The National Fire Protection Association (NFPA), defines heavy timber construction as a system having main framing members measuring no less than eight inches by eight inches and with exterior walls that are made of a non-combustible material.
The building industry is driven by money. The architect is driven by the need to create an edifice, but the builder just wants to do it as quickly as possible for the right price. Never is fire considered part of the equation. That is, except during the mid-1800s, when insurance companies were losing a lot of money for losses at manufacturing establishments. The insurance companies pushed for a type of construction that would be slow burning.
I'm sure after considering many burned-out structures, the inspectors for the insurance companies realized that wood has a natural tendency to resist fire - it starts to char first, which delays the combustion process. The thicker the piece of wood is the longer it will take to ignite. Also, during that period, the resources needed, labor and materials were cheap. This end result was referred to for many years as "mill construction" and it is now known as "heavy timber," "post and beam" or "post and plank."
This type of building construction was predominant in the New England area, but as in any successful venture it quickly spread throughout the country. Although textile factories and paper mills were the first to utilize this type of building, almost any manufacturing process or storage need was serviced by this type of construction at one time or other.
Although some measure as small as 50 by 50 feet, most buildings of this type are quite large. The majority are measured in hundreds of feet by hundreds of feet. Usually, housing was provided for the workforce and these homes surrounded the central area, hence the term "mill towns." When I was a volunteer firefighter in Clifton Heights, PA, there were no fewer than 12 of these buildings in our one-square-mile town. Between these structures and those in surrounding towns I had much experience in heavy-duty operations.
The Structure
After the land was cleared, the building of the structure began. This usually occurred in the spring, when a sawmill could cut the timbers and give them time to "dry out," as green lumber would be unusable due to its nature of cracking and shrinking. White oak was the predominantly used wood at first, but Georgia pine became the more economical resource as the 20th century arrived.
The basement was excavated as well as the footings. The concrete that was poured into the footings was primitive compared to today's. The exterior walls were required to be non-combustible. The materials used for the exterior were usually brick or a combination of brick and stone. These walls can be as thick as two to three feet on the lower levels and one to two feet on the upper floors.
The basement floor was left as dirt or pavers (solid bricks) were installed. There were times when the builders installed wooden floor joists right on the earthen floor - they used a powdered mix that was supposed to solidify like concrete and protect the wood from termites. It was called "Builder's Crete," but it should have been called "termite's deluxe."
The columns in the basement were set on stone or brick piers. The spacing for these columns and the remaining ones above on subsequent floors was approximately eight feet in one direction and 20 feet in the other. The columns measured eight by eight inches minimum. On these were placed beams and girders. Depending on the load, these were no less than six inches wide and 10 inches deep. If the loads were heavy when the building was constructed, expect to see framing members much larger than minimum. It is the connections between columns and girders that are the most vulnerable. Often, cast iron connectors were used and these will fail before the wooden members during a fire, causing various degrees of failure. Many of these structures are six to 10 stories.
Interior walls were added to cut down on the area to be framed and assist in fire control. These were constructed of masonry. Doors allowed passage between compartments. This type of configuration usually was done in equal increments throughout the building (thirds, quarters, etc.).
The main intent for the space planning in these buildings was the generation of revenue. To this end, stairs and stairways were viewed as necessary nuisances to be added to go from floor to another. These areas can be quite small - so small in fact that two firefighters cannot pass each other on them.
Windows were another necessary evil. The process first employed within the building will have dictated if and where windows will be found. Most often today, the windows will be bricked in. The absence of these vent points will significantly reduce your ability to fight a fire in these structures. Their absence also can reduce the ability to have an adequate or accurate size-up. The number of doors to these buildings only necessitated minimal entry points for obvious security reasons. This acute lack of entry and therefore exit points is a serious safety factor that must be addressed when committing firefighters to an interior attack.
The flooring in these buildings is a minimum of three inches thick and will be tongue-and-grooved. This is also referred to as planks. If heavy machinery was used early in the building's life, you'll find alternating layers of this planking. You may also find four-inch-thick planking with one-inch flooring laid crosswise. The flooring could have absorbed many chemicals over the years, especially hydrocarbons, during various manufacturing processes and this will accelerate the combustion and failure potential during a fire. In the case of cold storage, a coating could have been applied on the floors and walls to assist with the condensation and rotting factor. This could also have been applied to prevent floors from becoming slippery.
