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Shop Air Filtration #1: Media Filters

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Blog entry by Bob42 posted 01-07-2009 06:41 PM 10972 reads 18 times favorited 37 comments Add to Favorites Watch
no previous part Part 1 of Shop Air Filtration series Part 2: Energy Recovery Ventilators (ERV) or Air Exchanger »

I have been reading and commenting recently about shop air filtration and the concern for it. My decision to write this was to give the LJ’s community some facts about air filtration. Let me start with my knowledge base. I started my own air filtration business after my son was diagnosed with severe asthma at the age of 18 months. He is now 20 years old. My wife (an RN) and I immersed our selves into learning as mush as we could to make his breathing easier. We attended numerous seminars by some of the country’s leading Dr’s and filtration experts. After years of research we decided to open our own air filtration company mainly to provide people with similar problems a product that will work. As I was already a firefighter this was a second job. After receiving a career ending injury I was forced to retire from both the FDNY and my air filtration company. So now you have a little back ground on me, please let me give you some basic facts about air filtration.

I hear that some of you make your own filters from box fans, and that may work for a short time but think of the long term. What is the efficiency of that filter if you were able to test it and at what size particle? How is the filter attached to the frame of the fan? That doesn’t sound efficient to me. First let me tell you that the most respirable particles are below 2 microns and most are below 1 micron. That means that when you inhale you breath in most particles of various sizes and exhale most of them even though you don’t see them. The ones that are inhaled but don get exhaled are the particles in the range of 1 micron or less. That means they stay in your lungs and sinuses. Over time that builds up. It doesn’t mean that we all will get sick but, we should think about how much we invest in our tools and consider an air filter as one of the most important tools in the shop.

There are many types of filters out there. I am going to speak about mechanical filters such as pleated media. That includes HEPA and HEPA like or type.

In order to be a true HEPA filter it must meet or exceed a DOP rating of 99.97% @ 0.3 microns. Be wary of filters that don’t tell you the percentage and at what particle size. The DOP rating is higher than the MERV rating you may see on the filters at the box stores. Below is a chart to compare some filters.

Various Air Filters to MERV Ratings

  • Throw-Away Fiberglass Media MERV 1 -MERV 4
  • Pleated Media Air Filters 30% ASHRAE MERV 10 – MERV 11
  • Pleated Media Air Filters 65% ASHRAE MERV 13 ( 65% ASHRAE is about 20% effective on less than 1 micron particles)
  • Pleated Media Air Filters 95% ASHRAE MERV 14
  • True HEPA 99.97% @ 0.3 microns exceed the MERV rating

The reason some filters are called HEPA like or type is that they are also a pleated media. But are not tested and do not receive the DOP rating of a true HEPA.
One important concern with all filters is how does it seal in the frame. If is does not have a good gasket or seal then it doesn’t matter how good the filter is because contaminated air will bypass the filter.

This is a short list of particles and the sizes:
animal dander approx. 0.5 – 10.0 microns
lead pain dust approx. 0.3 – 2.0 microns
wood & tobacco smoke approx. 0.01 – 5.0 microns

These are just some samples of particles and their sizes. Although some do go past even the HEPA rating the HEPA does remove some of the smaller percentage of the smaller particles.

When choosing a filter of any type remember that the more air changes per hour the more you will filter. One question to ask: Is the cfm of the unit rated before the filters are installed or after? If they can’t tell you then you must assume that is is rated after. That will effect the cfm of the unit dramatically if it is rated before and puts a strain on the motor.

There is a lot more I can go into but I’m just trying to give some basics. As you can tell I am not a writer, but, in a future post I will go into some ERV.’s (Energy Recovery Ventilators) and carbon filters. I hope I haven’t confused too many but the concern for our health should not be forgotten or over looked. I understand that cost is a factor but what is the cost of getting sick. I have included the website of the supplier that I used to use and you can get some more info there. I want you all to know I get nothing in return. I just believe in protecting your lungs. Feel free to contact me.

pureairsystems.com

Thanks for reading my post.
Bob

-- Bob K. East Northport, NY



37 comments so far

View John Gray's profile

John Gray

2370 posts in 2581 days


#1 posted 01-07-2009 06:53 PM

Great job/post Bob, thanks!!!

All woodworkers should take heed to Bob’s advice here.

If not you may end up with COPD (Chronic Obstructive Pulmonary Disease) as outlined in my blog: http://lumberjocks.com/topics/5872

-- Only the Shadow knows....................

