Hazard communication signal words: what they mean and why they matter

Last updated 2026-07-09

What is a hazard communication signal word?

A signal word is the single word printed prominently on a chemical label to tell a reader how severe the hazard inside is. Under the Globally Harmonized System of Classification and Labelling of Chemicals (GHS), which OSHA adopted in its 2012 revision of the Hazard Communication Standard at 29 CFR 1910.1200, only two signal words exist: 'Danger' and 'Warning.' ^[1]

That's it. Two words.

OSHA's standard assigns a signal word to each hazard class in Appendix C to 29 CFR 1910.1200, and that word has to appear on the label. The agency picked this stripped-down approach on purpose. Before GHS alignment, manufacturers used 'Caution,' 'Poison,' 'Corrosive,' and dozens of other terms with no consistency, so a worker had no fast way to compare risk across products. Two words fixed that. ^[1]

The signal word is one of six required label elements under OSHA HazCom. The others are the product identifier, pictogram(s), hazard statement(s), precautionary statement(s), and supplier information. All six work together, but the signal word is the piece a worker reads first in a real situation, which is why the placement rules are strict. It has to sit in a prominent position and be large enough to stand out from the text around it. ^[1]

What is the difference between Danger and Warning on a label?

'Danger' means the more severe hazard categories inside a hazard class. 'Warning' means the less severe ones. That's the official split, and it's tied straight to the numbered category system inside GHS.

Here's how it works in practice. GHS numbers hazard categories from 1 upward, and Category 1 is always the worst. For most hazard classes, Category 1 and sometimes Category 2 get 'Danger.' Category 3 and above usually get 'Warning.' A few hazard classes have only one tier and one signal word, and some categories carry neither.

Take Flammable Liquids (GHS Appendix B.6):

• Category 1 (flash point below 23°C, initial boiling point at or below 35°C): Danger
• Category 2 (flash point below 23°C, initial boiling point above 35°C): Danger
• Category 3 (flash point between 23°C and 60°C): Warning
• Category 4 (flash point between 60°C and 93°C): Warning ^[1]

Acute toxicity by the oral route splits like this:

• Category 1 (LD50 ≤ 5 mg/kg): Danger
• Category 2 (LD50 > 5 to 50 mg/kg): Danger
• Category 3 (LD50 > 50 to 300 mg/kg): Danger
• Category 4 (LD50 > 300 to 2000 mg/kg): Warning
• Category 5 (LD50 > 2000 to 5000 mg/kg): no signal word ^[1]

This category-to-signal-word mapping is locked in OSHA's Appendix C. Manufacturers don't get to choose. Classify a product as a Category 1 flammable liquid and the label says 'Danger,' full stop. That consistency is exactly what lets a warehouse worker in El Paso and a lab tech in Boston read the same label and understand the same thing.

For a fuller look at the whole hazard communication standard and everything else it requires, read that next.

What if a chemical has multiple hazards with different signal words?

This comes up constantly, because most industrial chemicals carry more than one hazard. A solvent might be a Category 2 flammable liquid (Danger), a Category 4 acute oral toxicant (Warning), and a Category 1 skin corrosive (Danger) all at once.

OSHA's rule is simple: print only the higher-level signal word. If any hazard on the product earns 'Danger,' the label says 'Danger.' 'Warning' does not appear next to it. ^[1]

This single-signal-word rule keeps labels clean and stops workers from having to referee two competing urgency levels. The hazard statements and pictograms on the same label still spell out each individual hazard. The signal word just names the highest level of concern in one glance.

Here's the part that catches people off guard. If a chemical has multiple hazards and every one of them falls in a 'Warning' category, the label says 'Warning,' even with four or five 'Warning'-level hazards stacked together. The signal word reflects severity per category, not a count of hazards. A product with six 'Warning' hazards still says 'Warning,' never 'Danger.' That's a judgment built into GHS, and it's worth knowing before you second-guess a label.

Can a hazardous chemical have no signal word at all?

Yes. Some GHS hazard categories carry no assigned signal word. The most common examples are Category 5 acute toxicants and certain environmental hazards like hazardous to the aquatic environment (chronic, Category 4). ^[1]

A handful of health hazard categories, like some respiratory or skin sensitizer classifications, may also skip the signal word depending on the evidence behind the classification. OSHA's Appendix C lays this out category by category.

