Multi-use airtight booth

[darryl]

The thread on what oil for quenching got me thinking about this. I have intended for some time now to build a bit of a paint booth with hood, exhaust fans, and potentially some long sleeved gloves through the front so you can manipulate things inside with the front door closed. It occurs to me now that this booth could accommodate other gas-producing operations such as silver soldering, liquid plastic resin molding, heat treating, etc.

One concern I have is that combining flame-using operations and recently sprayed paint might be seen to be risky- though using common sense would make this a non-issue. You wouldn't go directly from a recent painting job to a flame polishing job, for instance.

In any case, the base size for my booth is already set because it's a bench top set at 34 inches above the floor. It's 34 inches deep and 52 inches wide. It centers below a window which I'll take out and replace with a vent fan system. Part of that system will suck fumes directly from the surface of the bench in case heavier than air gasses collect there. The bench will be surrounded by walls, a top, a front header and maybe a bit of an sill- and have doors with windows. This will all be made from 1-1/2 thick iso foam board, including the back wall. Perhaps I should face the inside with foil-

The bench will have a turntable in it, to which I could attach any kind of work-holding jig. I want to be able to rotate that with a foot pedal, and I think it might be good if it's not fixed in one position on the bench. This alone would be an HSM project.

Still wondering how to do the doors. I'm thinking three parts, two that are narrower and sit to the left and right sides of the bench. A central door would be just the right width so you could work without it in place much of the time and still get decent fume extraction. That's kind of what I'm trying to figure out right now, the right opening so I can still work easily in front of the bench and not have to have the fans at full tilt all the time.

I could make it a single lift-out door- it would not be heavy and I could just lean it against a wall when not using it. But I think with a full-wide front opening I'd be risking having some fumage coming into the room. Maybe this is something I experiment with once all the other constructions are done.

[BCRider]

A sealed compartment will build up fumes and dust and smoke to a degree where the inside would become dangerous in any number of manners or would become impossible to see anything. It has to have air flowing through it to both avoid a bad situation. So really what you are after is a fume hood/paint booth that will vent to the outdoors. And since you have to have an opening you may as well work through it. If the air is flowing into the booth at a reasonable rate you won't get much, if any, backflow of fumes, overspray or smoke other than by the most active actions on your part to fan it back out at yourself.

If you don't add large volumes of gases with your processes then you would be amazed at how little of a fan you need. But for spray painting other than with something like an airbrush or some forms of welding that produce a good volume of gases you'll have to raise the CFM moved by the fan. The obvious solution here is a decent fan that also has variable speeds.

I assume you want to use this area for other things than just the booth. So it would be nice if it can be broken down or erected from panels in a fairly short time and those panels fold up or otherwise break down to flat easily stored pieces.

And light. Trust me, you will want to have good light in this booth. Windows in what amounts to walls will still be too much blockage. So I don't like your idea of foam with "windows". The framing of enough foam plastic to hold things together will still be too much shading. Instead you want to aim at a strong and light framing that is quite slender and clad it with clear heavy gauge vinyl or other clear plastic so the shop lights can easily and fully light up the booth area. Something like 1/2" Schedule 40 plastic pipe and fittings would be good for the upper framing. And something like 1x5 MDF baseboard for the feet. And the panels should all have some click together sort of assembly so it all goes together easily and breaks down easily without any tools. If it takes more than 5 minutes to set up or take down that's too much.



For my model building that uses highly smelly lacquer like products for finishing I opted to make a tidy little "paint booth" of my own. It's a rather lightweight framed up rig shown below. The bases are old paint grade baseboard with 1/8" welding rod frames and skins of medium weight clear vinyl. And a top roof of the same clear vinyl closes it in. The overall size is 23" deep by 24"high at the opening and it's 70" long. So not much different than your area but not as tall I suspect. A couple of front panels can be set in place to close the front opening down to about 24" wide by 18" high. But I found that if I'm not waving things around and can live with the odd slight whiff of the solvent that I can get by with just one front panel and an access opening of 18" high by 39" wide. If I were adding air to the area such as if using an airbrush or rattle can I'd have to close it down with the last front panel to the 18" x 24" minimum size.

Suction for this is provided by a cheap and cheezy bathroom fan which is in the window box you see in the upper left corner of the picture and connected to the collection box with a short bit of flex duct. It's 6" duct because that's what I had And I didn't want to choke it at all since I didn't know how well the fan would work. The air is picked up via the 3" deep box with the pegboard front you see. It's 48x9 inches by 3 inches deep and connects to a 4 inch deep end box that uses a 4x10 to 6" diameter heating duct adapter.



