What happens after glass breaks: the first question to ask about safety film
Glass admits light and opens a view. Once it breaks, fragments can fall or fly, and the opening may let people, wind or debris pass through. A safety film specification is therefore about how a particular glazing assembly behaves after breakage, not a promise that the glass will never break.
This guide is an English adaptation of our Thai article, which was independently written from the International Window Film Association’s Safety & Security Education Guide (2023). It moves from glass types and film construction to event-specific tests, edge attachment and claim checking. It is an educational aid for owners, designers and facilities teams. The IWFA manual does not certify any MAXXMA product, and a qualified professional must assess the actual glazing and local requirements before specification.
Primary reference
IWFA Safety & Security Education Guide (2023)
The 37-page manual covers human impact, windstorm debris, seismic movement, blast fragments, forced entry and the evidence needed to support performance claims.
Read the original IWFA manual (PDF)Four glass types, laminated glazing and the role of the frame
Most flat glass begins with the float process. Annealed glass can be cut and is common in buildings, but it typically breaks into sharp pieces. Heat-strengthened glass resists more stress than annealed glass yet has a similar break pattern. Tempered glass is stronger and breaks into small pieces. Chemically strengthened glass is used mainly where thin, strong glass is needed; strength alone does not make every product suitable for safety glazing (IWFA pp. 2-4).
Laminated glass bonds two or more plies through an interlayer such as PVB. That layer can hold broken glass together. It differs from tempered glass, which breaks into small pieces but needs the opening to retain them. Purpose-built ballistic or blast-resistant glazing can combine multiple glass and plastic layers with a specially designed frame. It cannot be equated to a film fitted to an existing pane (IWFA pp. 4-5).
A window may use a single pane, an insulated glazing unit, a laminate or a specialist protective assembly. Its performance depends on the glass, film, adhesive, seal, frame and frame-to-building connections. A film-only data sheet does not establish what the whole opening will do after impact.
03 · FILM CONSTRUCTIONHow film can hold fragments together, and where it can fail
Clear safety film may use one or several laminated polyester plies. A pressure-sensitive adhesive bonds it to the room-side glass; a scratch-resistant coating often protects the exposed face. When the glass fractures, the film can stretch and absorb energy while holding fragments together. Sufficient force can still tear the film or pull the filmed pane out of the frame (IWFA pp. 6-9).
Thickness, ply count, tensile strength and tear strength describe the material, but none alone predicts an actual event. The adhesive that laminates plies may differ from the adhesive that fixes film to glass. Peel data depends on cure time, temperature and test angle. A weight hung from a strip on an installed window is not a controlled substitute for a standard laboratory test (IWFA pp. 8-9).
UV absorbers protect film materials and can address one contributor to interior fading. They cannot stop all fading. Solar safety film adds solar-control layers, which means the glass and film combination also needs a thermal-compatibility review.
04 · MATERIAL DATAWhat thickness, tensile, abrasion and peel tests can tell you
IWFA’s appendix identifies material tests such as ASTM D882 for tensile properties, ASTM D1044 for abrasion-related haze change, ASTM E84 for flame spread and smoke, and ASTM D3330 for adhesive peel. Reports should state the units, film direction where relevant, specimen construction and adhesive cure conditions (IWFA pp. 33-34).
These are useful material measures. They do not demonstrate blast, storm or forced-entry performance. For a safety objective, ask for a test that simulates that event on the glazing assembly being proposed.
Clear film, solar safety film and thermal-stress breakage
Thermal stress develops when one area of a pane heats faster than a shaded edge under the frame. A fracture can start at the edge and progress into the pane. The IWFA manual describes clear safety film as having little effect on this risk in typical circumstances. A solar-control safety film may change absorption, so its manufacturer’s film-to-glass guidance and the actual glazing, shading and insulated units need review (IWFA pp. 10-11).
Exterior safety film faces a different exposure. The IWFA guide does not evaluate its exterior performance in detail. Ask its manufacturer for product-specific service-life and system-test evidence rather than applying an interior-film result to an exterior installation.
06 · HUMAN IMPACTReading ANSI Z97.1 and CPSC 16 CFR 1201 impact results
These tests address people walking or falling into hazardous glass locations such as doors and low partitions. ANSI Z97.1 swings a weighted bag into a framed specimen. If glass breaks, the test limits the size of the resulting opening. The pass criterion does not require the glass to stay unbroken (IWFA pp. 12-13).
