Ed. note: In the Fall of 2015, building upon the success of cooperative efforts to develop and implement the Firefighter Training – Best Practices, State Fire Administrator Bryant Stevens convened a meeting of the state’s largest fire service organizations with the goal of examining and planning for the future of the fire service. At the table are the OFPC, New York State Association of Fire Chiefs, FASNY, Association of Fire Districts of the State of New York, New York State Fire Coordinators’ Association and New York State Professional Fire Fighters Association. The goal of this group, which has been designated “Moving Forward,” is to examine issues that the fire service is confronting in the 21st century and provide information to fire departments and districts about the ways these issues can and may be addressed. One of the ways the Moving Forward group has chosen to do this is through a series of informative articles to be published in the various magazines and newsletters the groups publish. The following article is part of this effort.
Unless you have been living in a cave, most know that they don’t build buildings like they used to. Modern construction techniques use less raw material in their natural state and have greater dependence on pre-engineered, manufactured “systems” that often replace more traditional materials. This trend results in lighter-weight materials being used.
While these construction techniques provide a number of benefits to the designer, contractor and owner of the building, they provide the fire service with a number of critical concerns when there is a fire in these buildings.
We all realize each building is unique, however, in many newer buildings, these modern-day combustibles and con-struction techniques pose distinct hazards and changes in how the building “behaves” in fire conditions.
A few of these include:
- The average size of the single family home has grown substantially in the last 50 years.
- These larger homes are built with open interior floor plans. The first floors of today’s homes are typically one large open floor space.
- Residential layouts have evolved from basic modular layouts to today’s more spacious and open designs.
- Stairways leading to upper and lower levels are typically open, exposing upper floors to rapid fire spreading.
- Open designs allow for more usable floor space for the inhabitants, but lack of interior dividers also increases the spread of fire and fire gasses.
- These large, open spaces are filled with petroleum-based contents and produce fires that grow much faster than their natural material predecessors.
- Fire-loading has increased.
- An increase in the use of plastics and treated fabrics has resulted in a substantial increase in fire spread rates.
- In the past, furniture was mainly made of natural fiber materials. Examples include leather chairs and sofas, metal and glass tables, and cotton drapes. Furnishings of today are typically synthetically based, such as microsuede upholstered chairs and couches, polyester drapes, and veneer wood paneling and tables.
- The synthetically based furniture of today contributes to accelerated fire growth and spread in today’s homes. Synthetic fuel loads, petrochemical-based contents and building materials create intense fire loads.
- Lightweight assemblies, whether protected or non-protected, fail significantly faster than “traditional” solid-sawn assemblies.
Preheating of wood structural members causes weakening of the structure prior to direct fire involvement. Preheating has greater impact on lightweight construction due to their reduced mass, use of composite materials and reliance on multiple connectors.
- Traditional assemblies tend to fail locally (smaller portion) while the newer lightweight assemblies tend to fail globally. The majority of cases involve sudden failure over large areas with no warning.
- Traditional dimensional lumber’s biggest asset in the event of fire was the mass of wood.
- The dimensional lumber could lose some mass and retain its load-carrying capability for a longer period of time because it has more mass to sacrifice.
- When lightweight or engineered wood products such as wooden I-joists begin to lose mass, they become a critical issue because the component has been designed to a specific load factor.
- Lightweight wood components cannot afford to lose any mass without serious risk of failure.
- Fire propagation and fire growth in residential fires has changed dramatically. The “built-in” fire resistance of sawn/traditional lumber has been engineered out of today’s lightweight construction.
- The combination of larger homes; open floor plans; increased fire loads; and ceiling, floor and attic voids that are predominately made from lightweight components means faster fire propagation, shorter time to flashover, shorter escape times, and shorter time to structural collapse.
- Many of our time-tested methods of “reading the fire building” no longer apply in the newer lightweight construction. Examples include:
- Sensory indicators (sight, sound and touch) are not reliable indicators of impending collapse with lightweight construction.
- Failure in lightweight construction will not be precipitated by the traditional feeling of sagging or weakness.
Recent tests by Underwriters Laboratories on lightweight building components have identified several concerns including:
- Deflection times – Although a computer model predicted that the test floor assembly using engineered I-joists would retain its strength longer during a fire than the traditional wood platform, the opposite was the case. Furthermore, the engineered wood supports began to fail and deflect almost from the start of the test and proceeded to degrade in stages, leading to floor vibration, noise, collapse and burn-through.
