14.3 Transport Hazard Class(es)
Transport hazard classes are standardized categories that identify the type of hazard presented by dangerous goods during transport. This section explains the international classification system, how hazard classes are determined, and why they are critical for safe transport.
What are Transport Hazard Classes?
Transport hazard classes are internationally standardized categories that classify dangerous goods based on their primary hazard. Each class represents a specific type of hazard (explosive, flammable, toxic, etc.) and is identified by a specific number and hazard symbol.
Transport hazard classes serve several essential purposes:
- Indicate the primary danger posed by the material
- Determine appropriate handling, packaging, and stowage requirements
- Guide emergency response procedures
- Establish segregation requirements from incompatible materials
- Provide quick visual identification through standardized hazard labels
The hazard class must be included in Section 14.3 of the Safety Data Sheet for any material classified as dangerous for transport.
Important for SDS compliance: If a material is classified as dangerous for transport under any transport regulations (ADR, IMDG, IATA, DOT), Section 14.3 must include the appropriate transport hazard class(es) and division(s). If the material is not classified as dangerous for transport, this should be explicitly stated.
The 9 Transport Hazard Classes
The UN system recognizes 9 primary hazard classes, with some classes divided into divisions to specify particular hazards more precisely.
Class 1
Explosives
Class 2
Gases
Class 3
Flammable Liquids
Class 4
Flammable Solids
Class 5
Oxidizing Substances
Class 6
Toxic Substances
Class 7
Radioactive Materials
Class 8
Corrosive Substances
Class 9
Miscellaneous Dangerous Goods
How Hazard Classes Are Determined
The assignment of a transport hazard class is based on the material's inherent properties and specific criteria outlined in transport regulations:
- Physical Testing: Materials are tested according to standardized methods to determine properties like flash point, boiling point, corrosivity, toxicity, etc.
- Regulatory Criteria: Test results are compared to established thresholds in transport regulations to determine the appropriate classification.
- Precedence of Hazards: When a material has multiple hazards, the primary hazard is determined according to a hazard precedence table.
- Specific Entries: The Dangerous Goods List in transport regulations provides specific hazard class assignments for common materials.
For mixtures and solutions, the hazard class is typically determined by testing the mixture itself or by applying calculation methods based on component properties.
Subsidiary Hazards
Many dangerous goods present more than one hazard. While the material is assigned a primary hazard class based on its most severe hazard, additional "subsidiary hazards" may also need to be communicated.
Example of Multiple Hazards:
Acetone Cyanohydrin (UN 1541)
- Primary Hazard: Class 6.1 (Toxic Substances)
- Subsidiary Hazard: Class 3 (Flammable Liquids)
This means that both hazards must be communicated during transport, with the toxic hazard considered primary according to the precedence of hazards rules.
In Section 14.3 of the SDS, all applicable hazard classes and divisions (both primary and subsidiary) should be listed.
Common Classification Mistakes:
- Confusing GHS hazard classes with transport hazard classes (they are different systems)
- Omitting subsidiary hazard classes or divisions
- Using outdated classification criteria
- Not considering physical state (solid vs. liquid) which can affect classification
- Failing to update the hazard class when formulation changes
- Misapplying the precedence of hazards rules for multi-hazard materials
Classification Differences Between Transport Modes
While the basic 9-class system is used globally, there can be differences in how materials are classified between different transport regulations:
| Transport Mode | Regulation | Key Differences |
|---|---|---|
| Road/Rail (Europe) | ADR/RID | Has specific European classification provisions; uses hazard identification numbers |
| Sea | IMDG Code | Emphasizes marine pollutants; special provisions for sea transport conditions |
| Air | IATA DGR | Generally more restrictive criteria; some materials forbidden on passenger aircraft |
| US Transport | 49 CFR | Uses slightly different terms for some classes; has US-specific provisions |
When providing information in Section 14.3 of an SDS, you should indicate the hazard class for each applicable transport regulation if there are differences.
Hazard Identification Systems
In addition to the class numbers and labels, several supplementary systems are used to communicate transport hazards:
Placards
Large versions of hazard labels used on transport vehicles and freight containers
Kemler Numbers
Used in Europe (ADR), these are hazard identification numbers that appear on orange panels
Marine Pollutant Mark
Additional mark for materials classified as harmful to the marine environment
Transport Hazard Classes vs. GHS Hazard Classes
It's important to understand that transport hazard classes (Section 14.3) are distinct from GHS hazard classes (Sections 2 and 3 of the SDS):
Transport Hazard Classes
- Developed specifically for transport safety
- 9 main classes with divisions
- Focus on physical hazards during transport
- Classification based on UN Model Regulations
- Used for shipping papers, labels, and placards
GHS Hazard Classes
- Developed for hazard communication in all contexts
- Multiple physical, health, and environmental hazard classes
- More comprehensive for workplace and consumer safety
- Classification based on GHS criteria
- Used for workplace labels and comprehensive SDSs
While there is some alignment between these systems, they have different purposes and criteria, and one cannot be directly translated to the other without proper evaluation.
