What tests are required before commissioning an ATEX mixing plant in Germany?
Before a mixing plant in a potentially explosive area is first commissioned, the operator must have the plant inspected for explosion safety. The basis for this is, in particular, the Ordinance on Industrial Safety and Health (Betriebssicherheitsverordnung), the Hazardous Substances Ordinance (Gefahrstoffverordnung), the explosion-protection document, and TRBS 1201 Part 1. The inspection covers not only the mixer but the entire explosion-protection-relevant plant network, including dosing, conveying technology, filters, ventilation, inerting, discharge, control and connecting lines.
An inspection is also required before restarting the plant if changes subject to inspection have been made. Recurring inspections must subsequently be defined in the risk assessment and carried out within the specified deadlines.
Risk assessment and documentation
A complete risk assessment must be available before the inspection. It must evaluate the explosion hazards presented by the materials actually processed and by the operating states. This applies to normal operation, start-up, shut-down, filling, emptying, cleaning, maintenance, malfunctions and product changes.
The explosion-protection document must contain, at a minimum, the underlying protection concept, the zone classification, the safety-related material data, the selected equipment and protective systems, and the technical and organisational measures. TRBS 1201 Part 1 requires that the safety-related documents needed for the inspection be complete and that their content be plausible.
The documents typically to be provided include the explosion-protection document, zone and layout plans, process flow diagrams, safety data sheets, safety-related characteristic data for the dusts, EU declarations of conformity, ATEX markings, operating and maintenance instructions, circuit diagrams, evidence of earthing, and documents on pressure relief, explosion suppression, decoupling or inerting. For safety-related control systems, the specification of the safety function, functional tests and, where applicable, evidence of functional safety are also required.
Technical inspection
The technical inspection determines whether the plant was erected in accordance with the explosion-protection concept, whether it is in a safe condition under the specific installation conditions, and whether the intended protective measures function effectively. It comprises a documentation review and an on-site technical inspection.
For an ATEX mixing plant, the correct selection and installation of equipment, protective systems, and safety, monitoring and control devices are typically inspected. This includes the ATEX marking and suitability of the electrical and non-electrical components for the defined zones, the installation of motors, sensors, lights, switches, shafts, seals, couplings, flaps, conveying equipment and filters, and the conformity of the actual installation with the planning documents.
The inspection also covers ignition-source avoidance. Relevant points are the safe design of moving parts, possible tool-to-wall contacts, the clearance and condition of rotating components, temperature monitoring of bearings and seals, protection against blockages, foreign-body management, permissible surface temperatures, and protection against electrostatic discharges. Earthing and equipotential bonding must be complete, durable and functional; this also includes pipework, flexible connections, filters, container-changing stations and metallic fittings.
Where electrical installations are present, their safe installation and function are inspected. This can include, for example, the degree of protection and integrity of enclosures, suitable cable routing, insulation resistance, equipotential-bonding connections, the Ex suitability of the equipment, and the function of emergency-stop, alarm and shutdown devices. The specific depth of inspection depends on the design, the zone and the protection concept.
Protective systems and inerting
Constructive explosion-protection measures must be checked for suitability, proper installation and function before commissioning. This applies, for example, to explosion pressure relief, flameless venting, explosion suppression, explosion-pressure-resistant or explosion-pressure-shock-resistant construction, and explosion-technical decoupling. For decoupling devices, the installation position, orientation, pipework geometry, throughput and conformity with the intended protective function must be assessed.
Inerting and ventilation systems are explicitly part of the inspection. What must be assessed includes, in particular, the tightness of the plant, the inert gas supply, purging and release sequences, oxygen measurement, alarm and shutdown values, safety interlocks, and the safe response to failure of the inert gas supply or the measuring chain. The inspection includes whether the permissible oxygen content has been correctly defined for the specific product-inert gas system and can be reliably maintained during operation. TRBS 1201 Part 1 explicitly names inerting equipment, ventilation systems, gas warning devices, and equipment, protective systems and safety, monitoring and control devices as subjects of the inspection.
Alongside technical measures, the organisational measures are also assessed. These include operating instructions, marking of Ex areas, training, cleaning and maintenance schedules, rules for container changes, release procedures for hot work, and alarm and emergency measures. The inspection therefore confirms not just the safety of the mixer, but the functionality of the entire explosion-protection concept until the next scheduled inspection.
Inspection responsibility and release
The inspection of explosion safety before initial commissioning and after changes subject to inspection must be carried out by a person competent to perform the inspection. For certain plants subject to monitoring, or where additional approval conditions apply, an approved monitoring body may be required. The specific responsibility follows from the Ordinance on Industrial Safety and Health, the type of plant and, where applicable, the requirements of the competent authority.