The takeaway for employers is blunt: no signal word does not mean the product is safe. It may still carry hazard statements, pictograms, and precautionary statements. Workers need to read every label element, not scan for 'Danger' or 'Warning' and move on. Train them on this specific point, because it's easy to miss.

Where exactly on the label does the signal word go?

OSHA requires the signal word to appear on the label but does not fix a geometric spot like 'top center.' What the standard does require is that the signal word sit in a "prominent position" and be distinguishable from surrounding text. In practice, GHS-compliant labels almost always put the signal word near the top, next to or below the product identifier and above the hazard statements. ^[1]

Font size matters too, though OSHA's label rules don't name a minimum point size for signal words. The requirement is that all label information be in English, legible, and prominently displayed. Some states running their own OSHA plans add requirements, so check your state plan if one applies to you. ^[2]

For shipped containers, the label goes on the container itself. For workplace containers (a transfer container, for instance), either the original label or a workplace label with the product identifier and hazard warnings works, but include the signal word on workplace labels when space allows. OSHA's whole aim here is worker awareness, so lean toward including it.

How do signal words connect to Safety Data Sheets?

The signal word on a label and the data on a Safety Data Sheet (SDS) come from the same hazard classification. Section 2 of every GHS-format SDS, 'Hazard Identification,' has to list the signal word that appears on the label. ^[1] So if the label says 'Danger,' Section 2 of the matching SDS says 'Danger.'

That cross-reference earns its keep two ways. A worker who wants to know why a product carries a given signal word can open Section 2 and see the full list of hazard classifications behind the choice. And if the label and SDS disagree on the signal word, something is broken, either a labeling error or an outdated SDS, and you want to sort that out before anyone uses the product.

For a real example of what SDS information looks like on the page, the hcl safety data sheet article walks through a corrosive chemical's full SDS structure.

Employers have to keep SDS documents for every hazardous chemical in the workplace and make them reachable during every shift. That requirement lives in 29 CFR 1910.1200(g). ^[1]

What are OSHA's labeling requirements for signal words in the workplace?

Manufacturers and importers build and apply the compliant label before a product ships. Employers who receive those products have to keep the labels on the containers and legible. ^[1] That's the basic split.

Employers pick up extra duties the moment a chemical goes into a secondary container. Pour acetone from a manufacturer's labeled gallon jug into a spray bottle for daily use and that spray bottle needs a label. OSHA allows simplified workplace labels here, but the label has to include at minimum the product identifier and words, pictures, or symbols that give workers general information about the hazards. ^[1]

Workplace labels don't have to use the full GHS format (signal word, every pictogram, every hazard statement), and OSHA doesn't ban the full format either. Plenty of safety pros just print a full GHS label for secondary containers to stay consistent and dodge training confusion. That's what I'd do. A worker who learns to read 'Danger' on a manufacturer's label should see 'Danger' on the secondary container too, not a handwritten note that says 'flammable.'

One failure shows up in inspection after inspection: labels defaced, painted over, or peeled off and never replaced. OSHA cites this under 29 CFR 1910.1200(f)(9), which requires employers to make sure labels aren't removed or defaced. Penalties for other-than-serious HazCom violations run up to $16,550 per violation, and willful or repeated violations can reach $165,514 per violation. ^[3]

How does employee training connect to signal words?

OSHA's HazCom standard requires employers to train employees on what labels and label elements mean, signal words included, before those employees are exposed to hazardous chemicals. ^[1] This isn't a one-time new-hire box to check. Training has to happen whenever a new chemical enters the workplace, not only when a new person starts.

Good signal word training goes past 'Danger is worse than Warning.' Workers need to know what the word tells them to do differently. 'Danger' on a flammable liquid means no open flames, no static discharge, containers closed when not in use. 'Warning' on a mild irritant means ventilate and keep it out of your eyes. The signal word is a trigger for behavior, not a reading quiz.

Training records carry weight in a compliance check. When an inspector asks how workers were trained on HazCom label elements, you need documentation. A sign-in sheet with dates and topics is the floor. A written training program with a quiz is better.

