HCS 2024 moves US hazard labels from GHS Revision 3 (2009) up to primarily GHS Revision 7 (2017) — and that jump adds two new physical-hazard classes (Desensitized Explosives and Chemicals Under Pressure) and a new non-flammable Category 3 inside the existing Aerosols class, splits Flammable Gases into 1A and 1B, and rewrites several SDS and label elements. Nothing on a chemical actually got more dangerous; the classification system simply got more precise. The job for every safety manager is a crosswalk: map each old 2012 classification to its 2024 equivalent so labels, SDSs, and training are right before the November 20, 2026 employer deadline (29 CFR 1910.1200(j)).

This is the complete converter — every change in one place, with the appendix cites, a master conversion table, a worked example, and what to do next.

Why the standard changed (and why it isn't optional)

The 2012 HazCom rule was built on GHS Revision 3. The rest of the world kept moving — the EU, Canada, Australia, and others adopted later revisions — leaving US labels increasingly out of step with the products crossing the border. OSHA's 2024 final rule re-anchors the Hazard Communication Standard to primarily GHS Revision 7 (with a handful of Rev 8 provisions), under 29 CFR 1910.1200. Construction employers are pulled in automatically through 29 CFR 1926.59, which adopts the 1910.1200 standard by reference.

Adopt a "converter" mindset: a class you knew in 2012 may have been split, renamed, expanded, or newly created. Miss the change and you get the two classic failures — an under-labeled container (missing a pictogram or signal word) and stale training that doesn't mention a hazard your crew now handles. Both are citable under 29 CFR 1910.1200(f) and (h).

The master conversion table

This is the at-a-glance crosswalk from the GHS Rev 3-based 2012 classes to the HCS 2024 (Rev 7) classes. Appendix cites are to 29 CFR 1910.1200, Appendix B (physical hazards) unless noted.

Two things this table makes obvious: most chemicals keep the same hazard category (the system got more granular, not stricter), and the real work is concentrated in a handful of new or split classes. Note that OSHA still requires only 8 pictograms — the ninth Environment symbol (GHS09) remains voluntary, because environmental hazards are EPA's domain, not OSHA's. (Full breakdown: The 8 OSHA Pictograms vs the 9 GHS Pictograms.)

The four changes that actually matter

1. Flammable Gases split into 1A and 1B

Under Appendix B.2, the old single Flammable Gas Category 1 is now divided into Category 1A and Category 1B based on flammability limits and burning velocity, with 1A as the higher-hazard group. Critically, pyrophoric gases and chemically unstable gases (A and B) are sub-categories that sit inside Category 1A — they are not the definition of 1A itself, a distinction the old standard blurred.

Field impact: crews using acetylene or specialty welding/shielding gases will see "Category 1A" appear on shipped labels and SDS Section 2. Training should explain that 1A flags the most reactive, fastest-burning gases — including those that ignite in air (pyrophoric) or that react/decompose even without air (chemically unstable).

2. Aerosols becomes a full class — with a non-flammable Category 3

The narrow "Flammable Aerosol" category is replaced by a full Aerosols hazard class at Appendix B.3 with three categories: Cat 1 (extremely flammable), Cat 2 (flammable), and the new Cat 3 (non-flammable). A Category 3 aerosol carries the signal word Warning and hazard statement H229 "Pressurized container: may burst if heated" — because the pressure hazard exists regardless of flammability — but Appendix C assigns it no pictogram at all. Do not reach for the gas cylinder: GHS04 is not an Aerosols pictogram. It belongs to Gases Under Pressure and to Chemicals Under Pressure, whose own Category 3 does carry it.

Field impact: common "safe" construction products — silicone sprays, contact cleaners, dry lubricants, air dusters — that previously shipped with no physical-hazard label may now arrive bearing the signal word Warning and H229 "Pressurized container: may burst if heated" — and still no pictogram, because Appendix C gives Aerosol Category 3 "No Symbol". The gas-cylinder pictogram GHS04 belongs to the neighbouring Chemicals Under Pressure class, not here. Train crews that "non-flammable" no longer means "no precautions." Deep dive: Aerosols Reclassified: the New Category 3.

3. Desensitized Explosives — a brand-new class

Previously such materials were often filed under Flammable Solids. HCS 2024 creates a dedicated Desensitized Explosives class at Appendix B.17 with four categories (Cat 1–4), ranked by corrected burning rate, all using the flame pictogram (GHS02). These are explosive substances deliberately wetted (water, alcohol) or diluted with a phlegmatizer to suppress their explosivity — for example, wetted nitrocellulose. The danger returns if the wetting agent dries out.

Field impact: storage and handling protocols must guard the wetting agent — sealed containers, humidity awareness, FIFO rotation. The training message is blunt: drying out is the trigger. Deep dive: Desensitized Explosives (Appendix B.17).

4. Chemicals Under Pressure — closing the gap

The new Chemicals Under Pressure class at Appendix B.3.2 captures liquids or solids pressurized with a propellant gas in a non-aerosol container — spray-foam insulation kits, some pressurized adhesives and sealants — that don't fit "gases under pressure" or "aerosols." It has three categories (Compressed, Liquefied, Dissolved) and uses the gas-cylinder pictogram (GHS04).

Field impact: two-part spray-foam kits and similar pressurized products will now classify cleanly here, with storage/handling data that reflects both the chemical hazard and the stored-pressure hazard. Deep dive: Chemicals Under Pressure (Appendix B.3.2).

