Washtub for catching the fumes

[bepnewt]

Goal of this Post: Choose a tub to use for the fume collection.
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Now that I've rearranged my area, I'm adding real ventilation.

I'm on a Bravo in a garage. I mostly use the center-fire, but do fire up the outer now and then. The desk I torch on is 30" deep with the torch mounted at the very front. The back of the desk is open, ie. no wall behind it. The torch is angled slightly upwards, but I'm open to changing the angle if needed.

The space behind the desk is a walkway so I can't impede it too much.

I've decided to go with a washtub at the end of the ductwork as the "fume hood". I'm trying to figure out which kind to go with.

My choices appear to be a round tub or a pill shaped like Mary did in her studio build:
LE Thread: http://www.bluebetween.com/studio.htm
Personal Site Thread: http://www.bluebetween.com/studio.htm

My mind tells me that the pill-shaped tub situated so that it hangs long-ways going front-to-back makes the most sense since I won't have a backsplash. If the fumes and crud were rising in a perfect circle, I'd say the round tub, but the movement of air away from the face of the torch makes me think the pill-shaped one is best.

Crude image of what I think makes sense - position of the tub will be based upon fume tests, this is just a general pic so you can see what I'm talking about:


What do you guys think on this? Lowering the back of the tub some may help, too.

I will, of course, do all the proper tests after I have it set up to make sure it's getting all the bad air. I've read a lot in this forum so I'm cognizant of what duct-work to get, what fans to look at, where to go for the CFM calculator, etc. This one decision is holding everything up and I don't want to have to buy multiple tubs because I made an illogical decision.

So: Which tub shape should I get and why?

Thanks,
-BEP

Examples of what I'm talking about:
Round Tub


Pill-Shaped Tub:

[Speedslug]

I don't have the experience to give a definitive answer and I hope one of our very experienced lamp workers will chime in..... but....


My gut tells me that you are going to need to seriously increase the CFMs that your vent system will move if you are going to go without the backsplash.
I am guessing here that you will want to move something like four times the CFMs with out a backsplash of some kind.

Even if you could cover just a third of the tub on the back side, which ever one you chose, will help the "capture effect" a huge amount.

I guess it could be accomplished somewhat by lowering the back end of the tub in which case the longer 'pill' shape would be the one I lean towards.
I would want to see it rather close to the surface of the bench, about 30 inches above it at the farthest away from you.

You might get better 'capture' altogether by just expanding your duct work up a couple of steps and pointing your torch right into it similar to what the Italians do.

If you are working say 12 inches from the front opening of some 12 or 14 inch ductwork then you wont have a need for either of these tubs.

Just my 2 cents and worth what you paid for it.

[bepnewt]

Originally Posted by Speedslug

Just my 2 cents and worth what you paid for it.

Check is in the mail!

I appreciate the input, Phill. I'm going to go forward with the pill-shape and probably lower the back some. After I get the rest of the duct work and buy the fan and get it all connected, I'll finagle with it until it works.

Worst case, I can make a pseudo-backsplash of some sort.

I just need to get _something_ going that is safe.

-BEP

[Speedslug]

You could go with thin plastic curved to shape if lighting is an issue. Good luck with it and let us know what you learn as you get there.

[jhamilton117]

What ever you do don't let the hood get to hot! Galvanized metal off gasses toxic and deadly fumes starting at 5-600°F. It can be some nasty stuff if your not careful! That's why kitchens use stainless steel, and why I'm spending the extra for stainless over a tub myself.

[Speedslug]

Aye, Galvanized is lots of zinc. Zink poisoning is not fun and very easy to do.


ETA: Good call Jeremy