GHS Signal Words: Danger vs Warning — When Each Applies
GHS uses exactly two signal words: Danger and Warning. They appear on every hazardous chemical label and SDS, yet many EHS professionals are unsure which one applies — and why.
What Are GHS Signal Words?
A signal word is a word that indicates the relative level of severity of a hazard. Under the Globally Harmonized System (GHS) and its regional implementations — CLP in the EU and OSHA HCS in the US — only two signal words exist:
- Danger — used for the more severe hazard categories (Category 1 and 2 in most hazard classes)
- Warning — used for less severe categories (typically Category 3 and 4)
If a substance has no hazardous classification, no signal word appears on the label.
Danger vs Warning: The Rule
The choice between Danger and Warning is determined by the hazard category, not by the number of hazards. A single Category 1 hazard is enough to require “Danger”, regardless of how many other Warning-level hazards exist.
Key principle: Danger always takes priority. If a substance has both Danger-level and Warning-level hazards, only “Danger” appears on the label. “Warning” is suppressed.
Which Categories Use Danger
| Hazard Class | Danger Categories |
|---|---|
| Acute toxicity (oral/dermal/inhalation) | Category 1, 2, 3 |
| Skin corrosion | Category 1 (H314) |
| Serious eye damage | Category 1 (H318) |
| Flammable liquids | Category 1, 2 (H224, H225) |
| Explosives | Division 1.1–1.4 |
| Carcinogenicity | Category 1A, 1B (H350) |
| Reproductive toxicity | Category 1A, 1B (H360) |
| STOT repeated exposure | Category 1 (H372) |
| Acute aquatic toxicity | Category 1 (H400) |
Which Categories Use Warning
| Hazard Class | Warning Categories |
|---|---|
| Acute toxicity | Category 4 (H302, H312, H332) |
| Skin irritation | Category 2 (H315) |
| Eye irritation | Category 2 (H319) |
| Respiratory/skin sensitisation | Skin sensitiser Cat 1 (H317) |
| Flammable liquids | Category 3 (H226) |
| Carcinogenicity | Category 2 (H351) |
| Reproductive toxicity | Category 2 (H361) |
| STOT repeated exposure | Category 2 (H373) |
| Chronic aquatic toxicity | Category 2, 3 (H411, H412) |
Hazard Classes With No Signal Word
Some GHS hazard classes do not use signal words at all:
- Chronic aquatic toxicity Category 4 (H413) — no signal word
- Ozone hazard (H420) — no signal word in some jurisdictions
- Combustible dust — implementation varies by country
How Signal Words Appear on Labels
Under CLP (EU) and OSHA HCS (US), the signal word must:
- Appear prominently on the label, in bold
- Be placed adjacent to the pictogram(s)
- Use the exact wording — no substitutes like “Caution” or “Attention”
- Appear in all required languages for the market (EU multi-language requirement)
Signal Words in SDS Documentation
In a Safety Data Sheet, the signal word appears in Section 2: Hazard Identification, alongside pictograms and hazard statements. It must match the label exactly — any discrepancy is a compliance violation.
Common Mistakes to Avoid
Using both Danger and Warning together — Only the highest applies. If Danger is required, Warning is omitted entirely.
Using “Caution” instead of “Warning” — Caution is used in some older US systems (NFPA, ANSI Z129.1) but is not a GHS signal word and cannot substitute for Warning on GHS labels.
Omitting the signal word for Category 5 — Acute toxicity Category 5 does not require a signal word in most implementations, but check local regulations.
Practical Example
A cleaning product contains:
- Sodium hydroxide 5% → Skin corrosion Category 1 → Danger (H314)
- Sodium lauryl sulphate 10% → Skin irritation Category 2 → Warning (H315)
Final label signal word: DANGER only. The Warning from H315 is suppressed.
Quick Reference
| Signal Word | Meaning | Priority |
|---|---|---|
| DANGER | Severe hazard (Category 1–3 typically) | Higher — suppresses Warning |
| WARNING | Moderate hazard (Category 3–4 typically) | Lower — suppressed by Danger |
| (none) | No classified hazard or Category 5 | — |
Related Resources
- Complete Guide to GHS H-Statements — learn which H-codes trigger Danger vs Warning
- GHS Hazard Symbols and Meanings — all 9 pictograms explained
- GHS vs OSHA HCS 2024 — signal word requirements under updated US rules
- H-Statements Reference →
Reference: UN GHS Rev.9, Chapter 1.4. CLP Regulation (EC) No 1272/2008, Article 20. OSHA HCS 2012/2024, 29 CFR 1910.1200.