Ammonia-dissolved pre-vulcanized latex is of everyday usage to make flexible
moulds and peelable protections. In this last case, it is mainly
used in ceramic decoration, to carry out resists in the application
of engobes, glazes or colorants.
The liquid latex solution is applied with a brush to the dry
area to protect for less than 15 minutes, then becomes rubbery.
After application and drying of a layer of engobe, colorant
or glaze, one withdraws the solidified latex film by gently
separating it from the ceramic object with a pair of small pliers
or a blade. The elasticity of latex facilitates the removal
and generally the pieces are withdrawn as a whole and in one
go. The parts protected by latex are free of engobe, colorant
or glaze.
This technique is particularly appreciated when products of
very different colors must be superimposed while being well
delimited, or if the color of the ceramic object or shard must
appear non-colored in the case of application by spraying or
dipping.
Attention - if the porosity of the object is too important
the layer of latex will be difficult to withdraw. Always make
a test before launching into it.
It is necessary to proceed in a well ventilated room to avoid
breathing ammonia vapor. In the case of a daily and long use
of this technique, it will be necessary to consider means of
suitable protection and ventilation. Brushes must be washed
between each application and drying of latex.
[Editor's note: in my experience, latex
brushes cannot be properly washed. They should only be used
for that purpose.]
© Article by Smart.Conseil / July 2003
Gary Molitor made the following
observations in regards to using Liquid latex resist: "The
product ceramists should be using is prevulcanised liquid latex
rubber (e.g. Douglas & Sturgess's "LATEX NUMBER 10
WHITE" - http://artstuf.com/flexmold.html).
This product has a very light odor. I use this same material
in my work. Also, I work for a paint manufacturer where we make
latex paint.
Ammonia is used to stabilize the pH. Breathing pure ammonia
is quite harmful and our guys wear chemical respirators as a
safety precaution. However, the amount of ammonia one breathes
as a result of using small amounts of latex rubber is very small."
Ammonia
by Edouard Bastarache
Molecular Formula: H3N
Uses and sources of emission:
Ammonia is used mainly in the manufacture of fertilizers and
of many other products in a very large variety of fields. It
is used as a cooling gas in the industry of industrial refrigeration.
One can also find it as a cooling gas in arenas, and as an air
contaminant in breeding settings (examples: pigsties, henhouses).
Ammonia is also found as liquid ammonia which is in fact gaseous
ammonia dissolved in water (solution of ammonia at 28% or ammonia
at 28%).
Hygiene and Safety:
I-Appearance: Ammonia is a colorless gas with a characteristic
and prickly odor. It is a suffocating gas at high concentration.
II-Exposure Characteristics: Exposure to ammonia in
the work environment occurs mainly as a gas, because of its
very low boiling point and its great volatility. The exposure
to liquefied ammonia generates a significant gas concentration
because of its very low boiling point and its high volatility.
The exposure to liquefied ammonia is increasingly frequent because
of its use in refrigeration systems. Moreover, concentrated
aqueous ammonia solutions can emit ammonia vapors at high levels
of concentration.
III-Exposure to the gas: The prickly odor characteristic
of ammonia can be detected at 16,7 ppm, which is in the same
order of magnitude as the VEMP, 25 ppm or 17 mg/m³; at
a VECD of 35 ppm or 24 mg/m³; at an IDLH value of 300 ppm
or 209 mg/m³ and at the lower limit of explosiveness at
13 % or 13 000 ppm; so that it can be a sign of adequate warning
before the exposure becomes dangerous. An olfactive fatigue
occurs following repeated exposures, therefore the odor cannot
be an adequate sign of warning to an exposure exceeding the
VEMP or the VECD. However, the olfactive threshold is sufficiently
low to prevent a situation of IDLH.
IV-Exposure to the liquid: Ammonia is a liquid at -33,35°C.