- Class C: 12-inch drop, approximately 100 ft-lb
- Class B: 18-inch drop, approximately 150 ft-lb
- Class A: 48-inch drop, approximately 400 ft-lb
Within the test framework described in the manual, CPSC 16 CFR 1201 Category I corresponds to Class B and Category II to Class A. A credible claim names the class achieved, glass type and thickness, and the installation tested. A human-impact result does not establish storm or blast performance.
07 · WINDSTORMSWhy debris impact and repeated wind pressure must be tested together
A storm pushes and pulls on glazing in repeated cycles. Flying debris can break an opening; a breached building envelope can then alter internal pressure and load other parts of the structure. That is why storm testing considers the complete window and its connection to the building, not a filmed pane alone (IWFA pp. 14-17).
ASTM E1886 sets out the impact and cyclic-pressure test method, while ASTM E1996 addresses windborne-debris performance and missile categories. The manual discusses small projectiles and larger pieces of lumber in different risk conditions. Historic Miami-Dade examples combine impact with thousands of pressure cycles. Wind maps, code editions and regional requirements change, so a Florida provision is an example of a test context, not a Thai building rule (IWFA pp. 15-21).
At the time of writing, IWFA knew of no retrofit safety film on previously noncompliant existing glass and frames that had passed the specified nine-pound large-missile impact followed by cyclic loading. Passing a small-missile test on one assembly is not approval of a full hurricane protection system. Ask for the applicable authority’s written approval of the specific assembly rather than relying on a general “storm proof” phrase (IWFA pp. 16-21).
08 · EARTHQUAKESSeismic movement, cracking and glass fallout
During an earthquake, the frame and pane can move relative to each other. Seismic racking tests increase that movement and distinguish a serviceability drift limit (SDL), where damage calls for replacement, from an ultimate drift limit (UDL), where fallout poses a hazard. The studies summarised by IWFA found strong fallout resistance for the laminated-glass specimens tested. A four-mil unanchored film improved some limits but did not match laminated glass; a top-anchored film improved retention in additional work (IWFA pp. 21-23).
Pane shape and size, frame flexibility, sealant and building form influence the result. A seismic claim therefore needs a report for the actual assembly and professional review. A small specimen cannot certify every façade.
09 · BLAST HAZARDSBlast tests measure fragment danger, not simply whether glass breaks
A blast can drive glazing inward and produce a later outward pull. A shock tube applies a controlled pressure pulse. An open-air arena can reproduce more of the event, but is far more costly. The manual cautions that dramatic side-by-side demonstrations with uncontrolled charge size, distance and specimen details are anecdotes rather than recognised standard tests (IWFA pp. 24-25).
Its reference list includes ASTM F1642 for the test method and ASTM F2912 for hazard ratings, GSA TS01 for complete window systems in GSA facilities, ISO 16934 for shock-tube loading, and ISO 16933 for arena air-blast loading. Ratings attach to a stated pressure, impulse, duration, glass construction and frame. They do not automatically transfer to a different threat or window (IWFA pp. 25-27).
GSA’s performance conditions range from glass remaining intact or retained in the opening to fragments entering the room at increasingly dangerous distances. Ask which condition was achieved, at which blast load, and where fragments landed. “Blast tested” without those details tells little (IWFA pp. 27-28).
The IWFA review observes that attachment to a suitable frame often improved fragment retention relative to daylight fitting under tested conditions. Yet filmed glass may leave the opening as one sheet if its edge or frame fails. No standalone film claim can make a building blast-safe.
10 · FORCED ENTRYUL 972, EN 356 and the limits of active-shooter claims
A smash-and-grab attack depends on speed. Delaying a usable opening can buy response time, but it does not guarantee that determined attackers cannot enter. UL 972 uses repeated steel-ball impacts under specified conditions. The manual notes that UL requires the frame as part of a passing system report rather than issuing one for glass and film alone. EN 356 P1A/P2A uses a heavier ball dropped in a set pattern at defined heights. The achieved level applies to the tested glazing construction (IWFA pp. 28-29).
For an active-shooter scenario, IWFA states that safety film on existing glazing is not bullet-resistant or bulletproof. A particular system test may measure how long entry is delayed, but its weapon, ammunition, distance, glass and anchoring must be disclosed. Entry-delay evidence cannot be turned into a bullet-stopping claim (IWFA p. 29).
Anti-graffiti film serves another purpose. It can act as a replaceable sacrificial layer against scratching or chemical marking. Surface protection is not evidence of forced-entry resistance.