The plant may only be commissioned once the required inspections have been carried out and documented and any deficiencies identified have been remedied. The inspection report should clearly record which plant components, protective measures, operating limits and organisational prerequisites were inspected, any deficiencies identified, and the conditions under which operation is released.
How amixon® supports the commissioning of an ATEX mixing plant
Documentation and apparatus design
For an ATEX mixing plant, a distinction must be made between the conformity of the individual apparatus and the explosion safety of the complete plant. amixon® can execute mixers, granulators, vacuum mixing dryers and mixing reactors with a product space suitable for Zone 20 applications and provide the associated apparatus documentation. The specific design – including equipment category, permissible surface temperatures, electrical and non-electrical components, seals, sensors and protective systems – is matched to the agreed process and material data.
The ATEX Equipment Directive 2014/34/EU concerns equipment and protective systems for use in potentially explosive atmospheres. The manufacturer's ATEX conformity documentation relates to the delivered machine and its specified configuration. It does not replace the operator's explosion-protection document, zone classification, or the inspection of the entire plant before initial commissioning.
For project-specific pressure, vacuum or inerting processes, suitable material certificates, welding documentation, pressure design documents and test certificates can form part of the delivery documentation. Whether an ASME design is required depends on the installation location, the pressure rating, the approval framework and the operator's requirements. A pressure- or vacuum-resistant design is not automatically equivalent to an explosion-pressure-resistant or explosion-pressure-shock-resistant construction. This must be expressly defined on the basis of the safety-related material data and the explosion-protection concept.
amixon® offers gas-tight, pressure-tight and vacuum-tight designs for certain apparatus. For vacuum mixing dryers and mixing reactors of the VMT and AMT series, the apparatus can be designed for vacuum and inert gas processes. The achievable vacuum level, tightness requirement and suitable inerting strategy must be defined on a project-specific basis. Safe inerted operation additionally requires an inert gas supply, oxygen measurement, alarm and shutdown values, safety interlocks, and safe handling of possible leaks.
Assembly and commissioning
Assembly and commissioning can be accompanied by amixon® specialist personnel. The machine-related functions, such as direction of rotation, drive, tightness, discharge, interlocks, sensors, temperature monitoring and, where provided, mixing, vacuum or inerting sequences, should be checked. For the entire connected plant, earthing and equipotential bonding must be checked together with the operator, the electrical installer and, where applicable, other plant suppliers. The check must in particular include the dosing, conveying, filter, discharge and filling interfaces.
The inspection before initial commissioning under the Ordinance on Industrial Safety and Health is not a mere machine acceptance test. It assesses whether the overall plant was erected in accordance with the explosion-protection document and whether the defined protective measures are effective. This includes equipment, protective systems, safety, monitoring and control devices, ventilation, inerting, and the effectiveness of the organisational measures.
Operator obligations and release
Before starting operation, the operator must carry out a risk assessment, prepare the explosion-protection document, define the Ex zones and specify suitable operating and protective measures. The basis for this includes, among other things, the safety-related characteristic values of the actual product, for example KSt, pmax, minimum ignition energy, ignition temperatures, moisture, particle size, electrical conductivity and possible hybrid mixtures. The mixer data are important input values but do not replace the material-related safety assessment.
Before initial commissioning and before restarting after changes subject to inspection, the explosion safety of the plant must be inspected. This inspection is carried out by a person competent to perform the inspection; depending on the type of plant, approvals and hazard potential, an approved monitoring body may be required. The plant may only be operated after successful inspection, documented remediation of deficiencies, and release.
amixon® can provide the apparatus-related documents and technical information and accompany the process-engineering commissioning. Operators, planners and explosion-protection specialists must derive the overall assessment of the plant from this, including zones, peripheral equipment, protective systems, inspections and organisational measures.
Process trials and discharge
Before production release, critical operating states can be trialled with the original product. This includes, for example, mixing behaviour, temperature development, wetting, product adhesion, vacuum operation, drying, inerting and discharge. The results support the definition of permissible operating parameters, such as fill level, rotational speed, mixing time, dosing profile, temperature, pressure and cleaning procedure. They do not, however, replace safety-related material testing or a formal inspection of explosion safety.
Good residual discharge can reduce product losses, cleaning effort and cross-contamination risks. For free-flowing products, cone and vertical mixers with suitable discharge components and, where applicable, ComDisc® support can improve discharge. However, specific residual quantities such as 99.98 or 99.99 percent are product-, apparatus- and process-dependent. They should not be used as generally guaranteed performance values, but should be verified with the original product, the fill level and the intended discharge configuration.