Propane forge ventilation

[C.D. Mitchell]

Here's a new one that I haven't seen anything written about:  What is the best setup/positioning for a mechanical local exhaust being used to provide ventilation for a propane forge?

 

There is already a ventilation system in place for use with welding and sucks a lot of air.  Cross draft or natural ventilation is not an option, which is why the local ventilation system was put in place.  The openings of the vents are similar to a standard sheet metal floor duct like the HVAC system in your house and were positioned on the welding table next to whatever was being welded.  The welding tables have now become forge tables, and I would like to use the ventilation system for the forges.  So, to repeat the question: What is the best setup/positioning for a mechanical local exhaust being used to provide ventilation for a propane forge?

 

Let me know your thoughts.

[Rich Hale]

Let me see if I can guess just wot you mean..........nope cannot,,,however perhaps some pictures with size reference wouild allow at least one of to.

[macbruce]

  What is the best setup/positioning for a mechanical local exhaust being used to provide ventilation for a propane forge?

Why do you want to ventilate your propane forge in the middle of January? If it weren't for mine I'd freeze....... :wacko: 

[Rich Hale]

The best reason is to prevent anyone from breathing the carbon monoxide fumes which can and does kill poeple.

[C.D. Mitchell]

The shop is already heated and even if it wasn't I wouldn't be concerned about losing heat.  I've had CO poisoning three times in my life and it's not something I want to have again.  I'm teaching a class of students at a school and I want to make sure the students and myself are safe.  I don't have pictures yet, but pending pictures I wanted to throw the general question out there to see if anyone has used a local exhaust or mechanical ventilation for a propane forge and how they set that up.  Again, this is in a high school where backwoods jerry-rigging or "it's good enough" doesn't cut it.  I want to teach these students how to forge steel...not how to get treated for CO poisoning.

[macbruce]

The best reason is to prevent anyone from breathing the carbon monoxide fumes which can and does kill poeple.

 

I shoulda died over 30 years ago then...............

[Dodge]

How big is you shop Mac? With garage door open (single car attached garage) my gasser set off CO detector inside the house after about 2 min of operation. I didn't run it very long inside to see I would get sick ;) Guessing your shop is bigger. None the less, if you have not been subjected to CO poisoning, I'm guessing enough of it vents somewhere, or you are lucky. That being said, is it really a good idea to suggest others take the same chances? I couldn't............

[Armand Tatro]

Do you have any co monitors installed?  I would want to think that would be the first thing to have no matter how good your vent. system is.  Armand

[macbruce]

I've never had any problems in all my shops large or small unless the flame is rich, and if that's the case it must be corrected......I know dozens of of other wild and crazy blacksmiths who have never used hoods over their propane forges...... :o .....

The pic is my unventilated living room fireplace that I bought at HF and it runs on propane and it has never set off the CO detector  in  5 years.....

I spose the regs for a school are what they are but I'll continue as I have till the bitter end..... :)

 

A home ventless fireplace is not the same as a forge

[ciladog]

Carbon monoxide (CO) is only slightly less dense than air (mostly oxygen and nitrogen) and if temperature is not a factor it will mix with air to create a homogeneous mixture.  Since you are producing CO using a propane forge and not producing O2, as time goes on, you are displacing the air with CO.  Without adding more O2 to the mix, you end up with elevated levels of carbon monoxide which is not a good thing to do.

 

But temperature is a factor in this equation when using a propane forge.  The carbon monoxide is coming out of the forge super-heated and rises as high as it can go until it hits the ceiling.  If it is not exhausted, it will begin to create a layer of hot CO+air starting at the ceiling and moving downward.  The longer it goes on the thicker that layer gets.  If it gets to the level where you are breathing then you begin to take in more and more CO.

 

As the hot CO and air mixture begins to cool it begins to fall towards the floor mixing with air and depending on how large your work area is, will create areas of increased CO in your shop.

 

So if you want to install a mechanical exhaust system to remove CO it should be above where the forge is and as close to the ceiling as possible.  Or install a hood somewhere above the forge.

 

And one more consideration; you need to have as much air coming in to the shop as you are exhausting. 

