Understanding UL 752

UL 752, Standard for Bullet-Resisting Equipment, is one of the most widely recognized ballistic resistance standards used for architectural security products in the United States.

The standard establishes defined ballistic threats and test conditions that allow products and systems to be evaluated using a consistent methodology. For bullet-resistant glazing, UL 752 provides an important framework for understanding what ballistic threat a tested construction is intended to resist.

A UL 752 designation should not be interpreted simply as a measure of how “strong” a piece of glass is. It represents demonstrated performance against a specific ballistic threat under defined test conditions.

That distinction is fundamental to understanding ballistic glazing.

What Does UL 752 Evaluate?

UL 752 establishes ballistic test requirements for bullet-resisting equipment.

For transparent security glazing, testing subjects the specimen to specified ballistic impacts and evaluates its performance according to the requirements of the standard.

Test parameters address factors such as:

• Ammunition and projectile characteristics
• Projectile velocity
• Number of shots
• Shot placement and spacing
• Test specimen configuration
• Penetration
• Protected-side performance

The purpose is to create repeatable test conditions so that ballistic products are not evaluated according to vague descriptions such as “handgun resistant” or “rifle resistant.” Instead, the ballistic threat is specifically defined.

Engineering Principle

A ballistic designation is meaningful only when the threat and test conditions behind that designation are understood.

UL 752 Has Evolved

For many years, the security glazing industry commonly described UL 752 performance using numerical designations such as Level 1, Level 2, Level 3, and Level 8.

These numerical levels became deeply embedded in architectural specifications, product literature, drawings, test reports, and everyday industry terminology.

The 11th Edition of UL 752 uses Performance Levels 1 through 10. The 12th Edition replaced this numerical classification system with threat-specific performance designations.

Under the 12th Edition:

• UL-HG designates handgun threats.
• UL-RF designates rifle threats.
• UL-SG designates shotgun threats.

Individual threats within these categories are identified by letter, such as UL-HG-A or UL-RF-E.

The letter designations should not be interpreted as a simple hierarchy of increasing ballistic severity. Each designation represents a specific ammunition and ballistic threat defined by the standard.

This change encourages a more useful engineering question.

Instead of asking, “What level of bullet-resistant glass do I need?”, the starting question becomes:

“What ballistic threat does the system need to resist?”

Why Threat-Based Classification Matters

A numerical level can be convenient, but the number itself does not explain the underlying ballistic threat.

Projectile geometry, construction, mass, caliber, velocity, and resulting impact behavior can all influence how a glazing system responds.

A threat-based designation communicates more information about the actual performance objective and encourages specifications to begin with the anticipated threat rather than simply selecting a higher number.

You May Still Encounter Both Classification Systems

The transition to the 12th Edition does not mean the older numerical terminology will immediately disappear.

Architects, engineers, security consultants, glazing contractors, manufacturers, government agencies, and facility owners may continue to encounter legacy numerical UL 752 designations in:

• Existing specifications
• Older test reports
• Architectural drawings
• Previously tested products
• Product literature
• Existing facilities
• Customer requirements

At the same time, newer testing and specifications may reference the threat-based designations used by the 12th Edition.

For this reason, the edition of UL 752 referenced by a project matters.

Specification Insight

During the transition to the 12th Edition, project teams may encounter both legacy numerical levels and newer threat-based designations. Always verify which edition of UL 752 is referenced by the project specification.

What Does It Mean to Pass UL 752?

A successful UL 752 evaluation involves more than simply stopping the projectile.

The tested product must satisfy the applicable requirements of the standard under the specified ballistic test conditions.

For transparent glazing, protected-side performance is especially important.

When glass fractures during a ballistic event, fragments can potentially be released from the protected side of the laminate. This rear-face fragmentation is commonly referred to as spall.

For a transparent glazing product to be UL Listed, protected-side spalling is not permitted. A product that releases protected-side glass fragments during the applicable ballistic test cannot be represented as a UL Listed transparent glazing product.