All rather basic and cheap as I said. But it works like a champ. The biggest upgrades for what you're after would be a bit more of a fan to deal with the gasses from spray paint and any soldering. And yeah, you would want to watch where the torch points both to avoid starting any over spray on fire and also to prevent the vinyl being burned. Also for spray paint you're going to need a paint rated fan. For my needs with just a little bit of brush painting the fumes are not an issue and the bathroom fan has no brushes or starting windings that might spark. And I turn it on before I open anything and turn it off long after when there's no more fumes. So it meets my needs and is more than safe enough. But for honest to gosh spray painting you need the proper sort of fan that is rated for flammable gasses. Or a fan that uses a separate outboard motor. that is on the suction side so air flown in through the belt or shaft opening.

[darryl]

Thanks BCRider. Some good ideas there. I have a dual 4 ft fluorescent directly above the bench and I can put a clear section in the top to allow the light in. I don't think it will be enough, so I plan to add some led lighting inside- light from more angles. The room lighting here is poor, so this is just another step in the project. The idea to line the booth with foil stems partly from the idea of spreading light around as much as possible. It might also help protect from careless pointing of a propane torch. As for the size of an opening at the front to work through, from what you're describing I should be ok with not having the center door in place.

I have a fan unit with dual squirrel cages on it, and it's three speed. It does not have any sparking issues, and I can protect it from flying paint, but I'd still rather have the motor outside the booth. I'm toying with the idea of using a cross-flow fan with a long impeller instead (about the length of the window, which is about 3 feet). The shaft can come through one side of the booth where I'd mount the motor. I'll put a false back in the booth to create a channel which will direct air up to the window opening where I'll need to have a gate to close it off when the fan isn't running. Don't need cold air coming into the booth from outside. With a vent area the width of the window it won't need to be very high, leaving me free to fill the rest of the space with a smaller window. It would be nice to still be able to see outside, and catch some rays coming in.

[fjk]

Hi
You mention “flame using operations”
I would be concerned about mixing flames and a plastic structure.

Frank

[alanganes]

Food for thought:

Another option for the fume removal is to make up a venturi type thing where you use a small tube to inject fast moving air into the larger vent pipe in your hood. You can use standard stove pipe, duct or PVC drain pipe or whatever to make the venturi and use your compressor or even the blower side of a vacuum cleaner to generate the airflow. The advantage is that the motor and moving part mechanical stuff is completely removed from the stream of ejected fumes (flammable, corrosive, coats everything, etc) and can even be located outside of the room or building to mitigate any noise issues, etc. Plus it's cheap and easy to build with stuff readily available, often harvested from junk for free. Easily and cheaply replaced if needed as well.

Not sure how flammable the iso foam you are considering is but if it is at all so, mixing it with flames and forced air draft may not be such a good idea. I know you are smart enough not to point a flame at the walls, but dumb stuff happens to the best of us. Just something to consider.

I have a half-formed idea for what amounts to a mini fume extractor made from the blower out of an old vacuum cleaner I have with a speed control, a length of flex hose that I can connect to some outside vent, and a flex inlet hose on a mag base or something like that. I don't have space I want to dedicate to a fume hood like you are considering, but the ability to quickly set up to pull out soldering and TIG welding fumes and the like from the shop would be handy at times.

[Mcgyver]

buy one of the cheap princes auto bead blasters and see how much work you can stand doing with gloves in a fixed position a window (tending toward scratched and dusty) to look through

[Duffy]

In case you have missed it, you are now in the field of either Chemical Fume Hoods or Biological Safety Cabinets. These have been VERY extensively researched for both safety AND functionality. The information should be readily available covering both how to build AND safely operate these units. One point that cannot be overemphasized:- there are NO opinions as to how these work, there are ONLY verified FACTS. The inflow air velocity MUST be within a fairly narrow range, regardless of the open area. If the open area changes for any reason, there must be time allowed for the airflow velocity and pattern to stabilize before resuming work.
Does ANYBODY follow these precepts? Not many if any. Why? Because NOBODY is EVER trained to safely use a fume hood. It is there in the laboratory so use it! If you try to learn by observing your more senior workers, you will learn THEIR bad habits, and the process goes on. How do I know this? I worked with scientific staff in almost every laboratory for every Canadian Government Department. I also prepared the protocols and supervised the dismantling of MANY perchloric acid fume hoods, (and never had one blow up!)
The good thing is that serious accidents related to the operation and use of fume hoods are almost unheard of, (dismantling--not so much!)
Daryl go ahead and build your as you think best; you will feel better about the care you take with your health and safety, and THAT is what really matters.

