Grounding metal pipe duct system

[Doug Edwards]

It has been my experience that the bulk of industrial wood shop dust collector fires have been related to shop workers using the duct system as an ashtray.

[Bob Borzelleri]

Bob,

You mentioned in one of your posts that you're doing underfloor ducting. There have been posts from folks with underfloor ducting who wished they hadn't gone that route. The main reason is the likehood that you'll want to rearrange your shop/machines as the shop changes/grows.

The static issue's been covered, so I won't beat that horse.

Rob

Rob...

I have been thinking about that possible downside and have come to the conclusion that since I have a raised floor with considerable crawl space, the most likely complication from a desire for future changes will be having to patch "up" holes I not longer wish to use. So far, I haven't come up with other issues. I'd be interested to hear if I am overlooking something.

I really prefer the notion of having free space overhead so I can easily break light fixtures while swinging long and cumbersome stock.



...Bob

[Dale Thompson]

This might sound a bit counter intuitive, but stay with me for a bit. I am designing my dust collection ductwork system and have come upon the following question while considering the "all metal" option.
Bob

Bob,
Save yourself some money and some "sheet metal" cuts on your hands and elsewhere. Go with PVC!! Also, minimize the "flex" hose. It's not a hazard but it does cost you some system efficiency. In most cases - A LOT!!

The static potential that you will build up in your system will NOT be a problem. Forget about grounding! It's a waste of time and material. Static electricity is only voltage. Voltage will NOT start a fire or an explosion (Theoretically the latter are the same. An explosion is nothing more than a rapidly moving fire). If you figure out a way to make an explosion in your DC, there are a lot of fire protection experts who would like to know your secret.

In fact, as I have posted before, even the dust explosions that occur in those massive grain elevators are 90% due to open fires from overheated motor bearings or conveyor components.

Just a thought from a retarded old relic who has been involved in the fire protection engineering business for about forty years.

Dale T.

[Steven Wilson]

So Dale, I guess you believe that the NFPA code 664 is a bunch of garbage then. For the rest of you you might want to download http://www.nfpa.org/assets/files/PDF/ROP/664-02-rop.pdf and have a look. Even though it does apply to commercial facilities the regulations apply to systems rated greater than 1500CFM, some of us have systems of this capacity. The published regulations will cost you $30 but the link above is to a fairly recent draft. The first portion of the document contains proposed changes (a rather interesting read), the second portion contains a draft revision of the NFPA code 64 Wood and Cellulosic Materials Processing.

[Dale Thompson]

So Dale, I guess you believe that the NFPA code 664 is a bunch of garbage then. For the rest of you you might want to download http://www.nfpa.org/assets/files/PDF/ROP/664-02-rop.pdf and have a look. Even though it does apply to commercial facilities the regulations apply to systems rated greater than 1500CFM, some of us have systems of this capacity. The published regulations will cost you $30 but the link above is to a fairly recent draft. The first portion of the document contains proposed changes (a rather interesting read), the second portion contains a draft revision of the NFPA code 64 Wood and Cellulosic Materials Processing.

Steven,
First off, I don't think that NFPA 664 is a "Code". It is probably a "Standard". There is a difference. Also, it is written for "Commercial Facilities". My shop could hardly be defined as a "Commercial Facility". My wife is probably closest when she refers to it as a "MESS"!

NFPA 664 is not "garbage"! It is, however, a "concensus" standard. That is the case with all of the NFPA Codes/Standards. What this means is that the contents are not necessarily practical but they are all "compromises". The fact is that many of the members of the various committees are from manufacturers who have an interest in selling their products. I know because I was one of them on several NFPA Committees. I can recall spending two or three days arguing over the use of the word "should" vs. "shall" in a single sentence of a given standard. That may sound stupid but the choice could mean many dollars to the manufacturers involved.

Whatever, if anyone is REALLY concerned about their shop DC blowing up their home, I would suggest that they contact an "unbiased" and "non-compromised" source. Find a website for Fenwal, Inc. or some other major manufacturer of explosion systems and ask to talk with an explosion-suppression engineer or technician. After they get off the floor from laughing, I'm sure that they will answer any question that they have.

Dale T.

