Light It Up
Ventilation & search & rescue ops in lightweight structures
Story & Photos by Stephen H. Higgs

Preservation of life—we all understand this critical part of our mission. These days, the question is often, “How do we ensure preservation of life in a lightweight structure?” In my February 2009 article in FireRescue magazine, “The Danger Within” (p. 64), I shared suggestions on how to understand fire behavior in lightweight structures and how crews can modify fire attack to be successful in these dangerous firefighting environments. In this article, I’ll address ventilation and search-and-rescue (SAR) tactics in lightweight structures.

Ventilation Basics You’ve probably heard the expressions, “As goes ventilation, so goes the fire”; “vent early, vent often”; “don’t vent until you’re ready to enter and extinguish”; “fire and smoke will follow the path of least resistance,” meaning that the fire will travel to the vent; and “a vented fire grows rapidly.”

These axioms are all true for venting fires in lightweight structures. The challenge comes when we consider how to ventilate the structure. What’s the goal? Get the heat and smoke moving in the desired direction as quickly as possible. Confine the fire and limit the horizontal spread by redirecting the heated fire gases out of the structure.

Vertical Ventilation
Once fire enters the combustible truss void or super-heated fire gasses build up under the lightweight steel roof, our ability to vent vertically is severely limited. That’s not to say it has been totally eliminated. We can still vertically vent under certain circumstances; we can also vent from protected positions.

Experience and research have taught us that once fire enters the lightweight wood void we have only minutes. Plywood and oriented strand board (OSB) will begin to burn through in as little as 2 minutes. Metal gusset trusses and wooden I-beams will fail within 2 or 3 minutes. The key to all of this: determining if the fire is in the void.

Safety First: Before we get into that, let’s back up and address vertical ventilation safety considerations. First, conduct a size-up before going to the roof. Where is the fire? Does it appear that the fire is in the void? What are the smoke conditions (volume, velocity, density, color)? Wind direction? Age and construction of the structure?

Second, ladder remote from the fire. Approach the fire, sounding the roof deck and making a visual assessment of the roof. Are there any indications of fire in the void? Any natural roof openings such as sky-lights, access scuttles, stairwell doors, etc.? Approach the vent point from a safe part of the roof, and vent as close to the suspected fire area as you can while remaining safe.

Once the vent is completed, punch the ceiling and evaluate conditions. Do you have time to extend the vent or is it time to get off and do something more productive? I realize that it’s really cool to hang out on the roof while smoke and flames blow skyward out of your vent, but it’s really stupid and not productive. Hey, this is coming from a truckie; I’ve been there.

Going Up: When is it appropriate to go to the roof? If you arrive early in the event and conditions dictate a vertical vent, you may have time to get the vent opened. This is a situational issue. Vertical venting is a time-consuming activity. Even the most practiced crews will take between 5 and 10 minutes to complete the vertical vent. Often in that timeframe the line has been extended and the fire blackened down ahead of the vent, facilitated by horizontal venting. Also in that timeframe the fire can extend into the void and place the firefighters on the roof at extreme risk.

The larger the structure, the greater the need for getting to the roof. The typical 1,600-square-foot dwelling can be quickly and adequately vented horizontally by creating vent openings nearest the fire and setting up some positive pressure ventilation (PPV) blowers to enhance the horizontal vent. In larger multiple dwelling or commercial structures, however, the need for vertical venting becomes a greater priority to keep the fire from spreading through a large combustible void over uninvolved areas of the structure. In this case, vents may be placed to cut off the horizontal spread of smoke and fire. This can include opening vertical vents near the fire and/or cutting defensive strip vents (trenching) remote from the fire to isolate uninvolved sections of the structure. This is not to discount the use of PPV in larger structures; it’s very effective and will enhance both vertical and horizontal ventilation if used properly.

Once on the roof of a commercial structure, you’ll get a clearer picture of the building layout based on the location of fire separation walls and parapets. You’ll be able to assess natural roof openings and observe HVAC and other roof-mounted equipment and structures. In these situations, defensive venting may be very effective. You can open inspection holes remote from the fire to determine the roof construction and conditions in the void. Of course, you must keep command informed as to what you’re doing and what you’re observing from the roof.

An Example: As a young truck officer, I responded to a commercial fire in a lawn and garden business. We were the first-due ladder. On arrival, flames were blowing out of the storefront windows on the south end (A/B corner). We laddered the north end (D side) of the structure remote from the fire and made the roof.

Once on the roof, it was obvious from the visible parapets that we had four distinct buildings or numerous additions to an original building. The roof over the storefront where the fire was venting was sagging, and the roof over the building section immediately behind the store front (C side) was also collapsing.

We cut our first vent along the parapet directly north of the involved store front. We cut a rectangular vent about 10 feet long and 4 feet wide. As we hinged the cut pieces and punched the ceiling down, we immediately encountered heavy black smoke and flame beginning to vent. We hopped over the parapet to the west and made an identical cut along that parapet. As we opened this vent, we had heavy brown smoke but no flame. With the two vents completed, we exited the roof.

