Through the window: Security glass magnified

April 26, 2019

by Matt Jacobsohn

Photo © Matt Jacobsohn[1]
Photo © Matt Jacobsohn

Security glass has mainly been used by the military and other government entities, such as prisons and jails, police stations, and healthcare facilities. The scope has now expanded to markets and industries where security, particularly glass, used to be an afterthought. For instance, until recently, schools, retail outlets, pharmacies, corporate offices, religious institutions, hospitals, and data centers were rarely threatened by violent crime, active shooters, digital warfare, and natural hazards, and therefore, did not require security glazing. These market segments are employing security glazing products, but much of the money spent on them is being done with limited direction and research.

Security glazing is designed to protect against an array of situations and meet numerous criteria. It comes in various materials, weights, and thicknesses. These products undergo tests designed for specific threats or events, and often require surrounding material to carry an equal rating. Whether a door, frame, window, U-channel, or fitting, all the components of a system are designed to work in tandem to mitigate a threat. It is important that safety glass employed in security glazing systems comply with the American National Standards Institute (ANSI) Z97.1, For Safety Glazing Materials Used In Buildings – Safety Performance Specifications And Methods Of Test, and 16 Codes of Federal Regulations (CFR) 1201, Safety Standard For Architectural Glazing Materials, Category I and II ratings.

Test methods

The standards mentioned above differ in many ways, including who mandates its use, types and number of specimens tested, and the overall details of test setup, analysis, and reporting. Federal standard 16 CFR 1201 preempts all non-similar and state regulations, and ANSI Z97.1 is determined by building codes and glass/fenestration specifications. Only one specimen of each glass thickness requires testing in 16 CFR 1201, but ANSI Z97.1 needs four of each thickness. Unlike ANSI Z97.1, 16 CFR 1201 does not perform tests on plastics and bent glass. Both tests have multiple categories with the highest one requiring a pendulum impact from 1219 mm (48 in.) high, and the second categories need a pendulum impact from 457 mm (18 in.) high. ANSI Z97.1 has a third test category involving a pendulum impact from 305 mm (12 in.) high. However, this is only applicable for fire-rated glazing materials. In both standards, the criteria to pass means selecting the 10 largest broken pieces and weighing them to see if they are lighter than a 6452-mm2 (10-si) area of the original specimen.

Figure 1: Ratings of bullet-resistant materials as identified by Underwriters Laboratory (UL) 972, Standard for Burglary Resisting Glazing Material. Image courtesy Cellular Material International Inc.[2]
Figure 1: Ratings of bullet-resistant materials as identified by Underwriters Laboratory (UL) 972, Standard for Burglary Resisting Glazing Material.
Image courtesy Cellular Material International Inc.

Many security glass test methods require complete system testing. However, some do not incorporate the system in which the glass is installed, thereby leaving its performance in field conditions unknown. The whole purpose of employing a strong piece of glass is lost if it falls out of its framing system post-installation.

Underwriters Laboratory (UL) 972, Standard for Burglary Resisting Glazing Material, measures the effectiveness of a 1.2 x 1.2-m (4 x 4-ft) glass specimen by laying it parallel to the ground and then dropping a 2-kg (5-lb) steel ball on it from four different heights. Failure of this test happens when the steel ball passes through the specimen. However, the test requirements do not cover the framing system used in the installation of burglary-resistant glazing material. In this author’s experience, the UL 972 test is usually specified because of its name and implication. People want glass that can stop a burglar. Therefore, designers looking for a test method are first directed to UL 972. To see the specifics of the test and its setup requires a test procedure document costing more than $500. This is where the research often stops, as people do not want to spend money on such documents. Hence, details of the test procedure and setup are missed and the test is taken.


It is important to note there is no such thing as ‘bulletproof glass.’ The term perpetuates the belief no bullet, not even one, will penetrate the glass. This provides a false sense of security and is widely misused. When glass passes a ballistic test, it is either referred to as ‘bullet-resistant’ or ‘bullet-rated’ to meet a specific level within a standard.

Bullet-resistant glass is tested according to UL 752, Protection Standards For Bullet Resistant Glass Products, or the National Institute of Justice (NIJ) 0108.01, Ballistic Resistant Protective Materials. The testing methodology employed depends on the client. NIJ is the U.S. State Department’s ballistics standard for the military and federal government applications.

