What are your options when it comes to spark control technology for a dust collection system? Mechanical spark arrestors and detect-and-suppress systems are designed to keep sparks out of the filter chamber and reduce the risk of a dangerous dust collector fire. Understanding your spark control options will help you make the right choice to improve the safety of your dust collection system.
Is Spark Control Required for a Dust Collection System?
Spark control for the dust collector is necessary if the intake for the collector or ductwork is near spark-producing processes. Spark arrestors play a crucial role in dust collector fire prevention by keeping sparks and flaming debris out of the dust collector filter chamber. Spark arrestance or detect-and-suppress technologies should be used when collecting dust from welding, grinding, cutting and other production processes that produce sparks.
Welding, cutting, grinding and many other applications produce small particles of floating, flammable debris (sparks). These sparks are carried along with the air currents that pull air into the dust collection system. If not controlled, they can easily become an ignition source for a dust collector fire or a dangerous combustible dust explosion inside the collector or the ductwork. Spark control technologies are designed to either extinguish sparks or prevent them from entering ductwork or the dust collector.
What Is a Spark Arrestor?
A spark arrestor is a device used to suppress sparks and flammable debris. They are used in areas where sparks are generated near flammable materials or explosive atmospheres. In addition to their use on dust collectors, they are commonly found on ductwork, chimneys and combustion engines.
Types of Spark Arrestors: Passive vs. Active
There are two common types of spark arrestance systems: passive and active.
- Passive, or mechanical, systems are designed to block the passage of sparks or slow down airflow enough to allow hot sparks to fall out of the airstream naturally. They include mesh or screen-type spark arrestors, baffle systems, strike plates, dropout boxes, and centrifugal spark arrestors.
- Active spark arrestors, such as detect-and-suppress technologies, directly extinguish sparks using water or a chemical.
Centrifugal Spark Arrestors
A centrifugal-type spark arrestor uses centrifugal force to trap and extinguish hot flames using vanes or deflectors. As air moves through the spark arrestor chamber, blades or vanes cause it to rotate and move in a “tortuous path.” Centrifugal force pushes the sparks against the walls of the chamber. This strips the thermal envelope from the spark, allowing it to begin cooling down. Particles are then either collected in the trap for disposal or carried through the ductwork to the collection unit. Centrifugal spark arrestors are often found on heavy equipment. They are also a good choice for dust collection in environments that have many sparks.
Screen-Type Spark Arrestors
A screen-type spark arrestor consists of a metal screen (or sometimes multiple layers of metal mesh) that catches larger embers and sparks while allowing gases and vapors through. It is a very simple type of spark arrestance technology. The metal screen blocks the passage of the sparks; as embers hit the wire, they are either instantly extinguished by the impact or trapped until they cool down naturally. Screen-type spark arrestors are often used on combustion engines (e.g., in the exhaust or tailpipe), at the top of chimneys, and at the entry to ductwork. They must be cleaned periodically to remove the build-up of particulate on the screens and allow air to flow through freely.
Strike Plates, Baffles and Dropout Boxes
Strike plates and baffles work on the same general principles as screen-type or mesh spark traps, but they look a little different. A strike plate is a simple system that places a (usually metal) plate in front of the airstream. Sparks run into the plate and fall out of the airstream, while the air itself moves around the plate. Baffle systems may use multiple staggered baffles; air flows around the baffles, and sparks are stopped by running into them or simply falling out of the airstream as air slows down. For some applications, a simple dropout box may be sufficient to reduce airspeed and allow sparks to fall out of the airflow. The dropout box may be equipped with baffles for additional spark protection.
Active Spark Control: Detect-and-Suppress Systems
A detect-and-suppress system is different from a mechanical spark arrestor. Instead of using mechanical methods to trap sparks and strip the thermal envelope, it uses water to extinguish sparks on contact. This type of spark control system is typically used in ductwork or conveyor systems. Heat sensors detect the presence of an active spark. When a spark is detected, the sensor triggers an extinguishing system to put it out, usually in the form of a directed water jet. Water may be replaced by CO2 gas or a chemical fire suppressant in applications where water is not suitable. Detect-and-suppress systems are often used in process industries with a high risk of fire or explosion.
What Is the Best Spark Arrestor System for Dust Collection?
The dust collection system provides an ideal environment for a fire or explosion if sparks are allowed to enter the ductwork or dust collector. If sparks are present near the dust collection system, some form of spark control must be used. So how do you know which type is right for your application? RoboVent has conducted extensive tests of the most popular mechanical spark arrestance technologies on the market, including both screen-type and centrifugal spark arrestors. We looked at two important factors when choosing a spark arrestance system: spark-reducing effectiveness and pressure drop.
Both metal mesh and centrifugal-type spark arrestance systems provide spark protection, but in general, centrifugal spark collectors let fewer sparks through. In our tests, metal mesh screens with a single screen all allowed sparks through; it took three or more screens, or the addition of a secondary baffle system, to sufficiently reduce sparks. However, these design modifications came with a cost in terms of pressure drop (see below). For applications that produce many sparks, a centrifugal spark arrestor may be the safer and more reliable choice.
Some applications, especially those involving explosive atmospheres, may require the extra protection of a detect-and-suppress system, which will actually extinguish sparks that make it through a primary spark arrestance system.
Pressure Drop and Spark Arrestance
One consideration in choosing a spark arrestor for a dust collator is pressure drop. This refers to the difference in pressure between two points in a system—in this case, before and after the spark arrestor. In the dust collection system, a drop in pressure corresponds to HP and energy costs and can lead to a drop in air speed, or CFM, over the life of your unit. Pressure drop is undesirable because it means that your system must work harder to maintain adequate CFM for efficient capture of particulate. Choosing a spark arrestor with low pressure drop will improve the energy efficiency of your system. Just make sure you are not sacrificing spark control performance.
Most types of mechanical or passive spark arrestors produce some degree of pressure drop. Metal mesh screens, in general, have lower pressure drop than centrifugal spark arrestors. However, they are also less reliable at stopping sparks. Adding additional layers of screening—two, three or even four layers of screens—improves their ability to stop sparks but also results in higher pressure drop. Pressure drop also increases as screens become loaded with particulate, making regular cleaning essential to maintaining an efficient system. Loaded screens can also create a fire risk of their own.
Delta3 Inline: Exceptional Spark Control. Low Pressure Drop
In 2020, RoboVent went back to the drawing board to reimagine centrifugal spark arrestance. The result is Delta3 Inline: a new, improved iteration of our Delta3 Spark Arrestor. Delta3 Inline delivers the same spark control performance with lower pressure drop than its predecessor. In fact, in rigorous experimental testing, Delta3 Inline tied for the lowest pressure drop among the centrifugal-style spark arrestors tested. It was one of only two models that allowed zero sparks through at all airspeeds tested.
Spark arrestance is a vital component of dust collector fire safety. With Delta3 Inline, manufacturers can have the best of both worlds: excellent spark control combined with low pressure drop and better energy efficiency.
Not sure what kind of spark control you need for your application? Talk to the fire safety experts at RoboVent.