- Charring – The rate at which engineered wood and traditional wood chars is similar. However, because of the very thin cross section of the I-beams, the report found that this charring rate poses immediate dangers to the mechanical integrity of the structure.
- Heat sensitivity – Oriented strand board beam sections exhibited initial charring at a much lower temperature than traditional wood, making it impossible to further test some properties of the material.
- Heat conduction – Due to compressed plies and binding material, the engineered samples conducted heat faster than other wood samples.
- Brittleness – Engineered wood product samples exhibited increased brittleness and loss of mechanical strength compared to traditional wood components when heated in an oven, even without being exposed to fire. Researchers suggested this was due to separation of the constituent compressed fibers under mechanical and heat stress.
Traditionally, home furnishings were manufactured using organic materials such as wood. When they burned, they were able to burn slower and more completely. The energy released from these furnishings was lower than that of today’s furnishings. Today’s home furnishings are made out of synthetic materials and use petroleum-based materials, which are full of hydrocarbons that, when they burn, burn incompletely. These hydrocarbons are released in the form of smoke, creating fuel-rich smoke. The amount of energy released from these furnishings is much higher than that from traditional furnishings and will quickly consume the oxygen in the atmosphere of the room. The fuel-rich smoke is high in heat and lacks the proper oxygenation to support combustion. As a result, it will seek a new oxygen source.
Smoke moves from areas of high pressure to low pressure or high temperature to low temperature, and it is moving constantly. When a room is on fire, heat is released, creating an area of expanding gasses and, thus, high pressure. Generally, this results in an area of high pressure at the ceiling – where higher temperatures reside – and an area of lower pressure near the floor – where cool air resides. The movement of hot to cold is known as convection heat transfer. You can see this very easily.
As an example, dye an ice cube blue and place it in a clear bowl filled with water. The dye will sink to the bottom as the cube melts. If you warm the water, the blue dye warms and moves to the top.
As one can imagine, all of these negative factors impact the fire department’s ability to operate efficiently, effectively and safely. The three primary causes directly related to firefighter fatalities during interior operations at structure fires are:
- Rapid fire progress due to modern-day combustibles.
- Structural collapse due to lightweight building materials.
- Firefighter disorientation due to large, wide-open floor plans.
Additional factors that result in a more rapid progression of fire with shorter time to flashover includes:
- Buildings today have become more energy efficient and secure. This energy efficiency traps the heat and fire gasses inside the structure, thus consuming more materials and causing a more rapid heat buildup.
- The contents of a typical present-day residential building burn faster, generating more heat and fire gasses than those encountered 30 years ago.
- Large surface-to-mass ratio, which contributes to a very rapid-moving fire and high heat release.
- Rapid collapse of roof, ceiling and floor assemblies that happens when fire impinges on these components.
Firefighters and fire departments need to realize that unprotected, lightweight wood assemblies can fail within six minutes of exposure to fire while more traditional solid-sawn dimensional lumber assemblies generally fail within 19 minutes of exposure to fire.
Given the fact that many times these new structural members have some type of inherent protection such as sheetrock coverings that may give the fire department a few extra minutes, we still do not have the available time to mount a proper attack that we once had.
This illustrates that the game has changed in respect to this newer lightweight style construction and we, as firefighters and fire officers, need to adjust the game plan to accommodate these facts.
There are a number of things that fire departments can do to address these newer hazards, and some things that they can’t.
Improved building technologies such as expanded use of fire sprinkler systems and other direct protection systems will definitely impact fire spread and fire growth. However, the presence of these systems is not something that individual fire departments have control of, as this is typically regulated at higher government levels.
So what are the fire department’s options? Simply put, because our time to react has essentially been shortened, we need to:
- Have a clearer understanding of these “new” hazards.
- Arrive on the scene in the earlier stages of a fire.
- Begin effective extinguishment sooner.
- Employ the most appropriate extinguishing method for the situation to effectuate the most positive change in a bad situation.
So, in other words, we need to be more efficient and more effective in our fire attack. Let’s take a closer look at each of the factors above.
