CFM Numbers - More Confused Then Ever

[Brent Simons]

I am in the process of setting up my duct system for my shop. In my research on a Google search I found a chart of requirements for Woodworking Operations on Bill Pentz’s cyclone site. Oddly I found that these numbers were much higher than any other agency recommendation. After an exhaustive search of the OSHA site I found two links: One on woodworking hazards:

http://www.osha.gov/Publications/woodworking_hazards/osha3157.html

and the other on dust collection:

http://www.osha.gov/SLTC/silicacrystalline/dust/chapter_3.html.

All of this is excellent information on dust collection, but I could not find any CFM requirements for WW tools published by OSHA as per Mr. Pentz’s chart. Here is a link to the chart…

http://billpentz.com/woodworking/cyclone/DC4Dummies.cfm

So then I decided to call OSHA. After speaking to several people they finally said they don’t publish CFM values for WW shops and the information on Mr. Pentz’s chart is wrong. They recommended that I contact ACGIH for the information that I needed and pick up a copy of the “Industrial Ventilation Guide” printed by the ACGIH which is the American Conference of Gov’t Industrial Hygienists. Their website is www.acgih.org.

ACGIH is a committee comprised of academics and engineers that publish the “Industrial Ventilation Guide” which includes how to set up duct systems for central dust collection systems. I purchased the book (very expensive) and after considerable research I didn’t find any of Mr. Pentz’s CFM requirements anything close to the values ACGIH publishes, although he states they are, ”updated from ACGIH.” The person I spoke to at ACGIH said that these machine CFM values for woodworking tools were developed by ACGIH engineers and industrial hygienists over a period of 50 years and are the current benchmark standard for industries. Mr. Pentz’s recommendations are in most cases approximately double the ACGIH recommendations. I am now totally confused.

Searching for the last column on Mr. Pentz’s chart titled “Medical (Euro) recommended Exhaust CFM” I ran into the same problem. I Googled extensively but could not come up with any information on Medical (EURO) exhaust CFM for WW tools that was anything like Mr. Pentz’s chart.

As a last resort I called the UK Safety Executive. This is roughly the equivalent of OSHA. A really friendly chap said that he never heard of any Euro Medical Organization that recommends CFM exhaust requirements for WW shops. For example Mr. Pentz’s Chart shows 889 CFM for a 12” radial arm saw. The ACGIH manual says 500 CFM. Mr Pentz recommends 889 CFM for this tool nearly twice the other recommendations. I am left wondering where Mr. Pentz gets his data from.

I took the liberty of posting ACGIH CFM diagrams and also Mr. Pentz’s chart. So far none of it has checked out with the agencies he has purported to have copied information from. Also, all agency CFM numbers I found are all rounded; for example 350 or 430 CFM. Based on the odd numbers on Mr. Pentz’s chart for example his numbers are 889 or 981 CFM. No agency that I could find lists numbers like this. I can’t find any information anywhere that supports his data or the reprinting of Agency data. Has anyone else researched this? Has anyone run into this? Where does Mr. Pentz get this information for his chart? I have to say that this is very disappointing. I trusted his info for my DC system and design. Can anyone help.

[Dave Anderson NH]

Many dust collection threads on SMC have a habit of degenerating into name calling and personal attacks. They also generate bashing of equipment suppliers products, often without supporting evidence.

Other moderators and I will be watching this thread closely. Posts which violate the SMC Terms of Service will be edited or deleted immediately.

Let's keep the thread on topic and the tone friendly and informative. Generate light, not heat.

Dave Anderson NH

[Eric Gustafson]

I have not read everything on Bill's website, but your diligence to detail is commendable. I do not know the guy, but I appreciate the knowledge he has shown.

My spin on what Bill has written is that the man is obviously passionate about dust collection. Rather than trust the numbers it seems he has done some objective research. Regardless, when it comes to CFM requirements, it seems that more cannot but help, rather than hurt. Excepting one's wallet of course.

Personally, I would rather be safer than sorry. I am in the market for a dust collection system right now and will use Bill's information as well as other sources before I make my final decision.

[Alan Schwabacher]

Have you tried sending this question directly to Pentz?

[Ed Labadie]

I agree with Eric, your diligence to detail is commendable.

