[Home](/)/[Resources](/resources)/PED fluid groups and categories CE / EUPEDPressure Equipment # PED Fluid Groups and Pressure Categories: How to Classify Equipment Under 2014/68/EU Annex II Under the Pressure Equipment Directive 2014/68/EU, a fluid is Group 1 if it is classified under CLP as explosive, flammable, oxidising, pyrophoric, self-reactive or acutely toxic (or is held above its flashpoint), and Group 2 otherwise. Fluid group, gas or liquid state, PS and volume or DN then select one of nine Annex II tables, which gives category I–IV or places the equipment under Article 4(3) sound engineering practice. Classification is set by Article 13 (it was Article 9 under the old Directive 97/23/EC), the scope thresholds by Article 4, and the modules for each category by Article 14. A wrong classification either over-specifies the conformity route or, worse, leaves out the notified body the Directive requires. Copy Link[Share on WhatsApp](https://wa.me/?text=https%3A%2F%2Fkrono-labs.com%2Fguides%2Feu-ped-pressure-categories-fluid-groups) At a glance Fluid groups Group 1 (CLP hazard classes) / Group 2 Gas vs liquid Vapour pressure at TS > 0.5 bar = gas Category range Art. 4(3) SEP, I, II, III, IV Annex II tables 9 (vessels 1–4, fired 5, piping 6–9) Legal basis 2014/68/EU Art. 4, 13, 14 & Annex II ## Fluid groups, gas vs liquid and categories — key concepts ### Fluid groups under Article 13: the CLP test Article 13(1) of Directive 2014/68/EU splits fluids into two groups. Group 1 is any substance or mixture classified under the CLP Regulation (EC) No 1272/2008 in one of 17 listed hazard classes: unstable explosives and explosives of Divisions 1.1–1.5; flammable gases cat. 1 and 2; oxidising gases cat. 1; flammable liquids cat. 1 and 2; flammable liquids cat. 3 where TS is above the flashpoint; flammable solids cat. 1 and 2; self-reactive substances types A–F; pyrophoric liquids and solids cat. 1; substances that emit flammable gases in contact with water cat. 1–3; oxidising liquids and solids cat. 1–3; organic peroxides types A–F; acute oral and dermal toxicity cat. 1 and 2; acute inhalation toxicity cat. 1–3; and STOT single exposure cat. 1. Group 1 also includes any fluid held at a maximum allowable temperature TS above its flashpoint. Group 2 is everything else. Propane, hydrogen, ammonia, chlorine and oxygen are Group 1; nitrogen, CO₂, compressed air, water and steam are Group 2. ### Gas or liquid? The 0.5 bar vapour pressure rule For table selection, the Directive does not ask what state the fluid is in when you look at it. Article 4(1)(a)(i) treats as a gas: gases, liquefied gases, gases dissolved under pressure, vapours, and any liquid whose vapour pressure at the maximum allowable temperature TS is more than 0.5 bar above normal atmospheric pressure (1013 mbar). Only liquids with a vapour pressure at TS of 0.5 bar or less above atmospheric count as liquids (Article 4(1)(a)(ii)). So water at a TS of 120 °C (vapour pressure about 1 bar gauge) is assessed as a gas; liquid propane in a tank is a liquefied gas and uses the gas tables. ### PS, TS, V and DN: the inputs PS is the maximum allowable pressure set by the manufacturer, in bar gauge (Article 2(7) and (8)). TS is the maximum or minimum allowable temperature (Article 2(9)). V is the internal volume of a chamber, including nozzles up to the first connection or weld and excluding permanent internal parts (Article 2(10)). DN is the nominal size: a round reference number common to all components in a piping system, only loosely related to manufacturing dimensions (Article 2(11)). The Directive only applies at all when PS is greater than 0.5 bar (Article 1(1)). ### Below the thresholds: Article 4(3) sound engineering practice Equipment at or below the Article 4(1) limits (shown as "Article 4, paragraph 3" on the Annex II tables) must be designed and manufactured in accordance with the sound engineering practice of a Member State and come with adequate instructions for use. It must not carry the CE marking for the PED. It may still carry a CE mark under other legislation, such as the Machinery or Low Voltage Directive, when that legislation applies. ### Categories I to IV and their modules (Article 14) Category I: Module A (internal production control, no notified body). Category II: A2, D1 or E1. Category III: B (design type) + D, B (design type) + F, B (production type) + E, B (production type) + C2, or H. Category IV: B (production type) + D, B (production type) + F, G, or H1. A manufacturer may always choose a procedure from a higher category (Article 14(3)). From category II upward a notified body is involved and its number follows the CE mark. ### Accessories, multi-chamber vessels and assemblies Safety accessories (safety valves, bursting discs, pressure and temperature limiters) are category IV by default; a safety accessory made for