View HokieMojo's profile

HokieMojo

2103 posts in 2424 days


#2 posted 01-07-2009 07:43 PM

I really appreciate this post and you seem to know quite a bit about this. As such, I’m going to ask you a question (hope you don’t mind). I’ve never heard of HEPA filters used for woodworking applications. I ussually hear about these in relatively clean environments where the purpose is to get the air in a clean place even cleaner.

Alternatively, in a woodshop, the objective seems to be to use this more like a vacuum cleaner for the air (make a mess and then suck it up). Won’t a hep filter get overwhelmed much quicker? Maybe thats the point, but I’d like to understand this better. I’m just thinking that if a filter pulls out more dust, there will be more dust on the filter, and it will clog faster.

Before you think I’m trying to make an argument that more dust should be allowed to pass thrhough the filter and get into our lungs, just so we don’t have to change filters as much, let me make it clear that isn’t what I’m saying. I’m just trying to understand the practicality of using the machines, similar to the ones in your link, for this purpose. I didn’t see any (I might have missed them) that look like they are intended to work in shop environments.

Finally, I just want to say thanks again for the post. I’m trying to get up the learning curve on this stuff and am actually putting new tools on hold until I can get comfortable with my air cleaning equipment (although I’m still working in the meantime). I’ll keep reading if you get a chance to post more!

View HokieMojo's profile

HokieMojo

2103 posts in 2424 days


#3 posted 01-07-2009 07:52 PM

Also, you asked what the efficiency of the filter/box fan results are. According to the filtrete FAQ, it looks like it is capapble of catching down to .3 microns if you get the right one. That being said, they don’t talk about the percentage of .3 micron particles they will grab (which I can see is important). Also, I have no way to know how efficiently my setup recirculates the air.

View Bob #2's profile

Bob #2

3808 posts in 2717 days


#4 posted 01-07-2009 08:02 PM

Thanks Bob 42 for the detailed information re filtration.
I have been interested in this aspect of wood working for some time and would like to offer the folllowing observations:
- The woodshop is self loading.
By that I mean that dust is being continously generated in the enclosed area.
It either settles or is picked up by various suction devices or remains ambient in the air.

The most effective way to reduce the fine particles ( ambients) is to leave a fine filter running during off hours of operation and to replace the primary filter frequently.

I use spun polyester cloth from the sewing center as a filter on my own systems . It is very similar to the material they make disposable facemasks from and is very cheap purchsed this way.

As the dust settles on the material the filter clogs up and finer particles are then trapped..
It’s simple matter of stopping the fan and folding up the polyester and tossing it in the garbage, dust and all.
This currently cost me about 25 cents a change.

I applaude the hepa style filters but they soon become overwhelmed when used in the woodshop making them an expensive investment that potentially prevents ambients from being picked up after they clog up.

-- A mind, like a home, is furnished by its owner

View PurpLev's profile

PurpLev

8476 posts in 2344 days


#5 posted 01-07-2009 08:37 PM

thanx for sharing, it’s one of those things in woodworking that is not too obvious, and does not produce any finished products (you could argue that…) but should be thought of as one of the most important aspects of working in a woodshop… easy to neglect, but a necessity none the less.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View Bob42's profile

Bob42

455 posts in 2486 days


#6 posted 01-07-2009 09:50 PM

Thanks to all for responding. These are exactly the questions I was looking for.
HokieMojo – First, I don’t mind at all that’s why I posted this. Second, You are correct about them being used in clean rooms and other types but they are being used in homes that are built very tight along with including outside air, as well as industrial such as lead and asbestos removal things of that nature. When looking for a HEPA unit for a shop you should get one that also has a prefilter. That is what will capture the large particles and the HEPA will take care of the smaller ones. One thing to remember is that the dirtier a HEPA gets the more effective it becomes until it reaches the saturation point and then needs to be replaced. Most good units will have a filter gauge on it to tell you when it’s time to change. The other thing is to try to capture the dust before it goes into the air. That’s were a dust collector and good HEPA vac comes in. The point is not to make the mess and then clean it up, it’s capture it first then your air filter and lungs will be more efficient. Any of those units in my link can be used it a shop and can be altered if you desire. They do mention stand alone units. that’s what you would use. They do have a model 350 that would be great for a small shop and is rated after the filters.
And yes you noticed they didn’t tell you what the percentage is on the filtrete. As far as the air exchanges you need to know the cfm rating of the unit and is it rated before or after the filters. and cu. ft. of the room.

Bob2 – Yes it is good to leave the filter on after you leave the room. Some fine particles can stay airborne for hours even though you don’t see them. Those are the most dangerous to us. The most effective way to control contaminates is how I just explained. Capture as much as possible at the point of source than have the air filter to capture the rest. Then you won’t have to change the filter as much. If you had a particle tester to test the system you are using, you would be very surprised at your results. With all do respect remember the old phrase you get what you pay for, 25 cents worth of filter for 25 cents worth of filtration. I would not suggest a HEPA filter if you do not have any type of dust collection. Then, yes it would clog very fast but that’s what I’m trying to get across. The need to capture at the source and filter.
I hope that helps.

