WATCH THOSE WALLS!

WATCH THOSE WALLS!

Ice formation during fire operations must be reckoned with by officer in charge

—photo by Captain F. c. Barth, courtesy Milwaukee F. D.

Part 2: Signs of Deterioration

OCCASIONALLY walls give warning signs of deterioration or indicate the possibility that a collapse is near. These may be visual, audible, or both. Some of the visual signs include smoke and/or steam pushing out of the mortar joints under pressure; water flowing through mortar joints; cracks appearing or widening in a wall. When the movement of a wall or portion of a wall takes place, it is time for fire fighters to evacuate the immediate area at once.

Another indication of structural change in a wall occurs when the water of a fire stream turns to steam as the fire stream hits the wall. The walls are heated from the fire on the inside and cooled on the outside by the fire streams. This sudden cooling is indicated by the steam forming. Walls should be carefully watched if this sign is observed.

Another common sign, which indicates structural change is taking place, is bulging. This, of course, is usually caused by the expansion of the contents of the structure. Contents such as paper, corrugated cardboard, rags, felt, sawdust, milled feeds, etc., are the type of materials likely to cause trouble. Another sign is the sudden change in the color of smoke. This may indicate that the fire has reached a different type of combustibles, or that a back-draft condition has developed. The usual change of color, in the case of back-draft conditions occurring, is from the “normal” smoke color to a yellow or grayish yellow.

Deterioration of walls may also be recognized by audible signs. The sounds of dropping bits of mortar upon a fire fighter’s helmet or around him is an example. This might also be considered a visual sign if it is possible to see the mortar dropping. Other audible indications are the creaking of floors or walls.

Nonbearing walls

Nonbearing walls may be panel walls, curtain walls, veneers or any other type of wall found in skeleton construction and supporting nothing other than its own weight. They are usually found to be thinner than similar (in height and area) bearing walls. Panel walls in buildings of skeleton construction are usually 8 to 12 inches thick for any of the common masonry materials. Other materials, such as glass, steel, aluminum, plastic or tile, may be used for the purpose of providing the curtain. In this case the walls may be much thinner.

The absence of a header or “tie-in” course, together with the absence of stars and plates which indicate the presence of tie rods and the lack of arches or heavy lintels over windows and doors are all indicative of nonbearing wall construction. However, modern remodeling and construction practices will many times conceal the stars, plates, arches and lintels behind a veneer or facing.

It must be remembered that in nonbearing wall construction all floor joists, roof rafters and/or trusses are supported by, and the loads are transmitted to, the foundations through a thoroughly connected framework. This framework usually consists of a series of girders and columns of steel, wood, or concrete and is relatively independent of the covering (walls). The enclosing walls, partitions, and floors are supported at each floor level by the structural framework.

Direction of collapse

Walls may fall out or they may fall in. Walls which fall in may sometimes kick out at that point w’here they break off, and as a result slide or fall out into the street.

Another type of wall collapse is called a “curtain fall,” that is, where the walls drop almost straight down. These occur particularly where there are large window areas, such as the front of a building. Bricks, debris and other materials fall almost straight down and may cover the sidewalk.

Walls usually fall out because heat expands them on the inside, and fire streams cool on the outside. This cooling of the wall, in turn, causes further straining and bulging, greatly adding to the danger of collapse. The failure of trusses or similar members supporting the roof may also push a wall out.

Panel or curtain walls have a tendency to bow in toward the fire or heat rather than out. Their relatively strong and rigid supports restrain them at the top, bottom and sides. The expansion caused by the heat of the fire is therefore directed inwards.

Dense smoke, steam, or water escaping under pressure through the mortar joints of a solid brick wall may indicate that trouble is not far off. When the mortar joints have been destroyed sufficiently to permit the passage of smoke, steam or water, the wall has become seriously weakened. The buildup of sufficient pressure to force the smoke out of the mortar joints also indicates the presence of conditions suitable for a back draft or smoke explosion.

Continued on next page

Concrete-block wall lying flat during collapse at fire in Tampa, Fla.

Wide World photo

Water flowing through mortar joints should also raise warning flag in minds of fire fighters. Sudden collapse is possible

Photo by Evanston Photographic Service courtesy Evanston, Ill., F. D.

Visible danger signal may be smoke pushing through mortar joints under pressure

—photo by Evanston Photographic Service courtesy Evanston, Ill., F. D.

Veneered wall of building with trussed roof fails during fire—photo by author

A brick-faced hollow tile wall, or a hollow tile wall, will sometimes fail when water is thrown on the hot face of the wall, causing the bricks or tiles to crack off. Under the right conditions, the tile may seem to literally explode when cold water hits the hot wall. This is also a characteristic peculiar to almost all nonporous building materials. For additional informations refer to Chapter 22, The Fire Chief’s Handbook, entitled “Effects of Fire on Building Materials.”