Building your HazCom training from scratch? SafetyFolio's safety program generator can produce a written HazCom program, signal word training language and all, in about 15 minutes. That covers the written program. You still have to deliver the actual training to real people.

For the broader osha training requirements beyond HazCom, that article covers what OSHA mandates across standards.

What GHS pictograms go with each signal word?

GHS uses nine standardized pictograms, each a black symbol inside a red diamond. Signal words and pictograms both come from the same hazard classification tables, so they track each other, but they aren't one-to-one. A single pictogram can land on labels that say either 'Danger' or 'Warning' depending on the category. ^[1]

Here's a quick reference for the most common workplace chemical hazards:

Pictogram	Symbol description	Example signal word assignment
GHS01	Exploding bomb	Danger (most explosive categories)
GHS02	Flame	Danger (Cat 1-2 flammables) or Warning (Cat 3-4)
GHS03	Flame over circle	Danger (Cat 1 oxidizers) or Warning (Cat 2-3)
GHS04	Gas cylinder	Warning (compressed gases, most categories)
GHS05	Corrosion	Danger (Cat 1 skin corrosives) or Warning (Cat 2)
GHS06	Skull and crossbones	Danger (acute tox Cat 1-3)
GHS07	Exclamation mark	Warning (acute tox Cat 4, irritants, sensitizers)
GHS08	Health hazard	Danger or Warning depending on category
GHS09	Environment	Warning or no signal word (aquatic hazards)

The skull-and-crossbones (GHS06) is the clearest case: it only shows up with 'Danger.' The exclamation mark (GHS07) only shows up with 'Warning.' Most other pictograms swing either way depending on the exact hazard category. ^[5]

When a product label would carry both GHS06 (skull) and GHS07 (exclamation), OSHA says drop GHS07, since the skull already flags the higher hazard and showing both is redundant. Same 'show the most severe' logic, applied to pictograms. ^[8]

How do signal words apply to physical vs. health hazards?

GHS sorts chemical hazards into two broad groups: physical hazards (flammable, explosive, oxidizing, and so on) and health hazards (acute toxicity, carcinogenicity, reproductive toxicity, and so on). Signal words apply to both groups using the same 'Danger for severe, Warning for less severe' logic. ^[1]

Physical hazards read easier for workers because the consequences hit fast and you can see them: fire, explosion, pressure release. Health hazards are trickier to communicate, since many of them, carcinogens above all, produce no symptoms during a normal short exposure. A carcinogen might carry 'Warning' (Category 2) or 'Danger' (Category 1A or 1B), and the signal word alone won't tell a worker whether the risk is immediate or stacking up over years.

This is where the hazard statements earn their place next to the signal word. 'H350: May cause cancer' (Category 1A/1B, Danger) versus 'H351: Suspected of causing cancer' (Category 2, Warning) say genuinely different things about the strength of the carcinogenicity evidence. Workers trained to read the full label, more than the signal word, make better protective calls.

For how OSHA enforcement works across both physical and health hazard violations, the osha overview explains the agency's inspection and citation process.

What does OSHA inspect and cite related to signal words?

OSHA's Hazard Communication Standard lands in the top three most-cited standards nearly every year. In fiscal year 2023 it ranked second overall with 2,906 violations cited. ^[4] Most of those citations aren't about signal words in isolation. They're about missing or illegible labels, absent SDS documents, or thin employee training, all of which can pull signal word compliance into the picture.

An inspector checking HazCom compliance will usually: 1. Walk the facility and eyeball chemical containers, checking labels for all required elements including signal words. 2. Ask to see the SDS for chemicals in use and verify Section 2 matches the label. 3. Ask how employees were trained on label elements and request the documentation. 4. Check secondary containers.

A label missing the signal word entirely violates 29 CFR 1910.1200(f) and is citable. A wrong signal word (say, 'Warning' on a product that should read 'Danger' based on its classification) is also a potential citation, though the inspector has to review the SDS classification to prove it.

The scenario I see most: a label gets wet, torn, or painted over in a storage room and nobody replaces it. That's cited under 1910.1200(f)(9). Beat the inspector to it with regular label audits, quarterly is a reasonable pace.

