The Fireman’s Guide to Main Street: The Old Mill
A five part series by
Lex Shady & Chris Tobin
This will be a five part series exclusively examining five different types of legacy construction, each with its own article as it pertains to firefighting. The types of buildings were selected based on their prominence in today’s main streets and historic districts. These specific types of buildings exist in small towns from coast to coast but are more commonly found East of the Mississippi River where our national building stock originated before moving Westward. The five buildings are the old house, the taxpayer, the old mill, the vacant theater, and the bowling alley. Today we examine...
Part 03: The Old Mill
The Building
The old mill: What would a town be without the mill? Nonexistent, that’s what. Unless you’re in a planned bedroom community platted in the 21st century then it’s highly likely your town grew around industry during the American Industrial Revolution. Such times gave us terms like “mill town”, “company town,” “factory house,” and “mill village.” The first mills were built in the countryside along powerful waterways and were wheel driven.
The advent of steam power did away with this type of construction, and lead to the hulking heavy timbered factories that would dominate the landscape for the next century. It was due to both the prevalence and their inherent construction features that so many of these buildings still exist in towns all over America. Textile mills were more common in New England, but as with everything else that expanded westward, so did industry and its buildings. Whether you lived in the corn belt, rust belt, or the cotton belt didn’t matter. Every town needed jobs, and those jobs were in one of many large factories that were surrounded by neighborhoods of their workers.
The term “mill type construction” originally in reference to the large New England textile mills is now used interchangeably with any such type four heavy timber factory. These buildings are exclusively legacy or heritage era construction with rough cut sawn timbers and joinery. The exterior walls are noncombustible masonry that are a thicker width at the bottom. Generally 24 to 36 inches thick at the ground level and tapering up as the building rose in height to typically no more than six stories. All four walls will be load bearing. Type lV “heavy timber” can be numerous types of occupancies such as churches, gymnasiums, and even residential. Mill type is a subtype of this construction, specifically referring to commercial use, such as factories or warehouses with masonry walls and specific dimensions on components such as floors and roof decking. It all comes down to what building code was used, and when it was published. It’s important the reader understand that Type lV construction can exist in numerous types of occupancies such as places of worship, lofts or restaurants, not just old mills; even though the construction features are the same. This article will be focusing solely on Type lV heavy timber mill type buildings.
The definition of Type IV heavy timber is commonly confused with Type V heavy timber wood framed buildings such as heritage framed construction or old barns. While the heavy timber framing may exist, Type V is still a wood framed building, thus not mill type construction due to the lack of masonry walls. There can be some variance amongst building codes, however all adhere to the minimum dimensions for heavy timber mill construction which is defined by the NFPA as follows:
– Noncombustible exterior load bearing walls.
– Main framing members being no less than eight inches by eight inches.
– Wood columns supporting solely roof members shall be no less than six by eight inches.
– Beams and girders supporting floor loads shall be no less than six by ten inches.
– Beams and girders supporting roof members shall be no less than four by six inches.
The idea behind heavy timber is its inherent fire protection based on mass. Simply put the beams will char, while structural integrity isn’t effected as severely as smaller diameter wood. While heavy timber is typically slower to ignite, once ignited it conversely has the potential to become unstoppable. This was no secret and why Mills were designed in quarters or thirds separated by true fire walls with fusible linked rated metal clad fire doors. The first automatic fire sprinkler systems were also installed in these buildings as early as 1874. These buildings were designed around the idea of passive fire protection in a time when fires were devastating the textile industry. These passive construction features will be a major part of any modern attack strategy, the key is knowing how to use them effectively during operations.
The Hazards
The connections between columns and girders are far more susceptible to collapse than the beams themselves. The connections were often made of cast iron, which we already know is unreliable and fails at variable temperatures, unlike steel which has uniform failure points. Additionally, cast iron fails completely and catastrophically without warning. This is due to how the fire effects the variance in the casting process, not cold water hitting hot metal. In some cases there were cast iron floor columns as well.
Depending on the load requirements for the building some floors would have cast iron columns and others heavy timber. It just depended on what the manufacturer wanted. The floors of these buildings also pose a special hazard over time. Layers of floor, typically layered tongue and groove (also known as planks) made up the flooring system. Years of chemical spills, and oil from machinery add risk. Cold storage facilities typically had a coating applied to help preserve the wood and keep the floors from being slippery add yet another layer of risk. These both can make floors a fire hazard as they speed up the combustion process which obviously then increases collapse risk. You could also expect to see floor joists in these buildings having fire cuts. Fire cuts are angled cuts at the ends of beams along the exterior masonry walls. The purpose of these cuts was to maintain structural integrity of the exterior walls, having the interior floors collapse inward, onto themselves instead of forcing the walls out. Great for exterior firefighters, not so great for ones inside. Keep in mind fire cuts were designed in an era before interior firefighting with the idea of keeping the exterior operations safe Lack of windows, whether from original construction or bricked in later significantly reduce the ability to vent these fires. Few entrances also make safe operations a concern. Another hazard created when one of these buildings becomes vacant are the presence of unmarked open shafts. When workers are present or the buildings routinely preplanned, elevator and freight lifts are known and marked, or railed for the workers safety. These things become absent when an old mill falls into disrepair. Railings are scrapped, lifts are removed, and what’s left is an unmarked, unknown large opening spanning multiple floors. The obvious fall hazard, combined with a now unprotected shaft acting as an interior chimney, should be an immediate red flag for anyone arriving on scene of an old vacant mill. These unprotected openings also allow for rapid vertical fire spread, so checking for extension on upper floors is key.