In the liquid state, it is thus necessary to take into account
all the aspects which comprise the exposure to a liquid at low
temperature. Immediately dangerous to life or health (IDLH):
300 ppm
V-Inflammability and explosiveness: A-Inflammability:
The fire hazard caused by ammonia is relatively low, it must
be put in contact with materials or a surface having a temperature
of 651°C before igniting itself However the presence of
oil or other combustible materials can increase the fire hazard
by lowering this temperature of autoignition. Ammonia can ignite
in contact with strong oxidants. B-Explosiveness: Ammonia
requires a concentration of at least 15% and the presence of
a source of ignition to explode. Ammonia can explode in contact
with strong oxidants.
Toxicology:
I-Toxicokinetics: A-Absorbtion Ammonia is mainly
absorbed by the respiratory tract. Absorption by other routes
is negligeable. Du ring a short-time exposure (up to 2 minutes)
at concentrations varying between 57 and 500 ppm, 83 à
92 % of the inhaled dose is retained in the respiratory tract
(mouth, lungs, etc.), among volunteers. Following longer exposures
(30 minutes) among seven (7) volunteers exposed at 500 ppm,
it has been reported that the retention of ammonia in the mucous
membranes of the nasopharynx diminishes to 23 % when equilibrium
is achieved (after10 à 27 minutes). B-Distribution:
The few data available in man suggest that only small amounts
are absorbed into the blood circulation. Blood ammonia is distributed
throughout the body where it plays an important role the synthesis
of proteins and in maintaining the acid-base equilibrium. C-Metabolism:
Ammonia is an essential constituent of the human body. It is
produced during digestion and rapidly metabolized into glutamine
and urea, mainly by the liver. D-Excretion: The major
part of ammonia (70-80%) dissolved in the mucous membranes of
the upper respiratory tract was excreted unchanged in the expired
air following inhalation at 500 ppm during 10 to 27 minutes
by volunteers. Ammonia absorbed by the body is excreted by the
kidneys as urea and ammonia compounds. Less than 1% of the 4
grams of ammonia produced daily by the intestinal tract is excreted
in the feces. A certain amount may also be excreted in sweat.
II-Acute Effects: Irritation and corrosion:Ammonia being
absorbed very little by the body, its effects are limited to
its irritating and corroding capacity to the eyes, the skin
and the respiratory tract. Ammonia as a gas is irritating and
corrosive to the skin, the eyes and the higher respiratory tract
(nose and throat). The severity of symptoms may vary according
to the conditions of exposure (duration of contact, concentration
of the product, etc). The first signs of exposure are discomfort,
dry nose, watering and a burning sensation in the eyes. Exposure
to high concentrations may cause irritation of the skin, damage
to the cornea, cough, pain in the chest, respiratory problems
(dyspnea i.e. shortness of breath) and suffocation. In severe
cases, one observes laryngeal oedema which may evolve to pulmonary
oedema and death by asphyxiation. The symptoms of pulmonary
oedema (mainly cough and other respiratory difficulties) often
appear after a delay which may go up to 48 hours. Physical exertion
may worsen these symptoms. Rest and medical surveillance are
consequently essential. Accidental exposure to high concentrations
can also cause a bronchial irritation syndrome (RADS, Reactive
Airways Dysfunction Syndrome, an asthma-like condition or asthma
without a latency period). Very high concentrations may lead
to corrosion of the skin, eyes and upper respiratory tract.
Contact with liquefied ammonia gas can cause frostbites as well
as corrosion of the eyes and the skin, following a direct contact.
III-Dose-effects relationship:
| Concentration in (ppm) |
Probable effects following acute exposure
|
| 17 |
Olfactory detection limit. |
| 20-25 |
Discomfort among non-accustomed workers. |
| 25 (VEMP) |
(Quebec's time weight average exposure limit.) |
| 32-50 (5 mn) |
Nose dryness, slight irritation of the nose and
throat. |
| 35 (VECD) |
(Quebec's short term exposure limit.) |
| 135 (5 mn) |
Eye irritation, watering. Irritation of nose and
throat. |
| 300 IDLH |
" Immediately dangerous to life or health " |
| 500 (30 mn) |
Severe irritation of the respiratory tract. |
| 2000-3000 |
Severe cough. |
| 2500-7000 (30 mn) |
Respiratory troubles, bronchospasm, pulmonary oedema.
|
| 5000-10.000 (30 mn) |
Rapid death by suffocation or by accumulation of
fluids in the lungs. |
IV-Chronic effects : Repeated or prolonged exposure
can generate a certain tolerance, i.e. the irritating odor and
effects will be felt at higher concentrations.
