Trench Cuts

The trench cut, aka "strip ventilation," is a truck company vertical ventilation tactic that can be utilized to stop the spread of fire across a long, narrow structure, thereby achieving containment of an extending fire by confining the fire to a specific area.

As with any vertical ventilation operation, careful consideration must be given to the safety of the operation. This assessment begins with the determination of the need for vertical ventilation. Once this need has been determined, fire conditons and its impact upon the the building prior to the arrival of the fire department must be given shrift.

Ask yourself the following:

"What is burning?" Is this a "room and contents" fire, or an actual structure fire in which components integral to the construction of the building are being compromised?"

"How long has the fire been burning?" Was there a delay in notification of the fire department? Is it an advanced fire condition upon arrival of first-due companies?

"What type of structure is the building?" Is the class and means of construction and occupancy immediately evident? If answering "no" to this question, carefully and continually assess the need for and safety of roof operations-especially where any truss roof construction may be suspected.

Once we have committed to the roof, fire conditions must be continually monitored in conjunction with a careful assessment of the progress companies are making toward the extinguishment of the fire.

Before we address the components of the trench cut itself, it is essential that we understand that this is a tactic that is undertaken in ADDITION to vertical ventilation measures, and not in replacement of same.

A solid foundation in vertical ventilation is essential. The vertical ventilation operation should be completed over the fire to alleviate the build-up of the products of combustion for potential victims and the advancing engine and truck companies before any trenching operation is commenced

The trench cut tactic is akin to creating a fire break ahead of the extending fire. This strategy may be employed to combat an unchecked fire found to be extending in the voidspace ahead of companies opening up on the top floor of the structure. The thought process at work here is that by operating carefully ahead of the difficult to reach and extinguish fire, we can cut off the extension of the fire prior to it taking possession of the remainder of the fire building.

Once, the fire is discovered to be extending rapidly in the void space, the decision to make the trench cut may be made. This decision should be communicated to all members on the fireground as coordiantion between the roof operations group and companies operating on the top floor of the fire building is essential. The need for additional companies/alarms should be weighed carefully.

The trench cut should be made as far ahead of the extending fire as possible; twenty (20) feet is a commonly referred to distance. At several points on both sides of the trench site, kerf cuts or inspection holes should be made to monitor the progress of the extending fire. and to assure that the trench is being made in a viable location that the fire has not in fact passed. To review: kerf cuts are made the width or our rotary roof saw blade with one cut into the roofing material, and inspection holes are made in a triangle shape by joining three (3) kerf cuts.

The trench site should be beyond the ventilation opening, and in such a position to allow truck company members easy access to a means of egress from the roof. The means of egress may be an aerial ladder, tower ladder basket, or ground ladder; it is imperative that the escape route be established and understood by all members of the roof operations group should conditions deteriorate to the point where a rapid exit is necessary.

Once we have chosen the site for the trench cut, we will begin the process of cutting the trench itself. The trench must extend from one exterior wall to the next. It is possible to utilize some of the roof features to your advantage to limit the length of the cut by utilizing features of the roof, such as doorways. The cut should be at least three (3) feet in width, although IFSTA does mention four (4) feet as ideal. A good guide to the width of the cut is to use the length of the ubiquitous Halligan tool as a guide. The cut should never exceed the width of an average person's stride, as it may become necessary to step across the cut once it is made. Cut the entire length in parallel fashion from one exterior wall to the other.

Now that we have made the cut, it is important that we deifferentiate between making the trench cut, and opening the trench cut. We will wait to open the trench after assuring that we are in fact still ahead of the advancing fire (check and RECHECK the kerf cuts and/or inspection holes we have made around the trench site), and that companies operating on the top floor of the fire structure are prepared to open up in conjunction with handlines to knock down the fire in the void space. Now that we have assured the viability of the trench cut, and the companies have been notified that we are ready to open the cut, we can now open the trench all the way.

Once we have pulled the trench cut, remember to punch out the ceiling below, and to completely open the trench-especially at the points where the trench joins the exterior walls. Constantly size up evolving conditions on the roof during any vertical ventialtion operation, and notify the incident commander (I/C) of both the progress of the operation and any changes that may impact firground safety.

Be Safe,

Chris