Ventilation Operations on Lightweight Roofs – A Viable Operation? Part 4

Continuing from last month (Part 3) with the perspective of Determining The Type Of Roof you are about to ventilate:

This can be easily accomplished by taking a plug out of a roof to help you determine the type of roof construction. A plug is a small triangular piece of composition (only) that is cut with a hand tool or power saw and then removed to reveal the type of roof decking below. As an example:

- If the plug reveals corrugated metal decking, the roof is probably a metal deck, built-up roof which in reality is a metal lightweight roof.
- If the plug reveals 1×6-inch sheathing, the roof is probably of conventional construction as 1×6-inch sheathing has not been used for over 50 years. Additionally, multiple layers of composition material should also be visible.
- If the plug reveals ½-inch plywood or OSB, the roof is likely a lightweight roof. Additionally, expect to see minimal layers of composition material. Although in this scenario you noticed the exposed 2×4-inch rafter tails from the ground, you made a quick check on the roof and noticed OSB decking with one layer of composition. You quickly have determined you are likely standing on 2×4-inch trusses covered with ½-inch OSB.

DETERMINE THE LOCATION AND EXTENSION OF FIRE
Prior to initiating ventilation operations, you must determine the location and extension of fire (if you don’t know). What did you see in your initial size-up? What areas of the roof are issuing fire or smoke? Ventilators, vent pipes, skylights, heat blisters and melting snow are excellent indicators. Consider the color, temperature, and pressure of any visible smoke. If necessary, a small opening can be made by your means of egress by using a power saw or the pick of a pickhead axe. Make a small (small is defined as not large enough for a firefighter to inadvertently step into and break an ankle, foot, etc) hole in the roof decking to see whether smoke or fire are below. Such an opening is often referred to as a kerf cut, an indicator hole, or an inspection hole. If any smoke is present, consider its characteristics. As an example:

- A lack of smoke would be an indicator that fire is not in the immediate area.
- Cold, white smoke would indicate that fire isn’t in the immediate vicinity of the opening.
- Hot, black smoke under pressure, is a positive indicator the fire is near.
- Fire is an indicator that you may be in the wrong place at the wrong time.
- For this scenario, let’s assume you make a quick indicator opening and notice white smoke with moderate pressure and little heat You now initially know the status of the attic (in your area) has not been compromised and you can proceed with your ventilation operation. However, it can be advantageous to make occasional indicator openings as you approach the intended area of your operation to verify the status of the attic.
- From the opposite point of view, let’s assume you initially make an indicator opening and see black-hot smoke or fire. In this case, roof ventilation is not a safe operation and your next priority would be to exit the roof in a timely manner. If you think making indicator openings requires too much time, it is preferable to falling into a burning structure with a collapsing roof.

WALK THE STRONG AREAS OF A ROOF
Ventilation personnel should always concentrate on walking the strong areas of a roof, whether during fireground operations or training evolutions. In this scenario, it would be the perimeter or the ridge of the roof.

SOUND YOUR PATH OF TRAVEL
It is possible for plywood/OSB decking to weaken or burn away without burning through the composition covering. Therefore, although a roof may look normal from the top, it may not support any weight. Keep the sounding tool in front of your body to provide maximum stability in case you encounter a weak portion of the roof. Sound the roof along your entire path of travel.

WORK FROM THE WEAK AREA TO THE STRONG AREA/MEANS OF EGRESS
Start ventilation cuts in the weakest portion of the roof (near the fire) and work away toward the strongest portion (unburned section). Spend as little time as possible on the weak portion. In this scenario, you would start as close to the two-story structure as possible and work back to your ladder.

KEEP THE WIND AT YOUR BACK
When possible, plan ventilation cuts so the wind is at your back, with smoke and heat moving away. Today, personnel are plagued with the by-products of plastics which have been proved to be carcinogenic. Consider using breathing apparatus when ventilating while in smoky environments.

ONLY CUT AS DEEP AS NECESSARY
Personnel using power saws for ventilation purposes must control the depth of the cut and know what is needed to accomplish specific ventilation operations. Unless otherwise necessary, make ventilation cuts through the roof decking only. Cuts deeper than the roof decking increase the possibility of severing structural members. For this roof in our scenario, a cut deeper than two inches can begin to compromise the structural members of the lightweight roof.