[alt-photo] Interesting notes on chemical safety from one who clearly knows a thing or three on the topic

[Judy Seigel]

I was e-mailing with Andras Ssgor of Budapest, Hungary, who had just 
acquired the nine of Post-Factory, when, in response to one of its 
articles, he addressed some issues of safety in the process involved. 
I found his descriptions so awesomely beyond the familiar (at least to 
me), yet so commanding of respect (plus, frankly, a certain amount of 
terror) that I asked permission to share his commentary with the list...

Permission gladly granted.

Judy

PS. I daresay I risk excoriation from whatshisname for adding that, as far 
as I can remember, Andras is the first P-F subscriber from Budapest, even 
-- if my stuttering memory serves, from Hungary -- and that I am totally 
thrilled about that...

(She ducks.)

PPS. Spelling errors, if any, are mine own.

----- Forwarded message ---------

from Andras Ssgor, Budapest, March 1, 2010:
============================================
Because of my profession, I was captured by the dispute on safety issues 
following the publication of DIY gold trichloride. You may skip this part, 
if you are not interested in my opinion about the dispute. I dare say that 
both the author and his opponents overemphasized some aspects and 
neglected others. I think gold trichloride can be prepared at home as 
described, BUT -- the safety of the procedure relies on the small 
quantity.

One should never try it on a larger scale. This is the major safety 
rule-of-thumb in the industry when hazardous chemical processes are 
conducted. The role of oxidable impurities [must not be] overlooked. There 
is a major hazard in pouring aqua regalis on easily oxidable materials. In 
this case, for instance, fatty matter could come with the old jewelry 
[used as source of gold], or the worker may have failed to keep his/her 
vessels clean, or, why not, the yellowish pieces of metal could turn out 
to be less precious (and more reactive ) alloys. All these cases may lead 
to heavy decomposition of HNO3, or even explosion, should the rule of 
working with the smallest quantity possible be broken.

Then the author misinterpreted the rule of pouring acid into water and not 
vice versa. He claimed he made the operation safely by dumping a 
relatively large amount of water into the acid mixture. Yes, in this case 
he is right -- if the speed of dumping is high enough. The relatively 
large amount of water will function as thermal ballast and not allow local 
overheating, which causes the spreading of acids. I do not recommend 
repeating the experiment with a few drops of water. It's true, also, that 
aqua regalis contains water, which makes the reaction mild, compared with, 
let's say, pure sulfuric acid, or oleum.

Then about hydrochloric acid, which is a gas: the solution can be made of 
37% max. At room temperature that is the maximum solubility of HCl gas in 
water. You also have quite a large amount of water in system, which 
improves safety, diminishing the heat effect of adding more water. This 
acts as thermal inertia for overheating, because evaporation of water 
drains a lot of thermic energy from the system. Water has a high latent 
evaporation energy.

But there is NO safe ventilation for this operation. Exhausting the fumes 
from one place means that the hazard is simply transferred to another 
place. Industrial-strength solution requires ventilation AND 
neutralization/adsorbtion/absorbtion. Mounting a scrubber/absorber on a 
ventilation duct is well beyond what an amateur darkroom can manage. When 
thinking about ventilation, one should think about where the exhausted air 
will end up -- with special concern for children, pets and neighbours. The 
same applies to waste, with special-- *very special* -- concern for 
substances sensitive to acids/bases. Volume/dilution will usually salvage 
the situation. Common uranium salt is not hazardous because of 
radioactivity (tho it could be ), but for acute toxic properties.

A general item not given enough consideration is storage of chemicals. 
Storage means usually a longer period of time in which anything can 
happen, as described in safety manuals.

But.. enough with these things. One can perform every photographic 
operation with enough safety margin - if he/she knows where the margins 
lie.
=============================================================

[These words were followed by a few very kind words for P-F, which I, as 
editor, would be churlish to omit, yet may risk aforementioned obloquy for 
quoting. (Obviously, even without uranium salt, one can live 
dangerously)]: 
=============================================================

Many, many thanks again for the World Journals, I already learnt a lot of 
technical details and a much deeper understanding of what photography 
means.

Best regards,
Andras