© Dan T. Bradley, CJF

illustrated by Jonni Hill

published in ANVIL Magazine, February 1994

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What do the space shuttle, a boat in the America's Cup, an Indy-type race car, and horseshoeing have in common? All are fascinating types of industry, but the true common denominator is that each uses adhesives, fillers, sealers, and composites. The new age of horseshoeing has arrived, and the industry is not prepared. Glue-on shoes, hoof sealers, acrylics and polymers for bonding and filling; all are being used regularly, and for the most part, with good success. There is no doubt that these products are of immense value. However, there may be a substantial price to pay for improper, irresponsible, and unsafe use of these products. The price? Your health, and, quite possibly, your life.

I became curious, and then worried about the products I was using when I would feel ill after rebuilding a hoof wall or gluing shoes on. Around the late 1970s I began using various products and I never paid attention to my own exposure, nor did I use proper safety attire. As I started to research the ingredients in these products, I found I was working with some powerful - and potentially dangerous - chemicals. I also discovered that MSDS papers (Material Safety Data Sheet) are required by law to be available for each product. Manufacturers are required to assess the physical and health hazards associated with the substances they produce. The information must then be conveyed by labels and Material Safety Data Sheets. I requested MSDS papers from 22 companies; only seven responded. That is a shockingly low amount, considering the MSDS information is rightfully public knowledge. Here is a sample of what was on just one MSDS paper:

Acute effects of overexposure: Respiratory irritant. Skin irritant. May cause headaches and nausea.

Chronic effects of overexposure: May cause skin sensitization. May cause liver or kidney damage.

Medical conditions prone to aggravation by exposure: Respiratory allergies. Chronic diseases of the skin. Chronic diseases of the nose, throat, and respiratory tract. Chronic diseases of the eyes. Chronic diseases of the gastrointestinal tract.

WARNING: This product contains aniline and formaldehyde, recognized by the State of California to be a carcinogen and a reproductive toxicant.

As I continued my study, I found that there are three basic types of material in use:

  1. cyanoacrylate (superglue)
  2. methyl methacrylate (structural adhesive)
  3. polymers (urethane prepolymer)

It is important to note that the above chemical families share many of the same chemical components. For example, a superglue may contain an ingredient also found in an acrylic.

Cyanoacrylates, commonly known as superglues, are noted for their almost-instantaneous bonding ability. Superglues are so strong, so fast, that there is no time to deal with an unruly horse in an unsafe, dirty location. Therefore, it is imperative that the farrier be in control and prepared: The horse should be restrained or sedated, the location clean, dry, well ventilated. Safety glasses, gloves, and respirator should be worn.

Do not underestimate the bonding strength of superglues. The first time I used glue-on shoes on a foal, (circa 1984, back when you needed to be a rocket scientist to build the shoe), I thought I was well prepared: The foal was quiet and restrained, stall was rubber matted, clean, and well ventilated. The hooves were trimmed, smooth, and dry. The shoes had been constructed and fitted, and I was ready to glue. However, I had scarcely read the directions, ignored the suggestion to use the glue sparingly. I, of course thought more is better. Also, I neglected to wear gloves, glasses, and a respirator. Well, I ended up gluing the foal to the floor of the stall, which did not impress the owner and could have injured the foal. I also managed to glue my fingers together, which required rather painful skin tearing to separate them. I could only imagine what it would have been like to have glue splashed in my unprotected eyes! Lastly, I was nauseous, and plagued with headaches for days afterwards from breathing the fumes. Needless to say, I now follow the directions precisely, and use the proper safety precautions.

Although superglues have superior direct bonding strength, they have poor shear strength. Any imperfection in the bonding surfaces, along with any foreign matter on the hoof, must be avoided. Hooves must be clean, smooth, and dry. Acetone or lacquer thinner are good products to use, as they both clean and dry the hoof, but leave no residue of their own. However, neither product is safe to use without good ventilation and correct safety attire. Cyanoacrylates are excellent bonding agents, but they are not fillers. They are usually only .0004 inch in normal application. Therefore, if a filler is needed to smooth imperfections on a hoof before attempting to glue on a shoe, products made from polymers or methyl methacrylates will work.

And last, it is hard to imagine that anyone would want to make a superglue go off faster than it already does, but accelerators do exist and are obtainable. However, nowhere in the directions of any glue-on product does it mention the use of any glue other than the one provided. Follow the directions! Do not use other glues, do not mix glues, do not use accelerators! The result may be your own personal mushroom cloud of lethal cyanide gas.