UL 752 can be used for any other application where ballistic resistance is desired. The testing for ballistic resistance is set up with the end of the specified firearm barrel being 4.5 m (15 ft) from the surface of the glass, and a witness panel (aluminum foil or corrugated cardboard) placed 45 m (18 in.) behind the test specimen. If a bullet goes through the test specimen and the witness panel, the product fails. For instances where it is desirable to have exposed glass surfaces, a UL 752 tested product may receive an added layer of glass. If such a product is used, it will prevent bullet penetration as tested, however, it will be susceptible to spalling on the interior surface.

Figure 2: A comparison of forced entry testing. Images © Matt Jacobsohn[3]
Figure 2: A comparison of forced entry testing.
Images © Matt Jacobsohn

The ballistic testing per UL 752 has eight primary levels with a few (levels nine, 10, and shotgun) additional, less common ones. Each level contains provisions for different firearms and/or number of bullets fired at the glass (Figure 1).

The firearms used are capable of carrying magazines with varying numbers of bullets. In a majority of cases, these firearms hold more than 10 bullets in a magazine. It is important to note the number of shots fired during the UL 752 test is five. The test protocol does call for these bullets to be in a concentrated area based on the level being tested. For example, levels one to three, which are handguns, require three shots within a 100-mm (4-in.) triangle. Levels seven and eight—for assault rifles—need five shots in a 115-mm (4.5-in.) square. In both cases, if a shooter was to shoot more than 10 bullets into a UL 752-compliant product, the bullets would likely penetrate. This is based on a test performed by the author on a UL 752 Level 1 piece of glass with the corresponding firearm, where the fifth bullet penetrated the glass.

Bullet-resistant glass is heavy and thick, weighing anywhere from 4 to 23 kg (8 to 50 lb) per square foot, and ranging from 20 to 100 mm (¾ to 4 in.)
in thickness. Its laminated composition combines various layers of glass and/or plastics. A UL 752, ballistic-resistant product does not spall, meaning material fragmentation does not occur on the safe side of the material after being shot. This protects anyone on the safe side of glass from flying debris. To produce a no-spall, bullet-resistant glass, a plastic layer (typically polycarbonate) is laminated to the interior surface. Although effective, it does have its negatives—as with any exposed plastic, the risks of scratching and aesthetic degradation are greater than a traditional glass surface.

Bullet-resistant glass should always be installed into a bullet-resistant system (door/frame) with a matching rating. Otherwise, as mentioned earlier, the bullet-resistance rating of the opening will be compromised. These systems, particularly doors, can therefore become extremely heavy, weighing more than 227 kg (500 lb) in some cases. Although much of the weight is in the glazing, the door depending on the type, size, and the material to make it bullet resistant, can affect the overall weight. Doors may be aluminum, steel, wood, and fiber-reinforced polyurethane (FRP) with extra material such as kevlar or steel inside the door and frame. The weight of the frame should not matter as long as is it anchored appropriately. If steel is reinforced, the thickness, and therefore, weight of the steel may affect the level of bullet resistance a frame or door achieves.

Forced entry

Test methods for forced entry glazing vary greatly, such as:

In nearly every instance, until recently, these tests methods had one thing in common—they were all tested in similar glazing systems (framing).1

Forced entry glass, or transparent armor can be tested according to the following:

HPW test method

The following text was the premise for HPW to develop HPW-TP-0100.00, Transparent Materials and Assemblies for Use in Forced Entry or Containment Barriers, the first forced entry transparent armor protocol, in 1983.

Increasing levels of international terrorism and institutional disorder have extended to structures which have, heretofore, generally been free of such assault. The vulnerability of these structures to assault from ill-equipped and untrained attackers is well documented by the success of riots within penal institutions and the illegal occupation of government buildings. Analysis of such incidents indicates that physical barriers suited to the intensity and nature of the attack would have prevented the incident or contained the incident with a limited portion of the structure.

Additionally, “historically these elements have proven to be the most vulnerable portions of the barrier to overt forced entry- or exit-assaults.” The test included ballistics, blunt impacts, sharp tool impacts, thermal stress, and chemical deterioration.