[clm2431]

Don't know if anyone has really addressed this yet but here's my take.  We opened a school here in Rochester, NY in January 2012 and had to get approval from our town.  This is an excerpt from the report we submitted for approval, keep in mind the actual numbers used are specific to our shop and NY but it shows the concepts:

 

Recommended Rate of make-up air for Smithies:

 

   The recommended rate of make-up air for smithies is given as (6-7 liters/sec per square meter) 1.18-1.38 CFM per sq ft[1].  This recommends the shop have 2950 to 3450 CFM for the space.  The supply of outside air for combustion alone provides 400 CFM.  When the combustion intake air is combined with the natural ventilation provided by the two doors there is sufficient air exchange.   For an example of natural ventilation consider a 15 mph wind[2] blowing directly through a window with an open area of 36 sq ft can move 25,000 CFM or more through the building if the air can escape through a second doorway or other large opening. 

 

     Qwind = K x A x V, where

     Qwind = volume of airflow (m³/hr)
     A = area of smaller opening (m²)
     V = outdoor wind speed (m/hr)
     K = coefficient of effectiveness

If it is assumed in the winter the man door is fully closed and the overhead door is open between 6” to 8” (5 to 6.67 sq ft) the natural air flow will be between 2,461 to 6,577 CFM.

     Q = 0.4 (45 degree incidence) x 0.464 (0.620) sq m x 22,530.8 m/hr

     Q = 4,181 (5,588) meters cubed per hour = 2,461 (3,289) CFM

     Q = 0.8 (90 degree incidence) x 0.464 (0.620) sq m x 22,530.8 m/hr

     Q = 8,363 (11,175) meters cubed per hour = 4,922 (6,577) CFM

 

This gives the shop a total airflow of between 2,861 to 6,977 CFM in the winter.

 

 

Propane combustion air:

   For proper combustion and safety precautions it is necessary to provide the smithy with appropriate openings for fresh air supply while using the propane forges.  If the combustion air supply is limited incomplete combustion can occur, producing carbon monoxide.

 

NFPA 54 section 5.3: Air for Combustion Required by Gas fuel burning devices:

Minimum No. openings required  2

 

     The facility has two exterior doors and an air intake fan to supplement the indoor air for combustion during use of the propane forges.

 

Outdoor opening (sq. in./Btu h)  1/4000

 

     To verify that enough air is being provided with proper openings the amount of Btu’s generated needs to be calculated.  Since it is known that the proposed burners will use about 1 pound per hour during typical use and that propane holds 91,547 Btu’s/gallon and weighs 4.24 pounds/gallon usage can be determined.

 

     91,547 Btu’s per gallon/4.24 pounds per gallon = 21,591 Btu’s/hr per burner 

 

With 2 burners per forge and 5 forges there will be 21,591 Btu’s/hr/burner * 10 burners = 215,910 Btu’s/hr

 

An outdoor opening of 1 sq inch per 4,000 Btu’s/ hr is required: 

 

           215,910 Btu’s/hr/4,000 Btu’s/hr/sq in = 54 sq inches 

 

Using the 120 sq ft from the facility doors plus 28.274 sq inches for the 6” air intake for a total of 17,308 sq inches

 

   There is not any permanent duct work proposed for the propane forges since they are portable appliances.  To ensure that the forges are not overburdening the space or depleting the environment the volume of air used for combustion needs to be calculated. 

 

   It is known that propane needs 1 CF of room air per 1 CF of propane burned for ideal combustion, a simple 1 to 1 ratio.  Propane creates 2,504 Btu’s per CF burned. 

 

   Having already calculated that the forges could burn 215,910 Btu’s/hr it would follow that 215,910 Btu’s/hr/2,504 Btu’s/CF = 86.23 CF/hr of propane is needed for all 5 forges.

 

   We have established a 1 to 1 ratio so 86.23 CF of combustion air will be required every hour.

 

   Over the course of the 8 hour day the forges will utilize approximately 800 CF of combustion air, <0.02% of the shop volume.  This translates to about 2 CFM, the 6” air intake fan that was over sized for the coal forges can provide up to an additional 200 CFM of fresh air to the room.  To additionally ensure that the environment stays safe the amount of Carbon Dioxide, CO2, created during the ideal combustion process needs to be determined so the amount of Carbon Monoxide, CO, produced can be estimated.  CO2 is the final product of all hydrocarbon combustion.  With ideal propane combustion, nearly all carbon in the fuel is emitted as CO2, minor amounts, typically 0.01%, are emitted as CO.  So during inefficient combustion we can estimate up to 10% of the anticipated CO2 becoming CO.

 

   Carbon Dioxide, CO2, emission from propane is 3 pounds of CO2 to 1 to pound of propane.  The forges are burning about 10 lbs/hr resulting in about 30 lbs of CO2 each hour.

