Key Summary: H-statements (Hazard statements) are standardized phrases under the GHS and EU CLP Regulation (EC 1272/2008) that describe the nature and severity of chemical hazards. Each H-statement uses a code format of “H” followed by three digits: H2xx for physical hazards (explosivity, flammability), H3xx for health hazards (toxicity, CMR effects, organ damage), and H4xx for environmental hazards (aquatic toxicity). H-statements replaced the former R-phrases in 2015 and appear on all chemical labels and safety data sheets. A substance may carry multiple H-statements reflecting different hazard endpoints. They are fundamental to hazard identification, risk assessment prioritization, and determining workplace controls.
Hazard statements — commonly referred to as H-statements — are standardized phrases under the Globally Harmonized System (GHS) and the European CLP Regulation (EC 1272/2008) that describe the nature and severity of chemical hazards. They replaced the former Risk Phrases (R-phrases) in 2015 and are now the global standard for hazard communication on labels and safety data sheets. For occupational hygienists, H-statements are a fundamental tool for hazard identification, risk assessment prioritization, and the determination of appropriate workplace controls.
Structure of H-Statements
Each H-statement consists of the letter “H” followed by a three-digit number. The first digit indicates the type of hazard:
- H2xx — Physical hazards (explosivity, flammability, oxidizing properties)
- H3xx — Health hazards (toxicity, irritation, sensitization, CMR effects, organ toxicity)
- H4xx — Environmental hazards (aquatic toxicity)
The numbering within each series generally follows the order of hazard classes in the CLP Regulation. A substance may carry multiple H-statements if it is classified for several hazard endpoints.
H200 Series: Physical Hazards
The H200 series covers physical hazards that relate primarily to fire, explosion, and reactivity risks. Key statements include:
- H200–H205 — Explosive hazards (unstable explosives through mass explosion hazard)
- H220–H232 — Flammability (extremely flammable gas through pyrophoric liquid/solid)
- H240–H242 — Self-reactive substances and organic peroxides (heating may cause explosion/fire)
- H250–H252 — Spontaneous combustion and self-heating
- H260–H261 — Emission of flammable gas on contact with water
- H270–H272 — Oxidizing properties
- H280–H284 — Gases under pressure
While physical hazards are primarily the domain of fire safety and process engineering, occupational hygienists must be aware of them because they affect the design of ventilation systems, storage areas, and emergency response procedures.
H300 Series: Health Hazards
The H300 series is the most critical for occupational hygienists. It encompasses all health-related hazards from acute toxicity to chronic effects including carcinogenicity.
Acute Toxicity
- H300 — Fatal if swallowed
- H301 — Toxic if swallowed
- H302 — Harmful if swallowed
- H310 — Fatal in contact with skin
- H311 — Toxic in contact with skin
- H312 — Harmful in contact with skin
- H330 — Fatal if inhaled
- H331 — Toxic if inhaled
- H332 — Harmful if inhaled
The severity decreases from Category 1 (fatal) through Category 4 (harmful). For inhalation exposure in the workplace, H330, H331, and H332 are particularly relevant.
Skin and Eye Effects
- H314 — Causes severe skin burns and eye damage
- H315 — Causes skin irritation
- H317 — May cause an allergic skin reaction (skin sensitizer)
- H318 — Causes serious eye damage
- H319 — Causes serious eye irritation
H317 (skin sensitizer) deserves special attention in occupational hygiene. Once a worker is sensitized, even trace exposures can trigger allergic dermatitis. Substances carrying H317 require strict skin exposure prevention programs.
Respiratory and Organ Effects
- H334 — May cause allergy or asthma symptoms or breathing difficulties if inhaled (respiratory sensitizer)
- H335 — May cause respiratory irritation
- H336 — May cause drowsiness or dizziness
H334 (respiratory sensitizer) is one of the most significant H-statements for workplace health. Respiratory sensitization can lead to occupational asthma, which is often irreversible. Substances with H334 include isocyanates, certain wood dusts, and some enzymes used in detergent manufacturing.
CMR Effects (Carcinogenic, Mutagenic, Reprotoxic)
These are among the most serious health classifications and trigger specific regulatory obligations:
- H340 — May cause genetic defects (mutagenic Category 1A/1B)
- H341 — Suspected of causing genetic defects (mutagenic Category 2)
- H350 — May cause cancer (carcinogenic Category 1A/1B)
- H351 — Suspected of causing cancer (carcinogenic Category 2)
- H360 — May damage fertility or the unborn child (reprotoxic Category 1A/1B)
- H361 — Suspected of damaging fertility or the unborn child (reprotoxic Category 2)
- H362 — May cause harm to breast-fed children
Substances classified as H340, H350, or H360 (Category 1A or 1B) are placed on the Dutch SZW-list of CMR substances and are subject to the substitution principle. For more detail on CMR substances and employer obligations, see our CMR substances guide.