Conversion table for compliance officers

A more action-oriented view — what to do when you spot each old label in your inventory:

Worked example: converting one product

A contractor stocks a non-flammable silicone spray lubricant in 12-oz aerosol cans. The 2012-era label carried no physical-hazard pictogram — it was a non-flammable aerosol, which had no category to land in.

Walk the converter:

1. Old class: unclassified non-flammable aerosol (no GHS Rev 3 home).
2. New class: Aerosol Category 3 under Appendix B.3 — because it's a pressurized dispensed product that fails the Cat 1/Cat 2 flammability criteria.
3. New label elements: no pictogram at all — Appendix C's aerosol table gives Category 3 "No Symbol" — with the signal word Warning and hazard statement H229 "Pressurized container: may burst if heated," plus the usual precautionary statements (keep away from heat, do not pierce or burn). The gas-cylinder pictogram GHS04 belongs to the neighbouring class, Chemicals Under Pressure (Appendix B.3.2), and to Gases Under Pressure — not to aerosols. Figure C.1 allocates the gas cylinder to those, and aerosols appear in it nowhere.
4. SDS: Section 2 now lists Aerosol Cat 3; the supplier issues an updated sheet.
5. Workplace action: the shipped label arrives correct from the manufacturer; the employer must make sure any secondary/workplace container under 29 CFR 1910.1200(f)(6) and the training reflect the new pressure hazard.

The product is no more dangerous than it was last year — but it now communicates a real rupture-under-heat risk that the old scheme silently dropped. That is the entire point of the Rev 7 conversion.

Common mistakes during the conversion

• Treating it as "stricter," not "more granular." Most categories are unchanged; panic-relabeling everything wastes effort. Target the split/new classes.
• Forgetting the SDS. A reclassification changes both the label and the SDS (Section 2 especially). A new pictogram with a stale SDS is an inconsistency an inspector will notice.
• Assuming a 9th pictogram appeared. It didn't — OSHA still requires 8. GHS09 (Environment) stays voluntary.
• Confusing Aerosols (B.3) with Chemicals Under Pressure (B.3.2). Aerosols are dispensed via a propellant as a spray/foam/mist from an aerosol dispenser; Chemicals Under Pressure are pressurized liquids/solids in non-aerosol packaging.
• Ignoring the mixed-inventory window. Because dual compliance is allowed during the transition, your shelves will hold old and new labels side by side for years — train crews to read both.
• Missing that mixtures run on a later clock. Many construction products are mixtures, whose deadlines are the 2027 manufacturer and 2028 employer dates, not the 2026 dates.

The deadlines that govern the conversion

The dates come from 29 CFR 1910.1200(j), as extended by a January 15, 2026 final rule (FR Doc. 2026-00653) that pushed every original date back four months. These are the dates now in force:

During the interim you may comply with the 2012 HCS, the 2024 HCS, or both. Practically: start your library gap analysis now, flag every product that will shift class, and stage the relabeling/retraining so you're not scrambling against the November 20, 2026 employer date. Plan the work with the HCS 2024 Deadline Lookup and the HCS 2024 Relabel Action Planner.

What getting it wrong costs

Hazard Communication ranked second on OSHA's FY2025 list of most-cited standards. An under-labeled container or out-of-date training tied to a missed reclassification is citable under 29 CFR 1910.1200(f) and (h). A serious citation can reach $16,550 (the 2026 maximum, unchanged from 2025 — there was no inflation increase), and willful or repeated violations up to $165,514. Construction employers are covered through 29 CFR 1926.59.

Note: This is general guidance, not legal advice. OSHA-approved State Plans may adopt requirements at least as effective as the federal standard; verify your state's HazCom rules.

What to do next

1. Run a class-shift gap analysis. List every product whose class is in the table above and check the supplier's updated SDS. Start with the SDS Gap Analyzer.
2. Use the conversion wizard. Map old-to-new in minutes with the GHS Rev 7 Transition Wizard.
3. Reclassify flammable liquids precisely where flash/boiling thresholds matter, using the Flammable Liquid Category Classifier.
4. Regenerate workplace/secondary labels with the correct 8 pictograms via the GHS Label Generator.
5. Retrain on the new classes — a focused Toolbox Talk covers Aerosol Cat 3, Desensitized Explosives, and Chemicals Under Pressure. Background: Complete OSHA HazCom 2026 Guide and the Hazard Communication Standard 1910.1200 overview.

Related reading: HazCom vs GHS: Key Differences · OSHA HazCom 2024 Updates · Print Compliant GHS Labels (Rev 7 / Rev 8)

Sources & verification: 29 CFR 1910.1200 Appendix B (physical hazard classes — B.2 flammable gases, B.3 aerosols, B.6 flammable liquids, B.17 desensitized explosives, B.3.2 chemicals under pressure), Appendix C (pictograms), and (j) (compliance dates); HCS 2024 final rule 89 FR 44144 (May 20, 2024) and the deadline extension FR Doc. 2026-00653 (Jan 15, 2026); construction adoption via 29 CFR 1926.59; penalty maximums per 29 CFR 1903.15(d) (2026, unchanged from 2025). Facts verified against the HazComFast regulatory source of truth (ghsClassification, hcsDeadlines, oshaPenalties), last verified 2026-06-26. Not legal advice.