specific equipment may take that equipment's category (Annex II point 2). Pressure accessories such as valves are classified with the vessel or piping table using PS, V or DN and the fluid group, and if both V and DN are relevant the higher result wins (point 3). A multi-chamber vessel takes the highest category of its chambers, and a chamber holding several fluids is classified on the fluid needing the highest category (Article 13(2)). Assemblies under Article 4(2) go through the global assessment in Article 14(6). ## The 9 Annex II tables at a glance Each table plots PS (bar) against V (litres) or DN. The lowest line is the Article 4(1) scope threshold; below or on it, the equipment falls under Article 4(3). The demarcation lines mark the upper limit of each category (Annex II point 4). Values below are read from the tables in the Official Journal text — always confirm a borderline case against the plotted table. Table Equipment Fluid In PED scope when Category boundaries Special rule Table 1 Vessels Group 1 gas / vapour V > 1 L and PS·V > 25 bar·L, or PS > 200 bar I ≤ 50, II ≤ 200, III ≤ 1000, IV > 1000 bar·L. V ≤ 1 L: III above 200 bar, IV above 1000 bar Unstable gas in I or II is raised to III Table 2 Vessels Group 2 gas / vapour (incl. steam, air, N₂) V > 1 L and PS·V > 50 bar·L, or PS > 1000 bar I ≤ 200, II ≤ 1000, III ≤ 3000, IV > 3000 bar·L (but III if PS ≤ 4 bar). V ≤ 1 L: III above 1000 bar, IV above 3000 bar Portable extinguishers and breathing-apparatus bottles: at least III Table 3 Vessels Group 1 liquid V > 1 L and PS·V > 200 bar·L, or PS > 500 bar I up to PS 10 bar, II from 10 to 500 bar, III above 500 bar. V ≤ 1 L above 500 bar: II Highest category: III Table 4 Vessels Group 2 liquid (incl. water) PS > 10 bar and PS·V > 10 000 bar·L, or PS > 1000 bar I, or II when PS > 500 bar and V > 10 L Highest category: II. Solid-fuel warm-water assemblies: B (design type) or H Table 5 Fired or otherwise heated equipment Steam / superheated water above 110 °C V > 2 L, plus all pressure cookers I ≤ 50, II ≤ 200, III ≤ 3000 bar·L; IV if PS·V > 3000, PS > 32 bar or V > 1000 L Pressure cooker design: at least a category III module Table 6 Piping Group 1 gas / vapour DN > 25 I up to DN 100 and PS·DN 1000; II up to DN 350 / PS·DN 3500; III above DN 100 with PS·DN > 3500 (all DN > 350) Unstable gas in I or II is raised to III Table 7 Piping Group 2 gas / vapour (incl. steam) DN > 32 and PS·DN > 1000 bar I up to DN 100 / PS·DN 3500; II up to DN 250 / PS·DN 5000; III above DN 250 with PS·DN > 5000 Fluid above 350 °C in II is raised to III Table 8 Piping Group 1 liquid DN > 25 and PS·DN > 2000 bar I up to PS 10 bar, II from 10 to 500 bar, III above 500 bar Highest category: III Table 9 Piping Group 2 liquid (incl. water) PS > 10 bar, DN > 200 and PS·DN > 5000 bar I, or II above PS 500 bar Highest category: II "Gas" here includes liquefied gases, dissolved gases, vapours and liquids whose vapour pressure at TS is more than 0.5 bar above atmospheric. Pressures are gauge. PS·V is in bar·L; PS·DN in bar. ## Worked examples ### Propane receiver, 20 bar, 100 L Propane is a flammable gas cat. 1, so Group 1. It is a liquefied gas, so it uses the gas tables. Table 1, PS·V = 2000 bar·L, which is above 1000: category IV. Modules B (production type) + D or F, G, or H1. ### Hot-water buffer tank, 6 bar, 800 L, TS 95 °C Water is Group 2. At 95 °C its vapour pressure is below 0.5 bar gauge, so it is a liquid. Table 4 needs PS > 10 bar and PS·V > 10 000 bar·L. With PS = 6 bar it falls under Article 4(3): sound engineering practice, no PED CE mark. ### Nitrogen line, DN 80, 40 bar Nitrogen is Group 2 gas. Table 7 scope needs DN > 32 and PS·DN > 1000: 80 × 40 = 3200, so in scope. DN 80 is under 100 and PS·DN under 3500: category I, Module A. ### Hydrogen line, DN 50, 30 bar Hydrogen is a flammable gas cat. 1, so Group 1. Table 6 brings in all piping above DN 25. PS·DN = 1500, above 1000 with DN under 100: category II. For the wider PED picture — scope exclusions, essential safety requirements and notified bodies — see the [Pressure Equipment Directive guide](/guides/pressure-equipment-directive-ped) and the [PED deep dive](/guides/pressure-equipment-directive-ped-deep-dive). The [pressure equipment and simple pressure vessels course](/courses/53-eu-ce-marking-pressure-equipment-simple-pressure-vessels) works through classification end to end. ## How to classify pressure equipment — step by step 01 Confirm the PED applies: PS above 0.5 bar, and the equipment is not excluded by Article 1(2) (for example simple pressure vessels under Directive 2014/29/EU, or products covered by other directives at category I or below). 02 Identify the fluid and check its CLP classification in section 2 of the Safety Data Sheet against the 17 hazard classes in Article 13(1)(a). Check the flashpoint against TS. Record the reasoning in the technical documentation. 