ADR Class by Class: Which Dangerous Goods Create the Biggest Compliance Risk for Operators?

ADR dangerous goods classes most likely to create compliance risk for transport operators are Class 3 flammable liquids, Class 2 gases, and Class 8 corrosive substances. Together, these categories account for the majority of hazardous materials transported by road across the UK and Europe.

Dangerous goods transport is often associated with specialist chemical tankers or hazardous-materials fleets. In reality, hazardous substances move through a wide range of everyday road freight operations — from construction firms transporting fuel to logistics networks carrying paints, cleaning chemicals, and batteries.

Statistics from the Department for Transport show that around 77 million tonnes of dangerous goods were transported by GB-registered HGVs in 2024, accounting for roughly 5% of all goods moved by road.

While dangerous goods represent a relatively small share of overall freight, they carry significant regulatory responsibilities under ADR — the international framework governing the carriage of dangerous goods by road. ADR sets requirements for classification, packaging, vehicle equipment, documentation, and driver training.

For transport managers, the key compliance question is not simply whether ADR applies. It is which ADR classes are most likely to appear in everyday freight operations — and where compliance problems are most likely to arise.

ADR Dangerous Goods Classes That Dominate UK Road Freight

The most detailed breakdown of dangerous goods movements in Britain comes from the Department for Transport’s road freight statistics.

The 2024 data shows that a small number of ADR classes account for the majority of dangerous goods transported by road.

ADR Class 3 – Flammable Liquids

By a large margin, the most common dangerous goods transported on UK roads are ADR Class 3 flammable liquids.

In 2024:

• Around 50 million tonnes of dangerous goods transported by GB-registered HGVs were flammable liquids
• Representing roughly 66% of dangerous goods freight by weight

Typical Class 3 materials include:

• Petrol and diesel
• Paints and coatings
• Solvents
• Resins and adhesives
• Industrial cleaning chemicals

These products are used across many industries, which means they frequently appear in everyday freight operations rather than specialist hazardous-goods transport.

ADR Class 2 – Gases

The second largest category is ADR Class 2 gases.

In 2024:

• Roughly 9 million tonnes of dangerous goods transported were gases
• Representing around 12% of dangerous goods freight

Examples include:

• Propane and LPG
• Oxygen and acetylene
• Refrigerant gases
• Industrial gases used in welding and manufacturing

Gas cylinders are widely used across sectors such as construction, hospitality, facilities maintenance, and manufacturing, meaning they regularly appear in routine transport operations.

ADR Class 8 – Corrosive Substances

The third most common category is ADR Class 8 corrosive substances.

In 2024:

• Approximately 7 million tonnes of corrosive materials were transported by GB-registered HGVs
• Representing roughly 9% of dangerous goods movements

Examples include:

• Sulphuric acid
• Sodium hydroxide (caustic soda)
• Battery acids
• Concentrated industrial cleaning chemicals

Although transported in lower volumes than fuels or gases, corrosive substances present significant hazards if containment fails.

European Data Shows the Same Pattern

The UK pattern is broadly consistent with dangerous goods transport across Europe.

Data from Eurostat shows that flammable liquids account for more than half of dangerous goods transported by road across Europe, measured in tonne-kilometres.

The Eurostat database shows a similar distribution of dangerous goods across ADR classes, with flammable liquids, gases, and corrosive substances consistently representing the largest categories of hazardous materials transported by road.

Because the ADR regulatory framework is harmonised across Europe, these datasets provide useful context for understanding how dangerous goods typically move through transport networks, including the UK.

Why ADR Classes 3, 2 and 8 Matter Most for Compliance

Looking at the ADR classes that appear most frequently in UK road freight, three stand out from a compliance perspective: flammable liquids, gases, and corrosive substances. Each presents a different type of operational challenge for transport managers.

Class 3: High Exposure Across Everyday Freight

Flammable liquids appear across a wide range of supply chains, meaning many operators encounter them as part of routine transport rather than specialist hazardous-goods work.

These products move regularly through construction supply chains, distribution networks, and maintenance operations.

Because these goods are so common, compliance failures often arise through the assumption that ADR rules do not apply.

It’s important to understand where ADR exemptions apply. Although flammable liquids are common in construction supply chains, fuel deliveries to sites may be carried under the ADR small-load exemption provided the dangerous goods are packaged in approved containers and the total quantity on the vehicle remains within the limits specified in ADR 1.1.3.6.3.

In practice, issues frequently involve:

• Documentation errors
• Misunderstanding ADR exemptions
• Drivers lacking the correct ADR certification

In other words, the risk with Class 3 goods often lies in how frequently they appear in normal freight operations.

Class 2: Pressure Hazards and Cylinder Handling

Compressed gases present a different type of compliance challenge.

Rather than packaging and documentation alone, the key risks often relate to how cylinders are secured and handled during transport. Gas cylinders contain pressurised substances that can become extremely hazardous if damaged or released.

These commonly appear in sectors such as construction, manufacturing, hospitality, and facilities maintenance.

