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Modern Residential Fires
UL determined that fires today are more dangerous and pose more risks than in the past. Fire propagation is faster, and time to flashover, escape times and collapse times are all shorter.
UL’s research scientists and engineers have conducted a number of innovative tests and evaluated their results, and have identified that the modern home fire is a “perfect storm” of conditions and outcomes: larger homes + open house geometries + increased fuel loads + new construction materials = faster fire propagation, shorter time to flashover, rapid changes in fire dynamics, shorter escape times and shorter structural collapse times.
WHAT DID UL DO?
UL has conducted hundreds of analytical studies to understand individual aspects of home fires over the years. In 2012 UL brought its cumulative insights together in a series of unique tests to advance the science of residential fires. In order to understand the full implications of modern home fires, UL scientists conducted a series of experiments that took into account key changes to the modern home. These changes cover differences in the size and geometry of modern homes as well as the furnishings and construction materials used.
In the experiments, three modern home configurations were tested against three “legacy” configurations, defined as having furnishings from the mid-20th century and building materials from between 1950 and 1970. The tests showed a consistency of results among the three modern rooms and the three legacy rooms that we examined. All of the modern rooms transitioned to flashover — flashover occurs when the majority of exposed surfaces in a space are heated to their autoignition temperature and emit flammable gases — in less than five minutes, while the fastest legacy room to achieve flashover did so in just over 29 minutes. In the three sets of experiments, legacy- furnished rooms took at least 700 percent longer to reach flashover.1
The experiments revealed that the natural materials in the legacy rooms released energy more slowly than did the fast-burning, synthetic-furnished modern rooms, which leaves significantly less time for occupants to escape the fire. The experiments also demonstrate to firefighters that in most cases, the fire has either transitioned to flashover prior to their arrival or has become ventilation-limited and is waiting for a ventilation opening to increase its burning rate. This difference has a substantial impact on occupant and firefighter safety and leads to faster fire propagation, shorter time to flashover, rapid changes in fire dynamics and shorter escape times.2
Our advanced testing also examined four types of new construction materials: wall linings, structural components, windows and interior doors. The change in modern wall linings now allows for more content fires to become structural fires by penetrating the wall linings and involving the void spaces. This shift causes faster fire propagation and shorter times to collapse. Structural components have generally been made lighter by removing mass, which causes them to collapse significantly faster.4
In these experiments, an engineered I-joist floor system collapsed in less than one-third the time than did the dimensional-lumber floor system. Modern windows and interior doors fail faster than do their legacy counterparts. The windows failed in half the time, and the doors failed in approximately five minutes. If a fire in a closed room is able to access air to burn from a failed window, then it can burn through a door and extend to the rest of the house. As with the previous experiments, it was discovered that the use of new construction materials also leads to faster fire propagation, rapid changes in fire dynamics and shorter escape times for occupants and firefighters.5
UL’s first-of-its-kind testing also identified collapse implications. Specifically, in the modern fire environment, if firefighters arrive at eight minutes, collapse is possible as soon as 90 seconds later. Firefighters may not be in the house yet or may be just entering to search for occupants. In contrast, our research showed the legacy fire collapse begins 40 minutes after the arrival of firefighters. In a legacy home, the extra time before collapse would allow for a significant number of fire operations to take place while firefighters were reading the safety of the structure.6 UL is working today to make improvements in these systems, working closely with manufacturers and other important stakeholders.
WHY IT MATTERS
The overall finding of UL’s fire testing is that the changes in the modern home create fires that reach flashover more than eight times faster than homes built 50 years ago. This much more rapid progression to flashover gives residents, firefighters and other first responders much less time to react, creating significant hazards to health and property.7
The findings about modern home fires highlight that the conditions firefighters face today and will face in the future are very different than those faced by prior generations. Because of these changes, firefighting tactics need to change or be reevaluated to help assure they are effective. UL is working closely with the fire community to further examine and consider new methods and operational practices to advance safety.