-- Bob K. East Northport, NY

View Mike Shea's profile

Mike Shea

152 posts in 2690 days


#7 posted 01-07-2009 11:02 PM

great post bob. allot of great imformation. i am one to never wear a mask. “NEVER”. you name it. exotic woods, plywood, mdf. i was more concerned about urea formaldahyde resin in mdf then small wood particles. after reading your post and realizing how small these particles are and the damage that they can cause made me think twice about getting a filtration system and or wearing a mask “sometimes”. lol

my real question for you bob is more about the filter for my home heating and air conditioning unit. my Heater and A/C for the house is located in my shop just behind my lathe and workbench. there is no wall seperating the unit. all airborne dust particles build up on the unit itself. i remove and clean the filter regularly. maybey once a month. i think the filter is made of some tybe of carbon sandwitched beetween two nets and a metal gate. whener i hose it down large amounts of dark dusty water wash down the driveway. my question is what kind of filter do you think that is, and is it catching the majority if not all the dust that enters the duct pipes leading to the house. is there a better filter i can get. how should i clean it. and how often. or do you think a shop filtration system would eliminate most of the dust from entering the A/C filter all together. seeing how educated your are on filtration i thought you would know something about other filltration devices such as the one for my A/C. let me know what you think. THANKS

-- i can do all things through christ who strengthens me

View Bob #2's profile

Bob #2

3808 posts in 2717 days


#8 posted 01-07-2009 11:06 PM

I think where you and I might see things differently Bob is with the amount or shop time we each have and perhaps the exposure to the real world of woodworking.
I don’t mean to be insulting but my experience suggests that the production and control of dust particles in a practical surrounding is far different than in a class room or a book.
I pretty much agree with all you have mentioned above.

But… as I said it’s often just not practicle. ( a goal to strive for yes).
I think you will find that sanding is one of the worst dust producers followed closely with bandsawing and for blowback I give a prize to the 12” CMS.
Somewhere I have labs test that show without doubt the overhead dust filters actually can create currents of microscopic particles that simply “circulate” in the air as long as the filters operate.
Unfortunately that would apply to filters using Hepa technology as well.

I am not certain that you are familair with the spun polyester material that I am refering to as you dismissed it as not being adequate because of the price.
you get what you pay for, 25 cents worth of filter for 25 cents worth of filtration”


I urge you to try some in your own environment before you judge it as not acceptable.

http://lumberjocks.com/topics/3888

Cheers

Bob

-- A mind, like a home, is furnished by its owner

View Alan Veeck's profile

Alan Veeck

3 posts in 2122 days


#9 posted 01-07-2009 11:55 PM

Good Comments by Bob on understanding the workings of air filters. I too am part of the air filtration industry having worked for 25 years in the business and now Executive Diretor of the National Air Filtration Association (NAFA), trade group for air filter manufacturers and distributors, worldwide. In regards to the followup question about HEPA filters in a woodworking shop, the answer is how clean do you want your air? Since most wood shops are not air tight enclosures, like a cleanroom, you probably want the air cleaned of any lung-damaging particles – those in the <2.5 micrometer range. HEPA filters would be a bit over the top and a standard MERV 14/15 filter, like those found in the commercial units (with a MERV 6-8 prefilter) mentioned in a previous emails, will remove most all of this size of particle and are affordable. I would echo the sentiments expressed by a previous blog that airflow through the unit and air changes in the shop are the key to cleaning the air. The formula is l x w x h to get cubic feet of your shop, then find out cubic feet per minute (cfm) of air cleaned times 60 – divide and find out how many air changes per hour the unit provides.
AL

-- Alan C. Veeck

View Bob #2's profile

Bob #2

3808 posts in 2717 days


#10 posted 01-08-2009 12:30 AM

Welcome to LJ’s Alan.
I look forward to seeing your shop and some of your projects in the not too distant future.
Interesting perspective that you birng to the discussion.

Perhaps from your experience, you can recall just how much ambient “detritus” would be considered normal in normal air in most urban cities today?

It would be interesting to gauge that against a moderately “scrubbed” wood shop.

In Canada for instance the Govt is no longer recommending forced air furnace cleaning as an annual routine stating that normal dust in the air will almost immediately replace anything removed by the commercial vacuum trucks.

