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Go Back   Lampwork Etc. > Library > Safety

Safety -- Make sure you are safe!

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  #1  
Old 2016-03-01, 7:52pm
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Default Greenhouse Fan CFM Calculator

I'm wondering if the "greenhouse fan cfm calculator" would be applicable for lampworkers. http://www.littlegreenhouse.com/fan-calc.shtml

The website says: "This is the optimal exhaust fan CFM (Cubic Feet per Minute) rating for your greenhouse. A fan this size will exchange the air in your greenhouse at least once per minute which is recommended for venting small greenhouses."
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Old 2016-03-02, 6:58am
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If I remember the safety threads on venting I think the ball park numbers were 125 cfm for each square foot of 'barley box' front face opening.

If you don't have enclosed sides and back on your ventilation hood then you need to total the square footage around the rim of the hood ( 2 sides plus front and back ) from the bench up to the bottom of the hood.

Getting the fumes out needs a honking lot (technical term) of air movement if you can't capture the burnt gas cloud with sides and a back.
Working with the bench against a wall helps and it's even better working with the bench into a corner.

If you build a 'barley box' with one open face for you to work through and that opening is 3 feet wide by 2 and half feet tall then the math works out as 7.5 times 125 = 937.5 cubic feet per minute.

If you then add the resistance to flow from duct work and critter screening you will need close 1200 cfm for an ideal barley box.

The closer you can get the flame to the hood (or funnel like the Italian Masters use ) the relatively less air flow you need but I would not go below 850 cfm even if the funnel was being licked by the flame.


Another thought is that most of the numbers from the manufactures of bathroom fans and green house parts suppliers can be overstated because they are assumed for absolutely perfect engineering equations and no one really checks them because no one's health is on the line like with what we use them for.


There are several threads here and at other glass websites about ventilation and what works and what doesn't and what you -might be able to get by with- and it really is important that you get it right for your work area.

You only have to do it right once but getting it wrong can be very bad news for you and for your loved ones.



The air exchange rates listed on that site are only useful for controlling temperature and humidity and not for removing poisonous gases from fuel combustion and heavy metal fumes from colorants in the glass.

More than is needed is a whole lot better than just barely enough.

You also have to have enough force in the flow to fight unpredictable winds as well so the fumes don't get forced backwards into your breathing area.
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Last edited by Speedslug; 2016-03-02 at 7:02am.
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Old 2016-03-02, 3:26pm
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Nicely stated Speedslug! I'm no expert but you summed up nicely what has been said in so many vent/fan threads. I've been reading those recently as I am setting up a new studio. I sure appreciate you and those others that are knowledgeable on the subject, sharing what you know! I am planning for a funnel, with a slight slant up to the window, where it will vent. The span from funnel to fan is only a couple of feet. And you validated my fan cfm size I had waffled about. Thank you! Karen
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Old 2016-03-02, 10:45pm
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Thank you.

I am only passing along what has been given as a gift to me freely and without reservation.

We are all in this together.
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