How should small businesses build signal word compliance into their HazCom program?

OSHA requires every employer with hazardous chemicals in the workplace to keep a written HazCom program. ^[1] That program has to describe how the company handles labeling, SDS management, and employee training. Signal words belong in the training section, spelled out.

For a small business, here's a workable approach that skips the consultant:

First, build and keep a chemical inventory. You can't manage labels for chemicals you don't know you own. Walk every area where work happens, storage rooms, maintenance closets, cleaning supply cabinets, all of it.

Second, confirm every chemical on the inventory has a current SDS in GHS format (all 16 sections, issued by the manufacturer). If a chemical showed up with a pre-2015 MSDS instead of a GHS SDS, ask the supplier for an updated one.

Third, check that each container's label matches its SDS on signal word and pictograms. Once you know what to look for, this runs about 10 seconds per container.

Fourth, train every employee who works with or near hazardous chemicals on what 'Danger' and 'Warning' mean, what each one demands, and how to pull up the SDS for anything they're unsure about. Document it.

SafetyFolio's safety program generator can produce a written HazCom program built for your workplace in minutes, which handles the written-program requirement and hands you a training outline to work from.

For operations with heavy chemical use alongside equipment hazards, pairing your HazCom program with a lockout tagout program covers the two most common serious violation areas in manufacturing and maintenance.

Frequently asked questions

What are the two signal words used in GHS hazard communication?

The two GHS signal words are 'Danger' and 'Warning.' 'Danger' appears on labels for chemicals in higher-severity hazard categories, and 'Warning' appears for lower-severity categories. OSHA adopted both words in the Hazard Communication Standard at 29 CFR 1910.1200 when it aligned with GHS in 2012. No other signal words, like 'Caution' or 'Poison,' are allowed on GHS-format labels.

Does 'Danger' always mean more hazardous than 'Warning'?

Yes, within a given hazard class. 'Danger' always goes to the more severe categories and 'Warning' to the less severe ones. Comparing across different hazard classes gets messier: a Category 3 'Warning' flammable liquid can still hurt you badly. The signal word tells you where a chemical falls within its hazard category, not an absolute ranking against every other chemical in your building.

What happens if a product has both Danger and Warning hazards?

Only the higher-level signal word appears on the label. If a chemical qualifies for 'Danger' under any one of its hazard classifications, the label says 'Danger' only. 'Warning' is not printed alongside it. The individual hazard statements and pictograms still communicate all specific hazards, but the single signal word keeps two urgency levels from competing.

Can a chemical be hazardous but have no signal word on the label?

Yes. Some GHS hazard categories carry no signal word. Acute toxicity Category 5 has none, and certain environmental categories (like aquatic chronic, Category 4) have none either. No signal word doesn't mean the product is safe. Workers should still check the label for hazard statements and pictograms no matter what the signal word line does or doesn't say.

What is the signal word for a corrosive chemical?

It depends on the category. Skin corrosives in Category 1 (which includes 1A, 1B, and 1C) get 'Danger.' Category 2 skin irritants get 'Warning.' Serious eye damage (Category 1) gets 'Danger,' while eye irritation (Category 2) gets 'Warning.' OSHA's Appendix C to 29 CFR 1910.1200 has the complete category-to-signal-word table for every hazard class.

Is the signal word required on secondary or transfer containers in the workplace?

OSHA requires workplace labels on secondary containers to carry the product identifier plus hazard information sufficient to warn employees, but does not mandate a full GHS label with a formal signal word. Even so, many safety managers use full GHS labels on secondary containers to match their training. If space is tight, at minimum include the product name, a hazard warning, and who to call.

Where in an SDS does the signal word appear?

Section 2 of a GHS-format Safety Data Sheet, titled 'Hazard Identification,' must list the signal word. That section also includes the hazard classification, hazard statements, and precautionary statements. The signal word in Section 2 should match the product label. If they differ, that's a red flag that either the SDS or the label is outdated or wrong.

What OSHA standard governs hazard communication signal words?

Signal words are required under 29 CFR 1910.1200, OSHA's Hazard Communication Standard (HazCom 2012). The signal word rules for each hazard class sit in Appendix C to that standard. The maritime and construction versions (29 CFR 1915.1200 and 29 CFR 1926.59) point to the same GHS requirements.