Both roofs were constructed of lightweight, parallel cord, metal gusset trusses, with plywood decking. Once inside the building, I could visualize our vents from underneath. It was interesting to see that the truss nearest the fire was badly damaged; the truss in the middle of the vent was blackened; and the truss on the far side of the vent showed no heat damage. This was a very dramatic example of redirecting heat. The location of our two vents had stopped the fire from moving into the uninvolved sections of the building.

I share this example as a time when venting a lightweight roof was appropriate and did not place firefighters at risk. Our size-up on the ground indicated that the fire had not yet extended to the north sections of the building. This assessment was made by looking inside the storefront windows and through an overhead door on the north side of the building.

Once on the roof there was no indication that we had fire underneath. The two vent holes were cut and opened very quickly. I doubt that we were on the roof for more than 5 minutes. We made the cuts quickly with a chainsaw, and the cut pieces were hinged or removed with a pike pole and rubbish hook. We then used both tools to punch down the ceiling. While the first vent was being opened, the firefighter with the saw was already cutting the second vent. It probably took us as much time to assemble our equipment and ladder the roof as it did to make the vents.

If our size-up had indicated that fire had spread into the lightweight truss void, I would not have gone to the roof. Also, another minute or two would have changed the situation drastically. It’s all about the timing, where the fire is and where it will be by the time you get to where you’re going. We essentially vented from a protected (not yet involved) area of roof to redirect the smoke and heat. We went from safe roof to less safe roof, worked quickly, then retreated and exited the roof.

What would we have done if we could not have gone to the roof? If fire was already moving into the overhead of the area, we could have removed the storefront windows and directed an effective fire stream into the overhead and pushed the fire back to the involved areas. I’m convinced that would have worked. We also could have placed a fire stream in the overhead door to protect that section of the building. This would have amounted to horizontal venting and operating offensive/defensive streams from protected positions.

Remember, if you take out windows, you just made a vent and the fire is coming toward you. Don’t make the vent until you are ready to do something about it. My choice of fire stream in this case would be a 2 ½" hose with a 1 ¼" solid stream tip—now that’s a fire stream that will do something productive.

So what’s the bottom line? If the fire is in the roof void, or you suspect it will be in the roof void very quickly, look at an alternative to vertical venting, or look for protected positions to make defensive vents. It’s not worth the risk. These are disposable buildings, and you are not disposable.

Horizontal Ventilation
Horizontal ventilation in lightweight dwellings is very effective and provides the necessary ventilation when venting the roof isn’t an option.

First things first: Locate the fire, make some vent openings by removing windows and/or opening doors (air-out) and pressurize your entry point (air-in). Give the structure a few seconds to begin clearing. Check your overhead void. Is it all clear? If yes, then advance the line and blacken down the fire. Now from a protected position (in the door or hall), open the overhead void and check for extension. Extinguish any hidden fire, complete your primary search of the immediate fire area, and continue to reassess. This is quick and effective, especially in dwelling occupancies where there’s an abundance of windows and doors. It’s also effective in commercial structures; however, the openings are limited and multiple PPV blowers will be required to enhance the movement of fire gasses.

PPV and positive pressure attack (PPA) are controversial tactics to some and totally accepted by others. Pressurization is a tool that can be used very effectively and will improve the safety of firefighters and building occupants—in the right circumstances. Pressurization is not a cure-all and is not the right ventilation tactic for every situation. You must size-up your situation and decide which tactic works best for your circumstances.

I’ve seen PPV and PPA misused many times, so let’s do a quick review of the essentials. Pressurization is an air-volume, not velocity, operation. If you’re pressurizing a standard entry door (air-in), the surface area is approximately 20 square feet. Based on this, your vent opening (air-out) can be equal to or larger than this, depending on the blower(s). That means your vent could be 30 square feet or larger. A typical bedroom window may measure 3 by 5 feet, or 15 square feet of area. Also, ensure your vent (air-out) has been created before the structure is pressurized.

To enhance the volume of air entering the structure and, therefore, the effects of the ventilation, consider using two blowers in series. The first or rear blower provides the sealing cone of air at the opening or air-in point; the second blower is placed in front of the first blower to inject more air volume into the structure. This arrangement is easily accomplished and very effective.

The entire horizontal PPV evolution is accomplished from protected positions. You’re not placing yourself on top of or inside the structure. PPV will begin to cool and clear the interior environment and allow the firefighters to assess the overhead void before making entry. Once the void has been checked and cleared, entry can be made quickly, but only with improved visibility and less heat. Remember, that was the goal all along: Get the superheated fire gasses out of the structure so the nozzle can be advanced and the fire blackened down. This will facilitate the primary search and removal of any occupants. This will also improve the safety of firefighters entering the structure.

If you check the void and find or suspect involvement, deal with it from your protected (entry point) position before entering and placing yourself under an involved void that will certainly fail within seconds or, best case, a few minutes. You must ask yourself, is it worth the risk? Fight the overhead fire from your protected position, gain control, reassess and act accordingly.

