Void Spaces
DEPARTMENTS
BUILDING CONSTRUCTION
Training Notebook
Fire destroys a fully sprinklered dormitory.
Thirty-nine die in a tenement house crushed by a brick wall blown down during an icehouse fire.
An officer is killed in a backdraft explosion 1 1/2 hours into the fire.
Guests in a high-rise hotel are threatening to jump—the hotel itself is not on fire.
What do all these scenarios have in common? Void spaces.
Visible fire is a relatively easy target. In many cases, however, what you see is only the venting of the volcano, and this may not give a true picture of the full extent of the fire.
Voids or concealed spaces are an inherent part of almost any type of construction and pose a major problem for firefighters. Fires are often found hidden in these open areas, and size-up for such fires should start with exterior observation.
- Smoke (even light smoke) pushing from openings is an obvious clue to hidden fire. However, smoke detection is not always easy. At night, smoke can be concealed in the darkness.
- Sometimes the command post is too close to the fire building, giving the fireground commander only a limited view of the incident. It’s a good idea for the commander to make a circuit of the building before setting up the command post so it will afford the maximum view of the entire operation.
- Pump operators, who often have the best view of the fire, should monitor fireground traffic. They should be alert to report any external conditions that may not be apparent to those in close proximity to the fire building. For example, an outside observer may see heavy smoke coming from the roof area although inside units report only a light fire and smoke condition.
For the last year, this area of our magazine was devoted to the discussion of hazardous materials. While still a current and recurring problem to emergency personnel, extensive and valuable information on this subject is readily available from governmental and private agencies. Therefore, FIRE ENGINEERING feels that this space can be better utilized to address additional topics that are necessary to the safety and performance of our job.
In addition to timely articles on hazardous materials, we will include articles on safety, arson awareness, management for the fire service, building construction and more. Called “Training Notebook,” contributors such as Frank Brannigan will outline aspects of building construction trends and practices that concern firefighters and firefighting operations; Roger McGary will follow with tips for instructors on innovative use of computers; instructors and fire experts from both sides of the Mississippi will give their views on safe and effective firefighting procedures; and more.
In this issue, Frank Brannigan writes about voids and their contribution to fire spread.
I hope you enjoy it and, more important, find it helpful.
Tom Brennan
It is entirely possible to have a raging fire above a clear area. This was demonstrated at a taxpayer fire. A thirdalarm assignment was operating at one end of the block. At the other end, a sewing machine store was clear. I watched as the store’s pressed tin ceiling turned color from the heat condition in the cockloft space above it. Flaming paint dropped on the contents. Within moments, the store was fully involved.
The void space problem is not a recent discovery. The developers of true mill construction set “no concealed voids” as a cardinal principle. (Also known as heavy timber, plank-on-timber, and slow-burning construction, mill construction calls for bearing and exterior walls to be noncombustible and have a two-hour fire resistant rating. Columns, beams, and girders are commonly heavy timber, and wooden floors and roofs are built without concealed spaces.)
Concealed, combustible voids can exist in any building. Modern fire resistant buildings can have ceiling and floor voids loaded with combustible wiring. Steel-framed fire resistant buildings with “rated floor and ceiling assemblies” are vulnerable to the horizontal passage of fire from one occupancy to another through the floor void created by the bar joists. The American Society for Testing Materials (ASTM) E 119 test that rates floors for fire resistance does not anticipate this problem. In older “modernized” buildings, a new “fire-rated” suspended ceiling can conceal a dangerous old combustible tile ceiling.
Balloon-frame buildings have been with us for a century and a half, and for most of that time they were the only type of multi-story frame building built. Still, many fire departments are unaware of the interconnected voids in which the vertical studs run, unfirestopped, two or more stories from the foundation to the attic. This leaves the interior as one big “balloon,” with unprotected openings running the height of the building.
Although platform construction contains inherent barriers to fire spread through the walls, various offsets, such as soffits over built-in kitchen cabinets, connect floor voids to wall voids. Platform-frame buildings are of wood construction, with each level (story) having individual floor joists and wall frames.
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Remodeled buildings are a real problem. New voids are created and old ones are often interconnected in the renovation process.
Older buildings were built with high ceilings for summer comfort. Today, with the high cost of heating and modern-day cooling, many ceilings have been lowered a number of times, creating a series of combustible voids. In one instance, a college dormitory was remodeled and “fully sprinklered.” Originally, the interior finish was wire lath and plaster on wood studs, a type of construction that substantially resists fire spread. In the remodeling, an attractive mineral tile on steel grid ceiling was installed 18 inches below the original ceiling. The original ceiling was removed over large areas and opened up for utilities throughout the building. When fire broke out, it apparently penetrated the void immediately. The sprinkler protection did not cover the voids. The building was destroyed— fortunately without loss of life.
All the mistakes of the past and of the present-day remodeling are not wiped out just because the building is “sprinklered.” The voids must be sprinklered as well.
The term “trussloft” (adapted from cockloft) is being applied to lightweight wood truss floors and roofs that truly provide a new dimension in fire suppression problems and hazards. Fire in such a floor (or roof) makes it extremely hazardous for firefighters to maintain a position above or below the fire floor due to the potential for early collapse.
In your mind’s eye, see the building’s interconnected voids. If there is fire in voids, call for adequate help and get lines in place before opening the voids, since this will increase the air supply and the fire can quickly spread unchecked throughout the building.
Be realistic. We are not Superman or Wonder Woman. We cannot always cancel out the mistakes of others. The building may be doomed from the start and exterior attack preparations must be made early. Above all, remember that dense black smoke pushing from a void is an almost certain indicator of a coming smoke explosion that may be violent enough to damage the building’s integrity.