Specific Target Organ Toxicity (STOT)
- H370 — Causes damage to organs (single exposure)
- H371 — May cause damage to organs (single exposure)
- H372 — Causes damage to organs through prolonged or repeated exposure
- H373 — May cause damage to organs through prolonged or repeated exposure
H372 and H373 are especially important for occupational settings where chronic low-level exposure is the primary concern. The specific target organ is usually identified (e.g., “H372 — Causes damage to the liver through prolonged or repeated exposure”).
Aspiration Hazard
- H304 — May be fatal if swallowed and enters airways
H400 Series: Environmental Hazards
- H400 — Very toxic to aquatic life
- H410 — Very toxic to aquatic life with long lasting effects
- H411 — Toxic to aquatic life with long lasting effects
- H412 — Harmful to aquatic life with long lasting effects
- H413 — May cause long lasting harmful effects to aquatic life
EUH-Statements: Europe-Specific
The CLP Regulation includes additional hazard statements unique to the European Union, prefixed with “EUH”:
- EUH014 — Reacts violently with water
- EUH029 — Contact with water liberates toxic gas
- EUH031 — Contact with acids liberates toxic gas
- EUH032 — Contact with acids liberates very toxic gas
- EUH066 — Repeated exposure may cause skin dryness or cracking
- EUH070 — Toxic by eye contact
- EUH071 — Corrosive to the respiratory tract
These do not have GHS equivalents and are specific to EU labelling requirements.
H-Statements and DOHSBase Kick-Off Values
A key application of H-statements in DOHSBase is their role in the calculation of kick-off values. When a substance has no formal occupational exposure limit, DOHSBase assigns a kick-off value based on the substance’s most severe H-statement. The methodology works as follows:
- Substances are grouped by their most severe H-statement
- Within each group, the distribution of known OELs is analyzed
- The kick-off value is set at the 10th percentile tolerance lower bound of this distribution
This means the H-statement classification directly determines which kick-off value a substance receives, making accurate H-statement data essential for proper risk assessment.
H-Statement Data in DOHSBase
DOHSBase contains H-statement classification data from multiple sources:
- Harmonized classifications from ECHA Annex VI to CLP — these are legally binding EU-wide classifications established through a rigorous evaluation process
- Notified classifications from ECHA’s Classification and Labelling Inventory — submitted by registrants and importers, representing the broadest coverage
- Self-classifications where substances have been assessed but not yet formally harmonized
The database covers over 200,000 substances with classification data, making it one of the most comprehensive sources for identifying substance hazards and linking them to quantitative exposure benchmarks. For a visual overview of how H-statements connect to GHS pictograms, see our pictogram reference guide.
What Do the Percentages Behind H-Statements in DOHSBase Mean?
In the substance view of DOHSBase Online, each H-statement is shown with an accompanying percentage. This percentage represents the classification frequency: the share of notifications in ECHA’s Classification and Labelling Inventory that have classified the substance with that specific H-statement.
For example: if a substance has been notified by 100 different registrants to ECHA and 87 of them have assigned H351 (Suspected of causing cancer), DOHSBase Online displays “H351 — 87%”. The percentage is a direct representation of the level of agreement among notifiers.
How to interpret the percentages in practice:
- High percentages (above ~80%) indicate broad consensus among registrants on the classification. The likelihood that an independent evaluation would arrive at the same H-statement is high.
- Lower percentages indicate variation between notifiers, which can result from differences in available data, conservative versus permissive interpretation of CLP criteria, or historical differences that have not yet been corrected by later revisions.
- Harmonized classifications from ECHA Annex VI are typically shown at 100% because they are legally binding for all registrants within the EU. These take precedence over notified classifications when there is doubt.
Practical advice: use the H-statement with the highest percentage as the primary starting point in your risk assessment, but stay alert to H-statements with substantially lower percentages — these may indicate a hazard endpoint recognised by a minority of notifiers that proves relevant on independent review. For substances where you base control measures or a formal assessment on the classification, it is wise to consult the individual notifications on the ECHA website when the classification scores below ~80%.