DGSA Domain 2: All classes - Complete Study Guide 2026

What the All Classes Paper Actually Tests

Among the five examination papers that make up the Dangerous Goods Safety Adviser qualification, Domain 2 - the All Classes paper - is the one that separates candidates who genuinely understand dangerous goods from those who have only memorised surface-level rules. Where the Domain 1 Core paper establishes your grasp of regulatory frameworks and adviser responsibilities, Domain 2 pushes you into the technical detail of every dangerous goods class: what they are, how they behave, and precisely how they must be classified, packaged, marked, labelled, and documented.

The scope is deliberately broad. The nine classes of dangerous goods recognised under the international modal regulations - from Class 1 explosives through to Class 9 miscellaneous dangerous substances - each carry their own classification hierarchies, packing groups, special provisions, and exemption thresholds. Domain 2 expects candidates to be conversant with all of them, not just the classes most common in their day-to-day role.

This matters practically, because a DGSA certificate is a legal requirement for undertakings that consign, carry, or handle dangerous goods. Employers in chemical manufacturing, logistics, pharmaceuticals, waste management, oil and gas, and aerospace all need advisers who can field questions about any goods their organisation touches. Domain 2 is the paper that proves you can do that across the board.

Exam Format, Duration, and Open-Book Rules

The All Classes paper runs for 1 hour 45 minutes - the same duration as the Road, Rail, and Inland Waterways mode papers, and thirty minutes longer than the Core paper. That additional time reflects the sheer volume of regulatory material the questions can draw on. You need to answer correctly on at least 65% of the marks available; every required paper carries that same threshold, and there is no compensatory scoring between papers.

The examination fee is £135 per paper, payable to Qualifications Scotland, which administers the UK DGSA examination programme on behalf of the Department for Transport. The exam is conducted in person - there is no remote or online sitting option under the current programme.

The open-book rule is the feature most candidates focus on when they first read the regulations, and it is both a significant advantage and a potential trap. You are permitted to bring printed copies of the relevant modal regulations - ADR for road, RID for rail, ADN for inland waterways - along with other listed dangerous goods regulations. However, the questions are designed for someone who can navigate those documents efficiently. A candidate who opens their copy of ADR on question one and begins searching from page one will not finish the paper in time. The open-book provision rewards preparation, not improvisation.

For a full breakdown of how exam costs stack up across all the papers you will likely need to sit, see the DGSA Certification Cost 2026: Complete Pricing Breakdown.

Core Subject Areas You Must Master

The All Classes paper draws from a defined syllabus that mirrors the classification and general transport chapters of the modal regulations. The following domain boxes outline the main areas and what competent-level understanding looks like for each.

Classification: The Heart of Domain 2

If there is a single area where candidates lose marks disproportionately, it is classification. The regulations contain thousands of listed entries, a large number of generic and not-otherwise-specified entries, and a hierarchical decision process for assigning the correct UN number to a substance or mixture that is not explicitly listed. Domain 2 questions frequently test this decision process rather than simple lookup tasks.

You need to understand the order of precedence for hazard classes - the rules that determine which class takes priority when a substance presents multiple hazards. Class 1, Class 6.2, and Class 7 operate under specific primacy rules that override the general precedence table in the regulations. Getting these wrong in an exam question will cost you marks even if the rest of your answer is correct.

Packing group assignment is another high-frequency topic. For flammable liquids (Class 3) and many Class 4 and Class 8 substances, packing group depends on measurable physical properties: flash point, boiling point, and oral/dermal/inhalation toxicity values for Class 6.1. Questions will present you with data and ask you to assign the correct packing group. Knowing the thresholds by class is essential - and since the exam is open-book, knowing exactly which table in ADR gives you those thresholds is equally essential.

Packaging, Marking, and Labelling Requirements

The packaging chapters of ADR and the equivalent modal regulations are dense, but they follow a logical structure once you understand the hierarchy: class and division determine which packaging types are permitted; packing group determines which performance level is required; quantity and concentration thresholds determine whether simplified regimes like limited quantities or excepted quantities apply.

Candidates frequently underestimate the labelling requirements for subsidiary hazards. Many dangerous goods carry more than one hazard - a flammable toxic liquid, for example, requires both a Class 3 flammable liquid label and a Class 6.1 toxic label. The regulations specify which subsidiary hazard labels are mandatory and which are optional for each primary class, and that detail is fair game in Domain 2 questions.

For packaging marks, the UN specification mark is a string of information that tells the trained reader what the packaging is designed for. Domain 2 tests whether you can read that mark and assess whether it is appropriate for the goods you are proposing to use it with. This is a practical skill that advisers use routinely when reviewing consignment plans.