A school cafeteria’s exterior appearance provides no hints that the glazing system employed in this project actually has security glass.[4]
A school cafeteria’s exterior appearance provides no hints that the glazing system employed in this project actually has security glass.

HPW updated this protocol three times between 1983 and 2003, with the current standard referred to as HPW-TP-0500.03. A number of changes, deletions, and additions have occurred to this test throughout the three updates, such as:

ASTM test procedures

Strikingly similar to HPW-TP-0500.03 is ASTM F1233. It was first published in 1998 and has since had three revisions, the latest being in 2013. Both tests are class/step based (i.e. the ‘attackers’ take breaks between each step) and undergo five types of threats, such as ballistics (not required because the test report will either show results for bullet resistance if this is performed, or it will not mention ballistics

at all if the glass is not shot), blunt and sharp tools impact, thermal stress, and chemical deterioration, depending on how many steps a product lasts until failure. As these tests are designed for products used in correctional/jail settings, the person meant to be contained will never have a firearm and is not pertinent to the testing.

Lastly, these two test methods default to the same installation for setup where the steel glazing stop will be “oriented to support the entire periphery of the protected face of the distance of the sample for a distance of 25 mm (1 in.) from its edge.” This is important because standard commercial glazing systems, such as aluminum doors, storefronts and/or curtain walls, along with FRP and hollow metal doors and framing are unable to meet the 25-mm distance requirement, thus rendering these test methods as non-applicable for commercial installations.

ASTM F1233 allows glass and framing product manufactures to test the glazing system based on their recommendations. A company can test using a specific system if they desire, however, it is unlikely that system will be stronger than the default welded steel detention-like framing. When a specification is written, the only item listed referencing ASTM F1233 is the test itself and the class/level to be met. The door or framing the glazing is tested in is rarely, if ever, mentioned alongside the test. Hence, glass manufacturers test use the detention-style framing.

Using the same test setup with its 25-mm edge bite is ASTM F1915, Standard Test Methods for Glazing for Detention Facilities. This test method has four levels where the glazing is subject to an equal number of impacts from both the blunt and sharp impactor weights. This mechanical-based test uses weighted impactors on a pendulum where the object swings into the center of the glass pane. Level one is constituted as a 60-minute attack and receives 600 total impacts. Level two is a 40-minute attack and receives 400 total impacts, level three is a 20-minute attack and receives 200 total impacts, and level four is a 10-minute attack and receives 100 total impacts.

In each of these three tests—HPW-TP-0500.03, ASTM F1233, and ASTM F1915—failure occurs when a 203 x 203 x 127-mm (8 x 8 x 5-in.) cuboid, also referred to as ‘body passage,’ passes through the test specimen. Glazing products undertaking these tests are often laminated. In some cases there may
be multiple layers of glass, polycarbonate acrylic, or a combination of these materials. Thicknesses and weights are based on the product and the class or grade a manufacturer is looking to meet. These can be anything from a 10-mm (3/8-in.) polycarbonate at 2 kg (4 lb)/sf, to a 50-mm (2-in.) unit at 7 kg (15 lb)/sf.

5-aa protocols

The 5-aa1, 5-aa5, and 5-aa10 forced entry protocols are the most recent addition to the available lineup of forced entry glass testing methods. These methods require the testing to include all components of an installed glass and glazing system. The 5-aa protocols were created to develop a standard for forced entry glazing in infrastructure applications where 6-mm (¼-in.) monolithic and 25-mm (1-in.) insulated glass are used, the majority of commercial glass applications. Earlier, there was a void in the Division 08–Openings section for combining security with the everyday building because specialty security glass, such as bullet-resistant, detention glazing, blast-resistant glazing, and hurricane glazing, require specific systems to accommodate glass thicknesses and ratings. The 5-aa methods aim to accommodate the different types of security glazing systems—existing or specified—in commercial facilities, thereby not altering the look and alleviating additional costs for specialty doors, frames, and windows.

