Bedding and furniture are rarely the first items to ignite in a house fire. But once they’ve been lit, the synthetic materials in modern furnishings burn faster and release more smoke and toxic gasses than natural materials, which were more common in the past.
UL, a nonprofit organization that sets the safety standards for smoke alarms and other products, published a startling video showing two rooms burning side by side: one with largely natural materials and the other furnished with synthetics.
Within five minutes, the room furnished with synthetic materials—such as engineered wood and several types of plastic, including polyurethane foam stuffing—was engulfed in flames. The one filled with natural materials—like cotton, solid wood, and glass—took more than 30 minutes to reach the same point. UL ran this experiment four times, with similar results in each.
As we reported in our guide to smoke alarms, the typical time to escape from a house fire has fallen from 17 minutes in the 1970s to about three minutes today. Every minute matters, and the latest smoke alarms are tested to buy you extra time.
After more than a decade of research and planning by several government, nonprofit, and industry groups, these safety staples have finally caught up with the fire risks posed by modern furniture.
The most important update to the smoke alarm safety standards (known as the UL 217, 8th edition), which went into effect in 2024, means that new alarms are better at detecting both smoldering and flaming fires in polyurethane foam—the material used to stuff modern furniture and bedding.
Upholstered furniture and mattresses are a significant factor in nearly half of house fires, and they’re associated with more than a third of all deaths, according to statistics published by the National Fire Protection Association (NFPA). But polyurethane foam fires were a challenge for older household smoke alarms to detect, according to Shawn Mahoney, an engineer at NFPA. Burning foam creates a different kind of smoke than the previous generation of alarms had been designed to look for. The particles are both very large and very small relative to the makeup of other common types of fire.
Crucially, new alarms are more sensitive to furniture foam fires—without also becoming more sensitive to smoke from normal cooking. Testing by the federal National Institute of Standards and Technology confirmed that although a pan full of sizzling bacon might still set off a nuisance alarm, it happens at about the same rate as the older generation of smoke alarms.
When smoke alarms trigger too easily, it’s a problem. As senior staff writer Doug Mahoney (no relation) said on a recent episode of The Wirecutter Show podcast, “If [nuisance alarms] happen enough, people get very frustrated with them, and then they just take the smoke alarm off their wall, take the batteries off it, and then leave themselves with no early warning system at all.”
Estimates vary on how often people purposely disable their smoke alarms because of those nuisances. But the NFPA has pointed to it as a notable cause of deaths from house fires. One study found that 19% of homes with ionization-type smoke alarms—known for greater sensitivity to cooking fumes—had them purposely disabled, likely as a result of cooking-related nuisance alarms. So it’s not a rare occurrence.