Properly Completing Section 14.3 of an SDS
For a flammable cleaning solvent mixture containing acetone and isopropanol:
Correct format:
14.3 Transport hazard class(es)
- ADR/RID: 3
- IMDG: 3
- IATA: 3
For a material with subsidiary hazards:
14.3 Transport hazard class(es)
- ADR/RID: 8 (6.1)
- IMDG: 8 (6.1)
- IATA: 8 (6.1)
Where the primary hazard is Class 8 (Corrosive) and the subsidiary hazard is Class 6.1 (Toxic).
For a non-dangerous product:
14.3 Transport hazard class(es)
Not classified as dangerous for transport
Best Practice: Always refer to the most recent version of transport regulations to determine the correct hazard class for a material, as classification criteria may change over time. When in doubt, consult with a dangerous goods specialist or regulatory expert.
Class 1 - Explosives
Class 1 comprises explosive substances, explosive articles, and substances that produce a practical explosive or pyrotechnic effect.
Divisions:
- Division 1.1: Substances and articles which have a mass explosion hazard
- Division 1.2: Substances and articles which have a projection hazard but not a mass explosion hazard
- Division 1.3: Substances and articles which have a fire hazard and either a minor blast hazard or a minor projection hazard or both
- Division 1.4: Substances and articles which present no significant hazard
- Division 1.5: Very insensitive substances which have a mass explosion hazard
- Division 1.6: Extremely insensitive articles which do not have a mass explosion hazard
Examples of Class 1 Materials:
- Dynamite and blasting agents (1.1)
- Detonators and blasting caps (1.1B or 1.4B)
- Fireworks (1.1G, 1.2G, 1.3G, or 1.4G depending on type)
- Small arms ammunition (typically 1.4S)
- Airbag inflators and seatbelt pretensioners (1.4G)
Special Transport Considerations:
Class 1 materials have the most stringent transport requirements:
- Strict quantity limitations, especially for passenger transport
- Special packaging requirements with extensive testing
- Segregation from other hazardous materials
- Vehicle and routing restrictions
- Many require special permits or approvals
Many Class 1 materials are restricted or completely forbidden for normal commercial transport. Their transportation often requires special permits, approvals, and security plans.
Class 2 - Gases
Class 2 comprises gases compressed, liquefied, dissolved under pressure, or deeply refrigerated. Any material that is a gas at 20°C (68°F) and 101.3 kPa (14.7 psi), or has a vapor pressure greater than 300 kPa (43.5 psi) at 50°C (122°F).
Divisions:
- Division 2.1: Flammable gases (capable of igniting in a mixture of 13% or less with air)
- Division 2.2: Non-flammable, non-toxic gases
- Division 2.3: Toxic gases (known to be toxic or corrosive to humans)
Examples of Class 2 Materials:
- Division 2.1: Propane, butane, acetylene, hydrogen
- Division 2.2: Nitrogen, carbon dioxide, compressed air, helium
- Division 2.3: Chlorine, ammonia, sulfur dioxide, phosgene
Special Transport Considerations:
- Pressure vessels must meet specific design and testing requirements
- Flammable gases (2.1) must be kept away from ignition sources
- Many toxic gases (2.3) are forbidden on passenger aircraft
- Cylinders require periodic inspection and testing
- Valve protection is typically required
- Specific stowage and ventilation requirements apply for sea transport
Even small gas cylinders can pose significant hazards if damaged, particularly Division 2.3 toxic gases which can be immediately dangerous to life or health in very small quantities.
Class 3 - Flammable Liquids
Class 3 comprises liquids, mixtures of liquids, or liquids containing solids in solution or suspension that give off flammable vapors at specific temperatures. The primary criterion for classification is flash point.
Classification Criteria:
Class 3 flammable liquids are generally classified by flash point:
- Packing Group I: Flash point < 23°C (73°F) and initial boiling point ≤ 35°C (95°F) - Highly flammable
- Packing Group II: Flash point < 23°C (73°F) and initial boiling point > 35°C (95°F) - Medium hazard
- Packing Group III: Flash point ≥ 23°C (73°F) and ≤ 60°C (140°F) - Low hazard
Note: There are some regulatory variations in these thresholds between transport modes.