Figure 3: Contrast between the International Code Council (ICC) 500 and FEMA P-361. Photo courtesy[5]
Figure 3: Contrast between the International Code Council (ICC) 500 and FEMA P-361.
Photo courtesy

In the 5-aa tests, a 7.62-mm rifle (e.g. AK-47) is used. However, each one has different requirements for the number and placement of bullets. Ballistic resistance is not required, but is rather used as a means to test the products behavior after it has been compromised with bullet holes. After all, a standard door, frame, or window cannot stop these bullets. Each test is timed and meant to replicate an attacker with a firearm and/or tools trying to gain entry into a space. Failure in these tests is constituted as any means by which an attacker can create entry, whether a 100-mm (4-in.) hole is developed to allow someone to reach a door handle or panic device, unlock and open a window, or compromise the hardware on a door to open it.

The 5-aa1 test method sets standards for forced entry in both new construction and renovations of existing structures and systems. In this test, the glass is installed into the same or similar aluminum glazing systems specified or existing on the project, such as entry doors, storefronts, and curtain walls. Unlike HPW and ASTM standards, the 5-aa1 method provides a testing guideline to incorporate the entire system, rather than just the glass in a commercial building project. In this test, the glass is first shot five times with a 7.62-mm rifle in a concentrated area and then subjected to a barrage of attacks from bricks, a 454-g (16-oz) claw hammer to incorporate a sharp object, a baseball bat, and a 5-kg (12-lb) sledgehammer. All of these impacts are concentrated at the area where the glass was shot. The test is timed from start to finish, unless the ‘attacker’ needs a break (here the time stops). In a real-life scenario the attacker cannot afford to take a break because it provides time for first responders to arrive.

The 5-aa5 test method takes the 5-aa1 standard to another level by incorporating an entire aluminum and FRP entry system used in either the exterior or interior of a building. This test establishes standards for forced entry and the ballistic-resistant levels of protection for various threats based on the Federal Bureau of Investigation’s (FBI)’s report “A Study of Active Shooter Incidents.” Here, the test uses a full system setup where glass, door(s), framing, sidelight, and hardware are assembled as they would be in the field and are tested as a whole. Both 7.62-mm and 5.56-mm (e.g. AR-15) rifles are used. However, this time, 30 shots are fired at areas such as the glass, door-locking mechanism, door handle, hinges, doorframe, and areas around the door hardware. The ‘attacker’ is then given the same tools used in the 5-aa1 test to gain entry in any way possible.

The 5-aa10 test method was also developed as a result of the 2014 FBI active shooter report, but this sets standards for wood and hollow metal doors, frames, glass, and hardware because they are more commonly used in the interior of buildings. This test uses a greater number of 7.62-mm bullets fired at concentrated areas where entry can be made. Thirty shots are fired within a 150 x 150-mm (6 x 6-in.) area comprising the door handle and the locking mechanism and then 30 shots are fired in the same side area of the door glass closest to the handle. If applicable, 30 shots are then fired at the sidelight glass closest to the door handle. After this barrage of gunfire, the ‘attacker’ will have a minimum of three minutes using handheld tools and a simulated assault rifle to gain entry through the system.

Bomb blast

Prior to the 1995 Oklahoma City bombing of the Alfred P. Murrah Federal Building, there were no minimum physical security standards for non-military, federally owned, or leased facilities. As a result, the General Services Administration (GSA) and newly formed Interagency Security Committee (ISC) sought to develop standards for buildings subject to bomb blasts. From this, ASTM created ASTM F1642, Standard Test Method for Glazing and Glazing Systems Subject to Air-Blast Loadings. This test method provides a hazard rating of glazing systems that are subject to an air blast. Understanding these ratings provides one the ability to assess the potential risk of bodily injury and facility damage.

Air-blast testing requires the complete glazing system to be tested, not just the glass. The tests can either be as an ‘arena test’ performed outdoors in a remote area where larger curtain wall and storefront systems are tested, or a ‘shock tube’ method indoors with a testing capsule for smaller openings such as windows and doors.

Standard annealed or tempered glass will carry a performance rating of five, translating to a high hazard level as per GSA/ISC protection levels for glazing. Low- and no-hazard levels are mainly comprised of glazing that is either laminated or tempered/annealed glass with a retention film applied to the interior side. Both products have their positives and negatives, but laminated glass has the benefit of being tested to alternative security glazing testing methodologies like ballistic resistance and forced-entry resistance, in addition to its higher aesthetics.