Methyl methacrylates (commonly referred to as "acrylics"), are used for bonding shoes, filling and repairing hooves, and recently in attempts to glue shoes directly to the bottom of the foot without the use of tabs or cuffs. Acrylics belong to a diverse and complicated chemical family. There are literally thousands of acrylics, some formulated to bond to certain metals or plastics, and some designed to set at a certain degree of hardness. All acrylics give off fumes or vapors when curing, and they are toxic. The amount of time needed to cure varies - substantially longer than required for superglues - thus increasing the time that the farrier and any assistant are exposed to toxic vapors. Anyone, whether it be the owner, trainer, groom or apprentice who holds a horse during the application of an acrylic (or any of these products), should use proper safety attire. They should be informed of the potential risks in being exposed to the product. No veterinarian would allow anyone to assist in taking X-rays without providing lead-lined gloves and apron. No one should unwittingly be exposed to a toxic or hazardous substance without informed consent and proper protection. Once an acrylic has been applied and has cured, it must be sanded or rasped smooth to conform to the hoof. Care must be taken to not inhale any of the dust or particles. The effects are cumulative; particles stay in the lungs and, over time and repeated exposure, lead to reduced lung function, pneumonia and emphysema-like diseases. In addition, acrylics are pliable - almost liquid - before setting up, and care must be taken to deal with inevitable drips and spills, and to properly dispose of any extra or unused product.

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Polymers are used to glue on shoes, rebuild hooves, and as general fillers. Interestingly, the glue-on shoes that are routinely referred to as "plastic" are truly a polymer. Polymers have similar application and properties to acrylics, but they differ in that they require heat to bond and cure. Most directions recommend that the shoe (if using one), the polymer and the hoof be heated to a temperature of approximately 220 degrees! Obviously, it is easy to heat the shoe and the polymer (hair dryer or heat gun), but chasing a skittish Thoroughbred yearling around a box stall with a hair dryer and twenty feet of electric cord is sure to be a hair-raising experience! Seriously though, common sense dictates that the hoof just be warmed to a temperature that the horse will tolerate, and still allow the product to cure properly.

Compared with acrylics and superglues, the vapors released by curing polymers is somewhat less hazardous and toxic. However, the dust and the particulate matter release during the construction and shaping of polymer shoes, and, when smoothing a polymer patch on a hoof, pose a serious health risk. Grinding, sanding, and rasping all release dust and particles, which, if inhaled, are accumulative and can lead to Pneumoconilisis: a fibrous hardening of the lungs (a debilitating disease common among coal miners for generations).

Although relatively new to the farrier industry, polymers are proving to be versatile and indispensible products. Even newer, and possibly more promising, is the advent of the use of epoxies in farriery, but, like superglues, acrylics and polymers, the potential benefits of epoxies must be weighed against the possible health risks.

Undoubtedly education is the key. Without it, the industry is like a horse that ran off before the shoes were nailed on: not going to stay sound for very long. Manufacturers, distributors and retailers should provide informational literature and training programs for these new products. Unfortunately, this is the exception rather than the rule. Clinics, seminars and personal experience are all valuable sources of information, knowledge, and training. There is a good booklet distributed by the U.S. Department of Labor called Chemical Hazard Communication (OSHA 3084 revised). It contains excellent general information plus an OSHA Consultation Directory with telephone numbers for each state. The local library and telephone book are also good sources of information, as well.

Welcome to the 21st century - beam me up, Scottie.

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Glossary of Terms Relating to Toxics

ACGIH - American Conference of Governmental Industrial Hygienists. Determines standards of exposure to toxic and other harmful materials in the work area. Action Level - The exposure level at which certain OSHA regulations to protect employees take effect.

APR - Air Purifying Respirator

EPA - United States Environmental Protection Agency. Federal agency with environmental protection regulatory and enforcement authority.

Etiologic Agent - Organisms, substances or objects associated with the cause of disease or injury.

FDA - United States Food and Drug Administration.

HEPA - High Efficiency Particulate Absolute (filter).

HMAC - Hazardous Materials Advisory Council. Represents the hazardous materials industry.

HMIG - Hazardous Materials Identification Guide.

IDLH - Immediately Dangerous to Life and Health. Maximum concentration of a chemical in air to which one can be exposed without suffering irreversible health effects.

MSDS - Material Safety Data Sheet (OSHA Form 20). Contains descriptive information on hazardous chemicals under OSHA's Hazard Communication Standard. These data sheets also provide precautionary information on safe sheets as well as emergency and first-aid procedures.

NFPA Hazard Rating - Classification of a chemical.

NTP - National Toxicology Program

OSHA - Occupational Safety and Health Administration; oversees and regulates workplace health and safety. PPM - Parts per million.

STEL - Short-Term Exposure Limit. Maximum concentration for a continuous 15-minute period (maximum of four such periods per day, with 60 minutes minimum between exposure periods).

TLV - Threshold Limit Value. An estimate of the average safe airborne concentration that all workers may be repeatedly exposed to day after day without adverse effects.

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