Is your dust collector a fire risk? According to dustsafetyscience.com, dust collectors are responsible for nearly 15 percent of industrial fires and explosions in North America, resulting in 25 fires and four explosions in 2021 alone. That makes fire safety a critical concern for dust collector operation and something that fabricators and manufacturers should be aware of. Learning about fire prevention strategies and suppression options for industrial dust collectors is key to employee and facility safety.
Starting and sustaining a fire inside a dust collector requires three elements: fuel, oxygen and ignition. Together, these three elements are known as the “fire triangle.” Removing any of these three elements will prevent a fire from starting or spreading.
Dust collectors provide an ideal environment for a fire with plenty of fuel (filter media) and lots of airflow to fan the flames. The collected dust may also be flammable or combustible, adding additional fuel and risk. All it takes is a source of ignition, which may be a spark from industrial processes, heat or sparks generated within the dust collector blower/motor, or even static electricity.
Step 1. Spark control
A spark control strategy should be used whenever there is a risk of sparks entering the ductwork or filter chamber.
Spark control may be passive (mechanical) or active. Passive or mechanical systems physically block the passage of sparks, slow down airflow enough to allow sparks to drop out naturally or use centrifugal force to strip the thermal envelope from the spark. Options include metal mesh/screen spark collectors, dropout boxes and baffle systems, strike plates and centrifugal spark arrestors.
Active “detect and suppress” systems have a sensor system that detects the presence of a hot spark and a sprinkler or jet system that extinguishes the spark using water or a chemical. These systems are most commonly used in high-risk applications, such as when dealing with highly combustible dust or an explosive atmosphere.
A centrifugal spark arrestor is a good choice for most spark producing applications. These devices extinguish sparks by creating a spinning pathway that forces them against the sidewalls of the spark arrestor. They can be installed inline with the ductwork to prevent sparks from entering.
Step 2. Fire detection
Every dust collector should be equipped with a fire/smoke detector that sounds an alarm if a fire starts inside the collector. For dust collection systems, a dual thermal/ionization smoke detector is recommended. Ideally, the system will also shut down the blower to stop the flow of air that feeds the fire. Some systems also have an automated damper that closes to stop airflow.
Step 3. Fire suppression
All dust collectors should also be equipped with a fire suppression system in case a fire does break out inside the collector. There are three main options when it comes to fire suppression.
- A water sprinkler system uses the facility’s water supply. Sprinkler heads inside the dust collector direct cool water at the filters, extinguishing any flames or sparks. This is a simple and cost-effective fire protection method, but it does leave a mess if the sprinklers are activated.
- CO2 smothers the fire by displacing oxygen in the filter chamber. CO2 suppresses fires and prevents them from spreading, allowing time for professional firefighters to arrive. It does not necessarily extinguish the fire. CO2 gas is odorless, clean and safe for electronics. However, it is not safe for use in indoor areas where humans or animals are present.
- Chemical fire suppressants include firefighting foams, dry chemical agents and clean-agent gas systems. Of these, a clean-agent gas is the simplest and cleanest solution. Like CO2, a clean-agent gas works by suppressing the fire rather than extinguishing it. Unlike foams or dry chemicals, it does not leave residues on equipment and is safe for use around electronics. Many clean-agent gases can also be safely used in areas where people or animals are present.
The most important consideration in choosing a fire suppression system is the type of fire that will need to be extinguished. The National Fire Academy categorizes fire into five classes (A, B, C, D and K) based on the type of fuel present.
Most dust collector fires fall into Class A (ordinary combustibles). Class A fires can be put out or suppressed using any of the three methods. However, if collecting combustible metal dust such as magnesium, titanium or aluminum, there is the possibility of a dangerous Class D fire. Class D fires cannot be put out with water; this will only magnify the fire. A chemical agent, such as a dry powder chemical agent or an inert gas chemical agent rated for Class D fires must be used.
If flammable gases or liquids are present along with the dust, the fire may be classified as a Class B fire. A dry powder chemical agent system is recommended for these fires. If a facility is at risk for a Class B or Class D fire in its dust collection system, it should work with a knowledgeable system engineer to determine the best fire suppression option.
A fire suppression or extinguishing system may be either directly or indirectly triggered. A direct release system is directly triggered by the fire itself. For example, special tubing may burst when exposed to heat, releasing the agent. This method is failsafe (it is triggered automatically) but does not allow for precise direction of the agent.
An indirect release system is triggered by a sensor, such as a fire/smoke detector, that opens a valve to release the agent. Release valves can be positioned for precise direction of the agent toward the filter media. A dual-release system uses both methods and is often recommended to combine the advantages of each.
Step 4. Explosion protection
If a facility is collecting combustible dust, it will need an NFPA-compliant deflagration system in addition to the fire protection elements described. Combustible dusts include all organic materials (food, wood, paper, coal, etc.) as well as many metals. A dust collector deflagration system typically includes the following elements.
- Explosion vents (standard or flameless) are designed to safely release pressure when it starts to rise inside the dust collection system. A flameless vent will also contain flames.
- Isolation valves are used to prevent the propagation of a pressure wave back into the facility.
- A rotary airlock is installed in between the hopper and the collection bin to prevent collected dust in the bin from becoming added fuel in an explosion.
A qualified system engineer can help design a fire-safe dust collection system. If the current system does not meet fire safety standards and regulations, a facility can retrofit it with appropriate spark control, fire detection, fire suppression and explosion mitigation elements. Investing in dust collector fire safety now will go a long way toward reducing the overall fire risk for a facility.