[Jim Becker]

I found the document interesting, particularly in that they acknowledge that small shops with small, under 1500 CFM systems including cyclones can accomodate certain things that are total no-nos in their view for larger installations...like having the system indoors, etc.

[Dennis McDonaugh]

You are comparing apples to oranges Steve. Since NFPA seperates industrial units and "small" or "home" units at 1500 CFM I guess we can too. Call those smaller units whatever you like. If your unit is larger, by all means follow NFPA 664. I doubt many of us here have that problem in our "home" shops and I don't think most of us need to provide a continuous ground for our piping, but like you say its cheap peace of mind if you are worried about it.

[Doug Edwards]

Dale: "First off, I don't think that NFPA 664 is a "Code". It is probably a "Standard". "

Yes, it is a standard. but this standard has been adopted as code in many, many locations. It is also a requirement for the clients of the big industrial insurance companies. I know you know this Dale, but many others don't.

Dale: "There is a difference. Also, it is written for "Commercial Facilities". "

This is a very important distinction. The production processes in an industrial facility are very different than the home shop user. In several locations, the committee comments indicate that units under 5,000 cfm are not a big deal and that the safety records do not indicate a need for increased regulation of "open bag" type collectors. this describes virtually every collector mentioned on this forum. In reading through this document and the older NFPA version I have. It is pretty clear that they are not even addressing the typical small cabinet shop or furniture manufacturer. The bulk of the standard, and all of the heavy hitting requirements are for plywood, chipboard, MDF and other plants which use very flammable glues in the process and also for production finishing rooms using very flammable finishes.

Dale: “NFPA 664 is not "garbage"! It is, however, a "consensus" standard. That is the case with all of the NFPA Codes/Standards.”

Being a consensus standard, the committee will look to any available outside source to avoid having to make a serious decision. Since the NFPA standard for the conveying of combustible particulate solids (NFPA 650) requires metal duct and grounding, they will too. The duct requirements in this section are modeled very closely after that section and are consistent nearly all requirements. In none of the standards is non-metallic ducting recommended for combustibles except in cases where the conveyed material will react with the metal ducting. It is simply easier to require here what is required elsewhere than to make an exception for a small wood system.

As Dale implied, the risk of an explosion in the home system is miniscule. Even then the biggest risk is in the collector, not the duct. If you are really concerned about explosion, then you should investigate ways of protecting against damage from a DC explosion. This would require you to put you collector outside several feet from the shop with an XP damper between the collector and the shop. The fan would need to be post collector and be of spark resistant construction. There are several other requirements for this type of protection, but the NFPA decided that the risk was so low that they made an exception (the only significant one I know of) for small wood systems.

[Steven Wilson]

Dennis,

What I found interesting were the proposed exceptions for small comercial shops (some of the ones Oneida submitted) and that they were mostly rejected. As for the 1500cfm dividing line, well that's bascially between the 2HP and 3HP Oneida commercial systems (3HP being 1800CFM, 2HP at 1400CFM) - a fair number of hobby shops are close to that line so it's probably worth a read when designing your system. Too many people are dismissive of the risks associated with so called "hobby" dust collectors. I agree that the static discharge explosion risk is very small in the < 5HP systems but there are other risks that one should know about and then decide if you want to mitigate them. The NFPA guidelines are a good place to start if you want to know what some of those risks are and how to mitigate them if you choose.

[Dale Thompson]

Dale: "First off, I don't think that NFPA 664 is a "Code". It is probably a "Standard". "

Yes, it is a standard. but this standard has been adopted as code in many, many locations. It is also a requirement for the clients of the big industrial insurance companies. I know you know this Dale, but many others don't.

Dale: "There is a difference. Also, it is written for "Commercial Facilities". "

This is a very important distinction. The production processes in an industrial facility are very different than the home shop user. In several locations, the committee comments indicate that units under 5,000 cfm are not a big deal and that the safety records do not indicate a need for increased regulation of "open bag" type collectors. this describes virtually every collector mentioned on this forum. In reading through this document and the older NFPA version I have. It is pretty clear that they are not even addressing the typical small cabinet shop or furniture manufacturer. The bulk of the standard, and all of the heavy hitting requirements are for plywood, chipboard, MDF and other plants which use very flammable glues in the process and also for production finishing rooms using very flammable finishes.