Bob

-- A mind, like a home, is furnished by its owner

View Bob42's profile

Bob42

455 posts in 2486 days


#11 posted 01-08-2009 02:43 AM

Bob #2, No insult taken or meant to be given. It’s OK to disagree. That’s what makes us different. I have a wife and with that comes with a tough skin. ;-)
I am one that likes to keep a clean shop even when working. I will stop sometimes to clean up and then continue. A HEPA filter is still the best choice but consideration must be taken when making the choice of how clean do you want it and do you have a need. Such as someone with allergies or respiratory problems. If a HEPA filter is going to keep them in the shop then that’s the choice they have to make. My point again is to capture the contaminates as much as possible at the source and then you can have a better air cleaner that won’t dirty up as fast and you will be healthier in the long run.
Thanks for giving me the info on your filter material I will check it out. I do try to keep an open mind. As far as the tests that show air filters keep particles in the air as long as they are on, depends on the size particle and how strong is the filter unit is.

I have a HEPA unit installed in my central AC in a by pass configuration. It has been in for 17 years and when I check the duct work from time to time it is spotless. Along with the coils, I mean you could eat off it. No need to clean the duct work. It runs all year to filter the house.

Alan Veeck, Welcome to LJ’s.
Glad to see you jump in. As I said it depends on how much you have a need.

Mike Shea, I would be concerned that you are sucking in contaminates from the shop through the gaps in the duct work as well the filter. It’s hard to know what you have and I’m not here to try to fix it but, I would start by sealing up any leaks in the duct work such as where they join. and think about a partition wall to keep it separate from the shop. Check the duct work. That will tell you how good your air filter is.

That’s my opinion. :-)

-- Bob K. East Northport, NY

View Alan Veeck's profile

Alan Veeck

3 posts in 2122 days


#12 posted 01-09-2009 05:27 PM

Good Morning Bob in Canada…RE; your question about “detritus” in outdoor air versus the typical shop. While detritus leans more to organic matter in the air, there really are no difinitive data on this that I have seen. Particle counts in outdoor air vary from place to place but normally run from 1 million to 3 million paricles per cubic foot of air. Most of these are in the smaller diameter range. Indoors, 1-2 million would be high…for themost part I have seen in 300,000 to 500,000 range fairly standard.
If you run an air cleaner in an area with a MERV 14 or 15 filter and you are not adding more particles, you can clean it to under 50,000. Remember, your nose does a good job on those bigger particles…the ones >10 micrometers an above and your upper respiratory system helps clean down to about 5 micrometers. It is believed that very small particles, those <0.5 micrometers may very well go in and come back out depending on their composition.
Bottom line is cleaning the air of fine and ultrafine particles – those in the 2.5 to .5 micrometer range is healthy since your body does not have to remove these from your lungs.
AL

-- Alan C. Veeck

View Bob #2's profile

Bob #2

3808 posts in 2717 days


#13 posted 01-09-2009 05:47 PM

Hi Al:
Those stats are similar to what I have been seeing over the last 10 years or so here too.
Electrostatic filters are still pretty prevalent here and recommended by HVAC vendors for forced air furnace systems. They are not practical for wood shops as they load very quickly in the environment and take a period of time to be reconstituted for reuse.

In my own shop I use a 2 hp cyclone system with a gate at each stationery machine. (1 micron felt bag)

I use a portable vacuum with an automatic switch for hand held tools like sanders and routers.

For lathe work I use a filtered positive pressure helmet for protection.

I have an overhead ambient filter with 2 furnace filters to catch the large particles and a layer of spun polyester film to handle the fines.
At the end of each shift in the shop I “pressure wash” the surfaces with compressed air and leave the filters running for a couple of hours after I leave the area, ( I wear my dust filter helmet during this procedure)
My shop will pass the white glove test when I return the next day to work.

That’s about the best I feel I can do and still have some shop time.

Bob

-- A mind, like a home, is furnished by its owner

View Bob42's profile

Bob42

455 posts in 2486 days


#14 posted 01-09-2009 07:43 PM

Bob#2
From what you have described to Alan you seen to be taking a lot of good precautions. I wish more did the same.

-- Bob K. East Northport, NY

View Snoop's profile

Snoop

19 posts in 2106 days


#15 posted 01-24-2009 11:46 PM

Thank you very much for all of the information. I am pretty new to woodworking and want to make sure my dust collection is decent – no health issues needed here. I’m thinking of buying the Jet DC-1100CK http://www.cpojettools.com/products/708636ck.html
You mention that one key to dust collection is to get it at the source? Will the Jet I mention above do a good job of that? Will it be better than my shop vac?
Also, will it be able to collect well from my Router and ROS if I get a smaller hose attachment.

-- "Whether you think you can, or whether you think you can't, you're right."

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