Building Construction and Fire
This is the second in a series of articles on building construction features that affect fire fighting operations and planning. Additional articles wiU be published during the next few months.
The fire-resistive construction of the Empire State Building was accomplished by using steel for the frame, and each individual framing member was protected from fire by “fireproofing.” Though it is now recognized that there is no such thing as a “fireproof” building, the method of protecting steel from excessive heat during a fire is known as “fireproofing.” It will be discussed in detail in connection with steel frame construction.
Floors of the Empire State Building were made of reinforced concrete. In addition, the spread of fire or smoke from floor to floor was prevented by the enclosure of vertical openings. The interior finish was almost totally noncombustible.
In such a building it is possible for a fire department to fight a working fire in one occupancy without serious effect on other occupancies and often without any general evacuation. While any fire can cause loss of life, the odds are very long against a loss of life in such a building being due to any defect in the building itself.
The development of combustible, non-structural building elements has changed the picture markedly. A bewildering variety of surface finishes began to come onto the market in the late 1930s. Literally square miles of combustible acoustical tile, made of low-density fiberboard, was installed on ceilings, and to a lesser degree on walls, to provide noise conditioning and to hide deteriorating plaster surfaces. Plywood veneers, particle boards, fiberboard, hardboard punched with holes (thus increasing the speed of fire spread) and plastics of all types are used as surface finishes and to subdivide areas.
Just recently the writer consumed a high-priced steak in a restaurant, the walls of which were finished with weathered boards, torn from a dilapidated barn, to provide atmosphere.
Practically all of these materials possess one common characteristic: they ignite. They also spread fire and produce smoke and heat in much greater measure than the painted plaster surface.
The fire problem can vary tremendously between two identical fireresistive buildings, depending on the extent to which combustible, nonstructural, building elements have been added to the buildings. Fire can spread rapidly; higher temperatures are reached sooner; fire can spread from floor to floor by intense, even though possibly short-lived, fire coming out of windows; smoke and disabling gases may be generated in unbelievable quantities, and often the cause is not recognized by the fire forces because of the complete destruction of the offending material. For instance, after an intense fire, it is noticed that on the ceiling and walls there is a pattern of circles about an inch and a half in diameter, spaced about four to the square foot. How many fire officers will immediately recognize that the circles are the marks made by the globs of adhesive used to attach acoustic tile to the surface?
Fire spread via windows
A fire in New Orleans exemplifies the problem. Here the effect of combustible interior finish on a fire-resistive building was recognized. A fire which started on the 13th floor of a 24-story fire-resistive building required a fourth-alarm assignment. The fire spread to the 14th floor via the outside, even though the space between the top of the window on one floor and the bottom of the window on the floor above was 4 feet, 9 inches. The ceiling consisted of combustible acoustical tile cemented to the plaster ceiling with combustible adhesive, the same type of “improvement” responsible for the Hartford, Conn., Hospital holocaust.
How many pre-fire plans for highrise office buildings take note of combustible ceilings, wall finishes and partitions as presenting a serious potential for exterior extension? How many fire departments really expect to have a fourth-alarm fire in a fireresistive office building?
Serious as the combustible finish problem is, there is at least some measure of understanding and control. Many building codes have requirements to limit the flame spread permitted for surface materials. Often the restrictions are stringent only in exit areas, and thus might have no effect at all on a situation such as that in the New Orleans office building. In addition, the building code has little effect on alterations, particularly those for which the owner does not procure a building permit. It is difficult or impossible to determine the flame spread rating of a material after it is installed.
When the Empire State Building was built, heat was provided by steam radiators, and air conditioning was provided by opening windows. Today the air within a building is often a processed product. It has been filtered, cooled, warmed, dried, dehumidified and adjusted to a point where it has value and has to be saved, reprocessed.
Let us see what happens when we combine a fire in a few polyvinyl chloride connectors between the air conditioning ducts and the diffusers in the ceiling with the modern enclosed building. There is a trifling fire on the ninth floor from which fumes spread to the 32rd floor due to stack effect. (Stack effect is the movement of air through vertical channels in a high-rise building due to the difference between inside and outside temperatures.) Chlorine released from the burning plastic combines with the moisture in the air to form hydrochloric acid. The fumes are so irritating and frightening that workmen fleeing the 32nd floor by stairway are driven from the stairway at the 25th floor and are so distressed that they break out windows. Glass falling 25 floors to the street gives the first alarm of fire.
The fire service is in serious trouble in many modem high-rise buildings and, in most cases, we don’t even know it. The open window through which smoke can escape, fresh air can enter and at which a victim can take refuge of a sort is on the way out. If the builder gives the inhabitant windows which he can control, he might open them and let some of the valuable processed air escape. Sheet glass windows, or no windows at all, are features of modern architecture. The possibility of distribution of deadly gases throughout the building by the stack effect is but dimly recognized.
At a meeting bringing together fire protection experts and air handling experts, a top air handling expert remarked, “Your codes and standards are attempting to convert a modern building back into an Empire State Building and it can’t be done.”
Many fire department training programs recognize only the thermal updraft provided by the heat of the fire as significant in the spread of smoke and thus simplify ventilation to a matter of removing the skylight from a flat roof; the heat of the fire is probably the least significant of the mechanisms which will distribute smoke and gases through a high-rise building.
We have no adequate or safe method of venting the sheer glass walls of a high-rise, nor any protection for men, attempting to enter the fire building, from glass falling 40 stories or more.
The movement of combustion products in high-rise buildings is being studied sporadically. The present state of the art will be discussed further along, but it is by no means beyond the bounds of credibility that a tremendous loss of life can take place in a modern high-rise building because of the way in which air is confined in the building.
