Member States must take steps to ensure that pressure equipment cannot be placed on the market if, when installed, maintained or used, it endangers the health and safety of persons, domestic animals or property.

Essential requirements
In accordance with the principles of the "New Approach to Technical Harmonisation and Standards", the design and the manufacture of pressure equipment are subject to essential safety requirements.

This new approach means that Member States cannot prohibit, restrict or impede the placing on the market or putting into service of pressure equipment complying with the provisions of the Directive (bearing the CE marking).

Harmonised standards
The European Committee for Standardisation (CEN) is producing a series of harmonised European standards. Equipment manufactured in accordance with these standards is presumed to conform to the essential safety requirements of the Directive.

Classification of pressure equipment
As some of the Directive's provisions are applied differently to different categories of pressure equipment, a classification system has been established. To determine in which category specific equipment is placed, it is necessary to identify:

• the type of equipment: vessels, steam generators or piping;
• the physical state of the relevant fluids: gaseous or liquid;
• the group of fluids for which the equipment is intended: group 1 or group 2.

Group 1 comprises dangerous fluids, as defined in Directive 1967/548/EEC on the classification, packaging and labelling of dangerous substances. Group 2 comprises all other fluids.

On the basis of this classification, five categories of pressure equipment can be identified according to the risk: sound engineering practice (SEP), I (the lowest risk category), II, III and IV (the highest risk category). Risk is measured according to the pressure and/or volume limits set out in the Directive.

Requirements for the different categories of pressure equipment

Pressure equipment in the SEP category:

• must comply with sound engineering practice;
• is not obliged to meet the essential requirements relating to design, manufacture and testing;
• is not subject to conformity assessment;
• cannot bear the CE marking. However, it must have adequate instructions for use and bear the identification of the manufacturer or his/her authorised representative established within the Community.

Sound engineering practice applies to equipment that is not subject to conformity assessment but must be designed and manufactured in accordance with sound engineering practice in a Member State in order to ensure its safe use.

Pressure equipment in categories I, II, III and IV must:

• meet the essential requirements relating to design, manufacture and testing;
• satisfy the conformity assessment procedures;
• bear the CE marking and other information.

Conformity assessment and notified bodies
Before pressure equipment in categories I to IV can be placed on the market, the equipment's manufacturer must ensure that a procedure (module) is carried out to assess conformity with the essential requirements of the Directive. Different modules are provided for each category in which equipment is classified.

The participation of notified bodies appointed by Member States is required for the modules for category II, III and IV products. These bodies approve and monitor manufacturers' quality systems and test products directly.

As regards materials, pressure-equipment manufacturers must observe safety requirements by using materials that:

• either comply with harmonised standards;
• or are covered by a European Approval for Materials (a technical document issued by a notified body defining the characteristics of the materials used in the manufacture of pressure equipment not covered by a harmonised standard);
• or have been the subject of a particular materials appraisal.