A THERMAL PANE IN THE GLASS
EVER FEEL as though the older you get, the hotter the fires seem to be? Well, there’s more truth to that than you may think.
In past installments of “Training Notebook” I have discussed the various developments in insulation materials and their effects on our firefighting efforts (“Residential Roof Insulation: A New Headache,” March ’85; “Comercial Roof Insulation: An Old Headache Gets Worse,” October ’85; “Vertical Foam Insulation: Defeating the Firestop,” May ’87). Now let’s address what is perhaps the most prevalent method of energy conservation in use today: thermal-pane windows.
In the early seventies, the world was stunned by the energy crisis and the realization that cheap fuel could no longer be taken for granted. Home owners, landlords, and building owners scrambled for ways to cut down on their heating and electric bills. Studies showed that millions of dollars in heat and air conditioning were literally flying out the window.
The standard single-pane window, even with storm windows on the outside, was not sufficient. More and more people turned to thermal-pane windows for their homes, offices, and buildings. As the potential savings in terms of dollars and energy were realized, the industry itself grew and developed even more efficient units.
Unfortunately, with this increased use of thermal-pane windows, firefighters began to see a rise in flashovers, backdrafts, burns, and related problems. Many of these problems were masked by other developments, but evidence increasingly points to the thermal-pane window as being at least partially responsible.
To understand the problems, you have to understand the window. A standard window is normally constructed of a single pane of glass in either a wood, aluminum, or metal sash in almost any type of configuration-double-hung, casement, awning, or stationary (picture windows). The thermal-pane window will consist of a minimum of two panes of glass in either a wood, aluminum, or vinyl sash. Different manufacturers have different assembly methods, but the basic construction methods are the same. There is a ⅞-inch air space between the panes of most of the more recent models. Options include various types of tinting and screening to keep out the glare of the sun and keep in the heat. Several manufacturers offer a third pane. For our sake we will now get into the different thermal ratings of the various windows; however, keep in mind that they are designed to keep the heat in, and they do that very well.
Most of us know what it feels like to pull into a block and see fire blowing out of the windows, to hear glass shattering from the intense heat, or to spot the telltale signs of possible backdraft. Old-style, single-pane windows often fail w hen exposed to the intense heat of a fire. This allows the fire to vent itself early on in its progression. Of course, the fire might autoexpose an upper floor or extend to an exposure through this venting, but interior conditions are somewhat lightened. Smoke bank-down is relieved to an extent and progress along the floor is relatively easy. Responding units, before the advent of thethermal-pane window, generally knew what they were heading into, and there were few surprises in store. In fact, by general comparison, one could say that the fires of yesterday-when all we had > was the single-pane variety-were cooler and better-vented.
For the victims trapped in such a fire, the failure of the glass, while increasing the intensity of the fire, would also improve visibility at or near the floor level, increasing the chances that a would-be rescuer would find them by sight rather than having to rely on feel. Someone near the floor might even experience a “cooling off,” so to speak, as the fire and heat vented out of the window.
In a structure with thermal-pane windows, many of these actions are delayed or negated. These newer windows, even in simplest form, are twice as thick as the old windows and will take at least twice as long to fail. (When it does fail, it means twice as much broken glass to contend with.) Since the window is designed to keep heat in, one can expect higher interior temperatures, with a faster rate of heat buildup leading sooner to a flashover condition. Yes, old-timer, these fires are hotter.
The thermal-pane, by not failing as rapidly as the older windows, will also lead to greater smoke buildup, and the resultant banking down will make it extremely difficult for rescuers and interior attack teams to find their way. Use of SCBA is an absolute must. Visibility along the floor level will be decreased considerably and conditions may deteriorate rapidly. From the outside, the window may mask the signs commonly associated with a flashover or a backdraft condition. Officers and members performing size-up should note if thermal-pane windows are present, and anticipate the unexpected. Should the thermal-pane window reach the failure point, the amount of heat energy released can be extraordinary, with the resultant fire autoexposing several floors or seriously injuring firefighters. I am told of one case in which the arriving fire companies reported a light smoke condition, and, as they advanced into the building, the thermal-pane windows in the front let loose, with the resulting fireball reaching several stories up the face of the building and extending into the cockloft. When venting, personnel should look for signs of this potential energy release and ensure the safety of potential exposures, including themselves.
Personnel assigned to the outside vent team or the search team that attempts to vent as it goes should not take lightly the fact that there is twice as much glass than in structures with oldstyle windows. Also, they will find that thermal-pane windows will not break as readily as single-pane windows, especially if the panes are laminated. Personnel should remember to break both panes of glass if that is the method chosen to vent the window or door. At least one manufacturer places blinds between the panes of glass on the patio door model. Clean the sash out entirely. Depending on the manufacturer, the panes may shatter violently as trapped gas escapes from between them. If possible, the windows should be opened in a normal fashion rather than broken to reduce the chance of injury from glass shards.
On the flip side, however, the thermal-pane window also plays a beneficial role in our firefighting efforts. Cases have been reported in which thermalpane windows on exposure buildings have served to reduce the amount of radiant heat transferred from the fire building. Again, whereas single-pane windows might fail under these circumstances, the thermal-pane window is holding up a great deal longer and holding back the fire. Officers and personnel covering exposure buildings must take into account the presence of the thermal-pane window in their size-ups. Premature opening of the window will offset the hidden benefit it provides.
The concept of an energy-efficient structure has come a long way in a short time, and is here to stay. Between modern insulation materials, improved construction methods, and the thermalpane window, buildings are “tighter,” allowing firefighters a smaller margin of safety. We can expect higher interior temperatures, decreased visibility due to greater smoke concentration, and an increased risk of flashover and backdraft. It is incumbent upon firefighters and training personnel to learn as much as possible about these developments and, in some cases, take our heads out of the sand and develop new ways of accomplishing old goals.
Yes, as we get older, the fires are getting hotter, but we should be getting wiser.