[SkyHighLer]

Originally Posted by WaterFarmFan

Most helpful. Do you have a photo of the completed box and air knife portion? Is it basically a large lip in front?



Will check that out. I have to be as stealthy as possible, so a tall stack is probably out. I was thinking about creating a ducting system with two paths right off the hood using wye branches. I would only use carbon for the most hazardous solvents and sensitive times of the day, with the damper open for the rest. Something like this maybe:

View Image

This seemed to have some good info about filters - https://www.labconco.com/articles/co...-ductless-hood

From your link:

2. Will the chemicals involved in your application be effectively filtered with the available carbon filters?
Protector Airo Filtered Fume Hood is a ductless fume hood that uses Neutrodine Filters.Typically, ductless hoods will be outfitted with chemical specific filters. Specific filter types increase chemical trapping capacity for different chemical families; however, some chemicals cannot be safely filtered or aren’t filtered effectively enough to allow ductless hoods to be a financially viable option. Filtered fume hoods can filter out acids, bases, and solvents with one filter type, however, there are still some chemicals (low molecular weight solvents) that will not be effectively filtered.

...some organics (such as methanol) are very volatile, light weight, and are not effectively adsorbed on the organic filter.


There are a large number of videos on commercial and DIY design, construction, and testing of fume hoods at YouTube.

[Ringodoggie]

There are a number of components on Ebay that may be useful (if you're an eBay type person).

I had not considered a benchtop unit but at $200 to $300, I saw a number of quick answers.

There seemed to be several of these for sale...

https://www.ebay.com/itm/Labconco-39...AAAOSwmkpZ6rZ9

[WaterFarmFan]

Thanks for all the details! I am curious, is it standard operating procedure for labs (professional of all sort across industries) to just dump fume hood exhaust into the atmosphere? If I understand correctly, the tall stack mixes in fresh air to lower the concentration of compounds, but they are still getting expelled. Is it ethical to release methanol (for instance) vapor if people and/or pets could be in the area outside? Or are concentrations so low as not to matter?

[WaterFarmFan]

Originally Posted by Gray Wolf

If you wish to design exhaust systems, I highly recommend picking up a used copy of Industrial Ventilation, a manual of recommended practices, by the American Conference of Governmental Hygienists. I still use a 17th edition, which still works.

It is the standard for the industry and the bible that we used in aerospace to design ventilation and exhaust systems precisely by the numbers.

If you have to move 900 cfm from a 3' wide exhaust plenum, and you want the velocity at 1000 surface feet,

Since the air stream is moving at 1000 surface feet and you have to move 900 cfm, you need .9 square feet of slot.

900cfm/1000sf = .9 square feet of slot opening.

.9cu/ft/3' slot length = .3 feet slot width

.3' X 12 = 3.6" wide

3.6"/ number of slots = individual slot width

I will try and hunt down a used copy. I found this excerpt online and it is chalk full of useful info:

Examples of local exhaust ventilation - https://www.bwc.ohio.gov/downloads/b...3-1-5-99.2.pdf

[G.O. Joe]

Originally Posted by WaterFarmFan

Thanks for all the details! I am curious, is it standard operating procedure for labs (professional of all sort across industries) to just dump fume hood exhaust into the atmosphere?

Whatever the authorities allow. It would take a lot of butane to challenge any decent 8" inline to explode, as long as the fan was on first.

[Gray Wolf]

Originally Posted by WaterFarmFan

I will try and hunt down a used copy. I found this excerpt online and it is chalk full of useful info:

Examples of local exhaust ventilation - https://www.bwc.ohio.gov/downloads/b...3-1-5-99.2.pdf

Those were taken from Industrial Ventilation. Imagine the whole book.

[Gray Wolf]

Originally Posted by WaterFarmFan

Thanks for all the details! I am curious, is it standard operating procedure for labs (professional of all sort across industries) to just dump fume hood exhaust into the atmosphere? If I understand correctly, the tall stack mixes in fresh air to lower the concentration of compounds, but they are still getting expelled. Is it ethical to release methanol (for instance) vapor if people and/or pets could be in the area outside? Or are concentrations so low as not to matter?

DEQ monitors air quality and issues the discharge permits.

A company's discharge permit spells out how many tons of VOC's they are dumping per year and what it is.

A single cabinet would be a small source, and DEQ is after the big polluters, so unless someone is complaining about the smell, or you set something on fire, it is unlikely they will show up.

Dumping it high in the air and mixing the discharge using an evase is a dilution solution to smell and concentration.

For safety, the fumes going through a non explosion proof fan should be below Lower Explosive Limits, which is relatively low for alcohol and the alkanes. 1.2% for hexane, 1.4% pentane, 1.8% butane, 2.1 % Propane, 2.2% Iso, and 3.3% ethanol.

With an explosion proof fan an evase will help dilute the discharge below explosive limits.

We used an explosion proof confined space inline ventilator fan, readily available at your corner safety equipment store. https://www.industrialfansdirect.com...ns-and-blowers

[WaterFarmFan]

Thanks guys. I really need to think the exhaust path through. Will read more and post back soon.

[Gray Wolf]

Originally Posted by WaterFarmFan

Thanks guys. I really need to think the exhaust path through. Will read more and post back soon.

A question that should be considered when designing a system, is what will be the reaction of OSHA, et al, if they walk through your door.

In industry, all engineering avenues must be exhausted, before relying on personal protection, or challenging standards. When dealing with OSHA, the engineering values that you must meet, are taken from Ventilation Handbook.

They of course have averages and safety factors, and you can design below that and sometimes still be effective, but they are actually pretty accurate and while you can sometimes get away with values below them, you can't defend your position if it doesn't work.

I come from an industry, where OSHA is constantly at your door protecting us'n, so suggest considering all designs from that perspective. If challenged, is it defensible by the accepted authority and the numbers??

There is of course the really keen and significant up side to such a resource as Industrial Ventilation, which is that the governmental hygienist writing it, actually did know what they were doing and it does work, as judged from a professional lifetime of practical experience applying their principles.

[troutman]

I don't have a fume hood yet.

I do make sure my window is always open when I play with chemicals.

As long as my vapors get diluted by fresh outdoor air I think my chances of problems are greatly reduced.

I won't do chemical reactions without fresh air and I prefer when the temperature is less than 15C outside.

Cold air makes for easier distillations and solvent reclamation.