Bruce Springsteen memorably sang, “You can’t start a fire without a spark.” Indeed, nearly every manufacturing fire begins with a tiny spark generated by normal industrial processes. If these sparks wind up in your dust or fume collection system, they’ll often find a ready source of fuel that can become an inferno in minutes. Fortunately, it’s possible to stop sparks in their tracks. Spark arrestance technologies use simple physics to prevent sparks from turning into fires.
UNDERSTANDING THE “FIRE TRIANGLE”
Fire is the result of a chemical combustion reaction. Three things are needed to get a fire going: a fuel source, oxygen and a source of ignition. Take away any of these three and the fire dies. There are many different types of dust and emissions in manufacturing plants, often as a result from the manufacturing processes in the facility, but sometimes from other plant functions too, such as packaging. Many people are not aware that the dust and fumes produced by welding and metal cutting processes are often highly combustible. The particulate gathered in a typical dust collector, combined with the filter media itself, can form a perfect fuel source.
Oxygen is also found in abundance inside the dust collector. The airflow used to capture the fumes and draw them through the filters provides plenty of oxygen to feed and intensify a fire once it has started. Now all that is needed is an ignition source. Welding, plasma cutting, grinding and other applications can produce millions of sparks per day. It only takes one to ignite the ready fuel source waiting inside the dust collector.
STOPPING FIRES BEFORE THEY START
It’s impossible to reduce the number of sparks produced by welding, cutting and grinding – they are inherent to the processes. The key to eliminating fires in the dust collection system is preventing sparks from making it through the ductwork to the collector. Over the years, engineers have designed various approaches to spark arrestance. All of them rely on some method of extinguishing sparks while they are in the ductwork, before they make it through to the filtration system. To a degree, this happens by default when sparks are driven into the sides of the ductwork at turns and elbows. When sparks hit the cool metal ductwork, they are stripped of the thermal envelope that surrounds them, allowing them to cool and thus extinguishing the spark. Common spark arrestance technologies include:
- Baffles and metal mesh filters that are designed to provide a tortuous path for sparks, cause them to bounce off multiple metal surfaces.
- Fixed-blade mixing vanes that create strong turbulence in the air stream, another way to strip off the thermal envelope.
- Simple plates placed in front of the dust inlet, which are designed to deflect sparks from entering the ductwork.
All of these devices, while effective to varying degrees, have drawbacks in one form or another. Some require regular maintenance in order to be effective, and others create high restriction to airflow, driving up operating costs and lowering the effectiveness of the dust collection system. Worse yet, many do not effectively kill the sparks and hot embers, only providing a false sense of security to plant management teams. In 2015 we introduced a new spark arrestance system that uses a patent-pending technology that relies on centrifugal force to extinguish sparks. High air flow velocity is maintained on all surfaces of the device to make sure it is self-cleaning, yet there is very little resistance to airflow. The design was perfected using Computational Fluid Dynamics software that allowed engineers to simulate hundreds of different designs in order to optimize effectiveness. Over hundreds of hours of testing in heavy production environments, this system has proved to be the most advanced spark arrestance technology available today.
SELECTING THE RIGHT SYSTEM
Selecting the right spark arrestance technology for your operations comes down to two questions:
- How effective is it? Different technologies and models have different success rates in eliminating sparks. In a comparative test of commercially available systems that we conducted, one unit allowed 180 sparks per minute to pass through, another allowed 300 sparks per minute to pass through, and a third allowed a whopping 4,760 sparks per minute to pass through. Each spark that makes it through the spark arrestance system is a potential fire waiting to happen. Ideally, the number of sparks your spark arrestance systems allows to pass should be close to zero. In the same comparative tests, our spark arrestance technology stopped all the sparks from passing through to the collector.*
- How efficient is it? One of the major downsides of many spark arrestance systems is their impact on airflow within the dust collector. To check this out look at the “static pressure drop”; this is a measure of restriction to airflow, which will reduce the volume of air moving within the system. If air volume is reduced too much the system may not effectively capture the emissions from the process, allowing smoke and fumes to escape into the plant. Plant maintenance departments compensate for this by replacing the filters sooner, sometimes when they are only halfway through their life. The problem can sometimes be countered by replacing the blower with a larger one, but of course this is expensive, and significantly increases energy use.
Lastly, you may also want to factor in maintenance cost considerations. A self-cleaning system can reduce maintenance time and expense and help keep your system running at peak efficiency for longer.
BEYOND SPARK ARRESTANCE
Even with a spark arrestance system that is 99.99 percent effective, it is still advisable to have back up fire suppression systems for your dust collectors. These systems can be literal lifesavers in the rare event that a spark makes it through to the filters. To stop fires in the dust collection unit, we need to go back to the Fire Triangle. We know that the filters and particulate matter inside the collector provide an ample source of fuel. A stray spark provides the ignition. To prevent that small spark from growing into a raging fire, we need to tackle the third side of the triangle: oxygen.
When the dust collector is running, there is a ready supply of oxygen moving through the system as it sucks in air and particulates from the process and its surrounding environment. Stopping that oxygen flow is the next defense against fires that start within the collector itself. Your dust collector should be equipped with a detector device that is capable of sensing the presence of smoke that gets through the filters, which is a sign of either a torn or broken filter or a fire in the filters. In addition to sounding an alarm, this detection system must automatically shut down the blower, and also the compressed air cleaning system, to reduce oxygen flow to the fire. Damper systems that automatically shut when smoke or heat is detected can further cut off oxygen supply. Without airflow, fires will die down, allowing them to be attended to much easier.
If the fire is not attended to quickly, fire retardant chemicals provide the next line of defense. There are different types of fire suppressant systems available, ranging from dry chemical systems, special gasses and, of course, good old H2O. At a minimum, you should have readily available external fire extinguishers by every dust collector. For greater safety, consider an internal fire suppressant system. These systems target fire suppressant chemicals right where they are needed as soon as smoke or heat are detected inside the detector. This can significantly limit the potential damage done by an internal dust collector fire; instead of replacing a whole unit, your damage may be limited to a single filter. In addition, you avoid the mess of deploying an external chemical fire extinguisher. In most cases, the fire will be extinguished before sprinkler systems are activated, avoiding significant cleanup costs and potential water-related equipment damage.
Sparks may be unavoidable in your operations, but fires are not. Effective spark arrestance and fire suppressant technologies can dramatically reduce your potential fire risks.
* RoboVent claims that their new spark arrestance technology, the Delta3, is 99.99 percent effective.
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