Engineering Fundamentals | PA-EF-005
Bullet-Resistant vs. Forced-Entry Resistant Glazing
Bullet-resistant glazing and forced-entry resistant glazing are both
engineered to protect transparent openings, but they are designed to
address fundamentally different types of threats.
Overview
Bullet-resistant glazing is designed to resist defined
projectile threats.
Forced-entry resistant glazing is designed to resist repeated
physical attack and delay the creation of an opening through the
protected assembly.
The distinction is important because a glazing system designed and
tested for one type of threat should not automatically be assumed to
provide equivalent protection against the other.
Some security glazing systems can be engineered and tested to provide
both ballistic and forced-entry resistance. When multiple threats must
be addressed, however, each performance requirement should be evaluated
independently.
The Fundamental Difference: The Threat
The easiest way to understand the difference is to consider what the
glazing is being asked to resist.
Bullet-Resistant Glazing
A ballistic event involves a projectile traveling at high velocity
and delivering a large amount of energy over an extremely short
period of time and a relatively small impact area.
The glazing must manage that energy while resisting penetration by
the specified projectile threat.
Forced-Entry Resistant Glazing
A forced-entry event generally involves repeated physical attacks
over a longer period of time.
An attacker may strike, cut, pry, or otherwise attempt to defeat the
glazing and surrounding system until an opening can be created.
The glass may fracture during this process. The security objective
is for the laminated assembly to continue functioning as a barrier
despite that damage.
Engineering Principle
Ballistic resistance focuses on resisting a defined projectile
threat. Forced-entry resistance focuses on maintaining a barrier
during repeated physical attack. They are different loading
conditions and different security objectives.
How the Glazing Responds Differently
Both ballistic and forced-entry laminates can use combinations of
glass, interlayers, polycarbonate, and other transparent materials.
What changes is how those materials are selected and arranged to
address the required threat.
During a ballistic event, the laminate must manage a rapid transfer
of projectile energy. Glass may fracture, interlayers may stretch and
retain fractured material, and polymer components may deform as the
complete construction works to resist penetration.
During a forced-entry event, the glazing may experience repeated
impacts and progressive damage. Once the glass fractures, the
interlayer system becomes particularly important in maintaining
continuity and resisting tearing, displacement, penetration, and the
creation of an opening.
The same materials may therefore appear in both types of glazing
while performing within systems engineered around different
performance objectives.
Breaking the Glass Does Not Necessarily Defeat the System
This is particularly important when discussing forced-entry glazing.
Security glazing is not necessarily intended to remain visually
intact throughout an attack.
The glass can fracture extensively while the laminate continues
functioning as a protective barrier.
In forced-entry applications, the critical question is not simply:
Did the glass break?
The more important question is:
Did the attack create the opening or passage defined as failure
by the applicable test method?
A heavily fractured laminate can therefore still be performing its
intended security function.
Ballistic Resistance Is Threat-Specific
A bullet-resistant rating should not be interpreted as a universal
indication that a glazing system will stop every firearm or
projectile.
Ballistic standards define specific test conditions that can include:
- Projectile type
- Projectile construction
- Projectile mass
- Velocity
- Number of impacts
- Shot location and spacing
- Acceptable penetration and rear-face performance criteria
A laminate designed for one ballistic threat should not automatically
be assumed to resist another.
This is why the applicable ballistic standard and threat level are
essential parts of the specification.
Continue Learning:
PA-TS-001 — Understanding UL 752
Forced-Entry Resistance Is Attack-Specific
Forced-entry performance is also defined by the applicable test
method.
Different standards may use different:
- Impact tools
- Attack sequences
- Impact energies
- Number of strikes
- Attack locations
- Duration or resistance levels
- Pass/fail criteria
- Opening or passage requirements
Several standards can be relevant depending on the application.
ASTM F1233 evaluates security glazing through
defined physical attack methods.
ASTM F1915 addresses glazing used in detention and
correctional facilities, where resistance to physical attack and
containment are important performance considerations.
ASTM F3561 addresses forced-entry resistance
following simulated active-shooter weakening.
The rating therefore needs to be understood in the context of the
specific test method used.
A Ballistic Rating Does Not Automatically Mean Forced-Entry Rated
This is one of the most important distinctions in security glazing.
A laminate may successfully resist a ballistic threat without having
been evaluated for the sustained mechanical attack required by a
forced-entry standard.
Likewise, a forced-entry resistant laminate may remain an effective
barrier through extensive physical attack without being designed or
rated to stop a projectile.
Ballistic resistance should not be used as a substitute for a
forced-entry rating.
Forced-entry resistance should not be used as a substitute for a
ballistic rating.
If the project requires both, the system should be evaluated against
both applicable performance requirements.
Some Systems Can Provide Both
Ballistic resistance and forced-entry resistance are not mutually
exclusive.
A laminate can be engineered to address both threats.
