Types of explosion protection

Dust explosion protection

Because of the dust explosion is usually less fierce than the gas explosion, not only preventive measures can be accepted (like avoiding all possible kinds of ignition sources, avoiding using dusty materials or by inertizing the atmosphere), also protective measures (installation of the protective systems) can take place - and this way of securing the technology can be even cheaper and more effective than preventive means.
Generally, the explosion protection is realized by three different described below. For detailed information on our protective systems, please follow the links.

Explosion venting

Principle: sufficient area on the shell of the device is opened during the explosion, releasing the explosion pressure and flame and other effect of the explosion out of the device. This leads to stressing the vessel by much smaller pressure (regarding the pressure with protective system we speak about "reduced pressure") than if the vessel would be closed so the device is not destroyed.
Realized by: tearing or detachable membranes, rupture discs, venting panels, special valves, lids
Disadvantages: there is no interference to the explosion - it goes the whole way, so there is long effect of flame and pressure outside the membrane, sometimes even 50-60 meters from the venting hole, where rests of dust released out of the device by the pressure wave burns. There is pressure and sonic wave spreading out of the venting holes. These effects prohibitis using explosion venting indoor, even in large halls (besides special flameless venting devices). Membranes must be changed after each opening. Explosion is spreading through all pipelines and other connections (material transporting devices, dedusting pipelines,...) so combination of explosion venting with explosion barrier system is always requested.
Advantages: these systems are usually cheapest way of protection and its the only suitable solution for big volumes exceeding approx 50 m³.
Typical mistakes:
"venting is always cheaper than suppression system" - if the device is not placed outdoor, making holes through the external walls, installing ducting leading the explosion (which lowers the efficiency of the venting systems, so more elements must be used) than venting may be most expensive and leading to additional problems.
"if I place the device outside, I can use venting" - setting the safety zone for venting is not always possible. In this zone no risk of explosion may occur, there can be no people or obstacles, communications and so on. In industrial areals usually only way up is free - there are another buildings, pipelines, storage areas, roads, paveways and so on around the buildings. Also, some of the dusts cannot be vented to the atmospheres (poisons, dangerous substances,...)
"one solution fots all applications" - no, you cannot use one silo with membranes for any kind of dust because various dusts have various explosion characteristics so for some kinds of materials the venting area may be insufficient. Always ask the device's manufacturer if the explosion protection is suitable for your kind of dust.
What VST Engineering uses: 3-layer, bulging membranes ANTIDET RELIEF.

Explosion suppression

Principle: the effects of the explosion are detected inside protected vessel (pressure, flame or both) and after the signal is processed by the control unit and the false alarm is excluded the extinguish agent (powder) is sprayed inside the protected vessel. This suppresses the explosion in its early state and the pressure rising is stopped. The whole action from the point of detection to the extinguish agent distribution inside the device lasts only several miliseconds.
Realized by: by the stand-alone protective system consisting of the detectors, control unit and action elements (pressurized vessels with extinguish agent closed by special extra-fast valve). VST Engineering has the unique system certified for dusts of St 1 and St 2 classes and both with standard extinguish agent or sodium bicarbonate (food, pharmaceuticals) or Furex D (metalic dusts).
Disadvantages: usually (not always) higher price
Advantages: can be used outdoor and indoor, can be used in the zones with explosion risk (even in the zone 20! outside the devices!). If installed properly, can also avoid the risk of the explosion spreading to the connected devices. It is a modern and sophisticated system which can work independently or with the connection of the control system of the technology (passing the information about the system). There is many other advantages depending on the specific installation.
Typical mistakes:
"explosion suppression system is expensive" - doesn't have to be. If you would count really spent costs for the other types of the protection like moving the devices closer to the walls, making holes in the construstion, setting the safety zone, explosion isolation systems etc...
"system has flase alarms, stops the technology too often" - it depends if the customer used quality product wit all necessary certificates of EMC (electromagnetic compatibility) and with software protection against false alarms or the same-looking system with red bottles but without these elementary qualities. Explosion protective systems are designed to safe lifes but in the ideal way you shouldn't know you have one in your factory.
What VST Engineering uses: ANTIDET SUPPRESSOR - explosion suppression system.

