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Fan Systems Siesmic Fans

Seismic & Airplane Crash Qualified Fans

We design and manufacture ventilation fans qualified for Seismic and Airplane Crash (APC) loading in accordance with nuclear project specifications and site-specific response spectra.

All units are engineered using advanced Finite Element Analysis (FEA) to verify structural integrity, dynamic stability and functional performance under extreme loading conditions. Our calculation-led approach provides full traceability and compliance with EDF technical requirements and other nuclear standards.

Seismic Design & Qualification

Fans are designed to meet the applicable Site Specific Response Spectra (SSRS) and seismic classification.

FEA modelling is undertaken to assess:

Structural stress and deformation under multi-axis seismic acceleration

Casing, baseframe and support frame integrity

Anchor bolt and holding-down load transfer

Shaft and bearing stability

Maintenance of critical running clearances

Functional operability during and after the event, where specified

Dynamic & Modal Assessment

A full dynamic analysis of the rotating assembly is performed. Excitation frequencies generated by rotational speed, blade pass frequency and harmonic effects are calculated and assessed against the natural frequencies of the impeller, shaft, casing and support structure.

Modal analysis determines structural mode shapes and frequencies, ensuring adequate separation margins across the operating speed range. Where required, the design incorporates a defined safety factor between excitation and natural frequencies to prevent resonance and vibration amplification during normal operation and seismic events.

This ensures controlled vibration levels and protection of bearings and rotating components under both steady-state and extreme conditions.

Anti-Vibration Mount & Interface Considerations

Where anti-vibration (AV) mounts are used, transferred response spectra are evaluated to determine the loading transmitted through the isolation system.

Calculations verify mount stiffness, deflection limits, load distribution and stability under combined excitation. Interaction between the fan, isolation system and supporting structure is fully assessed.

Ductwork interface forces are also considered. Flexible connection lengths are specified to accommodate seismic displacement, preventing excessive load transfer to the casing while maintaining aerodynamic performance and gas-tight integrity.

Seismic qualification can be supported by physical shaker table testing where required, correlating measured results with analytical FEA models.

Airplane Crash (APC) Assessment

For installations requiring Airplane Crash resistance, transient impact and impulse loading cases are modelled using FEA to evaluate structural response.

Assessment includes:

  • Impulse and pressure loading effects
  • Global and local stress distribution
  • Support frame and anchorage capacity
  • Shaft alignment and rotor survivability

Post-event functional requirements, where specified

Designs are verified to maintain structural integrity, containment and continued operation where required by specification.

Engineering, Manufacture & Compliance

Our in-house capability spans concept design, FEA analysis, manufacture, inspection and documentation, ensuring full compliance with nuclear QA frameworks.

We manufacture axial and centrifugal fans in mild steel and stainless steel, including gas-tight and decontaminable configurations. Units may be direct drive, belt driven or coupled to suit project requirements.

Inspection and testing includes:

  • Detailed calculation packages and FEA reports
  • Inspection and Test Plans (ITPs)
  • NDE (CSWIP 3.2.1 Visual Inspection, DPI and MPI)
  • Performance testing to ISO 5801
  • Mechanical and overspeed testing where specified

Our engineering-led approach delivers ventilation systems capable of maintaining safety, reliability and performance within the most demanding nuclear environments.

Frequently

Asked Questions

What is ATEX and why is it important?
ATEX derives from the French “Atmosphères Explosibles” and refers to European/UK regulations controlling explosive atmospheres. The ATEX Directive 2014/34/EU (previously 94/9/EC) is mandatory for all equipment used in potentially explosive environments. Compliance ensures worker safety and legal operation in hazardous areas. Non-compliance can result in serious accidents, legal liability, and operational shutdown.
Zone 0/20 represents areas where explosive atmospheres are present continuously or for long periods—requiring the highest safety standards. Zone 1/21 indicates explosive atmospheres likely during normal operation. Zone 2/22 covers areas where explosive atmospheres are unlikely but possible. Our fans are certified for all zones, with specific designs optimised for each risk level.
Our ATEX fans incorporate multiple protection methods: explosion-proof motors prevent electrical ignition, spark-resistant construction eliminates mechanical sparking, earthing/bonding prevents static discharge, temperature control prevents surface ignition, and certified flame arrestors prevent flame propagation. The 10-bar explosion containment ensures any internal ignition cannot breach the casing.
ATEX fans are mandatory in chemical and petrochemical plants, pharmaceutical manufacturing, oil and gas facilities, paint and coating operations, distilleries and breweries, grain handling and food processing, mining operations, wastewater treatment plants, and any facility handling flammable gases, vapours, or combustible dusts. UK HSE regulations require ATEX compliance in all designated hazardous areas.
We require: zone classification (0, 1, 2, 20, 21, 22), gas/dust group (IIA, IIB, IIC, IIIA, IIIB, IIIC), temperature class (T1-T6), explosive medium details, ambient temperature range, required airflow and pressure, and installation environment details. Our engineers ensure correct selection and provide complete ATEX documentation including certificates, risk assessments, and operation manuals.
No, ATEX compliance must be designed and certified from manufacture. Retrofitting cannot achieve required safety levels and would violate certification requirements. We offer replacement solutions with minimal disruption, often utilising existing ductwork and infrastructure. Our team manages the complete transition including decommissioning, installation, and certification of new ATEX-compliant systems.