Examples of Class 3 Materials:
- Gasoline/petrol (UN 1203)
- Acetone (UN 1090)
- Ethanol (UN 1170)
- Paint and paint-related materials (UN 1263)
- Diesel fuel (UN 1202)
- Adhesives containing flammable liquid (UN 1133)
- Perfumery products (UN 1266)
- Alcohols, n.o.s. (UN 1987)
Special Transport Considerations:
- Must be kept away from sources of ignition
- Packaging must be able to withstand pressure build-up from heating
- Quantity limitations apply, especially for passenger aircraft
- May require electrical grounding during loading/unloading
- Some have specific temperature control requirements
- Additional precautions required for marine transport (flash point relates to fire hazard at sea)
Flammable liquids are one of the most commonly transported classes of dangerous goods. Despite their familiarity, they remain highly hazardous, particularly in transport due to potential for spills, vapor accumulation, and ignition.
Class 4 - Flammable Solids
Class 4 includes substances that are flammable in solid form or that can contribute to fire through friction, self-heating, or contact with water.
Divisions:
- Division 4.1: Flammable solids, self-reactive substances, and solid desensitized explosives
- Division 4.2: Substances liable to spontaneous combustion
- Division 4.3: Substances which, in contact with water, emit flammable gases
Examples of Class 4 Materials:
- Division 4.1: Matches, naphthalene, metal powders, nitrocellulose
- Division 4.2: White phosphorus, activated carbon, fish meal (unstabilized)
- Division 4.3: Sodium, calcium carbide, aluminum powder
Special Transport Considerations:
- Division 4.1 materials must be kept away from heat and ignition sources
- Division 4.2 materials may ignite without an external ignition source and often require air-tight packaging
- Division 4.3 materials must be kept dry and protected from water exposure
- Some self-reactive substances require temperature control during transport
- Special packaging techniques often needed to prevent friction or water contact
Division 4.3 water-reactive materials are particularly dangerous in emergency situations involving water (e.g., firefighting, rain, flooding), as they can release flammable gases which may ignite or explode. Emergency responders must be aware of this hazard.
Class 5 - Oxidizing Substances and Organic Peroxides
Class 5 comprises substances that can cause or contribute to combustion, generally by yielding oxygen or similar processes.
Divisions:
- Division 5.1: Oxidizing substances that are not necessarily combustible themselves but may cause or contribute to the combustion of other materials by yielding oxygen
- Division 5.2: Organic peroxides, which are thermally unstable substances that can undergo exothermic self-accelerating decomposition
Examples of Class 5 Materials:
- Division 5.1: Ammonium nitrate, hydrogen peroxide, sodium nitrate, calcium hypochlorite
- Division 5.2: Benzoyl peroxide, methyl ethyl ketone peroxide, dibenzoyl peroxide
Special Transport Considerations:
- Must be kept away from combustible materials
- May require special packaging to prevent contact with incompatible materials
- Some organic peroxides require temperature control during transport
- Many have specific quantity limitations
- Should be segregated from other dangerous goods, particularly flammable materials
- May have specific vehicle and stowage requirements
Oxidizing substances (5.1) do not burn themselves but provide oxygen that intensifies fires. Organic peroxides (5.2) contain both fuel (carbon) and oxygen in the same molecule, making them particularly dangerous as they can burn without external air.
Class 6 - Toxic and Infectious Substances
Class 6 includes substances that are liable to cause death or injury by poisoning or disease.
Divisions:
- Division 6.1: Toxic substances which can cause death, serious injury, or harm to human health if swallowed, inhaled, or contacted through skin
- Division 6.2: Infectious substances containing pathogens (microorganisms) that can cause disease in humans or animals
Examples of Class 6 Materials:
- Division 6.1: Aniline, pesticides, arsenic compounds, cyanide compounds, methanol
- Division 6.2: Medical waste, biological samples, laboratory cultures, clinical specimens
Classification Criteria for Division 6.1:
Division 6.1 is assigned based on oral, dermal, and inhalation toxicity data:
- Packing Group I: Very toxic substances
- Packing Group II: Toxic substances
- Packing Group III: Slightly toxic substances
Special Transport Considerations:
- Requires careful handling to prevent exposure
- Many are forbidden or severely restricted on passenger aircraft
- Often requires specialized packaging to prevent leakage
- Category A infectious substances (highly infectious) have very stringent packaging requirements
- Must be segregated from foodstuffs and animal feeds
- Emergency response procedures are critical in case of spills or leaks
Even small quantities of highly toxic materials (PG I) can pose significant health hazards if released. Infectious substances require special handling not only for safety but also to maintain the viability of the biological material in some cases.