Explosion isolation system - chemical barrier

Principle: the scope is the stop spreading of the flame by the pipelines, conveyors and other connections to the other parts of the technology. The principle of this system is the same as of the suppression system described above, the difference is in the software in the control unit and also in more frequent using of the optical detectors of the flame.
Disadvantages: higher cost comparing to mechanical dumpers
Advantages: works in both directions in round and also rectangular pipelines of DN 100 to DN 1000.
Typical mistakes:
"chemical barrier is expensive" - works in both direction so in some situations there is no other option. Besides that this system communicates with the control system of the technology, providing very useful data.
What VST Engineering uses: ANTIDET BARRIER - chemical (aka HRD - High Rate Discharge) explosion isolation system

Explosion isolation system - mechanical enclosure

Principle: the scope is to stop spreading of the explosion flame and also pressure through the pipelines
Realized by: backflow valves (passive system) or slide, butterfly valves (active system)
Nevýhody: only for round pipelines (rectangular pipelines can be equipped by special socket) of the diameter DN 100 to DN 500. Backflow valve works only in one direction. Active slide and butterfly valves are more expensive than one backflow valves, but works in both directions.
Výhody: system stops not only flame but also pressure so its used also for the protection of pressure sensitive devices (blowers and fans) or humans (vacuum cleaners). Valves are cheap, needs almost no maintenance, they have no pressure loss in the pipeline, needs no power supply or pressured air supply. Slide and buttefly valves works in both directions.
Typical mistakes:
"valve keeps clogging" - yes, most of the dumpers really suffer from clogging. ANTIDET DUMPER valve is unique by its design when its opened so its perfectly circumfluenced by the air, so there are no conditions for dust sedimentation.
"valve causes pressure loss in the pipeline" - yes, most of the dumper really causes pressure loss in the pipeline because their heavy plate must be opened by the airflow generated by the fan. ANTIDET DUMPER valve is held in open position independently on the airflow, so it has zero pressure loss.
What VST Engineering uses: ANTIDET DUMPER - explosion isolation system - backflow valve.

Gas and vapours explosion protection

Because of the speed and force of gas and vapours explosions in closed vessels, it is not possible to lower the effects of the explosion and the protection must be realized by preventive means, such as preventing any ignition source, in extreme situations by inertization. It is also critical to stop possible spreading of flame or explosion through the pipeline to other parts of the technology or from outer environment inside the vessels. This can be done by rather easy way - using flame arresters (also known as flame arrestors, detonation arresters, etc.)

Flame arresters (flame arrestors)

Principle: arrester stops spreading of the sparks, flames, hot gases and also party the pressure stroke through the pipeline between two vessels or between outside areas and interior of the technology (typically through "breathing" pipelines). The principle of stopping the explosion can be different. There are mechanic, hydraulic, liquid and other types of flame arresters. The most common are mechanical flame arresters which are made of block of the solid material (usually stainless steel) with tiny holes or channels in it. The flame or hot gases have to split into thousands of these channels, which are several centimeters long. The flame loose its temperature by coming through the solid steel (the heat is passed and absorbed by steel) and thus the flame is extinguished and only non-dangerous gases slowed by the barrier can go through. Of course, normal air or gases, flowing with slow speed can easily go through.
Realized by: flame arresters of many possible types
Disadvantages:the channels in the mechanic flame arrester can be blocked by sediments and must be cleaned periodically or can be detrited by abrassive materials so the flame arrester's element must be changed.
Depending on their principle, flame arresters also cause significant pressure loss in the pipeline. The aim of all developers of the flame arresters is to minimize this pressure loss.
Advantages: only mechanical protection device with no need of power or any other medium supply. Flame arresters SafExty^® have low weight, compact shape and are equipped with adapters for easy connection into existing pipelines.