Canadian Occupational Safety

FEBRUARY/MARCH 2018 25 many industries, includ- ing aerospace, automotive and military. In health care, 3D printing is used to produce medical prostheses as well as orthopedic and dental implants. Besides large commercial 3D print- ers, smaller desktop versions are becoming more commonplace as well, turning offices into small-scale manufacturing facilities. But studies have shown that commercially available printers produce large concentrations of ultra-fine emissions, some of them containing hazardous substances. Once inhaled, these par- ticles are deposited in the lungs, where they may cause inflammation, headaches and adverse cardio- vascular effects. Taking steps to reduce the indoor air pollution produced by 3D printers and follow- ing a health program can help maintain cleaner, healthier air for workers. A recent study conducted by the Centre for Research Expertise in Occupational Disease (CREOD) in Toronto concluded that regular exposure to 3D printers poses significant adverse respiratory heath effects. For the study, the centre surveyed 46 workers at 17 workplaces to collect data on their occupation and health status, such as symptoms, diagnoses and family history. The study had several main findings. Working full -time (more than 40 hours a week) with 3D printers is associated with various nega- tive health effects. Among workers who operated 3D printers: • 57 per cent experienced respiratory symptoms more than once a week in the past year • 22 per cent had physician-diagnosed asthma • 20 per cent experienced headaches • 20 per cent had cracked skin on their hands. Few workers use personal protective equipment (PPE). Among workers who operated 3D printers: • 48 per cent used PPE • 37 per cent used skin protection • 35 per cent used respirators or masks. Injuries were also reported. Among workers who used 3D printers, 17 per cent reported injuries, which were most often cuts or scrapes. The study conducted by Stephens and his research group in 2013 measured particle con- centrations and emission rates resulting from standard, commercially available 3D printers inside a typical office. They found printers using acr ylonitrile butadiene styrene (ABS) filaments were more dangerous to the health of workers than polylactic acid (PLA) filaments. "We showed that both types of printers emitted a large number of ultra-fine particles. And also, one type of printer filament (ABS), used in a printer operated at a higher temperature, emitted 10 times as many particles as the other type that we tested," Stephens says. In 2016, Stephens and his students tested emis- sions of particles and gases to determine the quantity and type of volatile organic compounds (VOCs) being emitted. They tested emissions pro- duced by five different types of printers and a wide variety of filaments, testing up to nine filaments in one type of printer alone. That testing led to two important findings. First, they found that several of the printers using ABS filaments emitted styrene, a VOC that is considered by some regulatory bodies, including the International Agency for Research on Cancer (IARC), as a possible human carcinogen. "That's generally known to be not a great thing that you want in indoor environments," Stephens says. "We searched around in different databases. We found some studies that estimated that high concentrations (of styrene) are likely to have some long-term cancer potency that may be worth looking at." Stephens also came across a study that associated very low levels of styrene with a risk of pulmonary infection. Second, their study showed nylon filaments emitted a compound called capra- lactum, a water-soluble compound used to produce a type of nylon. The presence of this compound can present a health risk, depend- ing on the printer and filament being used. Stephens says capralactum is listed by the Office of Environmental Health Hazard Assessment (OEHHA) in Sacramento, Calif., which advises a very low chronic exposure level. Thus, it is a cause for concern that, when his research team operated a printer with nylon filaments in a typical office environment, the capralactum emissions exceeded those levels. "You can very easily with some of these printers go over that level," he says. According to the Centers for Disease Con- trol and Prevention (CDC) in Atlanta, acute exposure to high concentrations of capra- lactum may be irritating to the eyes and respiratory track and may cause effects on the central nervous system. Some 3D printers use photopolymers, a polymer that cures, or becomes solid, when exposed to light, typically laser or UV. Many of these photosensitive liquid resins are toxic, says Kerry Stevenson, founder and editor at Winnipeg- based Fabbaloo, a blog devoted to 3D printing. Although some cartridges of photopolymers carry warning labels, most people still do not understand these resins can be toxic. "You find people merrily using these things. They pull the objects out of the machine and they're solid. But they're also wet with liquid material that has not been cleaned off. A lot of printers have an alcohol system to dissolve off this resin, but the substance can be toxic. Some of it is food grade, but a lot of it isn't," he says. As a result, any worker handling these resins should wear gloves, at least, to prevent it from get- ting on the skin. In some situations, Stevenson advises, it may also be a good precaution to wear a respirator or make sure the workplace is ventilated. Metal printing, typically done with a very fine metal powder, can also produce a respirator y hazard. The metal is placed flat on a powder-bed, metal 3D printer, and operators use a high-pow- ered laser to melt it. By repeatedly adding layers of powder and melting and fusing them together, operators build up the object. To produce a finely resolved object, however, the process requires a very fine powder and focused laser. The powder can become airborne and work- ers then risk inhaling metal particles, which can harm health because many of them are highly toxic, Stevenson says. Moreover, the metal powder is often explosive. Powdered titanium and powdered aluminum, for example, are common 3D printing powders and are both highly flammable. While there is no danger during printing, which is usually done in a sealed chamber purged of oxygen, the powder must sometimes be handled outside the chamber. Proper procedures for cleaning powder off the fin- ished object and for recovering residual powder must be followed. You find people merrily using these things. They pull the objects out of the machine and they're solid. But they're also wet with liquid material that has not been cleaned off.

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