The foregoing are but two of the more important developments in nonstructural building elements which increase the problems of the fire officer and demand that he possess and act on factual knowledge of modern building and decorating methods. He must be aware of what is permitted today under his local building code, what was permitted in the past, and what was done despite, or in the absence of, codes.
At one time it was fairly easy to distinguish between structural and non-structural elements of a building. For one thing, it was considered almost indecent to expose any structural wall, beam, or column to public view. All were carefully concealed by plaster. To study the construction of such a building, we must look up in the attic, or down in the boiler room, where there was less reticence on the part of the architect.
Today, however, many elements of a building combine both structural (load bearing) and non-structural (often decorative) functions. The usual fire protection evaluation of laminated wooden beams for instance, deals solely with the question of whether or not the beam will sustain its rated load after being subjected to fire. Many times, however, the beam not only serves a structural purpose but, beautifully finished, serves as a feature of the interior decor.
St. Paul Methodist Church in Kensington, Md., had a fast fire which was controlled in a few minutes by the fire department. The laminated wood arches lost none of their structural strength, even though they were charred all over to a depth of 1/4 to 1/2 inch, but the aesthetic loss was total.
Masonry structural (bearing) walls are often left exposed to eliminate the expense of finishing the interior. They are indistinguishable from masonary partition (non-bearing) walls in the same building. The repair or replacement of a fire-spalled concrete block wall would be more costly in the case of a bearing than a nonbearing wall. Sometimes the wall is left unfinished with the thought that the finished surface will be provided later as funds become available, or by the handyman at less cost than by the construction contractor.
Be on the alert for any hint of such a plan. Will the finishing material be in conformance with the code? In the absence of an adequate code, you can often persuade the owner to use a suitable material if you get your point over to him before the purchase of material is committed.
A most serious potential problem arising from the combining of structural and non-structural elements is the use of acoustical tile ceilings to provide so-called “membrane fireproofing” for steel structural elements. Even assuming that the ceiling is properly installed and that all the proper parts, type and size of wire are used (one student told of finding aluminum wire used to suspend a ceiling), it is all too possible that Murphy’s Law (if anything can go wrong, it will) will be governing and that changes during the life of the building can destroy the effectiveness of the fireproofing. In the event of a serious fire, local, or even general, collapse of a fire-resistive building becomes a distinct possibility.
Can it happen to you? Call your building department. Is membrane fireproofing permitted under your code? If so, are there any such buildings? Inspect the buildings from top to bottom. Is the membrane intact? Has the tile ceiling been removed, replaced or altered in any way? Are replacement tiles identical to those originally installed? Pay particular attention to storage areas, file rooms, workshops. The very places which might have the highest fire load are the most likely places for tile to be removed, perhaps to replace damaged tile in a more public place.
This subject will be fully explored later, but why wait? Determine now whether buildings protected by membrane fireproofing are being permitted to become potential disasters.
Classification of structures
Buildings can be classified in a variety of ways. Generally we tend to categorize them by occupancy: stores, churches, schools, hospitals, single family residences, multiple dwellings, heavy industrial, etc. Building codes divide buildings into types based upon the file potential, such as wood frame, ordinary (brick and wood joisted), heavy timber, noncombustible and then varying degrees of fire resistance. Section 8 of the “NFPA Handbook of Fire Protection,” 13th edition, which should be in your library, breaks down the building fire problem according to fundamental considerations of building design and construction as follows:
- Walls and partitions
- Floor and roof assemblies
- Floor surfacings
- Roof coverings
- Fire resistance of building materials and assemblies
- Interior finish
- Types of building construction
- Smoke and heat venting
- Protection against exposures
- Evaluating structural damage
- Special structures
- Construction operations, alteration and demolition
The 236 pages outlined above contain a vast amount of information, some of it directly applicable to our needs, so much so that if a subject has been covered adequately for our purpose in the “Handbook,” we will not discuss it fully here, but will refer to the “Handbook” for a full treatment. We will attempt to concentrate on our prime purpose, which is a guide to the fire officer who must deal with the consequences of the mistakes, omissions, exceptions, grandfather clauses, inadequate testing and perhaps even criminal acts of others, none of whom will be on hand when the balloon goes up.
Some years ago a genius in women’s ready to wear came up with the mix and match idea. The idea has been enthusiastically adopted by builders. Unprotected steel members are inserted into heavy timber structures, steel open-web joists replace wood, precast concrete floors are installed in steel frame buildings.
The new HUD building in Washington has exterior walls of 13-ton precast units. Precast girders span from the exterior walls to a cast-inplace central core. The exterior columns of the U.S. Steel Building in Pittsburgh are “fireproofed” with water. Seventeen-story brick high-rises have no wall thicker than 12 inches, and so it goes.
The “non-structural elements” cut across all types of construction. Combustible acoustical tile may be installed in any type of construction. Air conditioning ducts may spread smoke and fumes in any building. Fire-resistive ratings may be required even in frame construction. The code may require a one-hour fire-resistive enclosure around a boiler room of a frame residence converted to a nursing home.
Our subject matter, therefore, is not as straightforward as arithmetic, rather, it is like a merry-go-round, and we must jump on somewhere. The following matrix may help to understand the subject:
Note that any item in the vertical axis can be applied to any type of construction in the horizontal axis. After a discussion of structural principles, we will discuss each type of building in turn and then return to the other items in the vertical axis.
Copyright 1970 by Frank Brannigan. The contents of this article may not be reproduced in whole or in part without the consent of the copyright owner.