The Toxicology of Modelling

By Frank Mitchell

This article was first published on the Hyperscale website in August 2002. We feel it is such an important topic that we received permission from the author to reproduce it here. See the feedback at the end of the article for addendum notes sent in by interested readers.

By Frank Mitchell, D.O., M.P.H.
IPMS - USA #789

Toxicology: The study of the adverse effects of chemical agents on biologic systems.

Introduction

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these substances is real, there is also a lot of information floating around out there that is not accurate or is very out of date.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.

Respirators

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.

Safety Glasses

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.

Plastics

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.

Adhesives

"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 1950s.
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.

Paint

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.

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.

Miscellaneous

Future Floor Polish

One of the more useful products for modeling to appear in years.
A totally man-made mixture of several chemicals.
Essentially innocuous, but still should be used with some precaution since it was not designed for use in airbrushes and has never been tested for extreme exposures.

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).
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.

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.

Feedback

In October 2006 Mike Sloan sent us additional information:

I was reading the section on modelling safety, in particular the section dealing with respirators. I would like to add a couple of points to this:

Air-purifying respirators must be properly fit-tested on the person wearing it. Most, if not all, canister respirators come in three sizes. If the respirator does not fit properly, it probably will be ineffective.
The proper filters for the application must be used. When wearing a respirator, the person's face must be clean shaven. Stubble or a beard will render the respirator ineffective.
Each time the wearer uses the respirator, he must ensure that it is properly sealed to the face and there are no air leaks. The respirator should be cleaned after every use and should be stored in a clean and dry place.
When airbrushing, a respirator may be the most important piece of equipment a modeller should have, next to a spray booth.
Toluene is a toxic chemical which with long term exposure may impact the body's soft tissue such as your kidneys and liver. It can also affect your white blood cell count and bone marrow. 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.