11 · EDGE RETENTIONDaylight, edge-to-edge and anchored film installation
In a daylight installation, film covers the visible glass and stops a short distance before the frame. This common method can retain fragments in some human-impact and rapid-break-in scenarios. With shattered tempered glass or a larger load, however, the filmed sheet may leave the opening.
Edge-to-edge application covers the pane to its edges, commonly before glazing. An anchored assembly ties film to the frame through a mechanical fitting or a structural-silicone wet glaze. The manual gives a minimum 3/16-inch overlap onto film/glass and frame for the wet-glaze example, but the specification must follow the design and test report for the chosen system (IWFA pp. 29-31).
Anchoring can substantially improve retention under some tested loads. It needs more design and installation work, and it does not by itself certify storm, blast or intrusion performance.
The following MAXXMA channel video illustrates architectural and safety-film applications. It is context for the installation conversation, not a test report or evidence of a standards pass.
How to check a safety claim against its actual test report
IWFA’s advertising guidance calls for recognised, repeatable methods applied to the product actually sold. Where a standard has a pass criterion, the tested assembly must pass it. Where it has several classes, the claim must identify the class achieved rather than the class attempted. Reports should disclose glass type and thickness, specimen size, film, frame, attachment, units and test conditions. A comparative claim needs comparable filmed and unfilmed tests (IWFA pp. 11-12, 33-34).
The practical question is: Was the tested assembly the one proposed for this opening? Changing a thick pane to thin glass, anchoring to daylight fitting, or a new frame to an old one can invalidate an inference. Terms such as “bullet proof”, “hurricane proof” and “burglar proof” should not replace a matching system report and a clearly bounded result.
13 · STANDARDS AND PLACEInternational test standards do not approve a building in Thailand
The guide describes agencies including GSA, the US Departments of Defense, State and Homeland Security, and FEMA in their respective procurement, security and disaster roles. Mentioning an agency in a manual does not mean that every agency endorses a film product (IWFA pp. 31-32).
ANSI, ASTM, UL, EN and ISO methods give designers a shared language for testing. Actual building requirements depend on jurisdiction, building use, opening location and the current edition of each standard. For life-safety work, the responsible designer and local authority must check the current rules.
14 · DECISION CHECKLISTSix questions to answer before specifying safety film
- Which event is the project trying to mitigate: human impact, storm debris, intrusion, blast or another hazard?
- What are the existing pane type, thickness, dimensions, frame, seal and frame-to-building connections?
- Is there a test report for a matching glazing assembly, rather than film alone or a demonstration video?
- What level did the assembly actually achieve, under which standard edition, units and adhesive cure conditions?
- If solar-control layers are included, has film-to-glass thermal compatibility been checked?
- Has a qualified safety and building professional reviewed the design and local requirements?
To assess solar performance alongside safety, read our architectural RAT, SHGC and TSER guide. To begin a glazing assessment, contact MAXXMA with the glass details and the hazard you need to address.
15 · QUESTIONSFrequently asked questions about safety and security film
Does safety film stop glass breaking?
No. It can help hold fragments and reduce dispersion under tested conditions. Glass can still break, and the filmed sheet can leave the opening if the load or edge retention exceeds its capacity.
Is a thicker film always safer?
Thickness is one material property. The glass, adhesive, frame, attachment and event-specific system result determine what a claim can support.
Does an ANSI Z97.1 pass prove storm resistance?
No. ANSI Z97.1 concerns human impact. Storm tests combine specified debris impact with repeated pressure on a defined window assembly.
Is safety film bulletproof or blastproof?
No such general conclusion is justified. Film on existing glass is not bullet-resistant. Blast-fragment mitigation needs an achieved hazard level at a stated load for a matching assembly.
When should an attachment system be considered?
Start with the hazard and the required tested outcome. Anchoring may improve retention in an applicable system, but the frame, fitting and test report must match the actual opening.
References and limits of this guide
- International Window Film Association. Safety & Security Education Guide (2023). Primary source for this Thai-led editorial adaptation and the concepts behind the original illustrations. This is not an official IWFA translation.
- References to ANSI Z97.1, CPSC 16 CFR 1201, ASTM D882/D1044/D3330/E84/E1886/E1996/F1642/F2912, UL 972, EN 356, GSA TS01 and ISO 16933/16934 explain methods discussed in the IWFA manual. They do not claim that a MAXXMA product has passed them.
- Standards and building rules can change after 2023. Use the current official standards and applicable law when designing or approving a project.
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