Understanding These Hazards
Actions based on informed decisions always result in better outcomes, so the more we know about the fire building, the better our chances that this will be just another “routine” fire and not a tragedy.
As firefighters, we need to know what’s in our districts. We need to get out and see how buildings are built. We need to know what type of assemblies and components are in buildings so we can then have a better understanding of how they will behave under fire conditions. Just a few of the buildings factors that are critical for use include:
- Types of material
- Construction techniques
- Critical failure points
- Void spaces
- Vulnerable systems
- Inherent hazards
- Built-in protection features
We could go on and on with this list, but we hope you get the point. Knowledge is power and the more you know about a building, the better your control decisions and actions will be.
These new buildings and new construction techniques tend to throw out principles that many of us have depended on when making fireground decisions. The standard time-temperature curve is basically out the window.
Buildings are going to flashover conditions much faster than before. In fact, flashover may have occurred prior to our arrival. While this is not beneficial from a fire control standpoint, at least it isn’t as hazardous to our firefighters when the building is near flashover shortly after our arrival or just as we begin an interior attack.
The point here is that if we are to achieve a quick knockdown before flashover happens, we need to generally improve response times. We need to evaluate our current operational construct and see how this can be accomplished. Long term, it may mean station relocations and other significant undertakings, but there may be things that can be done immediately that may not require a capital cash investment.
Closest Unit Response
District boundaries often predate development and, in many cases, the department responsible for fire protection is actually not the closest unit. It’s obvious that, given everything else is equal, the closest unit will get there first. Seems almost too simple, yet there are locations in this state where the closet unit isn’t responding for a whole host of reasons.
When a citizen’s home is on fire, the last thing they care about is who pulls up in front of the fire building and what color the trucks are. All they want is qualified personnel to get there quickly and extinguish the fire.
If we truly put the people we protect first, then boundary disputes and which units should respond should be an easy fix.
“Time Out the Door”
Shortening the time period between alarm time and in-route time provides us huge benefits when confronted with fires in buildings with these newer construction methods. If you are a volunteer firehouse, has there been considerations of in-station duty crews? Such a system allows immediate response and the need to assemble a crew in those critical moments is removed. This can take a lot of different shapes and looks and can provide additional benefits beyond just response times.
Career stations should also look at their “time out the door” as well. While it is typically a very short period of time for them to be out the door, there may be ways that this time can be reduced even further.
Earlier arrivals do not mean excessive speed and dangerous driving habits are warranted. On the contrary, it means that our driving and response skills should assure response safety is paramount. Apparatus accidents resulting from excessive speed or dangerous driving habits mean the arrival will be delayed and it also means that resources now have two incidents to address.
Operators need to understand their emergency vehicle and understand the dynamics of their operation during emergency conditions.
Getting to the fire scene earlier is only half the battle. These efforts are all for naught unless you can actually begin fire extinguishment earlier as well.
In “newer” buildings, our arrival is often dangerously close to the time when the building is going to flashover or begin to experience structural failure, so it is critical that extinguishment begins as quickly as possible to reduce these circumstances.
Items that impact our ability to begin extinguishment earlier include:
- Adequate staffing
- Proper training
- Firefighters’ skills and abilities
- Fire officers’ knowledge and decision-making skills
- Adequate water supply
- Proper SOPs/SOG
Employ the Most Appropriate Extinguishing Method
If all of the stars align and we arrive on the scene with adequate resources and in time to make a positive outcome, we will still not be successful unless we make the proper tactical decisions necessary for the conditions present.
While this article is not intended to serve as a tactics and strategy training session, we do want to highlight a number of factors that fire officers need to consider when confronted with these buildings.
These factors include:
- Life hazard
- Available resources
- Available capabilities
- Exposure issues
- Pre-burn time
- Fire location within the building
- Fire’s potential impact on structural stability
As the years go by and technology evolves, so do the hazards we as firefighters face. Modern-day construction materials and techniques bring new challenges to our profession. In order for us to be successful, we must recognize these facts, understand their impacts and adjust our operations if we are to continue to be successful and safe during future responses.
This article is intended to make you aware that we, as firefighters, need to be educating ourselves constantly and considering all aspects of our responses if we are to be successful. Without this mindset and approach, our ability to affect positive change will not only be reduced, but the risk to our firefighters will increase.