Codes for Dust Collection in a Home Shop

Navigating the building codes for a woodshop over a residential garage is tricky. July 22, 2013

I'm building a garage with a woodshop above it for low volume cabinet construction. I was planning on installing my dust collection ducting in the floor between the shop and the garage. That is until the building inspector said I had to comply with the California Mechanical Code (same as UMC) for ducts conveying explosive dust. These codes require "explosion venting" and 18" clearance to combustibles. The latter requirement makes it impossible to put ducting in my floor (12" joists). One dust collection company pointed me to NFPA 664 which has an exclusion for small shops, but that didn't satisfy my inspector.

Does anyone know what codes relate to residential or small woodshops and dust collection? My inspector didn't seem to know. How often do dust collection systems catch fire or explode? Seems like small shops would be making the news if they were blowing up all the time.

Forum Responses
(Dust Collection and Safety Equipment Forum)
From contributor S:
If your inspector can't find the code, maybe it doesn't exist. Don't start your shop part until it has been inspected (duct work, etc.).

From contributor J:
I thought that there was an exception for ductwork under 10" diameter. Have you seen the code?

From the original questioner:
I haven't seen the exemption. There must be code that speaks to the small shop and dust collection. I don't have tons of experience, but I have never seen the requirements in the Mech code implemented in any small shop.

From contributor S:
Ask the inspector to cite the specific code(s) he is referring to and read everything pertaining to that particular code. You might find that the inspector is citing commercial building codes when only residential building codes should be used.

From Curt Corum, forum technical advisor:
No wonder everyone is confused. Some years ago, I provided a turnkey installation for a couple of industrial spray booths and make up air units. I was told I had to pull the permit for the installation. The application required pricing for all equipment provided and drawings of said equipment. I went to the town hall with all of the information they requested. The secretary forwarded my paperwork to one of the inspectors.

After about a half hour he came out with my permit and bill. I looked at the permit and it listed the installation of heating and air conditioning equipment. I questioned the inspector and he said, “that’s the closest description I have for a permit.“ It was apparent to me that they were only interested in the value of what was being installed for tax purposes. This particular municipality had numerous industrial companies.

We followed the NFPA guidelines for proper installation. But, why are they just guidelines that may or may not be adopted by a state or municipality? Why didn’t the permit mention anything about what was supposed to be done as far as regulations?

Do you follow NFPA, SMACNA, OSHA, EPA, DEP, UMC, CMC, NIOSH, ANSI…? Then we get into, do I follow NFPA 664, NFPA 91, NFPA 654 or do I follow all 3?

NFPA refers to SMACNA, SMACNA refers to NFPA. The Uniform Mechanical Code and California Mechanical code are the same? I’ll bet most people are not aware that the Uniform Mechanical Code has a 2009 edition.

As a manufacturer, supplier, and installer of dust collection systems, we had to make sure all various parties involved were satisfied with the installation. It was our utmost objective to provide a safe and operational system. The codes, regulations, and guidelines that had to be met may have come from various sources. Confusing? You bet. Well, how many pages is the Health Care Bill? Why can’t tax legislation be simpler?

Another thing confuses me. We all know the United States of America’s rise to success was based on manufacturing. Why has our government destroyed the manufacturing sector in our country? Now it’s so bad a fellow can’t even have a woodshop at his home. Many successful businesses have started in a garage or basement. Common sense and basic knowledge guided these people to do things correctly. We are now headed toward a service orientated economy! Who the heck are you going to service without manufacturing? Yet, we continue to import from countries that manufacture without any concern for environmental, worker, or consumer safety. U.S. manufacturers have worked very hard to become extremely efficient and safe. Now they are not even given a fair chance to perform. All of our progression is being wasted and is on the verge of extinction.

Here’s the latest. OSHA is now working on a study of Combustible Dust. They have provided an advance notice of proposed rulemaking (ANPR). Looks like woodworking facilities are included, though it appears to me they have had the least amount of combustible dust incidents.

To the original questioner: I looked over Chapter 5 of the Uniform Mechanical Code (2009). Looks like a dust collection system would be classified as a Product-Conveying System. Class 2 includes sawdust. Duct thickness is based on negative pressure. Fittings must be 2 gauges heavier than straight pipe, angle of entry no more than 45 degrees. These are typical specs for dust collection pipe. The 18” clearance is stated in 506.7.2 It says, duct systems operating at elevated temperatures above 140 deg F shall have clearances from combustible building construction or any combustible material of not less than 18”.

The only other mention I noticed referencing 18” was if ducts were run in a crawl space, there must be 18” clearance from bottom of duct to floor. 506.4 Explosion Venting. Ducts conveying explosive dusts shall have explosion vents, openings protected by anti-flashback swing valves , or rupture diaphragms. Openings to relieve explosive forces shall be located outside the building. This stipulation is normally applied to aluminum or other highly explosive dusts. But at this point, who knows.

(The preceding is for informational purposes only.)

From contributor J:
I am looking at the permit package that the city gave me when I installed my collector. They included a page from the 2003 International Mechanical Code. Section 510.7 requires automatic fire suppression system, but exception #2 states that it is not required if duct cross section is less than 10".

I guess in the end, the only code that matters is the one that the inspector is citing. One other note: I argued successfully that my duct layout was 100% temporary from the point where the main duct entered through the wall because my machinery location changed frequently. I also cited use of Nordfab quick connect to support this. As a result, they did not even look at the interior duct specs.

From the original questioner:
Thank you. I had found those passages in Chapter 5 of the UMC/CMC (roughly identical). Those requirements are what is making it difficult. To run the ducts in the floor is precluded by the 18" clearances. Explosion venting would be an option. The permanent nature of my installation is what is giving my inspector pause, although I don't see where in the code that is specified. In any case, what makes a permanent installation any more dangerous than a temporary one? I can certainly give a few arguments in the reverse.

So what have you dust collection installers run into for small installations?

From contributor M:
Are you sure you want to make your duct work totally enclosed? I don't know about you, but I have to stop at times and pull all the small edgings that fall off my saw out of duct work because it clogs up. If I had the duct work in the floor it would have been very difficult to do.

From the original questioner:
Your point is well taken. A separate post topic might have been to ask whether putting the duct work in the floor is just plain foolish from a practicality point of view.

The pros:
Cleaner looking installation.
No dust collecting on top of suspended duct work.
Easier to reconfigure this space for other purposes.

Difficult to remove obstructions.
Reconfiguring tool locations impossible without putting ducting on top of the floor.

So this might be a case of "be careful what you ask for."