What is the fine for a missing or wrong signal word on a chemical label?

OSHA treats most HazCom labeling violations as 'other-than-serious,' with penalties up to $16,550 per violation. Willful or repeated violations can reach $165,514 per violation. Inspectors usually cite the employer, not the manufacturer, for label problems on containers in the workplace, since employers are responsible for keeping labels legible and compliant on all containers.

How do signal words differ from DOT hazard labels on shipping containers?

GHS signal words ('Danger' and 'Warning') go on workplace chemical labels under OSHA's HazCom standard. DOT shipping labels use a different system built on hazard classes (Class 3 Flammable, Class 8 Corrosive, and so on) and don't use 'Danger' or 'Warning' as label text. Both systems can apply to the same product, but they serve different audiences and different agencies (OSHA and DOT).

What training do employees need on signal words?

OSHA requires employers to train employees on the meaning of GHS label elements, signal words included, before exposure to hazardous chemicals and when new chemicals are introduced (29 CFR 1910.1200(h)). Training must cover what 'Danger' and 'Warning' mean, how to tie a signal word to the right protective action, where to find the SDS for more detail, and how to read the full label including pictograms and hazard statements.

Do California or other state plan states have different signal word rules?

State OSHA plans must be at least as effective as federal OSHA. California's Cal/OSHA, for example, adopted the same GHS signal word system under 8 CCR 5194. Some state plan states add requirements around label language or training documentation, but none use signal words other than 'Danger' and 'Warning.' Check your specific state plan if you operate in a state plan state.

What is the signal word for a flammable aerosol?

Flammable aerosols fall under the GHS hazard class 'Aerosols.' Category 1 aerosols (extremely flammable) carry 'Danger.' Category 2 aerosols (flammable) carry 'Warning.' Category 3 aerosols aren't a flammable aerosol hazard and carry no signal word for that hazard, though the product may still have other hazards with their own signal words.

How often should employers audit chemical labels for signal word compliance?

OSHA doesn't set a mandatory audit frequency for label inspections, but the working standard among safety professionals is at least quarterly. Labels break down from moisture, abrasion, and UV in storage areas. A quarterly walk-through of every area where chemicals are stored or used, cross-checking labels against the current SDS, catches defaced or missing containers before an OSHA inspector does.

Sources

1. OSHA, 29 CFR 1910.1200 Hazard Communication Standard (including Appendices A, B, C): Signal words 'Danger' and 'Warning' are the only two GHS signal words; their assignment by hazard category; label element requirements; employer training and SDS obligations
2. OSHA, State Plans Program: State OSHA plans must be at least as effective as federal OSHA; states may have additional label requirements
3. OSHA, Penalties: Other-than-serious violations up to $16,550; willful or repeated violations up to $165,514 per violation
4. OSHA, Top 10 Most Frequently Cited Standards FY2023: Hazard Communication ranked second most-cited standard in FY2023 with 2,906 violations
5. United Nations Economic Commission for Europe, Globally Harmonized System of Classification and Labelling of Chemicals (GHS): GHS defines signal words, category-to-signal-word assignments, and the nine standardized pictograms
6. OSHA, Hazard Communication Standard Final Rule 2012 (77 FR 17574): OSHA adopted GHS in 2012, replacing prior inconsistent signal word terminology with 'Danger' and 'Warning' only
7. OSHA, Publications library (Hazard Communication small entity and guidance documents): Employer obligations for workplace labeling of secondary containers and required label elements
8. OSHA, Hazard Communication Standard Pictograms (Quick Cards and pictogram guidance): Nine GHS pictograms and their pairing with hazard categories and signal words; skull-and-crossbones with Danger, exclamation mark with Warning; omit GHS07 when GHS06 is present
9. OSHA, Standard Interpretations (Hazard Communication workplace labeling): OSHA interpretation on workplace label requirements for secondary containers and minimum required elements
10. California Department of Industrial Relations, Cal/OSHA, 8 CCR 5194 Hazard Communication: California adopted GHS signal word system consistent with federal OSHA; state plan at least as effective as federal standard