Safe concentration of Acetic Acid

[Rudeofus]

Acetic Acid is sold in all concentrations from white vinegar (~5%) all the way up to 99% and glacial, and there exists a variety of strong opinions (with associated flame wars) at which concentrations Acetic Acid is safe to handle. The target audience of this question are trained chemists or lab technicians, or people who professionally handle corrosive liquids or even Acetic Acid. The term "safe concentration" in this thread shall be defined as:

a photo amateur with some darkroom skills and a darkroom, but no fancy lab equipment, can handle this liquid with or without gloves and shall not expect nasty surprises like

1. Fumes that hurt or damage one's eyes or create a breathing hazard
2. Serious and irreversible skin/eye damage if acid splashes onto skin/eye even if it is immediately and thoroughly washed off with cold tap water
3. Violent reactions when because of inattention or by accident water is added to the concentrated acid
4. Excessive heat when diluted 1:1 with water (the right way)
5. Spills to the floor in moderate quantities (<100ml) can only be handled with hazmat equipment and/or with outside expert assistance
6. ...

 

[Gerald C Koch]

Concentrated acetic acid can cause burns and glacial acetic acid is a fire hazard. It is also an excellent solvent for some plastics including floor tile. Just where to put the cutoff point between safe and hazardous is a matter of conjecture. However the form that was most often sold in photo stores was 28% and I assume this was not arbitrary.

In Europe pre-EU, concentrations above 80% had to be marked as flammable. IIRC this was the concentration that Agfa sold for darkroom use. Don't know what today's EU regulations are. Probably anything stronger than what you would put on a salad.

 

[Ken Nadvornick]

The flashpoint of acetic acid is listed as a relatively low 40C/104F. Might also be worth asking your target audience if there are any concentrations/use cases where that could possibly also be a safety issue?

[Edit: I see Gerald has possibly already alluded to this above?]

Ken

 

[ic-racer]

at which concentrations Acetic Acid is safe to handle.

Any concentration can be safely handled by an educated adult with the appropriate cautions. Do you mean safe to touch?

 

[Photo Engineer]

Kodak considered 28% to be the max for safety for the casual user.

PE

 

[Gerald C Koch]

Do not assume that white vinegar is always 5% acetic acid. Some cheaper brands are only 4%. This can make a difference when using vinegar for stop bath. However the label should indicate the strength.

Kodak gave this recipe in their Darkroom Guides for making 28% acetic acid. Add 3 parts of glacial acid to 8 parts of water.

 

[MattKing]

My sense is that the hardener solution included with Kodak Rapid Fixer (Part B) is also strongly acidic. Can anyone advise how it compares to that 28% figure?

I've seen gallon jugs of it on upper shelves in at least one sort-of-local store, and thought that that presentation choice was somewhat unwise.

 

[Gerald C Koch]

My sense is that the hardener solution included with Kodak Rapid Fixer (Part B) is also strongly acidic. Can anyone advise how it compares to that 28% figure?

I've seen gallon jugs of it on upper shelves in at least one sort-of-local store, and thought that that presentation choice was somewhat unwise.

The hardener for their Industrex fixer contains 14% sulfuric acid according to the label. No acetic acid is listed.

 

[Arklatexian]

Do not assume that white vinegar is always 5% acetic acid. Some cheaper brands are only 4%. This can make a difference when using vinegar for stop bath. However the label should indicate the strength.

Kodak gave this recipe in their Darkroom Guides for making 28% acetic acid. Add 3 parts of glacial acid to 8 parts of water.

Not only did they give you that recipe but they also sold gallon jugs of glacial acetic acid. Where I worked, we sold gallon jugs of glacial to several professionals here who made their own 28% and from there made stop bath. We and the professionals were carefull not to let glacial get below 40 degrees F. Even today, I put 28% in the darkroom sink if we have cold weather predicted. I make sure the darkroom does not get that cold however. Would I keep glacial in the darkroom today? Nooooo! Have I, before today, ever heard of it causing fires? Noooo.......Regards!

 

[RattyMouse]

I didn't know acetic acid was flammable. Hmm..learn something new every day. Actually, anything is flammable I suppose at one point. But I had no idea that GAA was, in the standard fire scenarios of every day life.

Plenty of substances will never burn. Water, carbon tetrachloride, and anything inorganic. They might decompose, but that is not the same thing as burning.