For example, certain multi-ply glass laminates, glass/polycarbonate
constructions, or other engineered security laminates may provide
ballistic protection while also providing substantial resistance to
sustained physical attack.
However, the presence of materials associated with one type of
construction does not establish the other rating.
The required performance must still be demonstrated through the
appropriate testing or qualification.
This is particularly important when specifications call for
multi-threat protection.
What About Active-Shooter Glazing?
Active-shooter security introduces another important distinction.
The phrase active-shooter glazing can sound as though the
glazing must necessarily stop bullets.
That is not always the case.
Some active-shooter test methods use gunfire to
weaken the glazing or fenestration system before a
subsequent forced-entry attack.
ASTM F3561 is an important example. Projectile impacts are used as
part of the weakening sequence before mechanical impact testing.
Passing the forced-entry requirements of that standard does not, by
itself, establish a ballistic-resistance rating.
A system intended to provide both active-shooter forced-entry
resistance and ballistic resistance must satisfy
the applicable requirements for each.
Continue Learning:
PA-EF-006 — Active-Shooter Glazing Explained
The Complete Opening Matters
Neither ballistic nor forced-entry glazing should be evaluated only
as a piece of transparent material.
The complete protective opening can include:
- Glazing
- Frame
- Glazing stops
- Edge engagement
- Gaskets and sealants
- Anchors
- Hardware
- Doors or operable components
- Surrounding structure
A high-performing laminate installed in an inadequate frame or
retention system may not provide the intended performance for the
complete opening.
This becomes especially important in forced-entry applications
because an attacker can attempt to defeat the weakest accessible
part of the system rather than attacking only the center of the
glazing.
The glazing and surrounding assembly therefore need to be considered
together.
Selecting the Appropriate Protection
The starting point should not be:
“Do I need bullet-resistant glass or forced-entry glass?”
A better starting point is:
“What threat or combination of threats does this opening need to
resist?”
From there, engineers and specifiers can evaluate:
- Ballistic threat
- Forced-entry threat
- Required delay or resistance
- Applicable test standards
- Spall requirements
- Occupancy and use
- Frame and anchorage system
- Panel size
- Weight
- Thickness
- Optical requirements
- Architectural requirements
- Environmental exposure
- Maintenance
- Long-term service conditions
In some projects, ballistic resistance may be the primary
requirement.
In others, forced-entry delay may be the primary objective.
And in higher-security applications, the system may need to address
both.
A Simple Comparison
| Consideration | Bullet-Resistant Glazing | Forced-Entry Resistant Glazing |
|---|---|---|
| Primary Threat | Projectile impact | Repeated physical attack |
| Primary Objective | Resist penetration by the specified ballistic threat | Delay or prevent creation of a defined opening |
| Typical Loading | Very rapid, high-energy impact | Repeated mechanical impacts over time |
| Glass May Fracture? | Yes | Yes |
| Fracture Automatically Means Failure? | No | No |
| Interlayers Important? | Yes | Yes—particularly after glass fracture |
| Typical Standards | UL 752 and other ballistic standards/specifications | ASTM F1233, ASTM F1915, ASTM F3561 and other applicable standards |
| Can One System Address Both? | Yes, when appropriately engineered and evaluated | Yes, when appropriately engineered and evaluated |
Key Takeaways
Bullet-resistant and forced-entry resistant glazing address
different threats.
- Ballistic glazing is designed to resist defined projectile
threats. - Forced-entry glazing is designed to maintain a barrier during
repeated physical attack. - Glass fracture does not automatically indicate failure in either
type of security glazing. - A ballistic rating does not automatically establish forced-entry
performance. - A forced-entry rating does not automatically establish ballistic
performance. - Some security glazing systems can be engineered and tested to
address both threats. - Active-shooter forced-entry testing should not automatically be
interpreted as ballistic-resistance testing. - The glazing, frame, retention system, anchorage, hardware, and
surrounding structure should be considered as part of the
complete protective opening.
The threat should drive the glazing and system design—not the
product label.
Continue Learning
- PA-EF-001 — What Is Bullet-Resistant Glass?
Learn how ballistic glazing manages projectile energy and why
different laminate families exist.
PA-EF-002 — What Is Forced-Entry Resistant Glass?
Explore how laminated glazing can remain an effective security
barrier even after extensive glass fracture.- PA-EF-006 — Active-Shooter Glazing Explained
Understand the important distinction between ballistic weakening,
forced-entry resistance, and true ballistic protection. - PA-TS-001 — Understanding UL 752
Learn how ballistic-resistant equipment is evaluated against
defined projectile threats. - PA-TS-002 — Understanding ASTM F1233
Explore physical-attack testing used to evaluate security glazing. - PA-TS-003 — Understanding ASTM F3561
Learn how fenestration systems are evaluated after simulated
active-shooter weakening. - PA-TS-004 — Understanding ASTM F1915
Learn about security glazing requirements for detention and
correctional applications.