It might be a better start if you gave some basic information about your planned dust collection sytem and shop setup, then others can relate their experiences, both good and bad.
I referenced Bill's information when I did my system, it was very helpfull. The people at Oneida were also helpfull and patient with me.
Eventually you must start on the system, it can be a somewhat frightening task, but don't be intimidated, go slow and ask lots of questions as you move along.

Ed

[Dick Sylvan]

My spin on what Bill has written is that the man is obviously passionate about dust collection. Rather than trust the numbers it seems he has done some objective research. Regardless, when it comes to CFM requirements, it seems that more cannot but help, rather than hurt. Excepting one's wallet of course.

Personally, I would rather be safer than sorry. I am in the market for a dust collection system right now and will use Bill's information as well as other sources before I make my final decision.

I couldn't agree more. If you want to be conservative, use Bill's numbers. If you want to be less so, use the other set which I would doubt are really "tailored" to home woodworkers. Also, a major variable is the type of collection "at the tool" that you have. For example, my new Hammer has a dust collection shroud around the saw blade which directs the dust into the collection system. My old Jet cabinet saw (which I thought was a fine saw) merely had a ramp at the bottom which I thought was minimally effective for dust collection. So would I need a more powerful DC for the Jet over the Hammer? Probably, but I am still going with what I consider overkill for the size of my shop, i.e., a Clear Vue.

[Rob Luter]

I feel your pain Brent. I spent a number of years as a ventilation Engineer. The Industrial Ventilation Guide is a great resource. It presents a good framework to work within, with all else equal. The kicker is: all else is rarely equal.

The data presented in the IVG is a good place to start. In my experience, the conveyance of particulates (sawdust and chips) in an airstream is a function of not only air volume (CFM), but also air speed (duct velocity). You can be moving a ton of air but if it's moving too slow it won't have sufficient velocity to keep the particulates "moving down the highway". The velocity across the face of the hood or other duct termination where the dust is collected is important too. This is often referred to as "Capture Velocity". If the air isn't moving at a fairly brisk pace it won't suck the chips in unless they're directed right to the duct termination. If you can direct the chips straight to the duct using a shroud or other mechanical means, capture velocity is less important.

I took a quick look at the Bill Pentz site, and he does a good job of presenting these and other related principles. If the only issue you have with his information is CFM recommendations then I think you're in pretty good shape. Agency publications will generally cite minimum requirements for generic applications. Mr. Pentz appears to have chosen to use data based on field experience with specific applications. His sections on Airflow and Resistance spell this out pretty clearly.

If you set up your DC system and find yourself low on air, you're pretty much screwed. On the other hand, if you find you have excess airflow capacity it can be dealt with. It's a similar problem to having saw blades that are too sharp, fences that are too straight, Benches that are too flat, and joinery that fits too well.

My $0.02 worth ($0.015 after taxes)

[Ron Williams]

I do not know how complex your shop is but I simply used the info available on Oneida's web site to design my system and it works great. I have 8 machines that are hooked to this system. I worried about this alot before I jumped in and simply did it Good luck

[Art Mann]

Mr. Pentz has suffered some pretty serious respiratory problems that he attributes to wood dust. His opinions on what is and isn't safe are strongly influenced by that experience. One would do well to keep that information in mind when evaluating his recommendations.

Another thing to keep in mind is that the OSHA standards are for employees in the wood processing industry who are exposed to dust on a continuous daily basis. If you are a hobbiest, your relative risk is much lower than that of a professional woodworker.

[David Giles]

1. More airflow gives better dust capture.
2. More airflow requires bigger, more expensive ducts and more power consumption.
3. Life's full of tradeoffs. The sweet spot differs from person to person.

[Brent Simons]

I took a quick look at the Bill Pentz site, and he does a good job of presenting these and other related principles. If the only issue you have with his information is CFM recommendations then I think you're in pretty good shape. Agency publications will generally cite minimum requirements for generic applications. Mr. Pentz appears to have chosen to use data based on field experience with specific applications. His sections on Airflow and Resistance spell this out pretty clearly.

Rob what disturbs me is that Mr. Pentz is quoting numbers from OSHA and when I talked to them they had no idea what I was referring to. In other words they did not provide the data. The same for ACGIH. And then Euro Medical which I can't find any reference to.

These numbers are being presented as coming from a government industry and an engineering think tank. I feel this is basic misinformation. Where are the root sources for this information? Where can I find data that supports this so I know I made the right decision? Do we accept these numbers as blind faith?