V-Sensitization : Available data do not show that ammonia
can cause cutaneous or respiratory sensitization Justification
of effects : Some reports mention cutaneous eruption (urticaria)
following exposure to the vapors of ammonia and asthma-like
reactions following exposure to concentrations between 8 to
15 ppm of ammonia. However, these reports do not make it possible
to link these effects with a mechanism of allergic nature.
VI-Effects on development : No data concerning an effect
on the development was found in the consulted documentary sources
Justification of effects : Ammonia is produced by the body.
It is also an essential constituent for the normal development
of human beings. An exposure in the work environment is not
very likely to lead to an increase in the blood ammonia level
and thus, it does not represent a hazard to development.
VII-Effects on reproduction : No data concerning the
effects on reproduction was found in the consulted documentary
sources. Justification of effects : Ammonia is normally produced
by the body. It is also an essential constituent for the normal
development of human beings. An exposure in the work environment
is not very likely to lead to an increase in the blood ammonia
level and thus, it does not represent a hazard for reproduction.
VIII-Effects on breast milk : It is detected in human
mother's milk. Justification of effects : Ammonia is a natural
component of this milk.
IX-Cancinogenic effects : There was no data concerning
a carcinogenic effect found in the consulted documentary sources.
X-Mutagenic effects : The data do not make it possible
to make an adequate evaluation of the mutagenic effect. Justification
of effects : A study mentions a light increase in chromosomal
aberrations and sister chromatid exchanges in workers of a manufacture
of artificial fertilizers simultaneously exposed to several
chemicals among which ammonia.
First Aid :
I-Inhalation : In the event of inhalation of gas, bring
the worker in a ventilated place and place him in semi-seated
position. If he does not breathe, give him artificial respiration.
In the event of respiratory difficulties, give him oxygen. Transfer
immediately him to the nearest medical emergency department.
The symptoms of pulmonary oedema may appear after a delay of
several hours and are worsened by physical exertion. Rest and
medical supervision are consequently essential.
II-Contact with eyes : Rinse the eyes copiously with
water for at least 20 minutes. See a doctor.
III-Contact with skin : Quickly withdraw contaminated
clothing by using suitable gloves. Abundantly rinse skin with
water. See a doctor. In the event of a frostbite, apply lukewarm
water, rinse abundantly and see a doctor.
Prevention : When engineering
measures and modifications of working methods are not sufficient
enough to reduce the exposure to this chemical, the wearing
of individual protection equipment may be necessary. These protection
gears must be in conformity with regulation. I-Respiratory
tract : Wear a respiratory protection apparatus if the
concentration in the work environment is higher than VEMP (25
ppm or 17 mg/m³) or than the VECD (35 ppm or 24 mg/m³).
II-Skin : Wear skin protection. The selection of skin
protection equipment depends on the nature of the work to be
carried out. III-Eyes : Wear protection for the eyes
if there is a risk of splashes. The selection of ocular protection
depends on the nature of the work to carry out and, if it is
necessary, on the type of apparatus of respiratory protection
used. References : 1-CSST-Quebec, Repertoire Toxicologique,
2003 2-Toxicologie Industrielle et Intoxications Professionnelles,
Lauwerys R. last edition. 3-Sax's Dangerous Properties
of Industrial Materials, Lewis C., last edition. 4-Clinical
Environmental Health and Toxic Exposures, Sullivan J.B and Krieger
G.R., last edition.
