Sciencemadness Discussion Board

Alternatives to FRP panels for DIY fumehood walls?

Hockeydemon - 7-3-2013 at 22:28

Hey everyone,

I've been talking with radagast in a different thread about my fume-hood, but because we were discussing it in a thread unrelated to fume-hood design I wanted to re-post it for more input.

Ok so here is a picture of my actual desk:


Here is a google sketchup of the space..


This was my first go at it.. Using unistruts, plywood, and a house fan.


But radagast pointed out that my house fan's motor would be exposed to chemicals, and could spark.. In which case the fire is in a flammable wood box.. On top of the fact that the thing is pretty bulky with this design..

So I went back to the drawing board.. Using the idea of FRP plates, I changed the unistrut frame because it would be holding less weight. The glass was going to be acrylic glass held in by 4 'L' brackets that the glass can slide in, and out of..


I then calculated the square footage I need to cover everything up.. Roughly 396.59 sqft. Then I did the math of FRP panels which at home depot is $34/ 32sqft panel. I obviously need to pick a new material because I can't afford over $400 for just the walls of the box. I then calculated what it would cost with cheap 1/4" plywood from home depot which is $9/16sqft.. This is still too expensive though at over $223 :/

So what cheap, safe material could I use? Or am I not going to beat the 1/4" plywood?



watson.fawkes - 8-3-2013 at 06:55

Quote: Originally posted by Hockeydemon  
Then I did the math of FRP panels which at home depot is $34/ 32sqft panel. I obviously need to pick a new material because I can't afford over $400 for just the walls of the box. I then calculated what it would cost with cheap 1/4" plywood from home depot which is $9/16sqft.. This is still too expensive though at over $223 :/

So what cheap, safe material could I use? Or am I not going to beat the 1/4" plywood?
It's a good thing you had sticker shock at a plastic panel, because the fire hazard from those is rather worse than wood, not so much from its inflammability but rather from the toxic smoke they make when they do burn. There are fire-rated panels available, but they're even more money.

For structural material, OSB (oriented-strand board) is just as strong as plywood and significantly cheaper. (Note: this is not the same stuff as particle board.) For fire protection, the easiest thing to use on the inside is gypsum drywall. It takes quite a bit of heat to drive off all the water of hydration. As long as you're present when the fire starts (that's an important caveat), you'll have plenty of time to put out the source before the drywall fails.

As for budget, you're unlikely to get away with anything that's even moderately fireproof for less than a couple hundred bucks. You could, however, build out in stages and simply avoid working with open flame and other fire hazards at the start.

Just be aware that everything inexpensive is somehow a compromise. If you aren't paying for an impervious cladding, you don't want to generate a lot of free solvent vapors in the hood, as they'll absorb into the walls and desorb over time, even when (especially when) the fan is off.

radagast - 8-3-2013 at 08:21

Quote: Originally posted by watson.fawkes  


For structural material, OSB (oriented-strand board) is just as strong as plywood and significantly cheaper. (Note: this is not the same stuff as particle board.) For fire protection, the easiest thing to use on the inside is gypsum drywall. It takes quite a bit of heat to drive off all the water of hydration. As long as you're present when the fire starts (that's an important caveat), you'll have plenty of time to put out the source before the drywall fails.

. . .

Just be aware that everything inexpensive is somehow a compromise. If you aren't paying for an impervious cladding, you don't want to generate a lot of free solvent vapors in the hood, as they'll absorb into the walls and desorb over time, even when (especially when) the fan is off.


I'd second this advice. Gypsum drywall is a good choice -- not that structurally strong, but easy to manipulate, very cheap, and reasonably fire-resistant. Plus, if you're going with a modular unistrut or angled slot configuration, you can always modify the design and swap in new material as required.

Watson's second point and related point, regarding compromise, is also really important. Building a fumehood that can handle every possible toxic or flammable chemical is impossible without $$$. (Just to give an example, take a look at the number of different filters that are available for ductless hoods, depending on what you need to filter). So I think the practical approach is to build the fumehood around the specific experiments you plan to conduct. If you aren't working with large amounts of ether vapor or other ultra-volatile flammable vapors, then you don't need to worry as much about the potential fan sparking as much.

One other thing I forgot to mention was that I didn't see a gas washing bottle in your glassware pictures (it could be there, maybe I just didn't see it). Anyway, this is a pretty great way to neutralize potentially dangerous vapors before they have a chance to get out of control. To me, my fumehood is just a backup to what happens if my gas wash bottles fail.