Experts call it a fire crisis. New, lightweight residential construction methods, green building materials, open floor plans and larger square footage are making it harder and more dangerous for firefighters to safely extinguish house blazes and for occupants to safely escape them. "It's estimated that most homes built within the past 20 years contain these dangerous lightweight materials, which are designed to carry a greater load with less material by using prefabricated components," says Russell Fleming, president of the National Fire Sprinkler Association. The lightweight construction materials are more cost-effective and environmentally friendly, but they allow fires to spread much more rapidly, reducing the time homeowners have to escape a fire -- and the time firefighters have to safely extinguish it. Traditionally, floor joists that held up the floor would be a 2x6 piece of lumber every 12 inches, explains Peter Struble, practitioner in residence in the Fire Science Program at Henry C. Lee College of Criminal Justice and Forensic Sciences at the University of New Haven and the fire chief in Wallingford, Conn. "Now they're using what's called an engineered wood i-joist, which is much lighter weight and is not as substantial, and a lot of times it's thin pieces of wood glued together. It's extremely strong as long as it's not being attacked by fire," says Struble. "When it's attacked by fire, it fails abruptly," he says. The National Institute of Safety tested traditional wood floor joists and the engineered i-joist's burning rates. It took 19 minutes for the traditional wood to burn versus six minutes for the engineered wood i-joist, says Struble. That spells danger for firefighters, especially with basement fires. When a firefighter enters a burning residence, the floor may already be gone or the outside might just be a facade with everything inside burned away already. With a little bit of weight, the entire floor collapses and firefighters go down with it.