A: Eric Finley, Rembe, says:
This is a great question because prevention is a key piece to any safety concept. While properly designed explosion protection systems will ensure the equipment is safe, it’s still important to minimize any other risk through appropriate prevention means. In some applications, prevention techniques are even required per the NFPA to ensure a safe working environment.
First and foremost, it’s important to note that a dust hazards analysis (DHA) is required to be in accordance with NFPA 652: Standard on the Fundamentals of Combustible Dust before proceeding with any combustible-dust-related projects. This should be completed throughout the entire facility by a capable professional who is experienced in combustible dust hazards. A DHA will provide you with a report of what action steps are required to ensure the facility complies with the applicable NFPA standards. This should shed light into specific prevention techniques for your processes.
Once the DHA has been conducted, there are a few options that can be explored depending on the type of application. A few of these options are outlined here.
Education. One thing that’s important for any safety aspect in general is educating the entire company on the working hazards. Combustible dust is sometimes left off the list of hazards to discuss but ensuring that all employees are aware of the situation is vital. If employees are aware, then they can correct any dangerous actions or speak up if they see any potential risks. Education is the first and most important step in any safety strategy.
Managing hazards. Understanding where the combustible dust hazards can arise from in the first place is important. The potential hazards will range from identifying the ignition sources to dealing with combustible dust accumulation in the facility.
First, there are different types of ignition sources (13 categories to be exact), but there are a few common culprits in a manufacturing environment. A few examples include hot surfaces such as overheated bearings or drying processes, mechanical sparks from mills or grinders, electrostatic discharges from improperly grounded equipment, or even cigarette butts from employees. Some examples of ways to mitigate these ignition sources involve a ground monitoring system of material loading and unloading areas or temperature monitors for problematic bearings in bucket elevators.
Second, it’s important to prevent combustible dust from accumulating inside the facility. Most dust in a pile won’t ignite but it will ignite if enough dust becomes airborne. For this reason, NFPA 61: Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities states that dust accumulation shouldn’t exceed 1/8-inch over 5 percent of the plant’s processing area. This is a very small amount and essentially creates a zero-tolerance requirement for dust accumulation. Ensuring the rafters and top surfaces of equipment are free of accumulations is also important. This could involve the use of specially designed dust control fans near the ceiling of the facility to direct any combustible dust downward. The dust can then be cleaned through the normal housekeeping process. Finally, it’s important to never use compressed air to blow large plumes of dust inside the facility. This can easily produce a dust cloud that has the potential to ignite and create a large flash fire. Instead, explosion-proof vacuums should be the only equipment used to remove combustible dust from inside the facility.
Spark detection systems. There are also products available to help with prevention strategies. There are various spark detection and extinguishing systems available that will tie into any processing system. These systems’ sensors can range from hot spot detectors that scan large areas for any elevated heat signatures to spark detectors that scan for potential sparks in ductwork or mill discharge. These sensors can be connected to an emergency stop circuit or even a deluge system to douse the process with water or other inert substances. Other options include mechanical controls such as fire traps that stop the process flow, which may contain an ember, or diverter gates that redirect the process to a fire dump bin.
Overall, there’s a lot to consider in every combustible dust application, and creating a completely safe working environment is important. Explosion prevention is primarily based on proper housekeeping and maintenance strategies to sustain a safe facility. Having an expert look through the system to determine the optimal safety approach is also vital. This will ensure the facility remains safe for its workers and complies with the latest NFPA standards.
Rembe, Charlotte, NC, manufactures and supplies rupture discs as well as explosion safety systems and accessories.