Author(s): Ben Klaene, Russ Sanders
NFPA Journal®, November/December 2007
There are many reasons why accessing the roof during a structure fire might be necessary. In most cases, the primary objective of roof operations is vertical ventilation. Proper roof ventilation will control fire and smoke movement and allow firefighters working inside the building to quickly remove occupants and extinguish the fire. Another reason is for a rescue operation. Occupants above a fire in a multi-story building may seek refuge on the roof when encountering heat and smoke conditions in the stairway, as was the case at the 1980 fire at the MGM Grand in Las Vegas. Therefore, checking the roof for occupants is sometimes necessary, especially in buildings with easy roof access.
Safety is always the first consideration before placing firefighters on a roof because roof operations can be extremely hazardous. Firefighters placed on the roof to ventilate must be in full protective clothing and on air. Many times conducting roof operations from an aerial ladder or aerial platform is possible and desirable. A roof ladder should be used when checking peaked roofs if working from an aerial device is not possible. Also, a second means of egress should always be provided for firefighters working on the roof.
Truss roofs are particularly prone to early collapse, but other roof structures can also collapse without warning. Buildings that have undergone substantial renovation may add lightweight roof structures to replace heavy-duty structural members. Heavy roof loads, such as air conditioning units on the roof, can hasten roof collapse. Pre-planning information should warn firefighters of weakened, compromised or excessively loaded roof structures.
Some fire departments have decided to prohibit roof operations at single-family residential properties with wooden truss roofs. Roof operations are usually assigned to the truck company or the company assigned to truck duties. Sometimes department structural firefighting SOPs automatically assign firefighters to the roof. As important as roof operations might be, we do not agree with automatic roof assignments, because many times a roof will be unsafe for firefighters and roof operations are not always needed to achieve tactical objectives.
We have reviewed many case studies where firefighters were injured during roof operations when the fire had self-vented through the roof before firefighters gained access to the roof. In these cases roof operations were generally unsafe and unnecessary.
If the roof is deemed safe for roof operations and there is a need to ventilate the roof, two questions should be asked: “Where is the best place to vent?” and “What are the possible, unintended consequences?”
Deciding where to ventilate can be a complex decision. From a tactical standpoint venting directly over the fire is the most desirable location. Venting over the fire is also the location most prone to structural failure. A smoke plume with sufficient thermal energy will naturally be pulled toward a vertical opening. Therefore, an improper vent opening—placed away from the fire—will tend to pull the fire through unburned areas of the building, placing occupants and firefighters located in the ventilation pathway in even greater jeopardy.
When the fire is in an area below an attic or other concealed space, the ceiling must be removed to allow smoke and heat to flow through the roof opening. This is usually accomplished by pushing the ceiling down using a pike pole placed through the vent opening. If the fire has not already extended into this false space, venting operations provide the fire a pathway into a previously uninvolved area.
Placing the vent opening in the wrong location, such as behind the firefighters, could prove to be a deadly mistake. The fire will now be pulled into the concealed spaces above the firefighters working below, possibly blocking their means of egress and enveloping them in fire. Conversely, proper venting will channel fire and smoke directly out the roof, limit extension and provide a safer environment for the firefighters and occupants below. If a fire in significant volume has already extended into this false space before venting, there could be a sudden and dramatic increase in smoke and heat at the roof level requiring firefighters to quickly retreat. In these instances it is unsafe for firefighters to be on or under the roof. Remember, if the roof is too weak to place firefighters on it, it is also too weak to place firefighters under it.
Considering the unintentional consequences is critical when performing roof ventilation when the fire is on a floor below the top floor of a multistory building. Opening the roof will not achieve the intended purpose unless there is a pathway from the fire compartment to the roof opening. If the fire is not rapidly extinguished, everyone and everything in this pathway will be placed at increased risk. Timing extinguishment efforts to coincide with ventilation is essential. In the case of the multistory building, improper venting can draw fire into the stairway and result in injury and death to anyone in the stairway, including firefighters.
Conduct a risk-versus-benefit analysis before placing firefighters on a roof. Consider the structural stability of the roof structure and evaluate why firefighters are conducting roof operations. And remember that firefighters working on the roof create an additional load that may contribute to roof failure. Once the objectives for the roof crew have been achieved, firefighters should immediately leave the roof.
NFPA (National Fire Protection Association)
1 Batterymarch Park, Quincy, MA 02169-7471 USA
Telephone: +1 617 770-3000 Fax: +1 617 770-0700