 

     100 CF of CO2 weighs 12.36 pounds,

 

   So 30 pounds of CO2 amounts to (100/12.37)*30 = 242.5 CF of CO2

 

   With propane combustion, nearly all carbon in the fuel is emitted as CO2.  Of the remainder minor amounts, typically 0.01%, are emitted as Carbon Monoxide, CO.  This means that in an ideal system the created CO2 concentration would be less than 0.006% of the shop area volume each hour and less than 0.05% of the shop area for the day with the amount of CO created up to 0.00007%. 

 

   The burning of propane is:

 

            

           C₃H₈ + 5O_{2 --->}  3CO₂ + 4H₂O

 

   The incomplete combustion of propane is:

 

           2C₃H₈ + 7O₂ --->  2C + 2CO + 8H₂O + 2CO₂

 

   Most people will not experience any symptoms from prolonged exposure to CO levels of approximately 1 to 70 ppm, 0.007%.  At sustained CO concentrations above 150 to 200 ppm, 0.015% disorientation, unconsciousness, and death are possible.   To doubly ensure the safety of those within the space there will be 2 CO detectors placed within the forging area.

 

[1] Guideline from The Engineering Toolbox at www.engineeringtoolbox.com/ventailation-air-flow-rate-d_115.html

[2] Average Rochester, NY wind speed in the winter is 14 mph and the summer is 10 mph.

 

    So once you calculate numbers for your usage you should be able to design/size an exchange/exhaust system to accommodate your specific usage.  Typically if the forges are to be stationary an overhead fume hood for exhaust is utilized and is designed to draw air based on the calculated rates.  In conjunction with the hood you need to supply combustion air as well as room replacement air with some sort of intake vent/system.  If your forges are portable you need to ensure that the intake system and the exhaust system adequately cross the space to ensure the air is being moved and mixed through the room.

 

-c

[Jack Evers]

 

 It is known that propane needs 1 CF of room air per 1 CF of propane burned for ideal combustion, a simple 1 to 1 ratio

 

This value is way off the mark. I have a table in front of me from the Canadian Standards Assn. giving a value of 23.5 CF of air per 1 CF of propane.

 

 

Using the combustion equation from the excerpt :

 

           C₃H₈ + 5O_{2 --->}  3CO₂ + 4H₂O

 

 

You would need 5 CF of O2 for each CF of propane and considering air as 21% O2,  I would calculate a ratio of  5/0.21 = 23.8 in agreement with the Canadian standards.

 

 

The shop can still achieve this. I have not checked other values, but you need almost 25 times the air combustion volume given to the City fathers, which could send me off on a rant about unqualified people approving (or disapproving) various requests before them. If things are not opposed, they are likely not checked. Oh well that rant is for another day, but thought the OP might like a correct value.

[Dale M.]

Another thing to consider besides CO2  is  NOX or Nitrogen oxides.... Produced when "air" is heated in combustion  process.... The nitrogen (78% of air we breath) is converted to nitrogen oxides when combined with moisture is precursor to nitric acids.... I particularly  do not what to breath NOX fumes and have it converted to nitric acids in my lungs and cause permanent respiratory problems....

 

Good ventilation where combustion process takes place is a must today as we tend to make out building sealed up tighter and tighter for environmental reasons.... And we forget our building need to breath too..... This is where the "sick building" syndrome comes from.....

 

Dale

 

80% corrected to 78%

[clm2431]

Thanks for the catch, not sure how i screwed that one since my notes have it listed as a 1:24 ratio.  I think since we are providing more air flow than is required and have CO detectors mounted around the area no one bothered looking closer.  Kinda humorous though since they did give us such a hard time about absolutely everything, if i didn't think it would reopen a nasty can of worms i'd send them a corrected report to point out they missed it too  :)

 

For the NOX concerns we didn't really evaluate that since it wasn't asked for but with the ventilation we are providing and the openness of the shop i don't think it's a concern here.  Now if the shop was tightly enclosed then i think it would have been smart to look into it.

 

-c

[Dale M.]

I only mentioned the NOX thing so others who may not know about it can do the research and become better informed....

 

Dale

[Avadon]

Interesting thread. I've always been working toward getting a shop that has a very high STC (sound suppression) value so neighbors can't be annoyed by the hammering sounds. Unfortunately it seems like getting the shop super tight is a recipe for serious toxicity. I guess a heavily sound proofed shop with exhaust and windows open is probably less obnoxious than a totally unsoundproofed shop.

 

However, is there a way to have your cake and eat it too? Is it possible to exhaust over a large forge hood and also bring in fresh air without opening up large doors to expose neighbors to all the deafening noise? There must be some medium.

