By Michael Lee
|
Related Resources: |
The number of fatalities involving firefighters trapped in burning structures has essentially remained consistent over the past decade. To reduce these figures, we must become and remain aware of the total fireground environment — and not just the fact that fire is visible on scene.
The moth to the candle syndrome still drives a significant portion of on-scene tactics and causes tunnel vision. If we are to be taken as serious professionals, we need to learn how to understand the information and clues the burning structure is screaming at us. These will steer our decision making process through the risk-benefit process necessary to make the initial strategy choice of offensive or defensive fire attack pathways.
Nearly 65 percent of LODDs last year were caused by emergency scene operations, and of that number about 12 percent involved building collapse. The debate of offensive versus defensive tactics must be based on a variety of significant sub-topics and all will be discussed in this two-part article. Essentially we need to prepare the fireground commander with the foundational topics that will allow them to make the best risk benefit assessment possible.
The fireground commander must be intimately familiar with:
- Building construction techniques in general and specifically those that exist within their district
- The initiation and evolution of the various fire stages
- The burn characteristics of the building materials of the structures they may fight fire in and those clues that may warn them of an impending collapse.
It’s vital crews are trained and prepared — both physically and mentally — to face the challenges ahead of them. Know what capabilities your initial on-scene crews are able to handle and know where to obtain assistance with resources when necessary. Finally, train yourself and practice your ability to define risk benefit on all your scenes.
One of the most significant skills a fireground commander should possess is one they can obtain before ever showing up on scene of a fire. Knowledge of how a building is constructed will offer tactical clues regarding:
- Rate of fire spread
- Void spaces for hidden fires
- Weak areas that can be subjected to rapid deterioration secondary to fire
- How specific structures may collapse should an advanced fire weaken the structural support system for a given building.
Knowing the types of building construction classification is paramount to projecting the future evolution of fire within a structure:
- Type I - fire-resistive construction (walls, columns, beams, floors, and roofs made of non-combustible or limited combustible materials)
- Type II - non-combustible or limited combustible construction (similar to fire-resistive construction except that the degree of fire resistance is lower)
- Type III - ordinary construction (exterior walls and structural members constructed of non-combustible or limited combustible materials; interior structural members including walls, columns, beams, floors, and roofs completely or partially constructed of wood)
- Type IV - heavy timber construction (exterior and interior walls and their associated structural members made of non-combustible or limited combustible materials; other interior structural members including beams, columns, arches, floors, and roofs made of solid or laminated wood with no concealed spaces; wood must have dimensions large enough to be considered heavy timber)
- Type V - wood-frame construction (exterior walls, bearing walls, floors, roofs, and supports completely or partially of wood or other approved materials of smaller dimensions than those used in heavy timber construction)
Knowing how a building is constructed will greatly enhance the fireground commander’s ability to project the movement and speed of a fire that involves a building’s structure versus a contents fire. Try and take the time to get out to your buildings under construction in your area and see how they are put together.
The next tool for selecting proper tactical operations is to try and gauge what stage the fire is at upon arrival. Matching proper resources in the proper place at the proper time will almost always succeed against an unthinking enemy.
Fire development consists of a variety of stages:
Ignition
The period when oxygen, heat, fuel and chain reaction come together in proper rations to allow for the initial combustion process to occur. At this initial point in the fire progression, the fire is minimal and easily extinguished.
Growth
In this stage of the fire, the amount of heat being generated creates thermal updrafting which allows for the movement of air from the surrounding area to the seat of the fire to assist with maintaining oxygen levels to continue feeding the fire.
Flashover
This next stage occurs between the growth phase of the fire and the next, which is the fully developed stage. At this point in the evolution of the fire, heat from the growth stage has sufficiently heated up surrounding fuels to the point where their flammable vapors are sufficient in volume and heat to ignite all fuels within an area simultaneously.
Fully Developed
Post-flashover, all combustible materials in the area are burning with the degree of heat release based on the available air for combustion.
Decay
As the level of oxygen or the amount of available fuel for combustion begins to decline, the rate of heat release from combusting materials begins to decline as well. This lowers both temperature and oxygen levels in the fire compartment.
The evolution of the size of the fire is based on a number of items such as the size, amount and distribution of ventilation openings into the fire compartment, the volume of the area involved, thermal properties of the fire compartment walls and height of the ceiling. In addition, the size, composition and location of the fuel inside the fire compartment and what is easiest to be ignited will also define the size and speed of fire evolution within a given compartment.
