Sprinkler Required in Dust Collection Ductwork?

1/29/2021

I have an exhaust system serving a welding and metal fabrication lab at a school. They will utilize 70% ferrous metal and the remaining will be a mixture of stainless steel, coated steel and aluminum.

The largest duct diameter at the building exit is 30" round. The dust collector will be located on the exterior of the building and in a freezing environment.

Will I need to provide fire suppression within the ductwork both inside and outside as well as within the dust collector?

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5 Comments

Mike Ruck

1/29/2021 09:24:36 am

Fire suppression would be located on ductwork inside building.

Provide a spark detection system that senses "sparks" and it opens a solenoid valve serving a sprinkler head downstream of the sensors. I've specified Flamex in the past.

Franck

1/29/2021 10:37:48 am

The possible issue is related to pyrophoric metal, such as aluminum, especially when divided in small particulates (dust).

You can then have a fire and an explosion hazard.

The other issue with pyrophoric metals is that water is generally not a good idea (generates hydrogen with explosion hazard).

A spark/amber detection system inside your duct is a minimum.
A spark arrestor is even better if you want to avoid sparks to ignite a fire inside your duct/dust collector.
You can also activate a fixed fire protection system with water under some circumstances, but normally, with aluminium fires, only specific powders (Met-L-X, copper powder, dry sodium chloride) or dry sand are recommended (see NFPA 484).

Interesting NFPA standards in your case:
NFPA 69 – Standard on Explosion Prevention Systems
NFPA 484 - Standard for Fire Protection for Combustible Metals
NFPA 652 - Standard on the Fundamentals of Combustible Dust
NFPA 654 - Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids

CJ Bonczyk

1/29/2021 11:34:20 am

I would see if you can get all the cutsheet data and design for the exhaust system & dust collector itself. Many times these have particular standards (NFPA 45, 91, 68, 69, 652 & 654, 484), that are required for the fire protection and safety guidelines. Additionally ensure the materials are not UN Class 4.3 solid as tested using UN Class 4.3 water reactivity test methods. Specific detection i.e. smoke, spark detector, and any heat detectors may be required. Premanufactured nozzle/sprinkler locations may be required on the units/ duct themselves. The detection and system unit design will also help dictate which type of applicable extinguishing agent will be required as well. Make sure the project does not have to comply with FM Global as they have particular data sheet requirements on various dust collection systems. Check the life safety code documents for information regarding the occupancy and additional code requirements. Lastly ensure the local AHJ does not have any additional requirements. We have made the mistake in the of simply complying with code for our submittal and the AHJ required additional protection of the system to assist with their fire fighting operations. An example of this of this is we had to add a preaction system for a single sprinkler for two dust collectors located on the exterior of a building. This was not required by code and the design of the system, however a hydrant was within 50 feet and they did not want to expose the responding team to an exploding dust collection unit.

Jesse

2/1/2021 07:50:10 am

Great question. You'll need listed detection and protection downstream of the last material entry point for sure, and the comment about pyrophoric metals is very good.

There a re numerous pre-engineered system on the market.

Alternative solutions are listed high-speed abort gates (obviously exterior) interlocked to the detection method, but these have fallen out of favor a bit lately. Sometimes, a combination of detection, suppression and high-speed abort gates.

Finally, have the client check with their insurer and their engineering division. When I was an insurance loss control engineer, our requirements for dust collection protection were very stringent.

Greg Black of Baghouse Duct Design dot Com link

9/10/2021 01:00:56 pm

If you met NFPA requirements, and designed the internal duct system velocities to keep the particulate in suspension, you will not need any kind of suppression in the duct itself. The concept of applying low speed duct, and applying sprinklers for 'fires' is not only compliant with NFPA.

You did not say the distance from the dust collector, to the closest pick up point. If the duct run is 'long' any embers should 'burn out'. If the duct run is 'short' you should apply a drop out box, or mechanical spark arrester ( be sure to include the pressure drop in your fan pressure calculations )

You did not say if you are using a cartridge or felted fabric collector. For either case, you should use 'Nomex' and/or fire retardant treatment on your filter media.

For metal powders, you should apply/select a fan that is AMCA B or C

You do have an option of applying a wet collector, though those do not capture particulate under a couple of microns.

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Sprinkler Required in Dust Collection Ductwork?

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