Documentation Requirements Across All Classes

Transport documentation for dangerous goods is not simply a matter of filling in a form. The dangerous goods description must appear in the correct prescribed order, and additional elements vary by class. Class 1 shipments require the net explosive mass. Class 6.1 and Class 6.2 shipments carry specific description requirements. Radioactive materials (Class 7) require transport index and criticality safety index information. Each of these class-specific additions is a potential question focus.

The regulations also permit a range of exemptions from documentation requirements - small quantities, excepted quantities, goods carried under exemption provisions - and Domain 2 will test whether you know when those exemptions apply and when they do not. Misapplying an exemption is a compliance failure, and the exam reflects that by making exemption thresholds a recurring topic.

Practice navigating from a described scenario to the correct transport document content quickly. In 1 hour 45 minutes across all the question areas, documentation questions need to be answered efficiently. The Best DGSA Practice Questions 2026 resource explains the question formats in detail and is worth reviewing before your first timed practice session.

How Domain 2 Fits Into the Full DGSA Qualification

The DGSA qualification requires candidates to pass a combination of papers: the Core paper (Domain 1), the All Classes paper (Domain 2), and at least one mode-specific paper - Road (Domain 3), Rail (Domain 4), or Inland Waterways (Domain 5). Some candidates sit multiple mode papers if their organisation operates across more than one transport mode.

Domain 2 sits between the regulatory framework knowledge of Domain 1 and the mode-specific operational requirements of Domains 3-5. The All Classes content underpins everything in the mode papers: when Domain 3 (Road) asks about vehicle placarding or emergency information panels, the foundation knowledge is your Domain 2 understanding of what labels and marks are required. When Domain 4 (Rail) addresses wagon documentation, the dangerous goods description rules you learned in Domain 2 apply directly.

This interconnection means that studying Domain 2 thoroughly is not just about passing one paper - it makes every other paper more manageable. The DGSA Exam Domains 2026: Complete Guide to All 5 Content Areas shows how the five papers relate to each other and where their content overlaps, which is useful for planning your overall study strategy.

For candidates wondering how demanding the qualification is overall, How Hard Is the DGSA Exam? Complete Difficulty Guide 2026 provides a realistic assessment without overstating or understating the challenge.

A Realistic Study Schedule for Domain 2

Domain 2 rewards structured, progressive study. Because the content spans all nine dangerous goods classes, a random approach to revision leaves significant gaps. The following timeline assumes you are studying for Domain 2 alongside Domain 1 and one mode paper, which is the most common candidate situation.

The spaced repetition principle applies usefully here: review classification criteria for Classes 1 and 2 briefly at the start of Week 3, even though your primary focus has moved on. Because Domain 2 covers so many classes, the risk of forgetting earlier material while learning later material is real, and short review sessions at the start of each week counteract that drift.

Using Your Reference Materials Effectively

The open-book provision is often misunderstood as a safety net. It is better understood as an efficiency tool - one that rewards candidates who have prepared their reference materials as carefully as they have prepared their knowledge.

Before your exam, your printed ADR (or equivalent modal regulation) should have tabbed dividers at minimum for: Part 2 (Classification), Part 3 (Dangerous Goods List and Special Provisions), Part 4 (Packaging), Part 5 (Consignment Procedures - marking, labelling, documentation). Write the division or chapter topic on each tab. Within Part 2, mark the page where each class's classification criteria begins. Within Part 3, mark the dangerous goods list itself and the special provisions table.

During the exam, use your reference materials to confirm answers you are fairly confident about, not to discover answers you have no knowledge of. Candidates who use the open-book materials as their primary source of information rather than a verification tool consistently struggle with time management. The DGSA Exam Day Tips: 15 Strategies to Maximize Your Score covers reference material preparation in detail alongside other practical strategies for the exam sitting itself.

If you want to see how your preparation is progressing before the actual exam day, the DGSA Exam Prep practice test platform offers domain-specific question sets that mirror the format and difficulty level of the actual papers. Running timed practice sessions against Domain 2 topics is one of the most reliable ways to identify which class areas need more work before you sit.

Candidates who are still weighing up whether the full qualification is worthwhile for their career situation may find the analysis in Is the DGSA Certification Worth It? Complete ROI Analysis 2026 helpful alongside the practical study material here. And for those who have already passed and are looking ahead, note that the DGSA certificate is valid for five years - renewal requires passing the relevant exams again before expiry, as covered in the DGSA Recertification 2026: Requirements, Costs & Timeline.

The DGSA Exam Prep practice test site also includes a full-length All Classes practice paper that is worth completing under timed conditions once you have completed Weeks 3 and 4 of the study schedule above.

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