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Glass Breakage and the Consequences
What Causes Glass To Break, And What Are The Consequences?
There are many different factors that can result in glass breakage. The nature of the event is likely to determine the type and extent of damage done to person and property. The event and the manner of breakage need to be assessed individually in order to determine the effectiveness and performance of GSS’s products.
Glass breakage occurs in one or more of the following ways:
- Thermal stress from the absorption of solar radiation.
- Tensile strength from the weight of the glass itself.
- Mechanical flexing stress: positive and negative pressures, wind.
- Impact stress from flying objects.
- Twisting stress, i.e.: building movement.
The following are a list of possible events and the likely results:
Human Impact: One of the major causes of injury is the result of human impact: Simply, it is the act of a person unintentionally going through a pane of glass, which can cause injury. Safety glass is used where these possibilities exist. Local, State, and National safety glazing codes and legislation are enacted to help protect individuals from such occurrences. The most commonly recognized code, where safety glass is required is called ANSI- Z97 (American National Standards Institute). Types of approved safety glass are: tempered glass, laminated glass, and any glass with Glass Strengthening Systems film applied.
The Consumer Product Safety Commission reported that in 1995, there were over 2, 25,000 glass related accidents in the U.S. These statistics were gathered from the emergency rooms of hospitals and doctors throughout the nation. Glass Strengthening Systems decreases and virtually eliminates injury from this type of human impact. The tensile strength of the film, coupled with its elasticity and its high resistance to shearing greatly removes, if not eliminates, the ability of a person to break through by walking, running, or falling through glass.
Human impact standards were developed in the early 1970s to reduce the injuries to people who impacted glass in homes and buildings and caused it to break. The two main standards in the U.S. that deal with human impact are the American National Standards Institute (ANSI) Z97.1 and the Consumer Product Safety Commission (CPSC) Code of Federal Regulations (CFR) 1201, category II. The ANSI Z 97.1 standard is most commonly used for residential applications while the CPSC CFR 1201 is more often found in commercial applications for glazing. The ANSI Z 97.1 standard usually requires a 100- and 150-foot-pound impact on the glass while the CPSC CFR 1201, category II, requires a 400-foot-pound impact. Although both these standards can be tested at the same impact levels, the two mentioned above are used most commonly. These standards are the points of reference that require the use of tempered glass or the addition of film on annealed glass to bring the glass into compliance. If film is used to bring sub-standard glass into compliance, a compliance sheet and the necessary labeling to be applied to the treated glass must accompany it.
Natural Catastrophes: Climatic and geographic conditions can result in a variety of events such as hurricanes, tornadoes, earthquakes, and violent storms. Under these conditions, glass can unexpectedly and violently is subject to all the forces that can cause injury and property loss: pressure, mechanical, twisting stress, and impact. The difference between an explosion and natural born events is its duration. Unlike a single event explosion, natural catastrophes and its effects can last hours, even days. According to the National Insurance Institute, over 1, 00,000 panes of glass were broken nationally from natural, violent events in 1999. Even lesser events are cause of major concern for the insurance industry, which paid out over a billion dollars in damage and medical claims in 1999 for minor claims unrelated to major catastrophic disasters. GSS offers a high degree of protection against all the factors above. Even in cases where glass is broken, the film has been shown to keep the glass and the frame intact providing protection from wind and water damage. GSS product has been tested to keeping over 95% of broken, fractured glass to our film.
GSS films are resistant to hurricane impact and have garnered a considerable amount of attention since Hurricane Andrew struck south Florida in 1991. The damage caused by Andrew led to significant code changes for new construction at county and state levels, not just in Florida, but also in most coastal states. These code changes require the glass and glazing structures to pass missile impact and cycling tests, which simulate a hurricane environment. The severity of the testing will depend upon two aspects: the height of the structure and the location of the structure, along with its expected wind speed for that area. The height of the structure will determine the size of the missile (i.e., whether it will be large or small). Structures at ground level and no higher than 30 feet above ground will be subjected to the large missile and structures above 30 feet will be subjected to the small missile.
