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