 

[Xmas]

Plenty of substances will never burn. Water, carbon tetrachloride, and anything inorganic. They might decompose, but that is not the same thing as burning.

I did not know hydrogen was organic?

 

[Rudeofus]

Thanks for all those who replied, I guess we can draw the following conclusions:

1. There is no hard limit above which Acetic Acid suddenly turns into an extreme hazard while below it is completely harmless. It starts from being mostly harmless at low concentrations, becoming more hazardous at it becomes more concentrated until it eventually becomes too risky for amateurs to use on a regular basis.
2. At concentrations around 25-30% it doesn't appear more hazardous than other liquids commonly found in darkrooms, at least that's what Kodak concluded with their decades of experience.
3. At concentrations above 80% it becomes also flammable, which is not a property I particularly worry about in my darkroom (no smoking allowed!), but which does affect whether we can buy it over the counter and how we store it.
4. Since shipping is more expensive than the actual compound, online vendors tend to sell very concentrated forms of Acetic Acid. As amateurs, and especially if we are responsible for operating a darkroom with other (often less experienced) users, we are expected to dilute Acetic Acid down to 25-30% to make it safe for general use. Kodak did this, too, and expected darkroom operators to dilute glacial Acetic Acid down to 27% before it was used in regular darkroom operations.

A brief note on flash point, since this term confused the heck out of me before I looked up its definition: unlike autoignition point, a flash point of 40°C does not mean that on a hot Californian summer day an opened bottle of this compound will turn into an unwanted flame thrower. It means that above that temperature you are able to ignite this compound e.g. by throwing a match or whatever. Yes, extra caution is warranted with liquids that have a low flash point temperature, but not hysteria.

 

[gone]

Don't forget, chemical burns can be as bad or worse than skin contact, especially w/ stop baths. The first time that I got a full whiff of Kodak stop bath up both nostrils was painful and scary. There's a big difference between stock solution and working solution, and I wouldn't underrate the damage that acetic acid could do if it got in an eye or mouth, especially the eye. It's why I keep large printed darkroom instructions on the bathroom walls when I'm in there wet printing, as well as MSD sheets on everything toxic in the house. Mistakes happen.

My acetic acid is in a powdered form in a baggie (more like salt crystals than fine powder). When the vinegar's gone, the scheme is to go a 1% to 2% dilution w/ that. Sometimes I use no stop bath, just a couple of tank refills from the tap. If you wished, tap water bath-time could be factored back into development regime to achieve previous results.

 

[RattyMouse]

I did not know hydrogen was organic?

I meant to say most inorganic salts.

Back when I was in graduate school, my chemistry professor used to tell me to try try burning an unknown material if I wanted to test if it was organic or not. Ever since then I have used that is a simple test for "organic-ness".

 

[RattyMouse]

Don't forget, chemical burns can be as bad or worse than skin contact, especially w/ stop baths. The first time that I got a full whiff of Kodak stop bath up both nostrils was painful and scary. There's a big difference between stock solution and working solution, and I wouldn't underrate the damage that acetic acid could do if it got in an eye or mouth, especially the eye. It's why I keep large printed darkroom instructions on the bathroom walls when I'm in there wet printing, as well as MSD sheets on everything toxic in the house. Mistakes happen.

I have some acetic acid in a powdered form in a baggie (more like salt crystals than fine powder) for when my vinegar is gone, and the scheme is to go w/ 1% to 2% dilution. Sometimes I don't use a stop bath at all for negs, just a couple of tank fills from the tap. That water bath time could be factored back into the development regime to achieve your previous results.

I'll never, EVER forget the first time (and only time) I caught a whiff of pure gaseous ammonia. WOW..........absolutely nasty to the nth degree. Makes store bought ammonia based cleaners smell like Chanel No. 5.

 

[Rudeofus]

Don't forget, chemical burns can be as bad or worse than skin contact, especially w/ stop baths. The first time that I got a full whiff of Kodak stop bath up both nostrils was painful and scary. There's a big difference between stock solution and working solution, and I wouldn't underrate the damage that acetic acid could do if it got in an eye or mouth, especially the eye. It's why I keep large printed darkroom instructions on the bathroom walls when I'm in there wet printing, as well as MSD sheets on everything toxic in the house. Mistakes happen.

I think everybody here in this thread (and I daresay even everybody here on APUG) is aware that sticking one's nose or bare hands into random photographic liquids is generally a Bad Idea (tm). There is a big difference, though, between "watch out what you do" and "avoid this liquid if you can", and I wanted to know at which concentration Acetic Acid goes from the first to the latter stage. Evidently Acetic Acid is commonly sold to amateurs in the latter stage, and we should be aware of this.

