Q: Where do spark detection and extinguishing systems fit into the protection of dust collection systems?
A: These systems are one component of the layers of protection you can apply to a particular process. These systems are designed to prevent the introduction of an ignition source into a combustible environment. While very effective in situations where you have a high probability of embers or sparks being produced in the process, they are not a substitute for the application of an appropriate explosion protection solution. To fully protect the process vessels, the facility and personal, appropriate mitigation techniques; explosion venting or suppression and isolation should be applied.
Bob Korn
Director of Sales for Explosion Protection Products
Fike
A: Agreed, having these systems in place is just one aspect of protecting a dust collection system. In addition, having fire-resistant filter media will provide an added layer of protection for spark-prone applications.
David Steil
Pharmaceutical Market Manager
Camfil Air Pollution Control
Q: Define 'approved' for vacuums if dusts are not allowed to accumulate.
A: Approved vacuum systems are designed to collect dust without introducing an additional hazard. I would recommend contact with any of the manufacturers to fully understand the safety features built into these systems.
Bob Korn
Director of Sales for Explosion Protection Products
Fike
A: There are two aspects to “approved” for vacuum systems from the codes and standards perspective – systems made of the right components so as to be conductive and able to be bonded or grounded and where electric vacuum systems are employed, ensuring that the vacuum is suitable for the electrical area classification that might apply. As noted above, both of these issues can be more fully addressed by manufacturers of such systems.
Guy Colonna, NFPA
Division Manager
Q: What about static generation? That is the primary source of ignition that we worry about and struggle to understand. Additionally, charge relaxation times are often cited as relevant, but how do we relate those to handling and to things like MIE? What resources can you point me to for design basis for conveying static-prone solid such as a chemical reagent to a reactor?
A: There are many elements to understand regarding protection from static charge. Applying grounding straps, using appropriate materials for product transfer, grounding wires in flexible tubing or piping, are just a few. There are many experts on this subject; to fully understand the hazards in your process I would suggest you contact o one of these expert consultants. Chilworth is one of the leaders in this field.
Bob Korn
Director of Sales for Explosion Protection Products
Fike
A: The NFPA standards stress the importance of conductive materials and proper bonding and grounding. As noted above, there are industry consultants with expertise unique to this topic, Chilworth is one of those leaders.
Guy Colonna, NFPA
Division Manager
A: The system designers will be able to help guide the application of conductive materials with proper bonding and grounding as needed. The other key is to have the dust tested specifically to include the MIE so that a proper risk assessment can be performed. How operators interact with the process is also an element that is often overlooked and can have an impact on static generation.
David Steil
Pharmaceutical Market Manager
Camfil Air Pollution Control
Q: Please expand on methods of detection to trigger the abort gate.
A: Abort gate is a generic term usually applied to an explosion isolation flap valve. A typical explosion isolation flap valve is a passive device; the air flow from the process provides the force that opens the value under normal operating conditions. When an explosion occurs upstream, the resulting pressure wave will propagate through the duct or piping, against the air flow, and force the flap to close. Some type of locking mechanism is employed to keep the flap closed for a period of time after the initial event. Consequently no specific detection techniques are necessary for a passive flap valve. There are other isolation devices that are active, operated by compressed gas or pyrotechnic energy. Detection methods used to activate these devices include pressure detection of the explosion pressure wave, or optical detection of spark, ember or flame in a process.
Bob Korn
Director of Sales for Explosion Protection Products
Fike
A: Most passive back flow dampers or isolation flap valves are only rated for ST1 and ST2 dusts. If moving into the ST3 range, typically an active isolation system is required. When choosing a device, be sure that testing in accordance with applicable standards has been conducted to verify their performance. Also, there are very specific distances that these devices need to be located from the inlet of the dust collector depending on the dust characteristics and the type of device being used.
David Steil
Pharmaceutical Market Manager
Camfil Air Pollution Control
Q: When retro fitting an existing unit to bring it into compliance is it acceptable to leave the unit discharging into a standard55 gallon drum and lid ? assuming it is a positive latch type lid.
A: If the discharging system is designed to contain the maximum pressure generated during a potential explosion event, referred to as Pred, then it would be an acceptable method of protection. For most applications these reduced pressures, Pred, can range from 2 to 5 psig, most drum collection systems would not provide adequate protection and would present the risk of destructive failure. A typical best practice solution is to apply a properly rated rotary valve to outlet of the dust collector that will provide the necessary isolation of the discharge.
Bob Korn
Director of Sales for Explosion Protection Products
Fike
Q: Should I expect a Dust Control on conveyors as a subject? Doing Dust suppression instead of capturing using water instead of collectors?
A: Igor, if I understand your question; using wet dust collection dramatically reduces the potential for a combustible dust explosion. Conveying systems should be reviewed to understand the hazard and the potential or risk of an explosion. If the risk is high, appropriate prevention controls and protection techniques should be applied. Our office in Brazil, Fike Latina, would be glad to answer any addition questions.
Bob Korn
Director of Sales for Explosion Protection Products
Fike
Q: Do dust collectors handling aluminum dust have to located 'outside of the building'?
A: In general, explosion suppression and isolation systems can be applied to dust collectors located inside a facility. However, metal dust hazards present unique design challenges due to the high explosiblity of the material. A full hazard analysis and review by those that understand the extreme nature of metal dust should be performed to determine the appropriate protection solution for your application. In many cases a hybrid solution can be applied that employees both explosion suppression and explosion venting that does require the collector to be located outside in an area safe from personal exposure. Fike can review your application and provide a protection solution if you desire.
Bob Korn
Director of Sales for Explosion Protection Products
Fike
A: NFPA 484, Combustible Metals standard requires dry-type dust collectors to be located outside (Paragraph 8.4.6). For machining operations covered by 8.7 of NFPA 484, dry-type dust collectors must be located outside, while wet-type dust collectors are permitted to be located inside. As noted above, a hazard analysis should guide the selection of dust collectors as part of compliance with the NFPA requirements if they are applicable to the situation.
Guy Colonna, NFPA
Division Manager