Fume extraction in cfm please.

[CRS51]

Hello all, just looking at getting some fume extraction in my workshop for when I am welding. Haven't bothered as mainly using tig but gets a bit hazy with the mig and arc. Now can someone recommend a good cfm I should be looking at ?
My workshop is 11m long by 3.6m wide by 2.3m high and has doors at one end, flat roof and no windows / other ventilation. If I am using arc or mig I always have the doors wide open and weld near the entrance but gets a bit drafty.
Any help appreciated, thanks Chris.

 

[jonjoe]

safer just buying a air feed helmet or a mask

 

[PTvor]

I thought the usual thing was an elephant's trunk which you put in position near the work and it sucks up the fumes.

http://www.rapidwelding.com/dynamic/Category.aspx?c=MOBILEEXT&o=0&zl=2&sq=8

http://www.westcoweld.co.uk/fume-solutions/fume-solutions-from-nederman.htm

If it's general forced ventilation of a building and you are shifting enough contaminated air out to make a difference, the air's got to be replaced with new air which will be cold in winter - unless you pay to heat it.

 

[Drains]

It's mostly M3/hr or/m or/s these days rather than CFM, and as you've given the measurements in metres, that's probably the way to go. Anyways, you've got around 91 cubic metres there. Offices should have an air change of at least 6 changes per hour. For welding fume you probably want at least double that, so let's say 12 changes per hour, so that'd be 91 x 12, so 1000 m3 per hour. That's 0.27 m3/sec. You can buy a fan that'll do that for under £100 - (say, http://www.justfans.co.uk/systemair-rvk315-p-379.html), but it would need some ducting and external louvres, probably. I'd have it extracting, not blowing. Forced ventilation is unusual not least as it stops working properly as soon as you open a door or window. Extraction is less liable to be ineffective in the same circumstances, although you do want to ensure your entry louvre is positioned low at one end of the workshop and your extraction high, at the other, to ensure no still-air areas.

I'd put a louvre in the door and the fan up the other end. Good to have a closable shutter on the louvre for cold days - keep the drafts at bay.

Or you could get an elephant's trunk stylee extractor as suggested above. More effective but much more expensive.

 

[decepticon]

my old garage was abit smaller than yours but i stuck a secondhand 12" fan in, figured the more clean air the better. best too big and turn it off when not needed than too small