ductless fume hoods

[rivera1212]

hey guys

i’m trying to piece all the equipment needed to make dags and i had a questions about what you guys are using for fumehoods. i have a small outdoor shed that i want to uses to make B-dags and i dont really want to cut holes into for a fume hood. so can you guy give some advice about these ductless hoods, thanks

[photolytic]

If you are only making BDags you should save your money and buy a really good, glass lined, fuming box for your iodine. As Ken (Mercury) Nelson recently posted “My sensitizing boxes release such a tiny amount with each slide that we never smelled it, and iodine and bromine are odious at infinitesimal levels.

Iodine vapors are 8.8 times heavier than air and as such they tend to concentrate near the bottom of the fuming box. I’ve measured the concentration of the iodine fumes inside the top of my box and found them to be less than 2 ppm at 20C. Very little of this iodine escapes during the fuming operation. Only the last few seconds of fuming needs to be done in the dark so you can keep the shed door open for the initial fuming.

If you keep your shed door slightly ajar to improve the ventilation your iodine fumes should not be a problem. You may want to install a vent fan in the shed to improve the air flow.

Keeping the temperature and humidity in the shed may be an even greater problem as both affect the rate of iodine fuming, not to mention your comfort and health.

These occupational Exposure Limits (NIOSH, 1997; ACGIH, 1994) can be found at

http://oehha.ca.gov/public_info/pdf/TSD%20Iodine%20Meth%20Labs%2010’8’03.pdf

1. Ceiling Limit (C) (not to be exceeded at any time): 0.1 ppm (1 mg/m3)

2. Short-Term Exposure Limit (STEL or ST): Not established.

3. 8-Hour Time Weighted Average (TWA): Not established.

4. 10-Hour Time Weighted Average (TWA): Not established.

5. Immediately Dangerous to Life & Health (IDLH): 2 ppm (21 mg/m3)

In air, iodine vapor will be hydrolyzed by water vapor to iodate (IO3

?) and iodide (I?) ions, which have a relatively low order of toxicity.

[jgmotamedi]

Photolytic is correct in that the danger of iodine with a good fuming box is fairly minimal, and for Becquerel development a decent vent and a sealed box is probably enough.

That said (I know it is not what you are asking), I am concerned that ductless hoods will be seen as a viable option for mercury. They are not. The reason for this is that there is too much room for error. The story of Sandy Barrie (sp?) should be a warning. He poisoned himself with mercury fumes because he waited too long to change the filter of his ductless hood, or perhaps just forgot to change it.

[Mercury]

To me, “Ductless fume hood” is like “jumbo shrimp.”

(Pardon the analogy in English to all of our international readers… it is an oxymoron.)

I choose not to assume that any ductless fume hood that I can afford will filter and release air back into my environment safely. It is inherently a faith-based system. Other than by very expensive air sampling, which is historical and not real-time, how will you know that the filtered air is safe other than by believing what you’re told by the manufacturer of your ductless hood?

Thank you Photolytic, and I agree that for B-dags good room ventilation is fine if your I-box is tight.

If you want a fume hood, then go the distance: cut the hole in wall or roof, install the ducts and a good suction fan (preferably mounted outside the work room to pull air out through the hood), and keep the velocity of air entering the face of the hood above 125 linear feet per minute when in use. Get the bad air outside and away from you. I also heartily agree with jgmotamedi on this.

p.s. Sandy Barrie’s story is told by himself in the 1992 Daguerreian (Society) Annual. (Maybe CDags can get Sandy’s permission to reproduce it on this site?)

Thanks,

KN

[CasedImage]

Re Sandie Barrie – back in about 1993 he came to NZ and gave a daguerreotype demonstration at a NZ photographic collectors meeting in the NZ center for photography. Back then I had no idea what daguerreotypes were (though it is nice to now think that my first encounter was a contemporary plate). I remember him explaining the process which seemed to my 35mm home darkroom sensibilities to be a mixture of alchemy and gobbledygook, to the 30 something crowd of middle aged and elderly photo boffins. I can’t remember the sensitization and exposure bit but I do remember him removing the plate from the mercury pot to show us the developed image. At the time I though nothing much of the rather bare looking pot (no double dark slide or presence of a fume hood) but thinking back now to the mercury fuming away in front of us…. well yes.

This also reminds me of a certain daguerreian who a few decades ago was developing his plates on the kitchen stove, using a lensless inverted kodak bellows camera to funnel the fumes towards the plate… and himself.

I mention these horror stories in relation to the subsequent mercury poisoning to reinforce the lesson being told here that mercury is not to be toyed with.

www.CasedImage.com

[Mercury]

Wow. Lunacy must love company, because I reviewed a very similar set of published instructions for making daguerreotypes in the Daguerreian Society Newsletter, Vol.4, No.6, November 1992. (I give my immediate permission to CDags to reprint it, and I can supply a copy of the original publication to CDags as well… under the How NOT to Make Daguerreotypes department!)

In this case, the author recommended building a mercury pot consisting of an inverted metal 4-sided ‘chimney’-style kitchen food shredder and the top of a stainless steel roll-film developing tank filled with mercury; then wrapping that assembly in aluminum foil and perching it atop a Sterno ‘canned-heat’ (jellied alcohol) stove. He recommended doing this procedure in a darkroom with “adequate ventilation.” That was the sum total of his coverage of safety, other than to say not to spill the mercury (which would be impossible not to do with this contraption.)

He sold these booklets (all of 6 pages of text for the whole process), complete with ISBN number! I can only hope he didn’t have many buyers. Needless to say, my review was rather more searing than being directly in the open flame of his jellied alcohol.

Maybe there’s a future place on CDags for the Daguerreian Darwin Awards. No… I take that back. Rather, I hope that thanks to CDags and all it’s careful contributors, such antics are history and will be studied and learned from as such.

Dag safely, all –

K

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