The Risks of Dust Explosions
In a variety of processing industries, there will be small particles of material which, at various stages of the manufacturing process, are likely to become airborne. Once dispersed into the air, a potential risk of an explosion presents itself, posing substantial danger to life and equipment.
All that is needed for a dust explosion to occur is a flammable dust (such as flour, wheat, sugar, metal, wood), the dispersion of said dust into a contained environment (such as a dust filter, silo or bucket elevator) and an ignition source (such as a spark from faulty machinery or static). These contributing factors can be expected in all areas of processing, but particularly in industries such as:
- Food Processing/Handling,
- Grain Handling,
If all processing equipment is not assessed, maintained and monitored, the ideal environment for a dust explosion can quickly develop and put lives of personnel at risk. Another factor that will contribute is if there is a severe lack of cleanliness on site, and/or utilising incorrect cleaning procedures. Piles of product can accumulate on surfaces throughout a processing area, and these stationary dusts can become airborne by a slight disruption and thus impose an even greater risk of a dust explosion taking place.
An example of this situation becoming reality is the Imperial Sugar explosion – an event so catastrophic, that it is widely used in this industry to demonstrate the aforementioned risks.
The effects of an explosion can be devastating, not only in cost due to production downtime and repairs, but also to the safety of personnel.
If a production facility is not protected against the likelihood and effects of an explosion, it can rapidly propagate throughout an entire facility, from one section of the process to another via connecting ductwork and conveyors, at an alarming rate until all emergency fire and evacuation procedures on site will be impossible to follow. However, with the use of industrial explosion protection equipment and accessories, an explosion can be detected, controlled, relieved, isolated and even suppressed.
There are is a wide range of protection, mitigation and prevention methods used to combat the likelihood and effects of an explosion within an industrial process, such as explosion venting, explosion isolation, flameless venting and explosion suppression.
If the process needing protection is in a safe area, away from personnel and surrounding equipment, explosion venting may be used, if it can vent safely to the outside atmosphere. An explosion vent panel is installed directly on the vessel, the size of which is calculated using various factors, including the vessel specifications and the characteristics of the product being processed. When an explosion occurs, the panel will burst open in order to safely relieve the explosion pressure in a controlled manner. The explosion panel will activate to ensure the vented explosion pressures do not exceed the pressure resistance of the vessel itself – so the result is no rupturing of the vessel, and only a replacement vent panel necessary to restart production after an explosion occurs. See our vent panels here.
When venting to a safe area is not possible, flameless venting is a logical solution. A flameless venting device will house an explosion vent panel, surrounding it with a flame quenching mechanism that ensures flames and other burning particles/gases cannot pass. This means that, when an explosion occurs, all that is visible from the outside of the vessel is a puff of smoke from the flameless venting device. Personnel can safely occupy the area nearby the equipment, so use indoors is an option in most cases. See our flameless venting device by RSBP here.
As an explosion builds in pressure, it can look to propagate into connecting areas via ductwork. To prevent this, explosion isolation is used. There are various types of explosion isolation techniques, one of them being passive, such as the use of an isolation flap valve or barrier valve. Inside, the valve has a heavy flap mechanism that is held open during normal operation. When an explosion occurs, the initial pressure wave will slam the flap shut, thus preventing the explosion from travelling through the duct. See our explosion flap valve by RSBP here.
Another method of explosion isolation is the use of an active system, such as a rapid acting slide gate valve. This device is usually used in conjunction with a detector and a control unit. The detector (for example, an optical detector) will send a signal to the control panel to activate the system when a spark is detected within the vessel. The control panel then sends a signal to the rapid acting slide valve which will then slam shut within milliseconds, blocking the pathway of the explosion through the duct. See our rapid acting slide gate valve by RSBP here. Explosion suppression can also be used as a form of explosion isolation.
Explosion Suppression is widely considered to be the most flexible and effective form of explosion protection. However in most cases it can also be the most costly. With the use of detectors, a control panel and pressurised bottles containing powder suppressants, this system is a rapid acting and effective solution to a variety of process specifications and designs.
Much like with a rapid acting slide gate valve, the suppression system is activated by the detectors being used (optical detection, pressure detection etc). Upon activation, pressurised bottles release suppressants into the vessel at an astoundingly fast rate, extinguishing the explosion from the inside of the equipment and stopping it in it’s tracks from the get-go.
All of the above methods of explosion protection can be used in a combination to suit each individual vessel and process in order to provide fast, reliable and life-saving efficiency, preventing an explosion from posing a threat to livelihood, equipment and adjoining processing areas.