MSDS may be great help to physicians or hazmat teams who have to deal with injuries/poisonings/spills, but they are mostly useless to photo amateurs. If you don't believe me, try to follow the MSDS instructions for small quantities of Sodium Chloride next time you cook dinner. Also, if you ever have to deal with Glucose, make sure you have eye wash and safety showers nearby. The parody warning label for Dihydrogenmonoxide is nothing compared to these MSDSs.

My acetic acid is in a powdered form in a baggie (more like salt crystals than fine powder).

Unless you live in an igloo, I somehow doubt that this is Acetic Acid in your baggie. Chances are you have Citric Acid.

When the vinegar's gone, the scheme is to go a 1% to 2% dilution w/ that. Sometimes I use no stop bath, just a couple of tank refills from the tap. If you wished, tap water bath-time could be factored back into development regime to achieve previous results.

The reason I started this thread was my article about conversion of color BLIX concentrates/powders into separate bleach&fixer setups. The bleach part will need pH adjustment which can't be done with vinegar or tap water, and someone has pointed out to me that Formulary sells Acetic Acid in 99% concentration only. The safety implications of this product have been cleared up here in this thread (thanks, Jerry!), and the recommendation to dilute such a batch down to at least 80%, or even better 25-30% should eventually find its way into the article, or at least its comment section.

 

[mdarnton]

Just one data point here--years ago, in a distracted moment, I poured a bunch of glacial acetic acid over my hand. I mean like a real amount, not a splash. I washed it off immediately, and the result felt like a mild sunburn for an hour or so, but no damage. I wouldn't have wanted that in my eyes!

I am happy to have had a mother who worked in a lab. Her comment on toxicity was that anything can kill you--water can kill you, eating too many peaches can kill you (her examples at the time)--so you shouldn't approach anything with fear but rather, respect and appropriateness. A great lesson, from a great mom!

Too many people hear that something is "dangerous" and they run and hide. I feel sorry for them. For those in that camp, I offer this: http://www.dhmo.org/facts.html

 

[ic-racer]

Kodak gave this recipe in their Darkroom Guides for making 28% acetic acid. Add 3 parts of glacial acid to 8 parts of water.

Just for the record, I use goggles, darkroom smock and one of those twin cannister-style fume masks and gloves. It is really no big deal if one is used to using this type of simple safety equipment. One of my air cleaners in the darkroom has a carbon filter element, so I run that also.

I use the same precautions I used when diluting hydrochloric acid in chemistry class. Am I the last of the generation that used to do that?

 

[Jim Jones]

Long ago to save money, I diluted glacial acetic acid as needed for stop bath. Considering its many disadvantages, it was false economy. Reverting to 28% acetic acid was more practical and less unpleasant and dangerous.

 

[Xmas]

I use acetic acid when printing or for salad dressing or for French fries (chips) as white wine vinegar.

If you are careless and get it in an eye then head under cold water faucet (tap) quick.

Glacial is way too dangerous to buy, YMMV.

 

[Rudeofus]

Glacial is way too dangerous to buy, YMMV.

You may be right, but what should one do if it's the only form sold by Formulary? A Saturn V without payload couldn't bridge the gap between theory and practice sometimes ...

 

[Ken Nadvornick]

Glacial is way too dangerous to buy, YMMV.

Oh dear...

It's not like it's spent nuclear fuel rods, or something. Doesn't anyone remember all of the simple safety precautions from their high school or university chemistry classes? That's all you need. Knowledge is the universal antidote to danger and fear.*

Or does no one even take chemistry classes anymore...?



Ken

* Does anyone remember the formal name of SpaceX's drone ship landing pad??

 

[Photo Engineer]

I have never heard of a fire being caused by Glacial Acetic Acid in all of my years in chemistry!

PE

 

[cliveh]

I dilute acetic acid indicator concentrate 1:50. Still yellowish but harmless.

 

[Xmas]

You may be right, but what should one do if it's the only form sold by Formulary? A Saturn V without payload couldn't bridge the gap between theory and practice sometimes ...

I get white wine vinegar from grocery shop.

My photo shop does not stock it and would not ship if it did... it used to.
http://shop.silverprint.co.uk/Raw-Chemicals/products/461/