LumberJocks

TIW Ep 31 - Dust Collection in my Sawdust Factory Part 4

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Blog entry by Shawn Sealer posted 09-16-2012 02:37 AM 4071 reads 0 times favorited 9 comments Add to Favorites Watch


The final installment of hooking up my dust runs in my wood shop. Hooking up the drill press and Band saw.

-- -Shawn



9 comments so far

View thedude50's profile

thedude50

3515 posts in 1145 days


#1 posted 09-16-2012 06:05 AM

dude you need to ground dust collection systems.

-- when I am not on Lumberjocks I am on @ http://thisoldworkshop.com where we allow free speech

View nobuckle's profile

nobuckle

1120 posts in 1428 days


#2 posted 09-16-2012 01:10 PM

Shawn, thanks for posting this series. I have gained some valuable information.

-- Doug - Make an effort to live by the slogan "We try harder"

View Shawn Sealer's profile

Shawn Sealer

165 posts in 1781 days


#3 posted 09-18-2012 01:49 AM

This is why I did not ground.

Read Fine Woodworking issue 153 page 048 – PVC Pipe Dangers Debunked

An Article by Rod Cole

Home-shop dust-collection systems have become increasingly popular, but their safety has been hotly
debated. The primary issue is whether PVC pipe is safe for use as ductwork. Many claim that sparks in PVC pipe
due to static electricity may ignite the dust cloud in the pipe. The specter of a giant fireball consuming a shop and home is repeatedly raised. Others claim you can ground PVC, thus ensuring its safety.

Two years ago I had to decide for myself: PVC or metal ducts for my basement shop. Being both an avid woodworker and a scientist, I made a concerted effort to understand the issues. Fortunately, I have the resources of the library at the Massachusetts Institute of Technology (MIT) and a professor just down the hall who’s an expert in the physics of lightning. I studied static discharge from insulators, as well as the more general topic of dust ignition. I found that it’s extremely unlikely for a home-shop-sized system to have a dustcloud explosion. Commercial-sized systems have had dust-cloud explosions, but different phenomena come into play in larger systems, and 4-in.-dia. PVC is too small for use in such systems, where the airflow is much greater than in a home shop.

Sparks are unlikely in 4-in.-dia. PVC pipe In my research I turned to the Journal of Electrostatics, a publication
that covers the effects and interactions of static electricity, particularly in commercial applications. This journal
has published a number of studies on the combustibility of dust clouds by electrostatic sparks. The researchers were able to determine some of the conditions necessary to create sparks and ignite a dust cloud.

Sparks can be caused by a variety of conditions—one of which is static electricity. However, sparks are unlikely inside
a standard 4-in.-dia. PVC pipe that would be used in a home shop, and more importantly, any such sparks are extremely unlikely to be strong enough to cause an ignition. I can’t say it is truly impossible, but it is very close to impossible, and I do not know of a single instance.

The difference between metal and PVC is that one is a conductor (metal) and the other is an insulator (PVC). A conductor allows electrical charges to flow freely. If any excess charge is not given a path to ground, it can arc, creating a spark that in certain conditions can ignite a flammable substance such as dust. Grounding provides a path for this excess charge to flow harmlessly to the earth, which is why dust-collection systems in all commercial shops are required by code to be grounded. However, an insulator is a very poor conductor of electricity. While it’s possible to get a static shock from the outside of a PVC pipe, it is highly unlikely for sparks to occur inside.

Dust collectors with 3 hp or less pose little danger I published my findings on my web site. Rob Witter, a representative at Oneida Air Systems Inc., which makes dust-collection systems, said he largely agreed with my research. “We as a company have been trying to trim away at these misunderstandings for years,” he said. He added that plastic pipe will “probably never cause a problem” in a home shop. Finally, he pointed out that the National Fire Protection ssociation NFPA) puts no regulations on dust-collection systems of 1,500 cu. ft. per minute (cfm) or less.

All of this discussion applies to home-shop-scale systems. Larger systems, complete with ducts and filters that move
more than 1,500 cfm, require at least 3 hp and are not found in most home shops. Larger systems need larger ducts, and with that you have to begin to worry about more complicated forms of static sparks.

The real hazards In a home shop, the dust-collection fire hazards you need to worry about are not in the ductwork but in the collection bag or bin itself. A fire may be caused by a spark, which can occur when a piece of metal is sucked into the ductwork and strikes another piece of metal, or by embers from a pinched blade. The spark or ember settles into the dust pile to smolder, erupting into a full-blown fire hours later, often after the shop has been shut down and no one is there to respond. For this reason, my most important recommendation is to empty the collected dust every day or at least keep it in a closed metal container.

Rod Cole is a woodworker and mathematician who lives in Lexington,

-- -Shawn

View thedude50's profile

thedude50

3515 posts in 1145 days


#4 posted 09-20-2012 01:35 AM

very interesting however i know of two fires and both were in the duct work. one in metal and one in coil hose neither system was grounded and in both cases the fire marshal cited static discharge as the cause. I always thought metal systems were immune to the fires but that was not the case. grounding is simple and i will continue to ground better safe than sorry. I always empty the bag after sawing and routing.

-- when I am not on Lumberjocks I am on @ http://thisoldworkshop.com where we allow free speech

View Shawn Sealer's profile

Shawn Sealer

165 posts in 1781 days


#5 posted 09-22-2012 03:02 AM

I think the “Better safe than sorry” hits the nail on the head. Why not ground the system. I will do a Short Update on grounding my dust collector son. Were the two fires in home shops, with dust runs that only go 4 feet? Any suggestion on how to ground Rockler Dust Right Flex hose? And what should i ground too.

Thanks

-- -Shawn

View thedude50's profile

thedude50

3515 posts in 1145 days


#6 posted 09-25-2012 03:32 AM

My system is longer and their fore more prone to spark ignition. From what I have been told both the fires were in multi car garage shops with at least 6 machines set up and on two different sides of the shops. I have a small book I got for like 6 dollars on the basics of dust collection I followed their guide . I simply fished a cable wire from each side into the system and then grounded the dust collector and the pipe runs to the center screw on the dust collection plug it was quite simple and I believe safer. It was cheep to do and if it works fine and if it still catches fire I did everything I know of to prevent the fire. Some people ground the cable to each machine as well I guess this is better and so I did it that way. The Only tools that aren’t grounded are the ones I move My table saw and my planer which is a lunch box planer.

-- when I am not on Lumberjocks I am on @ http://thisoldworkshop.com where we allow free speech

View Shawn Sealer's profile

Shawn Sealer

165 posts in 1781 days


#7 posted 10-20-2012 04:20 PM

thedude50 Thanks, seems simple enough. Just to clarify the wire goes on the inside of the tube, and if so do you have any problem with clogs.

Thanks again

-- -Shawn

View thedude50's profile

thedude50

3515 posts in 1145 days


#8 posted 10-20-2012 10:50 PM

no problems with clogs in any of my dust hoses so far.

-- when I am not on Lumberjocks I am on @ http://thisoldworkshop.com where we allow free speech

View Shawn Sealer's profile

Shawn Sealer

165 posts in 1781 days


#9 posted 10-23-2012 12:27 AM

thanks

-- -Shawn

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