Sometimes referred to as ‘security films,’ blast-retention films were designed to prevent glass from becoming shrapnel in a blast. The advantage of using such film products, specifically in retrofit scenarios, is the film can be applied over existing glass and then secured by using either silicone or a mechanical attachment system. It is important to note, these films were only designed for blast that is a highly pressurized pulse of air. Such products do not perform as well when impacted by blunt objects and tear easier than laminated glass when a hole is developed. Common negatives associated with film products is their exposed plastic surface is prone to scratching, tends to yellow from ultraviolet (UV) exposure, and carry a shorter lifespan than laminated glass. It is also pertinent to remember, applying film to an insulated glass unit (IGU) will likely void its warranty. It is important to consult the IGU fabricator prior to applying any film.

Bullet-resistant glass stops .308 caliber rifle rounds while its thickness dwarfs the ejected bullet casings. [6]
Bullet-resistant glass stops .308 caliber rifle rounds while its thickness dwarfs the ejected bullet casings.

Laminated glass products often carry a low-hazard level in a bomb blast because it has exposed glass on both sides. Much like bullet-resistant glass that spalls when a bullet makes impact, laminated glass for a bomb blast spalls when struck by a blast wave. The fragmentation from laminated glass typically comprises small pieces unlikely to cause any bodily injury or damage to the interior space of a facility.

In retrofit projects, laminated glass is a more expensive investment than a surface-applied film. However, laminated glass might have a lower life-cycle cost due to the frequent replacement film products require.

Wind-borne debris

Glass and glazing systems designed to prevent against wind-borne debris follow the same idea as blast-resistant systems where the entire structure must be able to resist an event. If one component fails, the risk of injury increases and the building’s integrity may be compromised. Unlike blast, wind-borne debris testing requires missile (wooden 2 x 4 or 10 of 2-g [0.07 oz] steel balls) impacts at the glass and/or system along with positive and negative pressurized air. The two types of events prominently associated with wind-borne debris are hurricanes and tornadoes.

Applications designed to be hurricane-resistant must comply with one of the following codes:

FBC’s High Velocity Hurricane Zone (HVHZ) testing is more stringent than ASTM E 1886/1996 testing as the former needs two large missile (4 kg [9-lb] wooden 2 x 4) impacts on the glazing and one large missile impact on a surrounding framing member, whereas the latter requires just one large missile impact to the glazing. FBC’s HVHZ allows no opening greater than 1.6 x 127 mm (1/16 x 5 in.) while ASTM allows openings up to 76-mm (3-in.) sphere. When it comes to the small missile (10 of 2-g steel balls) test, the HVHZ testing requires all floors—9 m (30 ft) and above—to pass testing, whereas ASTM only requires floors 9 to 18 m (30 to 60 ft) to pass a small missile testing.

In both standards, the ‘Level D’ large missile testing is most common with projectile traveling at 50 m/s (34 mph). However, ‘Level E’ requirements are on the rise with the projectile traveling fast at 80 m/s (50 mph). Additionally, both standards require cyclic wind pressure testing where a test specimen after impact testing receives 9000 pulses of pressurized air based on design requirements.

With regard to tornado-resistance, which are tested similarly to hurricanes with the exception of a heavier 7-kg (15-lb) large missile and shorter duration of cyclic pressures, the International Code Council (ICC) 500, Construction of Storm Shelters, and Federal Emergency Management Agency (FEMA) P-361, Safe Rooms for Tornadoes and Hurricanes Guidance for Community and Residential Safe Rooms, are often referenced. However, there are slight differences between the two (Figure 3).

The glazing employed for systems compliant with ICC 500 and/or FEMA P-361 is always laminated and often 38 mm (1 ½ in.) or more in thickness, and contains a plastic interior surface. Much like bullet-resistant, no-spall glazing, the glass rating for tornadoes must also have zero spall. For this reason, and the limited size availability in glazing that has passed tornado testing, it is not common to employ glazing in safe shelters and rooms.


As architectural design continues to use more and more glazing, it is important to consider the use of protective glazing, especially in today’s world. One must understand the options, testing, and purpose for using such products and how to best implement them in either new construction or existing structures. Project teams must first determine what the glazing system is trying to prevent. For example, is the need to stop bullets, or prevent the assailant from getting into the building and then spreading bullets? Protective security glazing merely helps one prepare against a potential event. One must never assume it will not happen to them as history leaves no one untouchable.

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