Hybrid Construction: This process uses mixed types of materials and construction practices as the building is assembled. The variations in materials and design make it very difficult to prescribe this structure to any basic type of construction class. Moreover, it can be found in any type of occupancy (see Pk coohoto 6). The only way to truly identify its presence is through thorough pre-planning.
Bowstring Truss Roofs: Easily identifiable by its arch design from the exterior, this assembly has been the cause for many firefighter fatalities throughout the years. This roof assembly will push all four walls of the structure outward: the arched assemblies in compression force the walls outward as well as downward. Furthermore, hip rafters that connect the front and rear walls to the roof assembly will force out these walls when the roof fails. Many unsuspecting firefighters operating near the front wall have been seriously hurt or killed when the collapse occurs.
Setting the Aerial up for Success
Truck companies will find themselves in the front lines of the defensive attack, as the reach and penetration from the elevated stream allows for water to be applied without the risk to the firefighting crew. Take into account a few points to find the best spot to set up:
1. Wind direction – Set up upwind so that water spray from the elevated stream goes on the fire and the downwind exposure.
2. Monitor the collapse zone – The fire attacking the structure is damaging the “Gravity Resistance System” (Frank Brannigan refers to this in his book Building Construction for the Fire Service) in the construction and design of the structure. Furthermore, every stream that is flowing 500 gpm into the building is adding about two tons of additional weight to the structure. Be sure to stay out of the collapse zone, which is usually one and one-half times the height of the building, and take a flanking position from the exterior walls of the structure (photo 7).
3. Identify the most significant exposure – Ladder companies will be discharged with exposure protection, so determine which one is most at risk. Two major points to consider include the distance the exposure is from the original fire building, and the height of the exposure building. Spacing from the original fire building is advantageous as the heat transfer from convection and radiant heat will be limited the further the exposure is from the fire building. If the exposure building is taller than the fire building, then the exposed area immediately above the fire building is a vulnerable area.
4. Spot for maximum scrub – Setting up to cover the most area of the fire building and the exposure will maximize the efficiency of the device. Pick the location that will give the most access for the device, and consider any overhead obstructions that will be problematic for the operator (photo 8).
5. Water application – The chemistry of combustion and the rate of heat release remain constant, so the attack methods are similar, whether the attack is offensive or defensive. Keep in mind the condition of the roof or ceiling; as long as a roof/ceiling exist, then the application of water can be done through the center of the window, at a 30° angle upward towards the ceiling, played back and forth throughout the space. Once the roof has failed, the attack may be made from above, as long as it does not push the fire back downward throughout the rest of the structure (photo 9).
Firefighters can fall into a false sense of security while operating outside the structure. A belief that operations are completely safe from the exterior can result in catastrophic consequences when safe practices are ignored. Defensive operations and elevated streams from aerial devices can be extremely hazardous; make certain the safety parameters that are in place are strictly adhered to, so everyone goes home.
Until next time, stay focused and stay safe.
MICHAEL DALEY, a Firehouse.com Contributing Editor, serves as Lieutenant with the Monroe Township Fire District No. 3 and he was recently earned the Master Fire Instructor certification from the ISFSI. He is an instructor at the Middlesex County Fire Academy where he developed rescue training cirriculum and serves on New Jersey Task Force 1. He is a managing member of Fire Service Peformance Concepts and a monthly columnist on Firehouse.com. He has been on a guest on numerous Firehouse Podcasts, including: Basement Fire Tactics Roundtable at Firehouse Expo, The Buzz on Technical Rescue: A Look at the USAR Equipment Cache, and Rapid Intervention from East to West.