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The
Toxicology of Modelling
by
Frank Mitchell, D.O., M.P.H.
(IPMS/USA #789)
Toxicology:
The study of the adverse effects of chemical agents on
biologic systems .
In
modelling, we use a lot of what are often termed hazardous
materials. While the potential for harmful effects from these
substances is real, there is also a lot of information
floating around out there that is not accurate or is very out
of date. In this presentation, I will try to correct some of
that while providing information you can use to protect
yourself and your family.
First things first:
Dust Mask:
·
The simple paper mask found in any hardware
store.
·
Very effective against particles (dust) of the
sort generated by sanding wood, “resin dust”, etc.
·
Totally ineffective against chemical
fumes, such as superglue reactions, solvents in paints, etc.
·
Become ineffective after several hours
continuous use due to moisture from the breath, and should
therefore be replaced on a frequent basis.
Air-Purifying Respirator
·
Uses replaceable canisters that are typically
mounted on a half-face mask generally made of rubber.
·
Does not cover the eyes.
·
May have one large canister, or two smaller
ones; both equally effective.
·
Canisters should be changed periodically; for
modeling purposes, probably every couple of months is
sufficient.
·
Use canisters labeled for organic vapor.
Perhaps
the most important thing about respirators in modeling is
remembering to wear them. It is very easy to think that a
job will take only a minute, so why bother to get the thing
out? Wrong Thinking.
If you wear glasses,
make sure that the lenses are impact-resistant plastic. If you
do not, then buy a pair of safety glasses from your hardware
store and use them whenever you are doing something involving
power tools or some material that could splash. The glasses
are very inexpensive and could save your sight.
Now then, on to the substances that
we use:
Styrene
·
Generally polystyrene, a polymer of
liquid styrene.
·
Innocuous; some “nuisance” dust is produced
by sanding, but particles are generally too large to be taken
into the lower respiratory tract (the trachea and lungs);
machine-sanding can produce smaller sizes.
·
In general, about only possibility for
toxicological harm is burning; fumes can be irritating.
Vinyl
·
Often used for aftermarket and home molding of
canopies and other clear parts.
·
Essentially non-toxic.
'White'
Glues
·
Originally produced from animal parts (you
don’t want to know).
·
Today, are primarily water soluble emulsions of
polyvinyl acetate; may also contain small amounts of other
components to speed drying, produce different colors, etc.
·
Essentially non-toxic.
Solvent
Adhesives
·
Most are methylene dichloride, ethylene
dichloride, methyl ethyl ketone, toluene, or similar
compounds; they work by dissolving styrene plastic and
therefore weld the parts together.
·
Widely used in industry for many purposes.
·
Acute toxicologic effects generally due to
inhalation; first symptoms arise from involvement of the
central nervous system and are similar to alcohol ingestion.
·
May be absorbed through the skin and cause
de-fatting (drying); cracks and rash can occur; with
quantities typically used in modeling, these effects are
generally not seen.
·
In the eye, liberal washing (several minutes at
least), should suffice.
·
If more than a small drop, see a physician, but
eye toxicity not high.
·
Commercial tube and liquid cements may also
contain some solvents; also often have thickeners, retarders
and other substances added to slow drying and to discourage
glue 'sniffing'.
·
Always better to use the solvents in small
amounts; limits the possible health effects, and also serves
to decrease the number of parts that can be melted. I keep an
old decal solution bottle on the bench and fill it from the
larger container.
These
solvents are rapidly metabolized and eliminated by the body,
and they do not accumulate over time; thus no long-term
effects would be expected to occur. Although the potential
carcinogenic effects of these solvents have been widely
studied, there is no reason to be concerned if used as most
modelers would employ them. There is NO evidence whatever
that MEK or toluene, for example, causes cancer in
humans.
Cyanoacrylate
Adhesives ('superglues', CA)
·
Originally developed during World War II; widely
marketed in the late 1950's.
·
Used extensively in industry and in medicine for
repairing small holes in the eye and in binding metal
replacements (such as hip joints) to the surrounding bone.
·
Cyanoacrylates have many uses in modeling, and
in many formulations (very thin liquid, gap-filling, gel).
·
Cyanoacrylates can cause mechanical or
chemical effects.
Mechanical:
·
Do not 'dry'; they polymerize (or cure)
instantly, but this slows as the glue ages.
·
Accelerators supply base (opposite of acid);
therefore, due to the slightly basic nature of the skin, they
work very well for gluing fingers or other body parts
together.
Chemical:
·
Primary chemical effect of cyanoacrylates in
modeling is airway and eye irritation which can be intense
due to fume that is released during the curing process. Can
also cause more severe effects including permanent eye damage
and chemical asthma.
