Large Missile Impact Test for Hurricane Glazing: ASTM E1996 Pass Criteria

The large missile impact test for hurricane glazing is the ASTM E1996 procedure that fires a nine-pound piece of lumber at a window, door, or skylight at roughly 34 miles per hour, then puts the damaged specimen through 9,000 pressure cycles to see whether it can keep wind out of a building for the rest of a storm. A product passes only if the lumber does not punch through, the laminated interlayer holds together within strict tear limits, and no opening forms that would let a three-inch sphere pass. The test is run using the laboratory procedures in a companion standard, ASTM E1886.¹

The Nine-Pound 2×4

The projectile is a piece of Southern Pine or Douglas Fir lumber with nominal two-by-four-inch dimensions, weighing between 9 and 9.25 pounds. That usually works out to a length around eight feet, though anywhere from seven to nine feet is acceptable so long as the weight falls in range. The piece has to be sound: no large knots, splits, or defects that would cause it to shatter in flight instead of hitting the glass as a concentrated mass.¹

The choice is not arbitrary. In a hurricane, roofing material, fence boards, and framing lumber are the debris that actually breaks buildings. A nine-pound timber traveling at 34 mph delivers roughly the kinetic energy of that kind of debris striking a window during a major storm.

Two Impact Speeds: Level D and Level E

The large missile is fired at one of two speeds, depending on what the building is for.

Level D is the standard protection level: the nine-pound 2×4 at 50 feet per second, about 34 mph. This applies to most residential and commercial openings in hurricane zones at 30 feet above grade or below.
Level E is enhanced protection: the same lumber at 80 feet per second, about 55 mph. It is reserved for essential facilities like hospitals, emergency operations centers, and hurricane shelters.

Doubling the velocity roughly quadruples the impact energy, which is why Level E products carry a substantial price premium over standard residential glazing.¹

Openings high on a building, generally above 30 feet, are not expected to be hit by framing lumber and are tested instead under Level A, a small-missile protocol using a two-gram steel ball fired at 130 feet per second. That’s a different test with a different projectile, and a product rated only for Level A is not an impact-rated window in the sense most buyers mean.

How the Specimen Is Set Up and Hit

A minimum of three identical specimens are mounted into rigid test frames using the exact hardware, fastener spacing, and installation method the manufacturer specifies for the field. The test validates the whole system, not just the glass, so shortcuts in mounting would make the results meaningless. Before testing, the specimens sit in a controlled environment between 59 and 95 degrees Fahrenheit for at least four hours, bringing the glass and its polyvinyl butyral (PVB) interlayer to a stable temperature; the interlayer’s flexibility changes with temperature, and the standard narrows that variable before any lumber flies.¹

A compressed-air cannon with a quick-release valve launches the 2×4 at the calibrated speed. Each of the three specimens takes two hits: one near the center of the glass panel, and one at a corner roughly six inches from the edge. The corner shot is the harder of the two. It attacks the bond between the glass and the frame where stress concentrations are highest, and it’s where weaker products tend to come apart.¹

9,000 Pressure Cycles After the Impact

The impact is only the first half of the test. After the lumber strikes, each specimen moves into a pressure chamber for cyclic loading: 9,000 positive and negative pulses that alternately push and pull on the damaged panel. The sequence ramps through stages of increasing and decreasing intensity, replicating the fluctuating wind gusts that hammer a building envelope over the hours a hurricane takes to pass.

By the time the cycling begins, the glass is almost certainly shattered. The outer lite is broken. What holds the line is the PVB interlayer, the tough plastic film laminated between glass layers that keeps the broken pieces bonded and maintains a continuous barrier against the wind. If that film tears, stretches open, or pulls away from the frame during those 9,000 pushes and pulls, the building loses its envelope.

What Counts as a Pass

The first requirement is simple: the lumber cannot pass through the glazing on impact. If the 2×4 punches clean through, the test ends with a failure right there. If the missile is stopped, the specimen moves on to pressure cycling, and after 9,000 cycles the lab inspects the damage against two measurements.

No tear in the interlayer may exceed five inches in length and one-sixteenth of an inch in width. Cracks in the glass are expected and acceptable; the question is whether the film behind the glass has opened enough to let air through.
No opening anywhere in the glazing may be large enough to allow a three-inch-diameter solid sphere to pass through. This catches cases where there’s no single long tear but the interlayer has deformed or pulled away enough to leave a hole.

The glass must also stay anchored. Any significant pullout from the mounting system is a failure, because a panel that detaches even partially creates an opening large enough to pressurize the building interior. Glass, interlayer, frame bond, fasteners, and installation method all contribute to the pass-or-fail outcome.¹

Confirming a Product Actually Passed

A product that passes carries a permanent etching, usually in one corner of the glass, listing the supplier’s name, place of fabrication, date of manufacture, glass thickness, and the certifications met. If the etched corner had to be cut away during assembly, a removable sticker with the same information takes its place.²

If you are buying a home or replacing windows in a hurricane zone, that etching is the fastest check. Standard laminated glass can look very similar to impact-rated glass without ever having been tested to E1996. If there is no etching and the manufacturer cannot produce test documentation referencing both ASTM E1996 and ASTM E1886, the product has not been validated for windborne debris.

How This Fits into the Building Code

Building codes in hurricane-prone areas, including the International Building Code and the International Residential Code, require exterior glazing in windborne debris regions to meet the missile levels and pressure requirements in ASTM E1996, tested using the procedures in ASTM E1886.³ The two standards travel as a pair: E1996 defines what the product must withstand, and E1886 defines how the lab runs the air cannon and the pressure chamber. A product tested under E1886 to the thresholds in E1996 is what earns a hurricane rating.

The specific missile level and pressure that apply depend on where the opening sits on the building and where the building sits geographically. Local building departments determine the combination for a given installation. A ground-floor window on an exposed coast may need Level D or Level E; an upper-story opening in the same building may only need Level A. A product installed without the correct rating for its location will fail inspection.³

Hurricane shutters are an alternative path to code compliance. Panel, accordion, and roll-down shutters can be tested to the same ASTM standards and, if they pass, satisfy the windborne debris requirement without impact-rated glass behind them. Either option works at the code level as long as the product carries the rating that matches the opening.

1
ASTM International. E1996 Standard Specification for Performance of Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Windborne Debris in Hurricanes
2
Building America Solution Center. Windows Have Impact-Rated Glass, Fire-Resistant Glass, or Protective Coverings
3
Federal Emergency Management Agency. 2018 IBC Compilation Wind Resistant Provisions