How Impact Glass Is Tested
Missiles and Wind Pressure
Miami-Dade County has the strictest code approval requirements in the United States. In order for impact-resistant windows to be approved by Miami-Dade, the windows must be vigorously tested to ensure they meet all requirements. Two main tests conducted by manufacturers are the Missile Test and the Cyclical Test.
The Missile Test determines the glass’s ability to withstand impact. This does NOT mean that impact glass will not break, it simply means the window will remain intact and stay in its frame. Windows and glass doors that have been proven to resist the hurricane impact testing from large windborne debris are referred to as impact rated products. To test the glass’s strength a 9-pound, 2x4 piece of lumber, traveling 50ft-per-second is launched at the glass – twice. The lumber is considered a “large missile”. To test for ratings for “small missiles” ten 2g (gram) steel balls are simultaneously launched at 89mph, three separate times.
The Cyclical Test determines if glass meets pressure requirements for storm-force winds. Following the Missile Test, the glass is placed in a pressure simulator where positive and negative pressure flexes the glass pane for 4,500+ cycles. The results determine the pressure rating for the impact glass.