Common issues identified during inspections include:

• Poorly secured cylinders
• Incorrect vehicle marking
• Lack of driver awareness around emergency procedures

Gas cylinders carried by service engineers (exemption for use for maintenance, surveying or repairs and such things as service engineers when the carriage of DG is not their main activity but DG substances used to complete part of the work is the same exemption as above). Same for carrying batteries for tools etc.

Class 8: Smaller Volumes but Higher Immediate Hazard

Corrosive substances present another distinct risk profile.

While these goods may appear less frequently than fuels or gases, they require careful packaging and handling because even small leaks can cause serious injury or environmental damage.

These materials commonly move through agriculture, manufacturing, and facilities management supply chains.

For operators transporting corrosives, compliance risks often relate to:

• Packaging integrity
• Correct segregation of incompatible substances
• Appropriate emergency response arrangements

Other ADR Classes That Can Still Create Compliance Problems

While flammable liquids, gases, and corrosive substances dominate dangerous goods movements, other ADR classes can still create operational risk depending on the sector.

Class 5 – Oxidising Substances

Oxidising substances release oxygen and can intensify fires.

These materials frequently appear in:

• Fertiliser supply chains
• Chemical manufacturing
• Agricultural distribution

Transporting oxidising agents requires careful segregation from incompatible substances.

Class 9 – Miscellaneous Dangerous Goods

ADR Class 9 includes a wide range of substances, including:

• Lithium batteries
• Environmentally hazardous materials

The rapid growth of battery logistics and recycling operations means Class 9 goods are appearing more frequently within freight networks, particularly in electronics and e-commerce supply chains.

ADR Exemptions for Common Work Activities

Be aware that ADR recognises that some activities involve carrying small quantities of dangerous goods as part of routine work, and certain exemptions may apply where the risk is limited. For example, fuel deliveries to construction sites may fall within an exemption where no individual package exceeds 450 litres, including IBCs, and the total quantity carried remains within the threshold limits set out in ADR 1.1.3.6.3 (the small-load exemption).

Similar provisions apply where dangerous goods are carried by service engineers, maintenance personnel or surveyors as part of their work. In these cases, items such as gas cylinders used for maintenance or repair, or batteries for tools and equipment, may be transported where the carriage of dangerous goods is not the main activity but is necessary to complete the task. Even where exemptions apply, dangerous goods must still be safely packaged, handled and secured during transport.

ADR Compliance and Traffic Commissioner Risk

While no published dataset directly links specific ADR hazard classes to Traffic Commissioner cases, freight statistics provide an important indication of where compliance issues are most likely to arise.

Put simply, the more frequently a dangerous goods class appears on UK roads, the greater the likelihood that operators will encounter ADR compliance issues involving those goods.

With flammable liquids, gases, and corrosive substances making up the majority of dangerous goods transported by road, these are the categories transport managers are most likely to encounter in everyday operations.

For regulators, however, the focus is rarely the substance itself.

Instead, Traffic Commissioners are concerned with how well operators understand and manage their regulatory responsibilities.

ADR failures that raise concerns during regulatory investigations often include:

• Drivers transporting dangerous goods without valid ADR certification
• Incomplete or incorrect dangerous goods documentation
• Failure to carry required safety equipment
• Improper packaging or labelling of hazardous materials
• Lack of management oversight from the transport manager

In many cases, these issues arise where dangerous goods appear within routine freight movements, such as:

• Fuel deliveries to construction sites
• Gas cylinders carried by service engineers
• Palletised chemical products moving through logistics networks

Where regulators identify repeated ADR failures, it can suggest wider weaknesses in an operator’s compliance systems, which is what ultimately attracts the attention of the Traffic Commissioner.

What Transport Managers Should Focus On

For operators working in sectors such as construction, logistics, and agriculture, dangerous goods often appear within everyday operations rather than specialist hazardous-materials transport.

Practical steps to manage ADR risk include:

• Identifying dangerous goods within the supply chain using safety data sheets and UN classifications
• Ensuring drivers hold appropriate ADR certification where required
• Maintaining accurate transport documentation
• Auditing packaging, labelling, and vehicle equipment requirements

In many cases, the biggest compliance risk is simply not recognising when ADR rules apply to the goods being transported.

The Key Takeaway

Latest UK freight statistics show that:

• Flammable liquids dominate dangerous goods transport, accounting for roughly two-thirds of hazardous materials moved by road in Britain
• Gases and corrosive substances are the next most common categories
• European transport data shows a very similar pattern across the wider ADR network

For transport managers, this means ADR compliance issues are most likely to arise where operations involve:

• Fuels and solvents
• Compressed gases
• Chemical cleaning products
• Battery products and industrial chemicals

Understanding which ADR classes appear most frequently in your sector is the first step in ensuring operations remain compliant — and staying well clear of regulatory attention.

Transport operators that want to strengthen their compliance systems should ensure staff understand the basics of dangerous goods transport, even where ADR loads form only a small part of their operation.

Total Compliance provides specialist training and consultancy to help operators meet these obligations, including dangerous goods awareness training, ADR driver training and DGSA support services. These programmes help transport managers and drivers understand when ADR rules apply, how to manage dangerous goods safely, and how to maintain the robust compliance systems regulators expect.