Al Vangura Jr.
Since I introduced a new rescue tool to cut glass to the first responder community about a year ago, one of the top questions that invariably I have been asked regardless of the country I am in is, “What about the glass dust?” Many take the strong position that glass dust will cause silicosis and lung cancer and that a respirator mask must be donned anytime glass is cut during extrication procedures. With extensive background as a forensic bioengineer and biomechanical engineer, I decided to investigate this issue in more detail to determine the validity of the claims against glass dust. What my research uncovered will likely be hard for many to wrap their heads around considering years of training to the contrary. This article is intended to explain the results of that research effort in sufficient detail to convince many who will be skeptical. In the end, the rescue and extrication community, including fire, emergency medical service (EMS), and police, must come to terms with the fact that glass dust is not dangerous and way too much time has been wasted for a hazard that does not pose an unreasonable risk.
|(1) Tempered glass is subjected to rapid, controlled cooling during manufacturing to produce high, compressively stressed surface layers, which increases its strength compared with normal glass. Tempering creates balanced internal stresses, which cause the glass to crumble into small granular chunks when shattered instead of splintering into long, jagged shard. (Photos from Shutterstock unless otherwise noted.)|
Let’s start with the basics. Glass is a hard, brittle substance, typically transparent or translucent, made by mixing and heating sand or silica with soda, lime, and other ingredients. The molten mixture is rapidly cooled using controlled processes to make windows, drinking containers, vases, and other products.
Glass classified as safety glass has been toughened to provide increased resistance to impact or shattering into large, dangerous shards, which can injure nearby persons. Safety glass comes in two basic types: tempered and laminated.
Tempered glass is subjected to rapid, controlled cooling during manufacturing to produce high, compressively stressed surface layers, which increases its strength compared with normal glass. Tempering creates balanced internal stresses, which cause the glass to crumble into small granular chunks when shattered instead of splintering into long, jagged shards. The granular chunks are less likely to cause injury.
Laminated glass is a type of safety glass that is assembled using two or more glass sheets bonded together with an interlayer to form a clear, see-through barrier with enhanced impact and shatter resistance. Polyvinyl butyral (PVB) plastic is commonly used as the interlayer, which further enhances the glass by increasing sound insulation, minimizing vandalism, permitting tinting, and blocking nearly 99 percent of ultraviolet radiation. With sufficient impact force, the glass layers will shatter into the characteristic “spider web” cracking pattern, creating granular glass fragments. The PVB interlayer functions to hold the glass fragments together, minimizing the risk of flying glass impacting people.
|(2) Laminated glass is a type of safety glass that is assembled using two or more glass sheets bonded together with an interlayer to form a clear, see-through barrier with enhanced impact and shatter resistance. With sufficient impact force, the glass layers will shatter into the characteristic “spider web” cracking pattern, creating granular glass fragments.|
Almost all modern motor vehicles around the world are required to have some form of safety glass for windows. In the United States, laminated glass has been standard in automobile windshields since the 1920s. However in March 2011, the United States Code of Federal Regulations was amended to mandate all United States motor vehicles alter air bag and side window design to minimize the risk of occupant ejection by September 2017. Until this recent change, tempered glass has generally been used for side and rear vehicle windows.
During rescue operations, motor vehicle glass must be forcibly removed to gain access to injured occupants or for further extrication procedures. The use of these glass-cutting hand tools generates glass debris, which can range in size from powder to pea size particles. This debris may be small enough to become airborne and may be respired or breathed into the lungs of rescue workers. It is widely believed in the extrication community that this airborne glass dust is very dangerous and causes silicosis, lung cancer, and other respiratory disorders.
To determine when the issue of breathing glass dust began to creep into the extrication discussion, a review of extrication manuals, textbooks, journal articles, and magazine articles dating back to 1969 was undertaken. Although some cursory discussion of glass dust began in the early 2000s, and Vehicle Rescue and Extrication-2nd Ed. states that some “progressive” extricators are required by their fire departments to wear dust masks, a 2009 article titled “Extrication Tips: Raising the Roof-Laminated glass removal poses significant danger” appears to be one of the first in extrication literature to address and evaluate glass dust with its chemical name silica. The author, Randy Schmitz, reported on an observation he made while serving as a Transportation Emergency Rescue Committee (TERC) judge at a competition where the windshield was cut during a scenario and he observed that “… Everywhere I looked, for at least a 15-square-meter radius, were fine particles of glass dust that would not dissipate.” Schmitz then reports the results of his research into glass dust, which included a material safety data sheet (MSDS) for respirable crystalline silica, which is classified as hazardous to humans. Unfortunately, Schmitz’s research failed to discover that although glass dust is silica, it is not crystalline silica.
|(3) During rescue operations, motor vehicle glass must be forcibly removed to gain access to injured occupants or for further extrication procedures. Current glass cutting tools, clockwise from top left, include powered reciprocating saws, powered glass shears, fire axes, manual reciprocating saws, and spring-loaded center punches. (Photos from Shutterstock and by author.)|
Forms of Silica
Glass is manufactured using sand, otherwise known by its chemical name “silica dioxide.” Silica dioxide has two forms: crystalline and amorphous. It turns out that crystalline silica dioxide is hazardous to breathe and is well documented to cause silicosis and myriad respiratory disorders. Glass dust, however, is not crystalline silica dioxide but amorphous silica dioxide. As with many situations, the devil is in the details. Here’s a closer look.
