search  current discussion  categories  safety - toxicity 

salt firings or other toxic / harmful fumes etc

updated mon 31 mar 97


Fay & Ralph Loewenthal on sun 16 mar 97

Dear Gil et al, the point of my original warning was that
whatever advice or recipe is given on Clayart, any
potential hazard has to be warned against. One cannot
assume anything. No matter how long or short a period
one has been a potter, even 50 years, one can still learn.
If the student said that while being close to a salt firing
taking place their lungs hurt, it means there is something
harmful in the fumes. That is a fact no matter what the
chemical formulae prove to the contrary. Therefore it is,
IMHO, incumbent upon the teacher to ensure that all
safety measures are known by that teacher and the
students. It is criminal for any person teaching ceramics
to plead ignorance of the health hazards. In law
ignorance is no excuse. I am waiting to see the first law
suit against a pottery teacher for lung damage or
sillicosis or whatever.
I know HCL is in one's stomach, but do you know what
happens to you when it is let lose on unprotected parts
of your body. I have the unfortunate problem of a hiatus
hernia, with the accompanying reflux up oesophagus. I
had occasion, after one particularly bad "Acid Attack" to
vomit blood. I was frightened out of my wits and phoned
the doctor at midnight. He replied that so long as the
blood was not red then it was OK. If that is what HCL
can do to my oesophagus then I would hate to see what
it can do to my lungs. I trust you have all heard of ulcers,
bleeding and otherwise. Do you realise that it if you get
any liquid in your lungs it is bad. Any HCL can cause a
lot of damage.
Please, I emphasise again, whatever advice, recipies,
etc you give, please point out any potential health
hazards. Rather err on the side of caution. I know I
would rather be a healthy potter with a lousy glaze than
a sick potter with the most beautiful glaze in the world.
Enjoy NCECA you lucky folks who can get there, from a
rather envious Ralph in PE SA.

Gavin Stairs on mon 17 mar 97

Hi All,

I would like to make a distinction concerning the type of hazard posed by
salt vs. things like lead and barium.

The main concern in salt firing is the release of corrosives, namely HCl and
excess salt, plus the heat of the gas/mist. In soda firing, there is a
corresponding, but slight, risk from NaOH. These are acute risks, meaning
that the injury occurs promptly on exposure. Monona's testimony concerning
the acrid cloud which chased her down the hill was of this type. The
recently postulated case of the student who complains of a pain in his/her
lungs is another. These are similar to the result of aspirating stomach
contents into the lungs: lung tissue damage, edema, suppuration leading to
insufficiency. etc. No one should minimize the severity of these possible
injuries. There is a possibility of acute trauma leading to incapacity or
even death, and there is the possibility of long term reduction of lung or
mucosa functionality. That much is definitely true.

However, it is easy to overstate these risks. The emissions are visible,
and the indicator smells definite, and do not saturate, so the warnings
before grave danger occurs are unmistakable and alarming. The message is
GET OUT!, and it is an unusual person who does not heed such a message.
Monona ran from her cloud, and did not suffer any serious injury (or so I
assume). There is an equivalent, though lesser, risk in many other
combustion emissions, but we do not consider them to be immanent dangers.
We would not consider breathing the exhaust from an automobile. That is
thoroughly unpleasant, and may lead to death by asphyxiation. There are
corrosives in that smoke too, which may leave the throat raw and inflamed,
etc. Wood smoke, while pleasant to some of us in slight concentrations, is
definitely noxious and toxic to some degree in high concentrations. If you
have ever seen the inside of a smoke house, and are able to make the
connection to smoking cigarettes, you may well give them up.

But we are already drifting into the second kind of risk: the chronic,
delayed or deferred risk. The risk of smoking tobacco is one such. Heavy
metal poisons, and persistent organochloride and other toxins are another.
In these, the toxic agent may be introduced in small concentrations, but can
build up over long, chronic exposure, or may persist in active form for a
long time, so that the toxic activity, though perhaps slight initially, may
grow and become dangerous over time.

The first kind of risk is like the risk of being run over in an
intersection. The second risk is like the risk of sunburn on an overcast
day. In the first case, the risk is evident, and localized: with vigilance
and the example of others, it is possible to live with such a risk for a
lifetime with no harmful effects. However, let you guard down, and it can
get you in an instant. The second case is more subtle. You may not even be
aware that it is happening until it is too late. Even if you have been
forewarned, subtle differences in the exposure (for the sunburn example;
latitude, altitude, time of year, snow, water, etc.) may alter the degree of
danger substantially, changing a tolerable situation into one of
considerable danger.

We are now more aware of the danger of cigarette smoking and sunbathing, yet
we still live our lives bathed in both smoke and sunlight. We must all
understand that there is some degree of risk in all exposures, and there is
no such thing as risk free. We live with automobiles every day, yet they
are our leading killers.

To the best of my understanding, the dangers of salt kiln operation are
mainly of the acute, avoidable variety. I also think that the possibility
of very high concentration clouds of corrosives in a pottery kiln is slight.
If there may be concentrations of 50ppm HCl in a flue (one reported
measurement), and the allowable limit is 5ppm, that requires a dilution of
10:1. At any reasonable distance from the kiln flue, I do not consider this
to be abnormal. That doesn't mean that one should attempt to test the
hypothesis by standing in the cloud. That also doesn't account for the
additional risk from NaCl in the mist cloud. I consider that it may argue
for a higher than normal flue/stack/chimney, and that dilution of the gas
flue stream by air induction might be useful. Different measures may and
should apply to industrial scale operations. I am not addressing them here.

Environmental effects I have alluded to in other notes. The dominant
emission of environmental consequence from any fuel fired kiln is combustion
products. There may be a slight increased risk of emission of heavy metals
and organochlorides, but I have no evidence of this.

I don't live in the high litigation risk region, so I can't comment of the
risk of being sued for operating or instructing the use of a salt kiln. I
would think that a suitable, plain-language declaration of the probable
dangers, with a waiver, should be sufficient, but that won't protect against
frivolous or speculative litigation.

Monona has referred to an extensive literature, which I confess I have not
read. Not everyone has access to an extensive research library, and fewer
still have the skill to use one. I do, and I will make the attempt,
although I will have to do it during my "free" time. Perhaps at some future
date, those of us who are interested can do this work and make the results
available to the potting community through their chosen publications, and on
the web. I hope so, and then perhaps Monona will not have to bemoan the
abysmal lack of knowledge of her poor colleagues.