Handling
Cyanoacrylates:
·
Keep a supply of waxed paper handy; put a drop
on a small piece of the waxed paper and then apply the glue
with the eye of a needle or even a piece of wire that is stuck
into the eraser of an ordinary pencil. This system
allows only a small amount of the glue to be exposed. The CA
on the waxed paper will polymerize only very slowly so that it
will remain useable for rather long period of time. This
technique works well with either the thin or the thicker
gap‑filling forms of the adhesive. A side benefit of
this method is that it makes for neater models because it
allows for very precise placement of the glue and there is
less chance of glue going where you do not want it.
·
Keep a can of acetone nearby; it is the best
agent for removing CA from skin (or anywhere else).
·
DO NOT just pull stuck fingers apart. You will
almost certainly pull off at least one layer of skin and
severe injuries can result. Instead, apply the acetone
liberally and work the fingers apart.
·
When used on wood, cyanoacrylates can fume very
vigorously, so be especially careful when using it for this
purpose. The eye and nasal irritation can be severe.
·
The possibility for extreme irritation does not
end after the cyanoacrylates are cured. Cured cyanoacrylates
can produce significant fume when sanded—especially when
worked with a power tool.
If
you should get cyanoacrylate adhesives into the eyes, do not
waste time attempting to open them; immediately get to
medical care. Cyanoacrylate in the eye is a true medical
emergency and urgent care is mandatory.
In summary, the cyanoacrylate
adhesives are, in my view, among the most useful materials in
our tool boxes, but they are also, by far, the most dangerous.
Care must be exercised, or what is supposed to be a hobby can
produce unwanted and very serious adverse health effects.
Epoxy
Compounds
·
Composed of a number of different resins,
hardeners, diluents, etc., depending on the needs or products.
·
As adhesives, formulations may cure very quickly
to very slowly.
·
Often used today for casting individual parts or
entire kits. In this use, generally known by the generic term
“resin”.
·
Generally composed of two parts which are mixed
together in specific amounts; once combined, exothermic
(heat-releasing) chemical reactions cause the mixture to
harden.
·
It is the component parts, rather than the cured
material, that causes most of the problems related to epoxy
compounds.
·
The components are known to be sensitizers, that
is, they can sensitize the skin, lungs, and other organs so
that subsequent exposures can cause an increased reaction; the
response can occur after the first use, or after the
hundredth.
·
Therefore, care should be used while mixing the
parts together and until the substances have cured.
·
While many epoxies will say that they are cured
in 15 minutes, etc., care should still be taken for a
considerably longer period, even though they feel hardened.
·
When completely cured, essentially non-toxic in
a chemical sense.
·
On the skin, epoxies can also cause a
dermatitis, but that condition may or may not be related to
sensitization.
·
Can also cause eye damage; any incidents should
be seen by a physician as soon as possible. Most common way
into the eye: rubbing with an uncured epoxy-coated finger.
Sanding
cured resin produces particles which, for the most part are
too large to move into the lower parts of the respiratory
tract (trachea or lungs). These are termed “nuisance
dust”. However, a mask should always be used when sanding
these materials, particularly when using power tools which
can produce much smaller particles. They are usually cleared
within a short period of time, but it is obviously better
not to have them there in the first place. A simple
and inexpensive paper mask is sufficient, but should be
replaced frequently (maybe every 2-3 hours of use) as the
moisture from your breath eventually gets it wet. Always wet
sand if possible.
As with most other modeling
materials, the bottom line with epoxies is to use them in as
small quantities as necessary for the project. If large
amounts are required, then a better respirator and hand
protection (gloves) are in order.
The Basics:
·
All paints are mixtures of a number of
components.
·
They may include pigments, solvents (toluene,
xylene, lacquer thinners, etc.) carriers, dryers, stabilizers,
and whatever other components the manufacturer may choose to
include.
·
Whether the paint is labeled a lacquer or enamel
does not really matter; they differ chemically only in the
proportions of the various components.
·
Acrylic paints are often considered to be
non-toxic, BUT, the typical acrylic paint contains 2-6%
solvents (generally glycols and glycol ethers), plasticizers,
preservatives, and fungicides.
·
Some acrylic paints use water as a base while
others use alcohol.
·
Alcohol is not as volatile as the other
solvents, but can still produce some effects if the dose is
high enough.
It
must be apparent by now that paint formulation is a very
variable thing; the small bottles of paint we use and
take for granted contain a very sophisticated product, a
product that, regardless of what it may be called, is
capable of producing adverse health effects unless some
common sense precautions are employed.
·
When sprayed, the droplet/particles size of the
paint becomes small enough to be respirable; protection can
include an air-purifying respirator (NOT a dust mask), a paint
booth, or some other way of assuring that the amount of
inspired paint and paint components is minimized.