In the old days, natural materials with lower BTUs and that ignited less easily allowed for fire growth that was slower in reaching the flashover stage. Crews were able to get on scene and get water to the seat of the fire before the volume of fire caused flashover. But in today’s homes, the energy efficiency of the construction coupled with synthetic materials creates fires that burn much hotter and faster than half a century ago. The time to flashover is much quicker and statistically is reached about the time crews are just forcing entry and deploying their initial suppression lines.
The amount of heat being generated in today’s fires has also significantly increased. This higher heat content significantly impacts the ability of other construction materials such as steel to fail sooner into the fire.
Masonry exposed to higher temperatures subject the mortar to degrade quicker and weaken sooner.
Among the hazards to be aware of are:
- Cast iron may shatter when heated and then struck with cold water from attack lines
- Reinforced concrete soon loses its strength and begins to spall
- Glass with wire-reinforced wire may provide some thermal protection but does not serve as an effective deterrent to fire extension
- Fiberglass will soon lose the resins that keep the fibers together as well as add to the volume of combustible materials on fire.
Once a good understanding has been gained of how the structure involved in fire will react based on construction, fire stage, materials involved and the total fire load, a fireground commander should have the ability to make educated assessments on the speed and direction of the fire. In addition, the fireground commander and all firefighters within the structure must have a working mental reference of indicators of building collapse.
These include:
- Cracks or separations in walls, floors, ceilings, or roof structures
- Evidence of existing structural instability such as the presence of tie rods and stars that hold walls together
- Loose bricks, blocks, or stones falling from buildings
- Deteriorated mortar between the masonry
- Walls that appear to be leaning
- Structural members that appear to be distorted
- Fires beneath floors that support heavy machinery or other extreme weight loads
- Prolonged fire exposure to the structural members
- Unusual creaks and cracking noises
- Structural members pulling away from walls
- Excessive weight of building contents
Finally, before deploying their resources, the fireground commander must consider the operational readiness of their crews. Have they received the training and do they possess the experience necessary to keep themselves safe?
Ask yourself the following questions and be sure you are ready to face a harsh reality if your answers aren’t what you would like to hear:
Are your crews trained to carry out the instructions that you will assign them to meet the tactical plan you are building?
Are your engineers practiced enough to get the apparatus positioned for best utilization, and are they able to operate the pump or the ladder quickly and efficiently?
Are your officers practiced to perform a size up, develop an initial strategy, choose initial tactics to implement an effective initial strategy, lead a suitably aggressive yet safe suppression process, and coordinate any activities assigned?
Are your firefighters trained to perform the duties to which they will be assigned in a safe and effective manner?
Is your appointed safety officer capable of maintaining the overall safety of the incident scene?
Do you have sufficient staffing to meet assignments that the unit will be given in a safe and efficient manner?
Do your crews understand and practice the two-in-two-out procedures at all times?
Is there sufficient staffing on the apparatus to make an initial attack or provide support for an engine crew?
Are your personnel arriving on multiple pieces of apparatus to make up necessary minimum staffing for an assignment?
What total length of time it will take to have adequate staffing on the scene to initiate an interior attack while maintaining a rapid intervention team in place?
Do you have adequate apparatus response based on the hazard involved?
What are the possibilities that there will be a delay in arrival of some of the units due to road conditions, weather, travel distances, or units not being staffed immediately?
Do you need for specialized apparatus due to the particular hazard?
Does your apparatus have access to all sides of the location?
If you were able to answer positively to all of the above questions, well done! You should feel proud and confident that you can meet the majority of fire challenges your firefighters will face. If not, take a hard look at those items that can be corrected quickly through training and address them. In addition, be very aware of those thingsthat can cause safety issues, and plan for alternate strategies or assignments to ensure your personnel are matched with tasks they are capable of completing in a safe fashion.
As we can see, a well prepared fireground commander knows the structures they will be deploying firefighters into. You must know what the construction of that structure will be in that it will dictate the future of that structure when impacted by fire. Pre-planning is essential to know how and what hazards the building will present to the crews who will fight fire in.
Knowing how a structure is built will also dictate how it will burn and how it could collapse. If we have some minimal insight into what the fire will do to the building, you can plan and deploy resources accordingly, keeping firefighter safety as the primary concern. Next month we will connect the information presented here with a risk/benefit process to allow the fireground commander to make the best selection when deciding whether to initiate an offensive or defensive fire attack.