[BCRider]

Darryl, sounds like you're willing to make it far more permanent than I wanted mine to be. Once you start attaching lights and stuff it'll be a lot more trouble to easily break down and put up. But that works too if you don't mind dedicating that work space to a fume hood.

Duffy, that's quite true. Paint, fume and chemical hoods share a lot of the same features and needs. The paint hoods tend to be more industrial and use a lot more sheet metal and for obvious reasons explosion proof motors. And I don't doubt chemical hoods share that need. Biological I would expect recycles the air after some pretty intense filtering and perhaps even microwave and UV treatment to kill off any and everything? That's certainly more specialized than we need here though... But you're right though, the air needs to flow through the opening and not let any or much back to the operator.

A hood like this would also not be a bad place to do any wood sanding too. And with a good airflow amount an air line instead of a vacuum could be used to clean away any dust resting on the surfaces.

[Duffy]

Daryl, one design requirement for your hood to work safely;- inlet air velocity, (past you as you stand before the hood,) is minimum 80fpm and maximum 100 fpm. Less than 80 and you will not effect capture, more than 100 and you will have spill-out. These are the figures with which I had endless discussions with hood users. They were CERTAIN that these figure should be HIGHER. Why? Weeelll, it just made more sense! Usually on that note, I left the room.

[darryl]

This bench top is already in place so it's ready to convert to a mini booth. It would be nice if I can still use it for other things, but I seldom work in that area anyway. If it's a more or less permanent booth, that's fine. That's what I had in mind from the start. I just didn't want to fully dedicate it for painting if I could use it for other things too.

I've been doing some casting with plastic resin in the past couple months, and it will be good to have an area where I can keep a proper temperature and keep the smell down. I don't often silver solder, but when I do it will be nice to have this area to do it in. I'm sure that once I have the vent system operating and the booth boxed in, I will discover what else I could do with it. If I ever rig up an EDM machine, this might be an area to use it in. Same for any small-scale electron beam cutting or welding- even spot welding.

The foam board I plan on using is pretty good insulation, but I'm mostly using it for structure since it's easy to work with and I have lots of it. It's faced on both sides with a paper/fiberglass layer, which is not pretty but it gives it a decent amount of rigidity. I'm pretty sure now I'll be layering it with aluminum foil- and perhaps using something like thin aluminum sheet for the back wall. This will become part of the duct work in the ventilation system, and is most likely where an absent minded pointing of a torch would hit. I can't imagine aluminum foil lasting more than a second or two if a torch flame is played on it, but a sheet of perhaps 30 thou thickness would take this for much longer. I'll have to see what's available from one of the local places. As I said before, a bit of common sense goes a long way.

I'm re-thinking what I might do for lighting. It might make more sense to use the 20 and 30 watt halogen floods that I have instead of the leds- they are in ceramic bases and can stand way higher temperatures than I would ever need in the box. Maybe they ARE my heat source- and maybe the only lighting.

I have thought about the awkwardness of working with long gloves and looking through a window- not very comfortable, but only in extreme cases would I do this. I think for now I can forget making the center door and just experiment a bit with the width of the doors on either side of the front opening. As I said before, I can easily just make a drop-in panel if I wanted to close off the box from the front. And yes- airflow patterns will change with every change, whether it's fan speed, the box open or closed off, or me standing in the opening- there will be some experimenting for sure. If the box is closed off, the intake vents will have to be optimized for one.

[Mcgyver]

imo, a hood would be ideal is it doesn't impede movement, addresses the H&S of some of the things we do and leaves bench unencumbered. My knowledge is on the edge of the subject, but I have a sense that the real challenge is getting a powerful blower at a reasonable cost that will move the amount of air you need to. Fans (that slip) need not apply

[BCRider]

Darryl, based on your last post about liking the idea of using the area for other things here and there here's an idea.

So you build in the fan and collector on the wall and hook it to the window. You build it so the top panel is permanent and has your lights in place. Now you build the sides up so they are like two or three way hinged closet doors. In use for a fume hood you fold the sides out so two of the panels form the sides and the third on each side is available as a 1/3 door on either side. So you can leave both of these third wings either opened out and give yourself a full access or you can close off one side or the other or both and work through a fairly small opening or close it down and cut back the fan for keeping smells of stuff that is drying or curing from getting into the shop.

When you want the area for other uses you fold back the three part sides against the wall and have the bench area open and clear for the most part. The three part setup would fold back and inward and fill in only the area under the upper cover.

