Fire Studies: Fighting Fires In Heavy-Timber Buildings

Engine 38 arrived on location at 1 A.M. and reported a fully involved, three-story, heavy-timber-constructed building measuring 150 by 150 feet. The storage building contained Styrofoam. A defensive attack was initiated immediately.

Engine 38 gave a grim picture of their ability to stop the fire from spreading to the exposures. The Delta exposure was across a 15-foot driveway; it was one story in height, 35 feet wide by 150 feet deep, built of noncombustible construction and contained Styrofoam. Delta was already showing signs of being involved in fire. Delta 2 was identical to Delta and separated by a 15-foot driveway. It contained a machine shop with raw material and storage. Delta 3 was a 1½-story factory of ordinary construction. It measured 350 by 350 feet and was separated from Delta 2 by a 15-foot driveway. The exposure on the Charlie side was a 1½-story, ordinary-constructed building with a loading dock; a number of trucks were parked at the loading platform. On arrival of Engine 38, these trucks were already involved in fire that had spread from the original fire building. (Delta and Delta 1 are synonymous terms under the National Fire Academy sectoring system.)

 

Additional alarms called

The captain of Engine 38 requested a second alarm. Battalion 12 arrived and after sizing-up the scene recognized that Delta was lost. He focused his attention on protecting the Delta 2, Delta 3 and Charlie exposures. Battalion 12 immediately struck the third and fourth alarms. As the deputy chief arrived on location he performed his 360-degree walk-around and conferred with Battalion 12. There were many problems that needed to be addressed, including:

• A heavy-timber building with many exposed buildings that were constructed close together with no fire stops

• A water supply sufficient for most fires, but not for the conflagration that was developing

• A limited amount of initial resources on scene

The close proximity of the exposures to the fire building was allowing a rapid spread of the fire. The fire building was between an interstate highway and a river. This created many dead-end water mains. Two fireboats had been dispatched, but their response would take at least 20 minutes. Even then, the five-inch, large-diameter hoselines (LDH) from the fireboats would have to be hand stretched. This would be labor intensive and time consuming. The fifth and sixth alarms were struck.

It was determined that three companies with master streams could initially control the spread of fire on the Charlie side until additional units and water became available. The main concern was the Delta exposures. The fast-moving fire would shortly consume both Delta and Delta 2; Delta 3 now became the focal point to stop this fire. Battalion 8 was assigned as the Delta Supervisor. He had companies place master streams to protect Delta 3 and used units on the interior to extinguish fire that entered the building.

 

Strategy and tactics

Except where the fire was directly attacking the exposures, the original fire building was largely ignored. To the inexperienced eye it would appear that the firefighters were letting the fire burn itself out, when in reality the initial resources and limited water supply demanded that the tactical placement of hoselines be well managed.

Relay operations using LDH were created to supplement the limited water supply. The fireboats arrived and units were waiting to stretch five-inch lines from the large reels on the fireboats.

Containment of the fire occurred due to the improved water supply and the deployment of companies from the additional alarms. The original fire building, Delta and Delta 2 were destroyed. There was some minor fire extension into the Charlie exposure. There were about a dozen points where fire had involved Delta 3. Through the use of master streams and the interior attack, the extension of fire into Delta 3 had been controlled and extinguished.

The ensuing critique found that the early recognition of the severity of the situation and where the fire could be stopped was critical. They further identified that the strategic and tactical considerations and placement of the initial limited resources was a major factor in controlling this incident. The early calling for additional alarms and the use of multiple methods of securing water supplies were key contributing factors.

 

Construction factors

Heavy-timber, or mill, buildings are constructed with wooden timbers of large-dimension lumber. Through proper design, heavy-timber construction provides an excellent degree of fire resistance by requiring a minimum dimension for all load-carrying wooden members. The quality construction features of these buildings afford firefighters time to make an aggressive attack on a fire.

The exterior walls are of masonry construction and can be up to eight stories in height. Larger structures contain fire walls. A fire wall in heavy-timber construction is customarily a bearing wall of masonry materials that is a barrier to fire. Any openings in a fire wall must be protected with the same fire rating as the wall that is pierced. Door openings must contain self-closing fire doors.

If fire walls are located in a structure with a combustible roof, they must extend above the roof to prevent the spread of a roof fire. The roof can be supported by columns or fabricated of heavy-timber truss. The common truss configurations are:

• Flat and constructed of parallel chords

• Triangular

• Bowstring-shaped

The floors are built to carry heavy loads. This is accomplished through the installation of columns to support large floor timbers or parallel chord truss containing heavy-timber components. The truss permits large open spaces with fewer columns.

Columns must be a minimum of eight inches thick. Girders that span the distance between the columns must be a minimum of six inches thick. The thickness of the floor must be a minimum of three inches. This is often installed using tongue-and-groove, one-inch planks of lumber that are cross-laid.

The interior walls and ceilings are usually not finished. This leaves exposed masonry walls and creates few concealed spaces. This type of construction uses the underside of the exposed wood floors as the ceilings on the floor below.

Building modifications

Modifications to the structure include makeshift offices that can create problems for firefighters:

• They may be built beneath the sprinkler system and not contain sprinklers

• Portable heaters used in these makeshift offices can overload the electrical wiring

• An accumulation of paperwork and improper storage may set the stage for a fire to be well involved before activation of the building’s alarm system

Many of these buildings are still used as factories and warehouses; others have undergone major changes and are occupied by retail and wholesale outlets. Others have been converted to apartments and condominiums. Some are multi-use structures that include offices and warehousing.