Dale: “NFPA 664 is not "garbage"! It is, however, a "consensus" standard. That is the case with all of the NFPA Codes/Standards.”

Being a consensus standard, the committee will look to any available outside source to avoid having to make a serious decision. Since the NFPA standard for the conveying of combustible particulate solids (NFPA 650) requires metal duct and grounding, they will too. The duct requirements in this section are modeled very closely after that section and are consistent nearly all requirements. In none of the standards is non-metallic ducting recommended for combustibles except in cases where the conveyed material will react with the metal ducting. It is simply easier to require here what is required elsewhere than to make an exception for a small wood system.

As Dale implied, the risk of an explosion in the home system is miniscule. Even then the biggest risk is in the collector, not the duct. If you are really concerned about explosion, then you should investigate ways of protecting against damage from a DC explosion. This would require you to put you collector outside several feet from the shop with an XP damper between the collector and the shop. The fan would need to be post collector and be of spark resistant construction. There are several other requirements for this type of protection, but the NFPA decided that the risk was so low that they made an exception (the only significant one I know of) for small wood systems.
[color=black]


Doug,
Thanks for the knowledgeable response to my post! My only minor disagreement to your entire post is, "Being a consensus standard, the committee will look to any available outside source to avoid having to make a serious decision". I agree with the humor of that statement but I must add that, "sometimes they do and sometimes they don't!".

On my committees, we had two "weasel phrases". The most popular one was when we couldn't figure out a specific phraseology, we could always use the old standby, "Acceptable to the AHJ (Authority Having Jurisdiction)". The more recent "weasel phrase" is "use good engineering judgement". DUH? I have an engineering degree and have no judgement whatsoever - even BAD!!

Doug, I have even noticed lately that they are backing off of their historical theme of "Save Lives First". They are now saying that the preservation of life AND property are of equal value. Maybe they were thinking of my wife who realistically categorizes me as "property"!

As you have probably noticed, I am not a big fan of NFPA. They are interested in making money and most of their folks do not know "jack" about fire protection. However, since they are the only kid on the block, I would have to admit that they are better than nothing - just barely!!

Dale T.

[Ken Fitzgerald]

Boy have we learned more about DCs, NFPA, concensus by committee and all the guy wanted to know was should and how could he ground his duct.


Due to the relative low humidity in my area and the increasing size of the seat of my pants, everyday of the year even when it's raining, when I get out of my company van if I forget to grab the door before sliding off the seat to get out....I get a good static shock!

I don't have a DC yet I will in the future. While I have little or no concern about a DC fire caused by static build up I, for one, will probably run some checks to determine if my metal ducting is grounded and if not I'll probably run an small wire say....18 gauge copper to a single point on the metal duct and ground it to the dc metal frame. I will do this not to prevent fires but to prevent me from touching the ductwork and discharging the static buildup, if any, through my chubby body to ground. The plastic hoods/adapters should be grounded at the metal body of the tools to which they are attached. IF the tools are properly grounded and any metal ductwork is grounded....static shouldn't buildup in the first place....just my 2 cents worth.......

[Bob Borzelleri]

Boy have we learned more about DCs, NFPA, concensus by committee and all the guy wanted to know was should and how could he ground his duct.


Due to the relative low humidity in my area and the increasing size of the seat of my pants, everyday of the year even when it's raining, when I get out of my company van if I forget to grab the door before sliding off the seat to get out....I get a good static shock!

I don't have a DC yet I will in the future. While I have little or no concern about a DC fire caused by static build up I, for one, will probably run some checks to determine if my metal ducting is grounded and if not I'll probably run an small wire say....18 gauge copper to a single point on the metal duct and ground it to the dc metal frame. I will do this not to prevent fires but to prevent me from touching the ductwork and discharging the static buildup, if any, through my chubby body to ground. The plastic hoods/adapters should be grounded at the metal body of the tools to which they are attached. IF the tools are properly grounded and any metal ductwork is grounded....static shouldn't buildup in the first place....just my 2 cents worth.......

Almost makes me feel like an enabler of sorts.

...Bob

[Ken Fitzgerald]

Bob....are you sure you didn't mean "instigator"?

[Bob Borzelleri]

Bob....are you sure you didn't mean "instigator"?

Ken...

Another faithful implementation of the long revered, "Let's you and him fight" strategy.


...Bob