So it's built in and would support extra lighting but by the same token it's easily brought out to use.

Part of the front covering could also be a clear plastic panel that folds down from the upper panel to close up part of the front but leave you with the full width to work through.

I would really suggest you forget working through the fixed gloves like in a sand blaster cabinet. It's way too limiting and would make it a PITA to bring small things to the cabinet and put them inside. And it really gains you nothing worth mentioning either.

As semi fixed options go I quite like this idea of a three part folding "closet door" sort of arrangement for the sides and front side doors. You can play with seals or at least close fits to cut off unwanted air entry and you can cut down the access opening so you can run a lower power setting on the fan to avoid removing all the heated air in the shop in the blink of an eye.

Mcgyver, a simple over the top hood won't do much unless it's darn near pulling off our shirts. To work well the booth needs the sides and back and top that the work is done within. And by limiting the opening to the one side the air movement requirement is reduced by a massive amount yet can still be very effective. Case in point is my picture of my quickie fume hood that works for how I use it and which only uses a basic bathroom fan. Yet I get no paint fumes that I can smell in the area around the opening. So massive fans are just not needed if we set up a reasonable booth.

A basic cheapie kitchen range hood fan with similar side walls and some slight extension off the front edge of the range hood housing would work like a charm and be at least as good as my bathroom fan option. AND (Darryl, you reading this?) would have sockets for a couple of work lights to boot.

Mind you that's only if we are not using it for serious spray painting use. A bit of rattle can painting I think would be fine. But not a serious spray gun use. At that point we'd certainly want to see a proper explosion proof or remote motor that is out of the flow of the flammable fumes.

[darryl]

BCRider, I like the idea of the folding doors. What I might do is to build the fixed sides out a little over halfway. Then I can use a two part door to fill in the rest of the sides and come across the front a little. When open they will not fold all the way back to the wall- leaving room for the external fan motor(s) and possibly intake vents. The fixed side parts will support the top.

It appears that I'll have about 10 inches of headroom under the top, so I can make the top the full width and depth, and put a skirt on 3 sides of about 10 inches in height. The wall is the fourth side of the skirt. That way I can still use fixed sides to about 18 inches out from the wall, and the two part doors on each side, and they will close up against the skirt on the sides and front. I'll be left with almost 16 inches of bench sticking out past the fixed walls, which should be enough to give an open feeling to it. The bottom of the skirt will be about 73 inches from the floor, so at my height I'll have about 4 or 5 inches of headroom. I won't even have to think about ducking if I want to lean into the booth.

The skirt gives me over 8 inches of room down from the top to install lights inside it, which I would probably do on the inside front and both sides. If I use the halogens it will get hot up in that roof cavity. If the vent fan doesn't bring the heat downwards enough, I can use a secondary fan to do that as well. In the summer I may want to have the light, but exhaust the heat- that's easily done as well since the window opening goes right up to the underside of the top. One or two little fans will take care of that, and they will also assist slightly in removing fumes.

The foam board I'm using is rated for up to 300 degrees F, according to what I've read. The ceramic sockets can be mounted to aluminum sheet to spread any direct heat, so I don't think I'll have a problem with that. I've been using one of the 30 watt floods as a work light for a few years now, and it's a nice light to work under- I think I'll be good with perhaps 5 or 6 of them to light the booth. 4 might even be enough.

The plan is coming together- thanks for all the ideas.

[BCRider]

Happy to help. And I have to admit that it's nice when I've used my own booth to avoid unwanted smells in the house. The garage is a bit different. I can just open the doors and get a flow through. But the house isn't so easy..... .I cook bacon for breakfast and even by dinner it still smells like breakfast.... Not that smelling bacon all day is a BAD thing.....

[Paul Alciatore]

My shop in in our garage which is just a few steps from out kitchen and breakfast room. My wife is very sensitive to paint fumes so I only use water based paints there. For oil/solvent based paints I have set up an area in our lawn shed. It is not ventilated as I usually spray a few items with the door open and then leave until they are dry or ready for a second coat.

I have considered ventilation there. But I have worried about flammable paint fumes. I am sure there are spark proof motors, a standard fan motor (brushless, induction) may well have no sparks. But there is always the switch or other control that turns it on or off. If I do add a fan, it will be in the other end of the building and it will direct air INTO the shed, not out. I will arrange a one way louver near the painting area for the air to exit. And the switch will not be anywhere near the painting area.

And yes, it is lucky that my house came equipped with a nice sized lawn building.