This creates an important distinction between UL Listed no-spall glazing and independently tested low-spall glazing.

UL Listed vs. Independently Tested to UL 752

The terms UL Listed and tested to UL 752 should not be used interchangeably.

UL Listed

A UL Listed bullet-resistant glazing product has gone through the applicable UL certification process and satisfied the requirements necessary for listing.

For transparent glazing, this includes resisting the applicable ballistic threat without protected-side spalling.

UL Listing represents more than the existence of an individual ballistic test report. It indicates that the product has been evaluated through the applicable UL certification program.

Independently Tested to UL 752 Ballistic Requirements

Bullet-resistant glazing can also be tested by an independent third-party ballistic laboratory using the same ballistic threat, projectile, velocity, shot pattern, and general test methodology associated with the applicable UL 752 classification.

This type of testing can provide objective evidence that the laminate resists the specified ballistic threat, but it does not automatically make the product UL Listed.

This distinction is particularly important for low-spall bullet-resistant glazing.

A low-spall construction can be independently tested using the applicable UL 752 ballistic threat and test methodology. Controlled protected-side glass spalling may occur during this type of independent testing, but projectile penetration is not permitted.

Because a low-spall construction allows protected-side glass release, it cannot qualify as a UL Listed transparent glazing product.

Specification Insight

UL Listed and independently tested to UL 752 ballistic requirements describe different product statuses and should not be treated as equivalent claims.

Why Spall Matters

Spall is a critical distinction between UL Listed no-spall glazing and independently tested low-spall glazing.

A low-spall laminate may successfully resist the same projectile, velocity, shot pattern, and ballistic threat associated with a UL 752 classification while still allowing controlled rear-face glass release.

Because protected-side spalling occurs, that construction cannot be UL Listed.

This does not mean the laminate failed to resist the ballistic threat. It means its protected-side behavior does not meet the no-spall requirements necessary for UL Listing.

Other constructions are specifically engineered for no-spall performance. These systems commonly incorporate polycarbonate or another spall-control technology toward the protected side to prevent hazardous glass fragments from entering the occupied area.

When additional fragment protection is desired in an otherwise low-spall construction, a spall shield may also be incorporated on the protected-side glass surface.

These approaches represent different engineering solutions and should be described according to their actual tested and certified performance.

Ballistic Threat Resistance, Spall Performance, and Certification Are Different Concepts

When evaluating bullet-resistant glazing, it is useful to distinguish among several related but different terms:

• Ballistic threat resistance describes the projectile threat the laminate successfully resists.
• Low-spall performance means projectile penetration is prevented, but controlled protected-side glass release may occur.
• No-spall performance means hazardous protected-side glass release is prevented.
• UL Listed identifies a product that has satisfied the applicable UL certification requirements.
• Independently tested to UL 752 ballistic requirements describes third-party testing against the applicable UL 752 ballistic threat and methodology without representing the product as UL Listed.

Using these descriptions precisely helps architects, engineers, consultants, contractors, and facility owners compare products correctly.

The Test Standard Does Not Define the Entire Installed Glazing System

Another important distinction is the difference between a tested glazing specimen and the complete installed protective opening.

A piece of bullet-resistant glazing does not function independently once it is installed in a building.

The completed system may also include:

• Ballistic framing
• Stops
• Gaskets
• Anchors
• Fasteners
• Hardware
• Structural attachment
• Required glazing bite or edge engagement
• Adjacent wall construction

The tested performance of the glazing itself should not automatically be interpreted as establishing the ballistic performance of every framing or installation configuration in which it may be used.

Project teams should determine whether the specification requires performance of the glazing component, the complete assembly, or both.

Why Test Reports Matter

The ballistic designation shown on a product data sheet is only part of the information needed to understand the tested performance of a glazing system.