Class 7 - Radioactive Materials
Class 7 consists of materials containing radionuclides where both the activity concentration and the total activity in the consignment exceed specific values.
Categories:
Radioactive materials are categorized based on the maximum radiation level at the package surface and at 1 meter from the package:
- Category I - WHITE: Very low external radiation levels
- Category II - YELLOW: Low external radiation levels
- Category III - YELLOW: Higher external radiation levels
Examples of Class 7 Materials:
- Medical isotopes for diagnosis and treatment
- Industrial radiography sources
- Nuclear fuel materials
- Radioactive waste
- Certain measuring instruments containing radioactive sources
- Uranium and thorium compounds
Special Transport Considerations:
- Requires special packaging designed to contain radiation
- Transport index (TI) and criticality safety index (CSI) determine handling requirements
- Strict documentation requirements including details of isotopes, activity levels
- Specific separation distances from people, undeveloped film, and other radioactive packages
- Additional approvals may be required for certain materials
- Special training required for handlers
Transport of radioactive materials is heavily regulated not only by dangerous goods regulations but also by nuclear regulatory authorities. International shipments often require additional governmental approvals and notifications.
Class 8 - Corrosive Substances
Class 8 comprises substances which, by chemical action, can cause severe damage when in contact with living tissue, or can materially damage other goods or transport equipment.
Classification Criteria:
Corrosive substances are classified based on their ability to cause destruction of skin tissue or corrosion on steel or aluminum:
- Packing Group I: Very corrosive - causes full thickness destruction of intact skin tissue within 60 minutes of contact
- Packing Group II: Corrosive - causes full thickness destruction of intact skin tissue within more than 60 minutes but not more than 4 hours
- Packing Group III: Mildly corrosive - causes full thickness destruction within 4 hours to 14 days, or causes a specified corrosion rate on steel or aluminum
Examples of Class 8 Materials:
- Acids: Sulfuric acid, hydrochloric acid, nitric acid
- Bases: Sodium hydroxide, potassium hydroxide, ammonia solutions
- Other corrosives: Battery fluid, formaldehyde solutions, phenol
Special Transport Considerations:
- Packaging must be resistant to the corrosive action of the contents
- Many corrosives react dangerously with other substances
- Leakage can damage transport equipment (vehicles, aircraft) and other cargo
- Secondary containment or absorbent materials often required
- Vented closures may be required for some corrosives that generate pressure
- Special segregation requirements from other dangerous goods
Corrosive materials can cause immediate and severe tissue damage upon contact. Additionally, many corrosives have subsidiary hazards such as toxicity or oxidizing properties, making them particularly dangerous in transport incidents.
Class 9 - Miscellaneous Dangerous Goods
Class 9 includes substances and articles which present a danger during transport but do not meet the criteria for inclusion in any other class. This is essentially a "catch-all" category for materials that have transport risks not covered by other classes.
Types of Class 9 Materials:
- Environmentally hazardous substances: Materials that present a hazard to aquatic environments
- Elevated temperature materials: Substances transported at high temperatures (≥100°C liquid, ≥240°C solid)
- Genetically modified organisms: Those that can alter animals, plants, or microorganisms in a way not normally found in nature
- Lithium batteries: Due to their potential for short circuit, fire, and thermal runaway
- Magnetized materials: Those that generate a magnetic field that can affect aircraft navigation systems
- Aviation regulated substances: Materials that have anesthetic, irritating, or other properties that could cause discomfort to aircraft crew
Examples of Class 9 Materials:
- Lithium-ion batteries (UN 3480)
- Environmentally hazardous substance, liquid, n.o.s. (UN 3082)
- Environmentally hazardous substance, solid, n.o.s. (UN 3077)
- Dry ice (carbon dioxide, solid) (UN 1845)
- First aid kits (UN 3316)
- Vehicles, flammable gas powered (UN 3166)
Special Transport Considerations:
- Requirements vary widely based on the specific material
- Lithium batteries have extensive packaging, marking, and documentation requirements
- Environmentally hazardous substances require the marine pollutant mark for sea transport
- Dry ice requires packages that allow for the release of carbon dioxide gas
- Vehicle transport has specific fuel system and battery disconnection requirements
Don't be misled by the term "miscellaneous" - Class 9 materials can be highly dangerous. Lithium battery incidents, for example, have caused numerous fires in transport, and environmentally hazardous substances can cause severe long-term ecosystem damage if released.