Explosion isolation
Definition
Explosion decoupling is a safety measure within structural explosion protection that prevents an explosion from spreading from one part of a plant to neighbouring areas via pipework, conveyors or other connections. The aim is to confine the explosion locally and to protect connected vessels, silos, filters, feeders or downstream process plant from flames, pressure waves and secondary explosions.
In practice, explosion decoupling is particularly important when flammable dusts are being processed, for example in mixers, conveying lines, dust extraction systems or silos.
Principle of operation
In the event of an explosion, decoupling interrupts the connection between two parts of the plant within a very short time, so that the flame front and pressure rise do not propagate to the next part of the plant.
It is generally not a single, stand-alone protection system, but is combined with other explosion protection measures, in particular with:
- Explosion pressure relief
- Explosion suppression
- pressure-shock-resistant construction
Measures to prevent the propagation of flames and explosions
Common systems
Passive systems
- Non-return valves and explosion relief valves: close automatically due to the pressure generated by the explosion
- Rotary valves: can be used as a mechanical decoupling element between a silo and a mixer
- Double-gate systems: mechanically separate process chambers
Active systems
- HRD extinguishing agent barriers: Sensors detect the onset of an explosion; an extinguishing agent is then injected into the pipeline to suppress the flame front
Rapid-closing valves: close electronically controlled within milliseconds
Application on mixers
For mixers, explosion decoupling is particularly relevant at the interfaces with the rest of the plant:
Plant area Typical decoupling
Product inlet: rotary valve, non-return valve or other suitable decoupling element
Extraction and dust removal: non-return valve or chemical barrier
Product outlet: quick-closing gate valve or double-gate valve system
Intermediate hopper and conveying pipeline: active or passive barrier depending on risk and pipeline geometry
Particularly with powdery products such as sugar, starch, flour, milk powder, metal powders, plastic granules or pharmaceutical substances, preventing the propagation of an explosion via connecting pipes is a key safety objective.
Design and planning
The following parameters and boundary conditions, amongst others, are important for correct design:
- Kst value
- pmax
- Minimum ignition energy (MZE)
- Pipework diameter and geometry
- Installation location and length
- Mechanical and thermal load-bearing capacity of the system
Decoupling systems must be planned and designed in such a way that their ignition-proof integrity and mechanical load-bearing capacity are guaranteed under real operating conditions. If a hybrid mixture of dust and flammable gas or vapour is present, the flame speed increases; decoupling must then be designed to suit the characteristic values of the mixture.
Guidelines and standards
The classification and design of explosion protection measures are carried out in accordance with European and national guidelines and standards, in particular Directive 2014/34/EU and the relevant standards and regulations for explosion protection.
Key reference documents include:
- EN 1127-1 on the principles and methodology of explosion protection
- EN 14491 on pressure relief for dust explosions
national requirements such as the Industrial Safety Regulation and the Explosion Protection Document
Benefits for operators
- Personal protection through the prevention of secondary explosions
- Plant protection through the limitation of property damage
- Production reliability through reduced downtime
- Legal certainty through the implementation of the explosion protection concept in accordance with standards
The selection of the appropriate decoupling system should take place as early as the planning phase, so that product data, plant geometry and the protection concept are coordinated and the mixer can be safely integrated into the overall plant.