Explosion safety in facilities processing bulk materials is becoming one of the most significant areas of operational risk. The increasing scale and complexity of pneumatic conveying systems and dust collection installations raise the likelihood of forming explosive atmospheres and the propagation of explosions through ductwork. A central element of protective systems remains explosion isolation flap valves (explosion isolation flap valves), used as a protective system in accordance with the requirements of the ATEX Directive 2014/34/EU.
After eleven years of EN 16447 being in force, a comprehensive revision has been prepared in the form of draft standard prEN 16447:2025, which redefines the requirements for the assessment, testing and documentation of these devices. The new edition addresses the challenges faced by industry today: complex flow conditions, increasing mechanical loads and the need to validate performance under conditions representative of real operating environments.
Compliance with EN 16447:2014 establishes a presumption of conformity, but does not relieve the manufacturer from the obligation to demonstrate the actual effectiveness of the device in its intended application. Current experience has shown that the previous requirements were insufficient. Therefore, the key issue is not whether the device “meets the standard”, but whether its effectiveness has been demonstrated in the specific process application. In accordance with ATEX Directives 2014/34/EU and 1999/92/EC, protective systems must ensure a level of safety appropriate to the identified hazards and must be designed and selected in line with the current state of technical knowledge.
From theory to practice – fundamental changes in the normative approach
EN 16447:2014 was the first standardized document defining requirements for explosion isolation flap valves in Europe. It specified design requirements and minimum performance criteria, enabling the certification of the first generation of passive explosion isolation systems.
Operational experience, however, demonstrated that some assumptions made at that time were overly simplified and did not account for the flow dynamics present in typical industrial systems. Devices that achieved the required performance under laboratory conditions often showed limited effectiveness in installations with variable flow, large duct cross-sections or complex geometries that generate unsteady velocity fields and complex aerodynamic interactions.
One of the most significant aspects of prEN 16447:2025 is the shift away from simplified test scenarios toward testing that reflects parameters representative of real operating conditions. The draft standard describes in detail the requirements for testing explosion isolation flap valves, defining test scenarios, test stand configuration, minimum duct length and geometry, ignition conditions and flow parameters. It also describes the method of confirming isolation performance, introducing the requirement for repeatable, comparable testing and the consideration of differences arising from dust properties and installation characteristics.
In contrast to the previous edition, performance assessment is based on measured capability to stop the pressure wave and flame front under test conditions representative of real process installations.
Consequently, the performance of an explosion isolation flap valve can no longer be based on simplified qualification tests, but must be formally verified under test conditions that reflect its intended application.
Flow characteristics – a key challenge for designers and manufacturers
Explosion isolation flap valves were originally designed for installations operating under vacuum conveying. Modern conveying and dust collection systems, however, increasingly operate under positive pressure conveying or exhibit variable flow characteristics, generating unsteady and turbulent flow fields. These phenomena significantly influence pressure wave propagation, device activation time, aerodynamic forces acting on the closing element and closure stability during deflagration.
Draft prEN 16447:2025 explicitly requires that devices be tested under conditions corresponding to their intended application rather than simplified laboratory setups. In practice, this means that manufacturers claiming performance in positive pressure systems will need to provide appropriate test results supporting this declaration.
From the industrial user’s perspective, the critical issue is therefore not only whether the device meets normative requirements, but whether it has been verified in conditions corresponding to the real process environment.
Closure stability – a critical safety requirement
One of the problems identified in an accident investigation conducted by ISMA was the secondary opening of an explosion isolation flap valve after initial closure, caused by turbulent pressure fluctuations. This resulted in re-ignition of the dust-air mixture in the area that should have been protected by the isolation system.
This phenomenon is consistent with the characteristics of dust deflagration in ductwork, where combustion and the expansion of gases generate rapid, fluctuating dynamic loads. Under such conditions, one may observe: reflections of pressure waves from elbows, restrictions and branches; interference between pressure waves resulting from flow non-uniformity; local pressure peaks caused by gas compression; and rapid, turbulent transport of combustion products. The combination of these phenomena can generate short-duration reverse forces acting on the closing element of the explosion isolation valve.
Analysis of one such incident showed that the valve had been tested in a laboratory setup without a downstream duct segment, eliminating aerodynamic loads typical of real installations.
The new draft standard addresses this gap by requiring that explosion isolation flap valves must not only close in response to an explosion, but remain closed for the entire duration of the event.
What should purchasers focus on?
There is no single universal solution for all processes; however, several critical criteria should be considered.
- Scope and methodology of testing. The manufacturer should provide reliable technical information, including extracted test data confirming performance under conditions representative of real installations, together with a description of the test stand, duct geometry and ignition conditions.
- Flow direction and dynamics. The device must be certified for conditions consistent with the process (positive pressure / vacuum / variable), as isolation effectiveness is directly dependent on aerodynamic loads acting on the valve.
- Closure stabilization mechanism. The explosion isolation flap valve should incorporate a mechanism preventing re-opening due to aerodynamic loads following deflagration.
- Completeness of ATEX documentation. Of key importance are: instructions, declarations of conformity, risk assessment and normative harmonization.
Summary – implications for the market and industry
Draft prEN 16447:2025 introduces significant changes in the methods for assessing and testing explosion isolation flap valves, focusing on validation under conditions representative of real process scenarios. Moving away from simplified laboratory tests is critical in the context of modern process installations, where variable flow parameters, positive pressure and complex aerodynamic loads are present.
The new standard shifts emphasis from declarative compliance to evidence-based performance, requiring manufacturers to provide documented test results and users to make informed decisions based on the specifics of their process. Operational incidents have shown that devices compliant with the previous standard may not ensure adequate effectiveness during dynamic dust deflagration, highlighting the need for an updated approach.
Although the draft has not yet been officially published, its requirements already indicate the direction of necessary changes in the market. From an industrial perspective, this translates into a higher level of process safety and greater transparency and predictability of protective system performance. For manufacturers, it means the need to adapt designs and documentation to the new requirements.
It is worth noting that prEN 16447:2025 operates in connection with other standards, including EN 15089 on explosion isolation systems, which complements the new approach to evaluating flap valves. This context is further supported by horizontal standards such as EN 1127-1 and EN 14460.
Author: Sebastian Słaboszewski
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