These modifications change some of the inherent qualities of the original construction. Where few concealed spaces existed, renovations may include many voids. Pipe chases are installed to provide access for the utilities on the upper floors. They also afford a ready means for fire to extend from the lower to the upper levels of the building. Heating, ventilation and air conditioning (HVAC) systems are installed to provide centralized heating and cooling. Ceilings are suspended to reduce the living space needed for the changes in occupancy, creating more void spaces.

 

Building deterioration

The heavy-timber building as built is not prone to collapse. The large timbers will withstand attack by fire and give firefighters time to control and extinguish a fire. Many of these buildings, though, are quite old and have been modified or have deteriorated.

A serious problem develops when a building sits vacant for many years. It is subjected to deterioration due to the lack of maintenance and the attack by the weather on the building. Leaks can develop in the roof and window areas. The deterioration of masonry walls can occur due to water infiltration, combined with freezing and thawing of the water in these walls. Under fire conditions, these weakened walls can collapse, endangering firefighters and threatening nearby buildings with the extension of fire.

Rainwater from leaking roofs will rot the wooden roof planks and interior support beams, especially at the connection points. These deteriorating conditions may not be noticeable under normal circumstances, but may cause rapid failure under fire conditions.

 

Firefighting concerns

Fires in heavy-timber buildings can present unique challenges to a fire department. The fire service today does not have the number of large building fires as in the past. This is due to a number of factors:

• Better building codes

• Stronger code enforcement

• Fully sprinklered buildings

• Fewer buildings that present fire hazards

The reduction in these fires is positive for the community. One problem, however, is that it makes it difficult for firefighters to keep the necessary skills sharp to fight these types of fires

Heavy-timber buildings present a tremendous fire problem due to the contents, methods of stock storage and large amount of exposed wood. Once ignited, they generate massive amounts of heat. These fires are difficult to control and can severely threaten exposed buildings.

Since there are few concealed spaces in heavy-timber buildings that have not been renovated, firefighters are able to mount an offensive attack and control a fire in the early stages of development. The lack of concealed spaces permits hose streams to reach the fire. However, once a fire gets past the incipient stage, it can be difficult to control. These fires can and will spread rapidly.

Once the location of the fire is known, a hoseline should be stretched to attack the fire. This attack should not drive the fire into other areas of the building. When possible, the fire should be fought from the unburned side. Since these buildings can be of tremendous size, a decision on which direction to fight the fire must consider access, fire wall locations and minimizing building loss. A fire above the first floor will initially be fought from the stairways. The incident commander should designate which stairway to fight the fire. Should multiple stairways be used, close coordination is a must to prevent opposing hoselines. If the fire threatens the floor above, a hoseline should be immediately stretched to that location.

Hoselines must be stretched to back up the initial line and the hoseline stretched to the floor above. Backup lines must be either the same size or larger than the initial hoseline. Strong consideration must be given to 2½-inch hoselines. Smaller hoselines, though deployed much faster, do not have the knockdown and cooling ability of the 2½-inch hoseline.

Floor openings that allow interconnection of floors will work against the containment efforts. These openings could have been created for the use of large tanks or for conveyor belts that service multiple floors. Hoselines must be stretched to the floor above to check these areas for fire extension.

The large area of these buildings and the high ceilings permit an accumulation of heat at the ceiling level that may not be recognized by firefighters on an offensive attack. As the fire expands, it can flash over a large area, threatening the firefighters operating within the building.

 

Compartmentation

Compartmentation, accomplished through the use of fire walls and properly functioning fire doors, will assist in confinement efforts. This is also true in a large building where a defensive attack is underway. The incident commander should decide where a fire can be stopped. This consideration will depend heavily on resources and water supply.

The defensive attack will occur on a section of the fire building while other units are situated on the interior protecting other areas with an offensive attack. Companies deployed on the building’s interior should be located at the appropriate fire wall location and ensure that the fire doors are closed and that hoselines are in place to handle any minor extension that has occurred. In multi-story buildings, this takes coordination of companies from the ground floor up to and including the roof. The division or group supervisor must ensure that units on all levels are operating at the correct fire wall location. The goal of these companies is not to attack the fire in the areas in which a defensive attack is occurring, but to prevent any fire extension past those areas.

The sturdiness of these buildings allows the fire department flexibility. A well-involved fire can initially be attacked with exterior streams. This “blitz attack” can knock down large amounts of fire while interior hoselines are being stretched. After handlines are in place and the fire has been knocked down, the exterior lines can be shut down and an offensive attack initiated.

The success of any offensive attack will depend heavily on proper ventilation. Creating openings over the fire area and in advance of the hoselines is a must. Without adequate ventilation, the hoselines will be unable to push into the fire area, and the attack will be useless.

 

Summary

Through proper design, heavy-timber construction provides an excellent degree of fire resistance by requiring a minimum dimension for all load-carrying wooden members. The quality construction features of these buildings afford firefighters time to make an aggressive attack on the fire.

Naturally, the best method of protection is the installation and maintenance of a sprinkler system. Yet, even with protective systems, high-piled stock and poor housekeeping can reduce their effectiveness.

Large buildings can be dangerous to operate within. Safe fireground operations can be enhanced by using a pre-plan, on-site inspections and familiarization tours. n

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