03 Decide gas or liquid: compare the fluid's vapour pressure at TS with 0.5 bar above atmospheric. Above it, use the gas tables; at or below, use the liquid tables. 04 Decide the equipment type: vessel (V in litres), fired or heated equipment for steam or water above 110 °C (Table 5), piping (DN), pressure accessory or safety accessory. 05 Pick the table: vessels 1–4, fired equipment 5, piping 6–9. Plot PS against V or DN. If you sit on or below the Article 4(1) threshold, it is Article 4(3) sound engineering practice — no PED CE mark. 06 Read the category and apply the exceptions printed under the table (unstable gases, extinguishers, pressure cookers, piping above 350 °C). 07 Choose a module from Article 14(2) for that category, engage a notified body for category II and above, compile the technical documentation, issue the EU Declaration of Conformity and affix the CE mark with the notified body number where required. ## Frequently asked questions ### What is a PED fluid group? Under Article 13 of the Pressure Equipment Directive 2014/68/EU, fluid group decides how dangerous the contents are considered. Group 1 is fluids classified under the CLP Regulation in specific explosive, flammable, oxidising, pyrophoric, self-reactive, acutely toxic or STOT SE hazard classes, plus any fluid held above its flashpoint. Group 2 is every other fluid. Group 1 puts the equipment in a stricter Annex II table. ### Is water Group 1 or Group 2 under the PED, and what about steam? Water and steam are both Group 2. Hot water whose vapour pressure at TS is more than 0.5 bar gauge (roughly above 110 °C) is treated as a gas for table selection, so it uses Table 2 (vessels) or Table 7 (piping). Fired or otherwise heated equipment that generates steam or superheated water above 110 °C with V > 2 L uses Table 5. ### How do I decide if a PED fluid is a gas or a liquid? Look at the vapour pressure at the maximum allowable temperature TS. If it is more than 0.5 bar above normal atmospheric pressure (1013 mbar), the fluid is treated as a gas, along with liquefied gases, dissolved gases and vapours. If it is 0.5 bar or less, it is a liquid. The physical state inside the vessel at ambient temperature does not decide it. ### What does PED category IV mean for Group 1 gas vessels? In Table 1, a vessel for a Group 1 gas is category IV when PS·V exceeds 1000 bar·L, or PS exceeds 1000 bar for a vessel of 1 L or less. Category IV is the highest category and requires Modules B (production type) + D, B (production type) + F, G (unit verification) or H1 (full quality assurance with design examination), all with a notified body. ### What pipe size brings piping into the PED? Piping is in scope above these thresholds (Article 4(1)(c)): Group 1 gas, DN > 25; Group 2 gas, DN > 32 and PS·DN > 1000 bar; Group 1 liquid, DN > 25 and PS·DN > 2000 bar; Group 2 liquid, PS > 10 bar, DN > 200 and PS·DN > 5000 bar. Smaller or lower-pressure piping falls under Article 4(3) sound engineering practice and is not CE marked under the PED. ### Does the fluid group matter when buying a control valve? Yes. A valve is a pressure accessory, classified with the piping or vessel table for the fluid group and state it is intended for. The same DN 50 valve can be outside PED scope on nitrogen at 10 bar (PS·DN 500) and category II on hydrogen at 30 bar. Specify the fluid, PS and TS when ordering so the supplier can confirm the category on the Declaration of Conformity. ### What does SEP mean and does SEP equipment need CE marking? SEP stands for sound engineering practice, the industry name for equipment under Article 4(3). It has to be designed and made safely to the sound engineering practice of a Member State and come with adequate instructions, but it must not bear a CE mark for the PED and needs no PED Declaration of Conformity. A CE mark under other applicable legislation can still be required. **Disclaimer:** Educational resource only. Category boundaries are summarised from the Annex II tables of Directive 2014/68/EU as published on EUR-Lex; check the plotted tables and the Commission's PED guidelines for borderline cases, and consult a notified body before relying on a classification. 🇪🇺 CE Marking roadmap for your product Every standard, document, and test that applies — free, no account required. See your free roadmap[ Want an expert to take your product through 🇪🇺 CE Marking compliance for you? One consultant from Krono's compliance team takes your product from requirements to legal sale, with a fixed quote before any work starts. See compliance services](/services) Learn this properly In-depth course that teaches the full process, not just this one answer. [Start the course — $199](/courses/53-eu-ce-marking-pressure-equipment-simple-pressure-vessels)[Prefer to read? 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