There
are several designs of small paint booths available. If the
booth is not operating correctly, the paint exposure
to the modeler can actually be much worse than it would be
if no booth were used because the paint is hitting the sides
and back of the booth and returning directly into the
painter’s breathing zone.
When using a paint booth:
·
Filters must be cleaned on a regular basis and
any fans connected to the booth need to be checked for correct
operation.
·
Make sure that the exhaust is located so that
the emissions are not being re-introduced through a nearby
window or door.
Even without a booth, there are
techniques you can use to lessen the amount of paint
emissions; some are both simple and inexpensive.
·
First and foremost, wear a proper canister
respirator.
·
If possible, spray in front of a window that can
be opened.
·
Place an ordinary oscillating fan behind you.
This will push the emissions away from your breathing zone and
through the window.
·
Try to spray in a room that does not contain a
cold air intake for the furnace/central air; if one is
present, just cut a piece of cardboard that can be taped over
the inlet when spraying.
·
Closing outlet vents can seem counterintuitive
to keeping emissions from the rest of the home, but when the
fan is not on, the emissions can move through them.
·
Close the door of the room while painting.
·
Keep the fan on, the window open, and the door
closed for a period of time, say 30 minutes after spraying is
complete.
Future
Sharp Edges
·
Knifes, saws, razor blades, etc. are
designed to cut, and they don’t care what they cut. A little
care can prevent accidents. As one example, put some clay on
the handle of the knife so that it can’t roll around.
Power Tools
·
Extremely useful; I have three on my workbench
and use them every day.
·
Always consider the use of a paper mask and eye
protection.
·
Remember that the speed of the rotating bit will
generate particles that are smaller and will travel further.
·
Most of the tools I have seen rotate so that
they throw the particles directly at the user’s breathing
zone; thus, a dust mask can be very useful.
·
Be particularly careful when dealing with brass
or other metals since they can generate small pieces that can
produce eye damage.
·
Use caution when using thin cut-off disc to do
work on thick or hard materials because the discs themselves
can shatter and throw pieces some distance. I try not to
watch the cut from an angle, not at the direct plane of the
rotating disc; the odds would therefore be less that I would
get something in the eye
Wood
·
A paper mask provides protection, and can also
give comfort if you are annoyed by wood dust. Remember when
using cyanoacrylates on wood that it can bubble and send small
droplets a considerable distance, and the fume even further.
Soldering
Solder may contain
lead (although this has been phased out of most solders
today) and other heavy metals such as cadmium, zinc, etc.
·
Fluxes contain resins, binders, and other
chemicals that allow the metal to bond.
·
All these things can produce fumes which are
capable of causing short-term symptoms that are somewhat
flu-like.
·
At the very least, all soldering should be done
in a well-ventilated area.
Decal
Setting Solutions
·
Decal setting solutions generally contain acetic
acid or alcohol. They should not be of concern.
Summary
As
hobbies go, modelling is not one that most people would
consider dangerous. However, there are potential problems
that can arise if the materials that we use are not treated
with some respect. For the most part, what is needed is some
common sense and caution in the way we do things. Where
chemicals are concerned, whether in the workplace, at home,
or in our hobbies, familiarity definitely breeds some
contempt. Therefore, it really takes a little mental effort
to remember that these materials can cause problems; don’t
let those problems happen to you.
Copyright © 2002 by Frank
Mitchell
On 15 Oct 2006 Mike
Sloan wrote in to us with the following additional
information:
Good
Day
I
was reading the section on modelling safety, in particular the
section dealing with respirators. If I may add a couple of
points to this:
-
in
wearing an air-purifying respirator, they must be
properly fit-tested to the person wearing it. Most, if not
all, canister respirators come in three sizes. If the
respirator is not fit-tested to the wearer , it probably
will be ineffective. Also,
-
one
must have the proper filters for the application being
used. When wearing a respirator, the person's face must be
clean shaven. Stubble or a beard will render the
respirator ineffective.
-
Finally,
as a side note, the wearer must, each time he uses the
respirator, check to make sure it is properly sealed to
his face; no air leaks around the respirator, and clean it
after every use, then store it in a clean dry place.. With
spray painting and airbrushing, a respirator may the
most important piece of equipment a modeller should have,
next to a spray booth
Also
the chemical toluene is a toxic chemical which with long term
exposure may affect the soft tissue in a person's body such as
your kidneys and liver and also affect your white blood
cell count and bone marrow. All in all it is not a safe
chemical to be exposed to. It is usually found in certain
paints and thinners and if possible should be avoided
Thanks,
Mike
Sloan
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