Changing Fire Dynamics

Analysis of Changing Residential Fire Dynamics


Modern Day Fire Environment

The workplace of today’s firefighter is very different than it was even 25 years ago.  New building construction materials and the composition of home furnishings are drastically different.  Today’s home contents contain large quantities of petroleum-based products and synthetics that burn faster and hotter versus traditional, more natural materials such as wood and cotton.  Commonplace prefabricated materials and lightweight construction components are now the norm in homes and buildings constructed in the United States.

These modern materials are releasing heat at exponentially faster rates and reaching flashover faster than ever.  These combined factors have drastically changed the potential operational timeframe that firefighters have to make interior attacks.   That being said, there are some tactical considerations that can make interior operations safer for victims and ourselves.  See what today’s science is telling us about the modern fire environment.

Building Construction

The materials, construction methods and designs of today play an influential role in how fire now behaves and the revised tactics that firefighters must consider in order to safely and effectively fight these modern fires. With the majority of new homes today constructed with lightweight materials, there is a much greater risk for catastrophic structural collapse well within the operational time frames. Additionally, open floor plans, between both rooms and floors, allows for quicker fire spread throughout a structure.

Fuel Load

Today’s home contents are largely synthetic materials – carpets, plastics, composites – and have an exponentially higher rate of heat release than more traditional, wood-based materials of the past.  This creates an environment where fire grows more quickly and reaches flashover many times faster than in the past.  Flashover is now occurring regularly within the standard arrival time of many departments, thereby adding to the risk of structural collapse, as mentioned above.

Operational Time Frame

For years, incident commanders conducted fire ground operations using the “20 minute rule,” which suggested that a crew has approximately 20 minutes to make progress on extinguishing a fire.  Science is showing that this time frame is now outdated.  Due to the modern fire environment, building construction and fuel load, fire is accelerating faster and times to collapse and flashover are shrinking. Firefighters must be aware that the window of time they have to make an interior attack has greatly diminished.

Analysis of Changing Residential Fire Dynamics

UL’s analysis examines the all-encompassing effect from changes in residential environment in terms of fire dynamics and the implications for firefighter tactics. UL’s study examines the impact of the modern residence on fire dynamics and its impact on firefighting tactics. The residential fire conditions that firefighters arrive at today are very different than the conditions faced several generations ago.

The steady change in residential fire environment includes:

  • Larger homes (increase in two story homes)
  • Open home geometries (taller ceilings, open floor plans, two story foyers, great rooms)
  • Home Contents/Increased synthetic fuel loads (plastics and textiles)
  • New construction materials (engineered products, green/sustainable items).

UL compared the changes in home contents and construction materials through six experiments contrasting modern and legacy living room contents across three pairs of living room fires. Then the findings from these experiments were examined in the context of firefighting operational timelines.

The six experiments revealed that fire dynamics change rapidly in today’s modern rooms.

Faster Flashover

  • Modern rooms had flashover occur in less than five minutes, the shortest timeframe for a legacy room to transition to flashover was 29 minutes.
  • Demonstrated that the fire has transitioned to flashover in most cases prior to arrival of fire service or at the very least crews will encounter a ventilation limited fire.

Faster Fire Propagation

  • Modern window & interior doors fail faster than legacy counterparts.
  • The change in modern dry wall linings now allows for more content fires to become structure fires. Fire penetrates wall lining and fills the void and allows for faster fire propagation.

Shorter Times to Collapse

  • Modern home construction techniques have removed components that had prolonged collapse.
  • After unit arrival at eight minutes from ignition, collapse is possible as soon as 1 minutes 30 seconds later; the legacy room fire collapse hazard begins at 40 minutes after arrival.

Shorter Resident Escape Times

  • The impact of ventilation (flow paths) is the key to the fire development in structures
  • Fire departments must reexamine their tactics to ensure they are still relevant within this evolving fire environment