[Paul Hendrickson]

I'm a chemist with many years of experience with gov't agencies publishing data about what level is safe and what is not. I can tell you that some are silly in their unreasonableness, and others have me scared to death to think what is "legal and aceptable".

Having said that, respiratory problems are nothing to be taken lightly. Remember, it's not the particles you can see that hurt you. There is a reason why there is such fanaticism with regards to asbestos. It is not to be taken lightly.

If there is a decision to be made, I choose to err on the side of caution. Don't know Bill, but I appreciate his passion. His willingness to freely share information, rather than charge for it speaks to his character. You can learn all you want from him and build your own system and he won't make a penny off of you. That speaks volumes to me.

Finally, if you really want to know about Bill's numbers, why not ask him?

[Wilbur Pan]

This may not address all the data that you are looking for, but I posted a list of references to peer reviewed journal articles relating to the health risks of dust a while ago. One of those articles cites the ACGIH guideline for total dust exposure is 1.0 mg/m3 for an 8 hour period.

One of the articles found that a single sawing or sanding operation alone could expose a person to more fine dust alone than the amount of total dust he/she should be exposed to for an 8 hour shift. Couple this with the fact that most home shops are not as well ventilated as industry environments, and the assertion that hobbiest shops must be safer simply doesn't hold.

[BOB OLINGER]

Could someone advise of Oneida's website address as they are referenced several times here.

Thanks,

Bob O.

[Mike Spanbauer]

If you are a hobbiest, your relative risk is much lower than that of a professional woodworker.

I don't know if I agree with that Art, but certainly exposure to the hazardous particles is lower (not necessarily risk).

OP:
Some links for reference and the real authorities on dust regulation:
http://www.osha.gov/SLTC/healthguidelines/wooddustallsoftandhardwoodsexceptwesternredcedar/index.html
http://www.osha.gov/SLTC/healthguidelines/wooddustallsoftandhardwoodsexceptwesternredcedar/recognition.html#exposuresources

About 1/3 way down the second link you'll find the measure that the various agencies use for permissable particle levels in [FONT='Verdana','sans-serif']industrial[/FONT] environments. [FONT='Times New Roman','serif'][/FONT]

I did find the ACGIH materials linked, but they are fee based and require a membership or login. (ACGIH [1994]. 1994-1995 Threshold limit values for chemical substances and physical agents and biological exposure indices. Cincinnati, OH: American Conference of Governmental Industrial Hygienists)

The challenge as Art has pointed out though is that all regulations are for industry and not for hobby / home.

The suggested guidelines / CFM requirements for each tool that Bill suggests are just that, guidelines. They can't be hard and fast as each tool has a unique hood design, flow through, and chip / particle production measure. A contractors saw is a much worse dust offender than a cabinet saw by virtue of the open design and lack of integral DC port (only an example).

The issue of course, and the reason why this is such a volatile topic is that it is VERY difficult to determine exactly how dangerous wood dust is, in what volume, and what sensitivity level each of us has.

You know, it's ironic that such emotion gets raised over DC's. People want a warm fuzzy that they have good dust collection and they want to hear that there is no risk in wood working when they meet a certain level of dust collection equipment... The reality is that there IS inherent risk in woodworking. Dust, machinery, and Darwinism A moments carelessness can result in the loss of a finger or worse, but dust inhalation is a much, much slower and insidious affliction.

The ONLY way that anyone could state with absolute certainty there is no harm from wood dust is to stop woodworking all together. Of course, that's not acceptable to many here (myself included ) so we attempt to protect ourselves as best as we can. The only way to do that is by doing homework and taking measures to preserve our health.

Bill has invested a great deal of time and effort into raising the visibility / need for adequate dust collection in the home shop and for that I think that many (including those who don't support bill) will credit him with a good deed. Bill's efforts increased every dust collection vendors sales, and improved the air quality in many of our shops in so doing.

If you're looking for specific measures of CFM required at each machine, the only hard and fast figures would have to come from each machine vendor. Many do provide guidelines, but not necessarily specific machine figures. Consider the PM2000 with its very nice internal shroud around the blade vs. my PM66. I am certain that the PM2000 is a much more effective dust collector than my PM66... 600, 800, 1000? I can't tell you and I am not certain that Powermatic even did this testing.

Whatever you're comfy with is what you need to design for. Guidelines only get you so far

mike