Test documentation can provide important information including:

• The standard and edition used
• The ballistic threat or designation
• Ammunition
• Projectile velocity
• Number of impacts
• Test specimen configuration
• Protected-side behavior
• The laboratory performing the test
• The test date
• The reported test result

Reviewing the test documentation helps determine whether the configuration evaluated corresponds to the requirements of a particular project.

A ballistic designation without its underlying test context can lead to incorrect assumptions.

Testing Validates a Specific Construction

Ballistic testing validates the configuration that was actually evaluated.

Changes to a laminate can potentially influence its ballistic performance.

Examples include changes to:

• Glass thickness
• Glass type
• Interlayer material
• Interlayer thickness
• Polycarbonate thickness or grade
• Layer sequence
• Overall laminate thickness
• Spall-control components
• Other construction details

For this reason, two visually similar laminates or two laminates of the same overall thickness should not automatically be assumed to provide identical ballistic performance.

Testing provides objective validation of an engineered construction under defined conditions. It does not eliminate the need for engineering judgment.

UL 752 Is a Ballistic Standard

UL 752 addresses ballistic resistance. It should not automatically be interpreted as demonstrating performance against other security threats.

Projects concerned with prolonged physical attack or active-shooter forced-entry resistance may also reference standards such as:

• ASTM F1233 for forced-entry resistance
• ASTM F3561 for forced-entry resistance of fenestration systems after simulated active-shooter attacks

A security glazing system may therefore be engineered and tested against multiple standards when a project requires protection against multiple threats.

How Should UL 752 Be Used in a Specification?

A good ballistic specification begins with the actual performance objective.

Rather than selecting glazing simply because it carries a familiar designation, project teams should consider:

1. What ballistic threat is anticipated?
2. Which edition of UL 752 applies?
3. What performance designation corresponds to that threat?
4. Is UL Listing required, or is independent third-party testing acceptable?
5. What protected-side or spall performance is required?
6. Does the requirement apply only to the glazing or to the complete installed assembly?
7. Are additional threats or performance requirements also part of the project?

This threat-first approach provides a clearer basis for selecting and comparing bullet-resistant glazing systems.

Key Takeaways

• UL 752 is a ballistic resistance standard, not a general measure of security glazing quality.
• Ballistic classifications represent performance against defined threats under specified test conditions.
• The 12th Edition replaced the previous Level 1 through 10 system with threat-specific UL-HG, UL-RF, and UL-SG designations.
• The lettered 12th Edition designations should not be interpreted as a simple hierarchy of increasing threat severity.
• Always identify which edition of UL 752 is referenced by a project.
• UL Listed and independently tested to UL 752 ballistic requirements are not equivalent descriptions.
• For transparent glazing, a UL Listed product must provide no-spall protected-side performance.
• Low-spall products cannot be UL Listed because controlled protected-side glass release occurs.
• Low-spall glazing can be independently tested using the applicable UL 752 ballistic threat and methodology, with spalling permitted under the independent test criteria but no projectile penetration.
• Test documentation provides essential context behind a ballistic designation.
• Good ballistic design begins with the anticipated threat rather than simply selecting a level or designation.

Continue Learning

PA-EF-001 — What Is Bullet-Resistant Glass?

Learn the fundamentals of ballistic glazing, laminate construction, threat-specific performance, and system integration.

PA-EF-004 — Understanding Spall

Understand rear-face fragmentation and the differences among low-spall, spall-protected, and no-spall glazing approaches.

PA-ED-001 — How Engineers Design Security Glazing Systems

Learn how engineers begin with the threat and balance security, materials, weight, optics, architecture, durability, and testing.

PA-TS-002 — Understanding ASTM F1233

Explore how security glazing is evaluated against prolonged physical attack and forced-entry threats.

PA-TS-003 — Understanding ASTM F3561

Understand how ASTM F3561 evaluates fenestration systems against forced-entry attack following a simulated active-shooter event.