Bearing walls are subject to collapse more frequently than nonbearing walls. When the additional load they are expected to carry is taken into consideration, the reason for this is quite apparent.

Many times bearing walls are the side walls of a structure and are supported by, or adjacent to, the walls of an adjoining structure. These walls of the adjoining structure provide additional support to the bearing walls of the building involved with fire. It is possible under this set of conditions for the end walls to be affected and even collapse. This particular collapse is the result of the thrust being transmitted along the bearing wall to the front or rear wall, or both.

Experience indicates that many breaks or cleavages occur between windows or other openings in a wall. This appears to be one of the weaker areas in a bearing wall. In fact, many buildings presently in use have the visible beginnings of failure.

In other cases, where a particularly strong belt course or sill course can be found, the break is likely to be along this structural member. As a masonry wall is built, its various elements and members are bonded together to give it strength as a single unit. When a belt course or a sill course is introduced into a wall, the homogeneity is destroyed. The bonding or materials to be bonded together change, and should forces be exerted which will ultimately destroy the wall, the area along a belt course or sill course is where the cleavage may be expected.

Hollow block walls

In addition to the foregoing characteristics, the reaction of the intense heat of a fire can dry out blocks until they begin to crumble. This tendency, of course, has an important effect upon the ability of the wall to carry any weight during a severe fire. When hollow-block walls collapse, they will usually lie out flat. They often pave an alley or the ground when they fall.

Veneered fronts with trussed roofs

Veneered fronts with trussed-type roofs create special structural problems for the fire fighter. These brickveneered fronts are usually held up by their weight alone or laid upon or against an unprotected steel beam. Although the first truss may be within inches of the veneered front, the wall contains few, if any, bonds to the roof or truss. As these veneered fronts generally extend several feet above the walls of the structure, there is no tie-in to the walls. Should the roof or front part of the building become seriously involved with fire, these veneered fronts are very likely to collapse.

The factors which may cause walls to collapse during a fire are numerous. It is not easy to predict accurately the exact point where a failure will first occur, even if many of the factors are known and recognized. Nor is it possible to predict the precise moment when the first movement will take place. However, careful observation and the recognition of changes occurring to a given structure during fire fighting operations, will greatly aid in preventing injury and loss of life should the building collapse.

WATCH THOSE WALLS!

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WATCH THOSE WALLS!

PART I: Types of construction

Photo courtesy South Bend, Ind., F. D.

Fire fighting safety depends to a great degree on the stability of masonry construction

FIRE FIGHTERS responding to a structural fire must make a quick and reasonably accurate appraisal of the entire situation. This is called a sizeup and can be broken down into many factors, including the stability of the building. Going further, a building’s stability depends on its components, one of which is the masonry wall to which this article is directed.

A thorough knowledge of a building’s construction, its weaknesses and strong points, are necessary for a sizeup. This knowledge is only gained through a sincere effort to become familiar with various structures and their characteristics. The easiest way to accomplish this is through regular and systematic inspection.

To enable the fire officer make a quick, accurate appraisal of a building, we must first define certain terms familiar to the construction industry and then examine the structural stability of the various types of walls. Structures are described as those with “bearing walls” and/or “nonbearing walls.”

Bearing walls support vertical load in addition to their own weight. Roof and floor loads that are carried to the ground through the walls characterize a bearing wall building.

Nonbearing walls are those which support no load other than their own weight. They are found in buildings of skeleton-type construction, either steel, masonry or frame, which have panel walls, curtain walls, or filler walls. Roof and floor loads are carried to the ground through the skeleton framing rather than the walls themselves.

Party wall is one common to two buildings, which acts as one wall for both buildings. Brick load-bearing party walls are quite common in this country, particularly in older urban areas. The greatest hazard in this type results from unprotected openings such as common joist sockets.

Panel walls are nonbearing walls found within skeleton-type construction. These are built between columns or piers and wholly supported at each story. They are called “curtain walls.”

A similar type of wall construction is known as “filler wall” or “enclosure wall.” The main difference between an enclosure wall and panel wall is that the former is an exterior nonbearing wall in skeleton-type construction and anchored to the columns, piers or floors. It is not necessarily built between columns or piers. It may be supported at each story or at intervals of two or more stories, as best suits the situation and design. A panel wall must be wholly supported at each story level. Lintels are beams supporting masonry and other loads over an opening in a wall. The third series of factors are the thrust effects on the wall which can also result in bending. Thrust may be caused by any of these forces: Bulging of the wall due to heat on the inside; movement of floor joists in or out of their sockets; absence off “fire cuts” on ends of floor joists extending into sockets; movement of wall in or out, up or down from settling; and low-order explosions.