A crystal is a solid material that occurs naturally during cooling from its melting point where its molecules align in a very regular and organized manner. The resulting solid is a homogeneous solid with geometrically arranged plane faces. Respirable crystalline silica dioxide is most frequently found in metal, nonmetal, and coal mines and mills; in granite quarrying and processing, crushed stone, and related industries; in foundries; in the ceramics industry; in construction; and in sandblasting operations.
|(4) A crystal is a solid material that occurs naturally during cooling from its melting point where its molecules align in a very regular and organized manner. The resulting solid is a homogeneous solid with geometrically arranged plane faces.|
An amorphous solid material occurs during the cooling process from its melting point. However, the rate of cooling process is greatly sped up. This causes the molecules of the material to become irregular and will have no alignment or arrangement. This difference in basic structure drastically reduces its toxicity in animals and humans-so much so that the United States Food and Drug Administration has approved it for use as an anticaking material for keeping foods like shredded cheese from sticking together. Large quantities of synthetic amorphous silica are used, notably, for reinforcing elastomers; for thickening resins, paints, and toothpaste; and as free-flow additives.
The World Health Organization’s International Agency for Research on Cancer published a review article in 1997 titled “Monographs on the Evaluation of Carcinogenic Risks to Humans.” The committee conducted an extensive review of all epidemiological research studies regarding crystalline and amorphous silica dioxide and concluded that crystalline silica inhaled is carcinogenic to humans and that amorphous silica is not classifiable as to its carcinogenicity to humans.
In 2011, a second committee published a similar review article on crystalline silica titled “Food applications and the toxicological and nutritional implications of amorphous silicon dioxide.” It states, “Through extensive review of the published literature, two independent expert panels convened by the International Agency for Research on Cancer (IARC) Monographs Programme have classified crystalline silica as carcinogenic to humans while amorphous silica was not classifiable as to its carcinogenicity in humans. The panel remarked that “crystalline silica in the form of quartz or cristobalite dust causes lung cancer in humans.”
|(5) An amorphous solid material occurs during the cooling process from its melting point. However, the rate of cooling process is greatly sped up. This causes the molecules of the material to become irregular and will have no alignment or arrangement.|
Another extensive review article published in 2012 titled, “The toxicological mode of action and the safety of synthetic amorphous silica-A nanostructured material,” states that “…amorphous silicas…have widely been used in topical and oral medicines, food, and cosmetics for decades without evidence of adverse human health effects.” And, “In contrast to crystalline silica, SAS [synthetic amorphous silicas] slowly dissolves in aqueous environments and body fluids. None of the SAS types was shown to bioaccumulate and all disappear within a few weeks from living organisms by physiological excretion mechanisms.”
Bioengineers and doctors have recently been working together to develop effective drug delivery methods using amorphous silica nanoparticles. These studies include respiratory and direct implant studies.
The Bottom Line
Currently, there is a huge disconnect between the extrication and rescue community and other industries like the medical devices, drug delivery, and food and cosmetics and the Occupational Safety and Health Adminstration (OSHA) when it comes to silica dust. While rescue workers potentially lose valuable seconds dealing with a nonissue like glass dust, medical device firms and food and cosmetic manufacturers intentionally use glass dust particles to make their products-some with respirable applications!
After delving into the extrication literature, observing rescue challenge competitions, and speaking at length with many extrication experts and first responders including fire, EMS and police, it is clear that extrication procedures have been altered to accommodate this overemphasized hazard. One could easily envision that if this issue was to quickly become a nonissue, each individual extrication would become a little less complicated and a little more straightforward. One thing is certain, with the recent changes in United States motor vehicle glass standards by late 2017, extrication procedures will have to change to meet the new challenges for patient access with laminated glass in all portals. It is my hope that this information will be used to begin the process for positive change for every future crash.
AL VANGURA JR. is a degreed bioengineer with extensive work experience in medical devices, military helicopters, International Space Station, and sporting equipment and is often called to testify as an expert witness to determine the cause of injury in situations like vehicle crashes and product failures.