Fragment retention film provides optimum performance
against low velocity impacts. This performance is best achieved
when film is installed into the bite of a glazing. Fragment
retention film is not recommended for ballistics or blast
overpressure integrity. Film provides no fragment benefit to
polycarbonate glazing. Reflective film can provide benefits for
solar control as well as obfuscation for occupants of buildings.
The value of fragment retention film is in its ability
to reduce fragmentation damage and its low initial installation
costs. When the limitations and design considerations of film
are recognized and compensated for in a protective system, film
will serve its purpose. However, ignoring these aspects of film
could lead to an expensive security system that does not provide
This handbook does not furnish guidance on applying or
selecting fragment retention film. The U.S. Army Corps of
Engineers provides two documents for this purpose: CEGS-08850,
Fragment Retention Film for Glass, and ETL 1110-1-136,
Engineering and Design: Fragment Retention Film for Glass.
Thermally Tempered Glass (TTG). TTG laminates can be
obtained by lamination with polyvinyl butyral (PVB) or urethane.
Frame compatibility and light transmissibility sets a laminated
glass thickness of 2.5 inch (64 mm) as a practical upper bound.
However, if special circumstances warrant, thicknesses up to 5
inches (127 mm) can be commercially obtained.
When subjected to blast overpressure, laminated TTG
will exhibit strength and behavior between that of a set of
stacked plates and a monolithic plate, depending upon temperature
and duration of load. Conventionally, both the Government and
private industry have set the design strength of a PVB glass
laminate at ambient temperature under load at 75 percent of that
of a monolithic plate of the same thickness as the glass-only
portion of the laminate.
In terms of fragment retention, a laminated blast
resistant lite offers a significant advantage over monolithic
glass. If glass failure occurs, the interlayer material may
retain most of the glass fragments. Also, if a projectile passes
through the glass, most spalling glass fragments will be
retained. Increased safety for fragment retention can be
obtained in the event of a catastrophic failure due to a blast
overpressure by placing a decorative crossbar or grillwork on the
interior of the glazing.