 

I know when I used to have my shop in a basement that there was so much earth that not a lot of sound actually escaped the 3' wide 1' tall small storm basement windows, yet they brought in massive amounts of cross ventilation. My CO detector never went off when forging and I never had a hood over it.

[Avadon]

I definitely know from working around metals, fumes and toxic gasses throughout my life that just because your not falling over dead from an exposure, or even a dozen exposures, it doesn't mean that it's not immensely effecting your health. Sometimes these exposures are having a moderate to severe impact upon your health but aren't acutely recognized until some hugely alarming symptom arises. The best idea here is to remove as much risk as possible so there isn't a unknown build up in your body from exposure to a toxic chemical/gas/dust/etc.

[oclement]

Hi all

in the process of building my 1st, small forge and will use propane;

I plan on using that forge outside during summer, but I'm thinking of the winter days that will get boring and would like to use it inside (basement :S)

Now I do understand this isn't a good idea all by itself, but was wondering if use a kitchen range hood directly above the forge (or with a more powerful fan) with a chimney that would exhaust directly outside... would that still be a "why take the risk" situation?

 

Thanks

[newbieforge]

oclement,

 

I have also been thinking a lot about ventilation for my gas forge.

 

Here is my current plan for ventilating my 2 car garage, where I use my forge:

 

- Install an Air King 9155 or 9166 window fan in the garage window

- While using the forge, set the fan to suck in outside air, and leave one of the garage doors open about 12-24"

- Place the forge somewhere between the fan and gap in the garage door

- I may leave an oscillating fan on in the garage, to mix the air even more

 

This way, any CO emitted from the forge should be quickly carried away in the air draft from the fan.

 

The rated capacity of the Air King fans is 2500 cfm for the 9155, and 3500 cfm for the 9166. My garage is 30ft by 30ft, 10ft ceiling, or 9000 cubic feet. Even the small fan (9155) should exchange all of the air in the garage every 3.6 minutes. The oscillating fan will ensure that all the air moves around, with reduced stagnation in corners of the room for example.

 

The fans are very cheap (around $100-130) for their rated cfm capacity, and I won't even have to cut any holes in my garage roof for exhaust ducts or air intakes!

 

More info on the fans:

http://www.airkinglimited.com/pages/industrial/window1.html

 

 

Regards,
Markus

 

[Frosty]

Oclement: Propane forge in the basement? NO-NO-NO-NO!!!! Propane is heavier than air and WILL pool at the lowest point just waiting for a spark. Blow your house into the next county and the insurance company will LAUGH at your claim.

 

Ventilation for a school shop. Let a HVAC engineer do the calcs for make up air, etc. Just design with a safety factor of maybe 50-100%.

 

It's an old welding shop class with exhaust orts at different locations on the table. Perfect, simply duct to an overhead collector hood. Nothing big and fancy, just something to catch the superheated exhaust raising from the forges. They need to be deep enough to catch it all but so log as the exhaust system can keep a negative pressure in the collectors you're golden.

 

don't turn this into rocket science it's pretty straight forward. Oh sure, you'll need to lay a little rocket science on the folk who approve these things, liability is a PITA. Remember, you're going to need to impress a lawyer and school admin with little or no experience in this stuff so if you consult a HVAC professional and use an already approved system you should be okay.

 

More importantly the kids will be as safe as an inherently dangerous craft can be made.

Frosty The Lucky

[BobL]

The rated capacity of the Air King fans is 2500 cfm for the 9155, and 3500 cfm for the 9166. My garage is 30ft by 30ft, 10ft ceiling, or 9000 cubic feet. Even the small fan (9155) should exchange all of the air in the garage every 3.6 minutes. The oscillating fan will ensure that all the air moves around, with reduced stagnation in corners of the room for example.

 

Having worked with fans, dust exclusion and air movement for more than 30 years I can tell you it doesn't quite work like that.

 

What happens is  that within a short period of time (ie seconds) some of the air that is sucked in is also sucked out and an oscillating fan doesn't do anything to assist this happening. I have done measurements of ventilated laboratories and the very best one can expect is a 50% air exchange in the time calculated for one room air turn over, and that is provided that there are large vents at evenly spaced locations all around the walls at both floor and ceiling level. A 50% turnover means multiplying your 3.6 minute x two or 7.2 minutes. If you don't have the evenly spaced vents in the walls etc in practice it will be X3 or X4. Axial flow fans such as the air king model are not very effective at room ventilation especially if there are any sort of restrictions involved on the intakes. What is important for pollutant removal is where the extraction is located and the best place is as close as possible to the pollutant production e.g. a fume hood above or to y side of a source will be much better than just extracting air from a wall. eg 200 cfm close to a forge may be more effective than 2000 cfm on a wall.