These codes are variable and you should check your local building code requirements for impact-resistant glazing. GSS film can provide a significant level of protection, but cannot meet all the code requirements. Films have been tested that meet the lower wind speed (90-100 MPH) for large missile and cycling but they must be anchored to the frame. Films have also been tested to meet the highest wind speed requirement (> 150 MPH) for small missile and must also be anchored to meet the cycling requirement. Bear in mind that retrofit film applications do not have to meet new construction codes. However, be certain to require test results for the film performance, should you want to use GSS film to bring existing glazing up to a specific code.
Impact: Many windows are broken either intentionally or unintentionally by thrown objects. Whether by an errant golf ball or a smash and grab robbery attempt, the result is the same. Velocity and energy cause the glass to break.
The application of GSS product to these windows will reduce, if not completely eliminate, both damage to people and property. GSS product has a high degree of elasticity and energy shock absorbing capability. The energy at the point of impact is instantly disbursed outward to deflect the blow. In all but the severest cases the object is rejected without penetration or breakage. Even in severe cases where breakage occurs, the film keeps the glass intact eliminating a shower of glass fragments.
GSS films have long been used to enhance the performance of glass in areas where earthquakes often strike. In an earthquake, the glass is broken by compression due to the twisting or “racking” of the building. Using GSS film, glass can break catastrophically, but the shards will be held adhered to the film, thereby reducing the possibility of injury. Usually, a simple “daylight” application of a 4-mil or thicker film will suffice for this protection.
Almost any film can be helpful in thwarting the efforts of the “smash-and-grab” artist since he has a very short time limit. If the glass breaks “but” stays in place, the probability is that he will leave and usually will go to an easier target. However, when his more serious counterpart takes on a piece of glass, it is going to have to be protected to a higher degree. These fellows will try cut through film or push it out from the corner to gain entry, this is where GSS excels in protection with up to and over 95% of glass remaining adhered to film and frame and with some of the highest “Tear Strengthen” rating in the industry. In order to offer a significant level of protection, we suggest the use of thick films, 8, 10 to 16-mil, and anchor the film on all four sides when possible. The predominant test for determining the performance of applied film on glass for intrusion is the Underwriter’s Laboratory (UL) 972 for burglary resistance. This consists of a 5-pound steel ball falling from ten feet and striking the glass five times. No penetration of the ball is allowed.
Explosions: Whether accidental, as in an industrial gas leak or an intentional political or terrorist act, the results are always the same: massive devastation. A recent Government report concluded that 27 lives were lost in the Oklahoma City bombing with the primary cause of death being flying glass.
An explosion displaces air and creates a shock wave or as more commonly known: over pressure. This over pressure results in a vacuum being created where the blast has pushed air away from itself generating the shock wave. Almost instantaneously, a vacuum created by the over-pressure causes an immediate rush of air back to the point of origin, causing the glass to flex back towards the original direction of the shock wave. The results are that glass flexes from both positive and negative pressures resulting in catastrophic breakage.
GSS film on glass can dramatically reduce the effects of an explosion. GSS’s product has the ability to stretch without tearing and also has the characteristics to absorb a large portion of the shock wave. In many cases the glass may break, but due to the Bonding strength of our Secure-Bond Solutions, Acrylic Adhesive and the film itself, the glass remains adhered to the film and frame by up to and over 95% adhesion rating.
The most accepted test for determining the performance of glazing in a bomb-blast environment is the General Services Administration (GSA) Test for Air blast loading on Glazing and Glazing Structures. This test is based on producing a known pressure on the glass as would happen in a bomb blast. The pressures where safety and security films have shown a very good protection level are 4 (pounds per square inch) PSI and 10 PSI. These pressures can be produced either in an “open-air arena” in which an explosive mixture is detonated, or in a “shock tube,” in which air pressure is used. After the pressure is exerted upon the glass, how far the glass traveled into the ten-foot deep, closed structure grades the response of the glazing.
