33 Hazardous Materials in Prosthetics and Orthotics

by Ramona M. Okumura, CP, LP, Senior Lecturer

Introduction
Materials choices affect you, your coworkers, and the patients. Our exposure to the material is short term, however, our patients are exposed over a longer period of time.  Patients can over time have reactions to the residuals in the materials or the materials themselves.

Forms of Risk
Throughout the fabrication process, workers are exposed to off gassing and particulates of the materials while drying, when heated, while setting up, when sanded and off gassing of the finished material (dust, gases and fumes).  Most are merely irritants to your body’s filter systems in your eyes and respiratory system.  The hazards may present themselves as organic threats to the liver or kidneys, which try to eliminate these toxins from the body. Some affect the brain if they reach sufficient levels in the body.  Some are also classified as carcinogens, which over time can cause tumors, or teratogens with can cause birth defects in the developing fetus.  The insidious ones can cause sensitization over time to the materials, which result in dangerous bodily reactions such as respiratory complications and in the worst case, require that you leave the profession.

Prevention

1. Use the least toxic material that will meet the functional needs.
2. Equip the workplace to minimize employee/patient exposure to the hazardous elements of the chemicals or particulates.
3. Receive proper training and use personal protective equipment for protection against the by products not evacuated by the workplace equipment.

Personal knowledge of materials
This is your responsibility and the information you need should be available in your workplace.  Manufacturers of materials must be able to present a “Material Safety Data Sheet” or “MSDS” which itemizes the hazards, if any, and suggestions for personal protection for safe use of the materials as well as recommendations for spills and fires.

At the UW, the department of Environmental Health and Safety, EH&S (ehs.washington.edu), has set up MyChem. (Link to “MyChem” through UW: https://mychem.ehs.washington.edu/Links to an external site.  This lists the hazardous chemicals stored at the university by location or room.  The MSDS should be read prior to using the material.

Nonchemical Particulate Exposures
MyChem does not monitor the other materials such as the plastics and reinforcement materials used.  EH&S does provide training in safe practices to minimize exposures to various hazards and hazardous fabrication processes.  Plastics that are heated during the typical P&O fabrication process can off gas harmful gases even when heated properly and some when overheated are quite toxic.  Grinding and sanding from trimming out and finishing trimlines make particulates that can be harmful when inhaled or can damage the machinery.  Soldering and welding create other dangerous fumes from exposure to heavy metals from the extreme heat.

Examples of hazardous exposure

Promoters in solids:  No reactions are 100%.  Most often, promoters are the most hazardous elements of a material using 2-part use such as laminates or foams or glues.  A specific example is the promoter that changes liquid silicone to a more solid form.  The residual promoters can cause skin reactions when in contact with a patients skin.  Some patients may become sensitized when others might not.

• Safe use might include choosing a gel product that is the most hypoallergenic if the prescription recommendation requires a gel product.
• Do a skin test prior to fitting the patient with the product.
• Educate the patient about proper hygiene and signs of sensitization to a product.

Respiratory Carcinogens:  Carbon fiber particulates inhaled into the lungs cause “black lung” and pulmonary fibrosis and fiberglass dust can cause lumps to be formed in the lung tissue, as the dust is difficult to move out of the lungs.

• Safe practices should include knowing when use of these materials are required for function and if necessary, keeping them out of areas that will be sanded or ground.
• If sanding is necessary, the tools should have a good evacuation system and residual particulates from the sanding should be vacuumed up not blown off with using compressed air.
• Personal protection should be used properly.
• The machines will need maintenance as carbon fibers are conductors and can interfere with the function of electric motors.

Teratogens:  Methyl ethyl Ketone is commonly used as a thinner in glues as it “melts” the surface of many plastics allowing a better bond.  It is a known teratogen most often affecting oral development of a fetus in the animal models.

• Safe practices should include researching a new product by reviewing the MSDS and reading the product labeling prior to purchase.  Investigate less hazardous alternatives that might meet the functional goals.
• If selected, ensure that everyone is educated about the presence of the material so everyone can protect ones self from exposure.  Often many employees are working around the product, even though they are not directly using it.  Women who are of childbearing age and are planning to get pregnant should avoid exposure when possible.