 

The other thing to be very wary off are the CFM claims by most fan manufacturers. Some are theoretical numbers which are almost meaningless. Most ratings are for unconstrained fans, so as soon as any housing, grating or ducting is added their flow reduces very significantly. For example a 4"diam  opening simply cannot pass more than ~400 cfm of air at the sorts of pressures (<20" of water pressure) most axial/squirrel/impeller fans generate. A 6" diam duct can only pass ~1250 cfm.  If yoanur extraction system uses these duct sizes then these are the real figures that should be use in air turnover calculations.  I have done extensive measurements of many different fans and dust extractors to verify all of the above.

[newbieforge]

BobL,

That was very informative. Thank you.

 

My thinking was that it would be enough to create positive pressure inside the forging area (garage), in order for the general air flow to move toward the outside.

 

How do you make your air flow measurements? (I would imagine it might involve lighting a match in different parts of the room, and watching where the smoke trail moves?)

 

Would you figure that a couple of well placed ceiling fans, one blowing down, one blowing up, might help mix the air better?

 

I realize that proper commercial solutions are one thing, but I can't justify nor afford that kind of investment. I'm looking for something that will move enough air, while controlling my costs. That said, I'm willing to drop a bit of cash (maybe up to several hundred bucks -- the cost of an anvil, say) since I both value my health and enjoy forging.

 

Regards,

Markus

[BobL]

That was very informative. Thank you.

 

My thinking was that it would be enough to create positive pressure inside the forging area (garage), in order for the general air flow to move toward the outside.

 

How do you make your air flow measurements? (I would imagine it might involve lighting a match in different parts of the room, and watching where the smoke trail moves?)

 

Would you figure that a couple of well placed ceiling fans, one blowing down, one blowing up, might help mix the air better?

 

I realize that proper commercial solutions are one thing, but I can't justify nor afford that kind of investment. I'm looking for something that will move enough air, while controlling my costs. That said, I'm willing to drop a bit of cash (maybe up to several hundred bucks -- the cost of an anvil, say) since I both value my health and enjoy forging.

 

No worries about the information - I spent years working on this stuff as part of my day job where I designed and even built (some with my own hands) laboratories where we used and distilled our own chemicals like concentrated hydrochloric and nitric acid,  so I am happy that it is useful elsewhere. eg I have also helped many woodworkers with their dust extraction systems etc If anyone on this forum wants help setting up their exhaust systems them I am only too pleased to be able to do so.

 

For air flow measurements I use hot wire anemometers which are accurate air flow sensors that measure air speeds from 60 mph down to about 1mph.  I also have access to particle measuring instrumentation that can measure dust down to 0.3 microns in size so I can detect for instance combustion dusts from motor vehicle traffic and welding.I have not tried this in my shop ith the forge (awaiting installation of a natural gas line to my shop) but I will do so once I get everything running again.

 

I'm sorry I did not emphasise in my previous post that "any ventilation is better than no ventilation".  

A big axial fan in a wall and a wide open door or window is a good start, especially if the forge is in line with both.

 

RE; mixing the air in a shop with ceiling fans

This won't really help much. I always reckon it's better to devote fan energy into as much exhaustion as possible and preferably at the source of the problem which in our cases are forges.

If the bad air is already at ceiling level it makes more sense to exhaust it from there rather than trying to get it back down into the middle of the shop and then move it out from that area.

Of course not everyone can put ceiling mounted exhaust fans in their shop so they have to use sideways solutions.

The best solutions are overhead or side draft hoods ducted to outside the shop using 6" ducting which can move 1250 cfm - this requires a 1.5 - 2HP blower and generates quite a fast torrent of air which may be too much for some forges if the inlets are too close to the forge. I would think a ~1/2HP  impeller using 4" ducting (400 cfm) would be more than enough to exhaust the gasses from a small forge. My welding bay fume hood is a 1/2 HP motor , 6" diam metal ducting , 500 cfm unit that allows me to just park my (mobile) forge underneath it. 

 

BTW Your idea of using a push-pull system can be very effective when applied to arranging a steady draft between inlet and exhaustion points. e.g. If a "doorway"-"forge"-"exhaust fan" line cannot be set up, then using a second axial fan to push air into a shop to create an inlet-forge-outlet line will improve things.