SAR Essentials
Let’s start with a refresher on SAR tactics: Work in teams of two or more, try to reach the most threatened occupant(s) first, search closest to the fire first and then work back to areas of refuge. Search under the protection of a hoseline whenever possible. Stay oriented with the hoseline (visual, tool, rope, light, etc.) and/or your entry point and alternate egress. Use your thermal imager to assist with your SAR efforts. Remember, with lightweight construction, your SAR time is very limited, especially if the fire has flashed over and is breaking out of the container or room of origin.

Open vs. Closed Architecture: An important consideration: Are you entering a structure of open architecture or one of closed architecture (aka, an enclosed structure)? Dwellings are typically open architecture, as they have many windows and doors for ingress and egress. Commercial buildings are typically enclosed structures, and the absence of windows and doors adds elements of complexity and danger to your search. (Note: For more about enclosed structures, read Jim Baird’s article “Apples & Oranges” in the February 2008 FireRescue, p. 78).

What makes an enclosed structure so dangerous? First, the time it takes to exit the structure is typically much greater than it is in a 1,600-square-foot dwelling with windows in each habitable room, so air management is critical. Additionally, the deeper into the structure you get, the more dependent you become on a hoseline and/or search rope. If you leave the line and get lost or disoriented, odds are that you won’t survive. Thus, your search should always be oriented off-of or back-toward the hoseline.

Size-Up & Search: Complete a rescue size-up before you enter any structure. This process takes only seconds and will make your SAR efforts more effective. Look for alternate points of entry and egress. The size-up should give you valuable information on where to begin searching and where viable occupants may be located.

Use your size-up to help formulate a plan before you enter the structure. Know where you’re going to search, how you’ll conduct the search and what your limits are. Have an alternate egress plan and even identify additional locations for egress.

If your search takes you above the first floor, know whether there are ground ladders in place and, if so, where they’re located in relation to your search area. Who is placing ladders? Does the RIT team and IC know where you are? Do you know where you are? On this note, maintain situational awareness at all times, and stay oriented to your point of entry and your alternate egress point. Place a bright light at floor level in a doorway; this may help keep you oriented and assist you with locating the exit point. Other ways to maintain situational awareness: Orient off of the hoseline or use a search rope or long-handled tool. Be methodical and deliberate in your search efforts.

Never enter the structure empty-handed. Consider carrying some of the following: a pike pole, closet hook, pick head axe, forcible entry bar, search rope, thermal imager, flashlight, box light, radio and anything else that you think could help you stay oriented and safe.

The initial-attack hoseline has one very special purpose: Find and kill the fire. The firefighters advancing the attack line should not be counted on to conduct search and rescue; this will slow the advance and delay getting water on the fire. Obviously, if they encounter an occupant they should attempt to remove them and/or call for assistance; however, the nozzle should be advanced as quickly as possible to find and extinguish the fire. After all, nothing in the structure fire event will improve until the fire has been controlled.

The initial-attack line should be reinforced with a back-up line. The back-up line can provide protection for the search teams. Dragging a hoseline through every room is not an efficient method of searching. Instead, conduct an oriented search off the hoseline that’s protecting the means of egress.

The rescue size-up you conducted prior to entry will tell you where you can search safely and where you can’t. But remember, interior conditions can and will deteriorate very quickly in lightweight structures. You may consider entering through a window, and conducting a rapid room search.

This tactic of vent, enter, search (VES) works well in single- and multiple-family dwellings. If you exercise this option, close the room door to buy you some time. If the fire has taken the floor void, you’re done. Trying to search as your hands and knees are punching holes in the floor does not work very well—I’ve tried it before. With fire in the overhead void you may have only a few seconds to complete a rapid primary search. Thus, you must assess the overhead void before committing to the search.

Finally, ask yourself these questions: If I find an unconscious occupant, how will I remove them? How many firefighters will be required? How much time will it take? Can I get it done before I run out of time and air? Is the occupant really savable? Am I placing my life in jeopardy for a life that was gone before I arrived on scene? These are tough questions, but they are also realities.

In Sum
Lightweight structures present some unique challenges, so the importance of conducting an adequate size-up cannot be overstated. Checking combustible voids (overhead and floor) before committing to the interior or roof is critical. Additionally, operating from protected positions and modifying our standard tactics is absolutely necessary to improve firefighter safety.


Stephen Higgs began his fire service career in 1977 with the Salt Lake City Fire Department. He served as a firefighter/paramedic, lieutenant, captain, battalion chief and deputy chief over fire operations. In 2000, after 23 years with Salt Lake City, Higgs accepted a position as fire chief with the Midvale City Fire Department, where he is currently serving. Midvale City is a rapidly growing community 6 miles south of Salt Lake City. The Midvale City Fire Department serves more than 32,000 residents covering a 6-square-mile area. Higgs can be contacted at shiggs@midvale.com.