Effects of falling walls on apparatus are well known. This New York pumper was recently destroyed at warehouse fire

—Photo by James Heffernal

Chicago’s Engine 13’s quarters is good example of building with bearing walls. Note heavy arches over openings

—Photo by author

Course is a continuous horizontal layer of brick, stone, concrete, or similar material, consisting of blocks and forming part of a wall.

Belt course, or string course, is a horizontal band which nans across the face of a wall, flush with the wall surface or projecting, and is either plain or molded.

Sill course is a belt course which also serves as sills for windows.

Tie rods are structural steel rods used to reinforce or repair masonry wall deterioration or movement. In order to be effective tension devices, they should be fastened by stars or plates on the outside of the building at each end, and extend from masonry wall to masonry wall. Many times this practice is not followed and that which appears to be a tie rod from outside appearance may contribute little or nothing to the bracing of the wall. Dependence upon such a false brace can prove very dangerous.

Reinforced-concrete skeleton of this building contains brick panel walls

-photos by author

Sprinkler leakage into waste rags caused expansion and rear of this building fell into alley

Arches are curved load-carrying arrangements built of wedge-shaped masonry units which carry the same loads that would be borne by a lintel. False arches are made to resemble arches, but depend upon a lintel, hidden or visible, for strength.

Recognizing bearing walls

A header course of brick is one in which the 4-inch end of the brick is exposed. This usually indicates the brick extends at least 8 inches into the wall. Thus, the wall should be at least 8 inches thick and may be a bearing wall. The header course may consist of a series of headers or a combination of headers and stretchers. A stretcher is the brick laid flat with the long (8-inch) side exposed.

Warning: A series of header courses alone do not necessarily mean the wall is a bearing wall. However, when the header course is found together with stars or plates in connection with tie rods, and/or with arches or heavy lintels, a bearing-wall type of construction is strongly indicated.

As previously described, structuralsteel or wrought-iron tie rods are used to reinforce or repair masonry wall deterioration. Secured to walls by means of a star or plate, they should, for best and safest results, extend from masonry wall to masonry wall. This practice is frequently not followed in substandard construction, and many times tie rods are secured to a convenient floor joist or roof rafter. When this is done, there will be nothing left to hold such a wall from falling outward if the joists burn out. Examples of tie-rod type of construction may be seen in almost any community which has older brick structures. The plates vary widely in shape and design, and so do the methods of tying in the rods.

A third way to identify a bearing wall is to recognize the heavy lintels or arches found over windows. These lintels or arches transmit vertical thrust or load from the window area to the walls on either side of the window opening.

Structural stability of bearing walls

There are a number of factors affecting the structural stability of bearing walls. The first to be considered are loads on the wall itself that cause bending tendencies other than the weight of the wall. These include such exterior attachments as: Heavy signs; canopies or marquees; fire escapes; balconies; porches; copings; and cornices. Ice accumulating during fire fighting operations also develops a heavy load. Each of these change the center-of-load path (center of gravity) in a given wall and move that center of gravity toward the outside of the wall. This, in turn, causes a tendency for the wall to fall outward in the event that other bracing is burned or broken away.

The second factor includes the ratio of the length to the height and thickness of a given wall.

Heavy marquee canopy is literally pulling building apart due to its load on face of Wall

—photo courtesy Evansville, Ind., F. D.

Water accumulation on roofs or floors, or from flooding conditions. Should 1 inch of water accumulate in a 9-by-12-foot room, over 500 pounds will be added to the floor load. If water accumulates to the depth of 1 foot, the additional weight will be in excess of 3 tons. Water standing on a wood floor may cause the wood to swell and push the walls out.

Expansion of contents, e.g., paper, cardboard, rags, felt, sawdust, etc.

The fourth group of factors are those causing serious deterioration of the wall itself or a breakdown of the wall structure. Some of the things which may bring about this deterioration are neglect and lack of maintenance over a period of years; flooding or excessive dampness; heat from the fire; the chemical action of birddroppings; or nests built into the wall. Others in this category are overheating from a previous fire; explosions (high order); gases; openings for pipes and/or ducts; machinery vibrations, etc.

Additional factors which must not be overlooked as they also lead to structural failure during fires are:

Walls originally built in a proper manner, but which have been reconstructed with too many openings

Walls of insufficient thickness or which are poorly built

Exceedingly high wind pressure

Streams of water striking heated unprotected steel supports

Floor collapse

Recent removal by demolition, etc., of adjacent buildings which afforded a common party wall of substantial construction and support

Recent extended excavation work in close proximity to a structure involved with fire

(To be continued)