Sciencemadness Discussion Board

Creating a good (and safe) workingspace?

Taffsadar - 14-5-2005 at 10:35

To be honest, I'm the kind of guy who prefer to do things that explodes or creates a good flash of light. However I know that it is that kind of behaviour that often makes people loose their fingers/eyebrows/arms. I'm quite fond of my fingers/eyebrows/arms so I try to minimise the risk I am taking. At the moment am I having access to a "proper" school laboratory with a fumehood (I'm Swedish so I don't know the english names for everything but they look like this)

I will however move to a university this autumn which means that I loose access to this fully kitted out laboratory. Therefor am I going to try to build my own fumehood and various other things that I need altough the fume hood is my highest priority.

At first was I planning to use brass plates to shield the box that would become my dragskåp and put a fan at the back to take care of any gasses. Brass is however rather expensive and using a cheaper metal for the plating would allow me to spend more money on other things (which would be a huge plus since I'm becoming a poor student soon).

Therefor am I thinking about dropping the brass in favour of aluminium which is roughly 50% cheaper than brass. I could go for steel plates too which are even cheaper but the hardness of steel means that if somethings goes very wrong would the steel plate fragment and send razor shartp shards flying through the room, this combined with the risk for rust means that I prefer either brass or aluminium but I am abit unsure about the hardness of aluminium, will it shatter like steel or stick to gether like brass in case of an explosion?

I am also thinking about the fan which I will but in the "dragskåp". How much air should it atleast be able to suck out of the fumehood? Commercial ones seems to be able to suck out atleast 108 litres/s. The fans that seems to work the best for me are capable of sucking out 40 litres/s but my "dragskåp" will be alot smaller than commerical ones (probably around 1m broad, 0,5m deep and 0,75m high but that depends on the size of the plates I buy). Do you think two fans for a combined effect of 80litres/s would suffice?

[Edited on 14-5-2005 by Taffsadar]

[Edited on 15-5-2005 by Taffsadar]

Darkblade48 - 14-5-2005 at 13:48

I believe a "dragskåp" is a fumehood :)

I'm not quite sure about how powerful the fan on the fumehood/dragskåp must be, but I've read that people recommend that it should be powerful enough to suck the smoke you see from a blown out match from a certain distance (I'm can't remember the distance right now, this is what 4 hours of sleep does to your mind)

Magpie - 14-5-2005 at 20:46

There has been some recent incidental discussion of fume hood gas flow at
[url=www.sciencemadness.org/talk/viewthread.php?tid=3864[/]waterpumps[/url]

My 2002 Fisher catalog says that you should have a face velocity of 100 ft/min (0.5 m/s). For a hood opening of 1 m x 0.75 m the airflow would be (1)(0.75)(0.5) = 0.375 m3/s, or 375 liters/s. I think that more recent recommendations are for even more flow, i.e., 150 ft/min, which would be 1.5 x 375 = 563 liters/s.

I am also trying to build a fume hood and am struggling with what air flow I can reasonably provide, and need.

Rosco Bodine - 14-5-2005 at 22:57

A speed controlled blower is really what you want . At the least a two speed ,
and even better a three or four speed .
If you cant get a multispeed motor with
separate windings , you actually can use
a solid state speed controller on a blower
if it is permanent capacitor run motor type , or a shaded pole motor type .

The roar of too much airflow can get annoying when it isn't needed , and it can
make work difficult when you are trying to use a gentle flame from a burner , or adding powdered materials . It's nice to be able to simply dial up the speed you need . I am also a believer in a having a local flexible hose separate intake , having the end of the 4" hose mounted in a ring which can be clamped right onto a ringstand and positioned directly adjacent the opening of a beaker , also being the
intake for a separate speed controlled blower . This is very handy .

Taffsadar - 15-5-2005 at 06:35

Quote:
Originally posted by Rosco Bodine
A speed controlled blower is really what you want . At the least a two speed ,
and even better a three or four speed .
If you cant get a multispeed motor with
separate windings , you actually can use
a solid state speed controller on a blower
if it is permanent capacitor run motor type , or a shaded pole motor type .

The roar of too much airflow can get annoying when it isn't needed , and it can
make work difficult when you are trying to use a gentle flame from a burner , or adding powdered materials . It's nice to be able to simply dial up the speed you need . I am also a believer in a having a local flexible hose separate intake , having the end of the 4" hose mounted in a ring which can be clamped right onto a ringstand and positioned directly adjacent the opening of a beaker , also being the
intake for a separate speed controlled blower . This is very handy .


I haven't been able to find any fans with adjustable settings but by putting the fans on separate circuits should I be able to control the effect by simply shutting one or two of them down. A very simple way to change the effect of the fans would be to put one of the fans in a tube 1dm away from the fumehood and then put an adjustable shutter on the tube. Opening the shutter would reduce the air intake from the fumehood and thereby lower the effect.

Rosco Bodine - 15-5-2005 at 06:50

When you restrict the intake or the exhaust on a centrifugal blower it actually makes it speed up and make even more noise . The only way around this is to put a solid state speed control in the circuit .

Taffsadar - 15-5-2005 at 07:52

Quote:
Originally posted by Rosco Bodine
When you restrict the intake or the exhaust on a centrifugal blower it actually makes it speed up and make even more noise . The only way around this is to put a solid state speed control in the circuit .


I didn't know that it would make more noise, cheers for the info. However the reduction of air intake wouldn't work by restricting the air intake from the fume hood. It would work by opening the shutter which would make air from the room take up a portion of air in the airflow through the fan.

Fanregulator.JPG - 5kB

Rosco Bodine - 15-5-2005 at 11:49

I see what you mean now . You could actually use an existing exhaust fan in
a building ceiling area , and split off part of its intake down to your work table and/or fume hood .

fume hood safety

worker - 17-5-2005 at 21:45

safety...safety...steel panels, lightweight/easy to assemble/in industrial pressure areas such as dust collectors , a blow out panel is included in anticipation of the worst. Blow out panels for industry are enginered to pre set presures, using steel panel with cut out areas to met the designed stress/ think off a sheet metal panel with duct tape that will release the panel with moderate pressure increase...inexpensive and a safe option.

steel

neutrino - 18-5-2005 at 02:21

IMHO, any explosion powerful enough to shatter steel plate would kill you even (especially) if you only had only aluminum or the like as shielding. I wouldn’t worry too much about selecting steel plate for this application.

That release panel idea is interesting. Just make sure that the panel goes before your hood’s window does.