The roof framing members are also quite large - six by 10 inches and larger. You may find some of the earliest forms of trusses, especially if the roof is pitched. There were three main forms of this type of trussing: King Post, Queen Post and Fink Truss. These types of trusses utilized the geometric design of triangles and were constructed of large pieces of wood (six by six inches and larger), but cast iron rods with turnbuckles were used at each connection point. Also the wooden joints were often mortise and tendon. Once again the cast iron is the Achilles tendon.
On flat roof assemblies the same truss design was used, but the top and bottom chords had to be larger. The roof decking was the same as the floor configuration. It utilized three- or four-inch planking. Many of these buildings with pitched roofs had slate installed as roof covering. These slate tiles can be deadly when the roof starts to let go and they become missiles slicing through the air.
Many of these buildings may contain elevators. These spaces may be open and empty, especially if the building has been vacant for some time. The spaces also can be covered with only a layer of plywood with minimal framing. In any event, if the areas are choked with smoke, firefighters will not be able to see these dangers.
The utility requirements for these buildings were of mammoth proportions. If a building was constructed next to a river, the owner might have installed a waterwheel-driven power plant. The amount of piping that runs through these buildings is staggering, especially if they were used for cold storage or chemical manufacturing. This can hamper rescue attempts when it starts failing and falls to the floor. It can also trap firefighters as they move throughout the structure.
The same dangers hold true for the electrical wiring. Cold storage buildings may contain hazardous residue, which can have its own deadly implications. Cold storage facilities in that era used ammonia exclusively.
Firefighting Considerations
If there are buildings like this in your area that are still being used, then you must get into each of them to conduct a pre-fire action plan. Although it takes longer for these facilities to catch fire, when they catch, it will take a tremendous quantity of water and many firefighters to put the fire out. You will need to ensure your water supply adequacy and personnel availability before you would be able to commit to an attack.
If these buildings are vacant, and especially if they have been vacant for some time, campaign for their demolition. There is nothing good about these buildings for firefighters. If your size-up is compromised by the lack of windows and doors, your interior operations also will be. Firefighters will not have secondary exit points without windows and doors. Also, you cannot vent the area. The wall thickness will preclude breaching operations should the need arise.
Manpower Limitations
If you are hampered by limited manpower, then this is critical in your assessment of your capabilities. Due to the large size of these buildings, search efforts are almost impossible to conduct safely. Firefighters wearing one-hour self-contained breathing apparatus (SCBA) cannot adequately search areas of many thousands of square feet in unknown configurations with unknown hazards.
Each floor of a heavy timber building should be considered a separate operation with appropriate number of command staff dedicated to each area. Using the incident command system as recognized by the National Fire Academy, this would be divisions and groups with the amount of command staff to utilize it. If your department uses other nomenclature for these terms, ensure that it complies with the requirements of the NFA's FIRESCOPE.
One of the toughest decisions that any fireground commander must make is whether to order an interior attack. I believe with all of the problems associated with this type of structure a reconnaissance must be made of the problem with as few personnel as possible. Once they have given the incident commander a picture of what they face, only then can a decision be made as to the operations, in my opinion. If there are no windows, your original size-up is incomplete and therefore flawed. I don't believe in the statement "Risk vs. Gain"; I believe it should be "Firefighters vs. Gain." To this end I would rather err on the side of safety and delay my interior commitment.
These buildings have not stopped being constructed. They are now reappearing with layered laminated beams, girders, columns, etc. They are being reborn in churches, public assemblies and factories. The newest threat is quicker failure.
REFERENCES
1. The National Fire Protection Association Handbook, 17th edition.
2. The Professional Handbook of Architectural Detailing, 1977, John Wiley & Sons.
3. Carpentry, Gilbert Townsend, 1945. American Technical Society.
4. Collapse of Burning Buildings, 1988, Vincent Dunn. Pennwell Publishing.
