Is Your Dust Collector Explosion Venting to a Safe Restricted Area?

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Permalink Reply by Ged Begley on May 29, 2009 at 5:11am

Very good question. In my experience (in various cereal processing plants) it is relatively common to see unsafe venting arrangements on dust filters,bucket elevators,hoppers and silos,including venting into the workplace.

As well as not venting to a safe area I regularly witness other common issues :-

1)Vent ducts plated over to prevent weather ingress
2)Vent ducts corroded or too weak
3)Explosion Vent panels made of "homemade materials" (wood,rubber,gaskets) i.e of unknown bursting pressure.
4)Explosion vent panels not switched and interlocked to the plant.

I am of the opinion that there is a general lack of appreciation of the magnitude of the energy release when a dust explosion is vented and venting to a safe area is often an "afterthought" even at the design stage in newer plants.

Flameless vent devices for example,correctly sized and sited,can be particularly useful for existing plants where venting to a safe area is not a practical option.

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Permalink Reply by Mike Barnes on June 1, 2009 at 11:36am

NFPA 68 - 2007 provides a calculation to estimate the length of the fireball. We typically provide this information to customers when proposing a relief device. In my experience it is seldom less than 10 meters in length - often exceeding 25 meters.

Another aspect of a venting episode which seems to be infrequently considered is the thrust developed as the fireball exits the vent. The Standard also provides for an estimate of this. It should be carefully considered when adding venting to an existing collector, silo, etc. to ensure that the support structure is adequately sturdy to prevent the enclosure from overturning.

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Permalink Reply by Dave Price on June 2, 2009 at 4:30am

Some excellent points here, although I would like to advise that although Flameless venting devices are indeed suitable for some applications they still require a safe area.

They primarily function is to prevent the passgae of flame by using the minimum safe gap principle of flame quenching, however they still emit hot gases (Pressure) and products of combustion, a safe area is still required surrounding the device, manufacutureres will be able to advise on the distance required, although this safe area is usually in the magnitude of metres and not tens of metres.

In addition care should be taken when specifying flameless venting devices as they are only suitable for certain dusts, its advisable not to protect soluable dusts with these devices as their effeciency may be drammtically reduced due to partial blockage of the vent area, again verification of test and certification data is very important before choosing a product as your basis of safety.

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Permalink Reply by John Astad on May 29, 2009 at 5:22am

Ged, thanks for providiing further helpful iinput. You bring up some excellent points.

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Permalink Reply by Bob Taylor on June 2, 2009 at 5:37pm

Yep! Went through great strives to add the greatest level of protection to people and property including the need to shield some critical cable trays. On the other hand, why would EPA considering stating in the proposed subpart Y that in some industries, mechanical dust collectors are to be installed and monitored instead of promoting best available technology and methods to control dust at point of source versus moving it elsewhere and increasing risks?

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Permalink Reply by John Astad on June 3, 2009 at 6:48am

Great comment Bob. Can you provide more information with links to EPA subpart Y As I don't believe many of us in the ComDust group are familiar with it. Thanks

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