Sensitizers:  Overtime, depending on a person’s predisposition and collective exposure, some individuals can become sensitized to common P&O materials.  Components of epoxy resin, siegleharz, and other materials can include sensitizers.  The one with the most impact is sensitization to the Isocyanates present in Urethane products, which include 2 part foams and synthetic casting materials.  MDI (Diphenylmethane diisocyanate) and TDI (Toluene diisocyanate) are common in the promoters for urethane foam promoters.  MDI is the least sensitizing, however both products are sensitizers.  Reactions to exposure cause closing of the airway causing difficulty breathing.  Unfortunately, once sensitized, not even personal half face respirators can prevent reactions as even the minimal particulates that get through a respirator can elicit a reaction.  Particulates carried in the clothing of people working around the isocyanates can also become airborne and cause reactions in other areas of the workplace for sensitized persons. .  This sensitization can require leaving the profession and may impact exposure outside the workplace, as urethane foam products are ubiquitous.  The residual promoters are present in most urethane foam products and heating or heat modifying around them can release the free molecules.  Heating up the foam during the sanding and shaping process releases unused molecules.

• Minimize the quantity of foam used in the fabrication process if it is necessary to use it.
• Use it properly according to the directions.  (There was previously an “old school” practice to add water or saliva into the mixing process to increase the volume of the finished foam.)
• Use sharp sanding materials to minimize the heat formed when sanding.
• Let the machine do the work; do not put extreme pressure on the sanding media.
• Use machines with good dust collection systems.
• Wear proper protective gear to minimize your exposure to the errant dust and off gassed substances.

Less commonly used chemicals and materials

Chemical Carcinogens:  Some are suspected to be carcinogens; others are “known” carcinogens.  They are often present in thinners for paint products or thinners.  Methylene Chloride was previously very prevalent in P&O used as a thinner.  Most commonly used P&O products no longer contain it, because safer alternatives have been developed that function adequately.

• Safe practices should include researching a new product by reviewing the MSDS and reading the product labeling prior to purchase.  Investigate less hazardous alternatives that might meet the functional goals.
• If selected, ensure that everyone is educated about the presence of the material so everyone can protect himself or herself from exposure as often many employees are working around the product, even though they are not directly using it.

Off gassing during heat processes:  Kydex is an uncommon plastic used in P&O.  When overheated during a molding process or a post fitting modification process, it can off gas hydrogen chloride gas, which is a temporary irritant in small concentrations and can cause respiratory harm in larger concentrations.

• Safe use considerations might be to use care in monitoring the molding temperature or substitute a less harmful plastic.
• The oven should be vented to evacuate and/or filter errant fumes directly out of the workplace.
• When heat modifying it, do so in an area with good evacuation or ventilation.
• When grinding or sanding it, do not let it get too hot by using sharp sanding cones and applying light pressure against the tool.
• Lastly, wear a respirator that is rated to filter out the HCl.

Additional references:

If you would like to know more about the actual chemicals and materials listed, OSHA, the Occupational Safety and Health Administration has published hazard descriptions and exposure guidelines for most chemicals and hazardous materials, such as Hazardous Chemicals Desk Reference by Richard J Lewis.  The limits are not necessarily determined by research on humans, though some are retrospectively set after exposure and accidents in which humans were exposed.  Each chemical is assessed individually usually measured over a 40 hr workweek.  The typical use of materials in P&O is not set up this way, but rather exhibits very minimal amounts used for very short periods of time having many different exposures–a veritable chemical soup.  There are probably no studies involving the interaction of the chemicals we use, even though the same bodily organs are being taxed to manage the exposure.  Most valuable to the P&O industry is the description of the hazards as organic toxins to which organs and categorizing hazards as irritants, carcinogens or teratogens and the parts of the body or developing fetus affected.  Some states such as California have strict limits on quantity and transport of materials containing these chemicals.

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