As hurricane season approaches, ASTM International gave a history lesson on its windborne debris standards for glazing systems. David Hattis, president of Building Technology Inc., led a webinar titled, “Windborne Debris Standards in Hurricanes for Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems,” as part of ASTM’s resilience in construction series.
Hattis explained that Hurricane Alicia, which hit Houston in August 1983, was when the industry originally recognized that windborne debris is a major source of glass breakage during hurricane events. In the case of Hurricane Alicia in Houston, roof gravel caused a large amount of glass breakage on commercial buildings.
“If debris breaks the building envelope, windows or glazed openings it causes pressurization,” said Hattis, adding that when a building is partially enclosed the interior pressure increases significantly and can lead to a partial or full building collapse.
The immediate response to the recognition of the problem was windborne debris impact research conducted by professor Joe Minor at Texas Tech. The laminated glass industry, including DuPont and Monsanto, which both manufactured PVB at the time, began working on windborne debris impact requirements. According to Hattis, glass and window manufacturers opposed these requirements.
“They didn’t see the need for impact testing and breaking glass in a laboratory,” he said.
In the late 1980s or early 1990s, Minor and Hattis brought the issue before the Southern Building Code Congress International (SBCCI).
“PPG was so opposed they sent top executives to where we were meeting in Birmingham, Ala., to kill the idea of windborne debris impact requirements,” said Hattis, explaining that the decision was made to move the standard to ASTM instead of the SBCCI.
ASTM Task Group E06.51.17 was established in the early 90s with Hattis as chair. Their goal was to develop a test method followed by a specification. The first part of the test involves impacts by missiles representing windborne debris. The second is pressure cycling, which represents hurricane winds with positive and negative pressures.
The impact test includes two types of missiles: a large missile and a small missile. The large missile is a 2×4 of timber to represent the structural elements while the small missile is a steel shot, which represents roof gravel. The missiles are shot from two types of apparatus: an air cannon and a bungee. However, Hattis said that most tests currently use the air cannon.
The glazing system is then subjected to 9,000 pressure cycles, which can take seven to eight hours.
ASTM E1886, Standard Test Method for Performance of Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Missile(s) and Exposed to Cyclic Pressure Differentials, was first published in July 1997 after four years of work. ASTM E1996, Standard Specification for Performance of Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Windborne Debris in Hurricanes, was first published in September 1999. The ASTM task group completed the two standards in preparation for the International Code Council’s codes in 2000. ASTM E1996 was recognized by ASCE7 and the International Building Code.
Three specimens must be tested for the large and small missile tests and three impact locations must be chosen for each. For the large missile test the glass must be hit in the center, in one corner and then in the opposite corner. For the small missile test the glass must be hit in three different spots at one time. Missile tests are determined by wind zone and building type. To pass, fenestration can have no tear formed longer than 5 inches nor any opening through which a 3-inch sphere can pass.
Hattis said one of the most important changes that’s been made to the standards is impact protective system substitutions. He explained that manufacturers wanted to be able to change out minor details without having to retest three identical specimens. Four substitution categories were created:
- Automatic: No additional testing or analysis necessary;
- Engineering analysis: Demonstrated or documented performance through a review of materials that predicates a minimum of equivalent performance required;
- Single specimen: One specimen to be tested, identical to the original specimens qualified with the only difference being the elements to be substituted; and
- Not allowed: A substitution not qualified by testing of a single specimen. Three identical specimens out of four are required to qualify the substitution, such as a new product.
“This was an important adjustment to meet the needs of the industry,” he said.