Even after the fires out one often often over looked hazard is the post fire collapse zone. These buildings will burn and smolder for days and without constant supervision the collapse zone becomes less enforced with time. Crews from different shifts may arrive days later and meander into an area with deadly consequences. The walls of these buildings will stay free standing up to heights of many stories and fall without warning. Keep any collapse zone set up at the time of the fire clearly marked with tape even after the fires out.
The Playbook
The interior ops margin for mill type construction is narrow. These fires are either catastrophic block long conflagrations or mundane rubbish burning from vagrants or industrial processes. The play here is for the few fires that are still vent limited and deep seated, requiring interior lines stretched, searches for both fire or victims, and interior exposure protection.
Confinement is key, use the inherent construction features to your advantage. The closing of the fire doors should be an early task done simultaneously with line advancement. The firewalls in these buildings were constructed of non load bearing isolated masonry that goes from the basement up through the roof. There will be fire doors on each level typically directly above one another in the floor plan. The worst case scenario is a well off fire of unknown location. This will be even further complicated if it’s discovered sub grade in a basement. These buildings lack basement windows and stair wells are very small; making the idea of laboriously advancing a large diameter line into zero visibility vent limited conditions seem suicidal. Tag lines while good in theory, will be of no practical use with stock or palletized goods to maneuver around. Members not operating on a hose line must have a TIC. Becoming lost and low on air is a high probability in these buildings. Accountability and forward thinking of committing members inside must be at a higher level of scrutiny due to this risk. Multiple RITs should be assigned due to the size and reflex/travel time requirements. Too much manpower is just as much of a problem as too little. Use your crews accordingly and diligently, not wasting manpower on things such as utilities or lesser important tasks at hand. Searches must be limited to reflect good intel and not comprehensive like on typical residential fires. You can not send crews searching into oblivion, these buildings demand a conservative search strategy. If you have an employee onsite, it’s imperative a role call is done to account for the workers.
Once the life safety objectives have been addressed, the fire must be located and the fire doors closed. If the fire can’t be located but the doors can be shut, then you’ll soon find out what section you’ve written off. If the fire can’t be located and doors not shut, then you will lose the building and every piece of property in it. Once the fires been located, it’s a battle against time and GPM.
Keep in mind a small fire in a big building is actually a big fire anywhere else. Don’t let the optics play tricks on you. What seems like a one line fire may in reality take multiple lines and even master streams to extinguish. If conditions have not improved after 10-15 minutes, start considering a shift to confinement over extinguishment. It’s better to save 3/4s of a building than none at all. Once the fire has extended up through multiple floors it’s no longer extinguishable from the inside. Lapping will soon follow once the fire reaches the windows. Now you’re confronted with horizontal interior fire spread and exterior vertical fire spread by combustible window frames. You can see how narrow the margin is for successful interior operations. You will only have one shot with an interior attack.
The decision to transfer to interior confinement over extinguishment can be based on some benchmarks.
– Interior streams showing no improvement in conditions.
– Fire showing on more than one floor upon arrival.
– Unable to locate the fire for an extended period of time under deteriorating conditions.
– Hazardous material making a direct attack unsafe.
– Localized structural integrity problems such as a portion under construction, floors missing, etc. making entry into the involved section impractical.
Confinement is a last chance strategy to save the remaining unaffected parts of the building and its property. This strategy should only be attempted when there are no indicators of compromised structural integrity, and the fire hasn’t spread to multiple floors for an extended period of time. If the building is sectioned off by firewalls, the decision needs to be made on where to hold the fire. Depending on conditions this may be the next closest fire wall or two sections away if it’s a fast moving fire or resources are slow to deploy. The objective is to hold the fire doors containing the spread of fire to the original section of origin as much as possible. These buildings may carry large quantities of stored products so as with any property conservation strategy, the risk should be taken accordingly. Interior streams and personnel should be positioned on the protected sides of firewalls only long enough to set up portable ground monitors. Once the interior streams are in place aerial master streams should be positioned at the upwind side of the fire wall and directed onto anything burning through the roof. If the fire doors are missing or the fire walls have been compromised this tactic shouldn’t be attempted and operations should transfer into a defensive posture using only exterior master streams. Unfortunately, due the robustness of heavy timber roof construction, fire will spread horizontally unchecked from one section to another instead of quickly burning through like in other types of construction. This makes exterior master streams completely ineffective when trying to stay ahead of the fire. Roof ops are limited to existing openings such as skylights, roof top stairwells, and HVAC vents. Keep roof crews on the protected sides of firewalls if they’re monitoring conditions. Don’t waste the resources on heavy timber roofs, the fire will likely outpace you with tradition vertical ventilation tactics. Once exterior operations are warranted, position aerial master streams at corners and junctures of firewalls in long runs of masonry walls. After resources are positioned it’s then a war of water, from here GPM wins the day.
The Short Staffed Response
Manpower! Manpower! Manpower! Followed by water and even more water. The bigger the structure, the more people you will need. It’s important for Officers to have a clear understanding of their departments resources, and even more so, their limitations. Remember, fires in these structures can be deceiving. Like we discussed above, what appears to be a small fire in these buildings can be rather large, purely due to the size of the structure, and you need to be prepared. These fires are definitely what one would consider a high risk, low frequency event, so extra command staff may prove to be beneficial. Accountability and continuous 360’s will be important for safety on these fires. Extra eyes on the outside can also help identify fire spread on additional floors, as it may look contained to an interior crew. Depending on the size and location of the fire, you may want to consider assigning division or operations chiefs, as well as water supply management responsibilities to additional officers. Doing so allows command to focus on the bigger picture.
Accept the fact that complete interior searches will be next to impossible to complete safely due to the size and complexity of these structures without adequate manpower and prior training on large area search. Even more so than the other fires we’ve discussed, preplanning is key. Command needs to know how long it will take mutual aid or additional staffing to arrive on scene. Preset mutual aid assignments can potentially help with these response times. Prior knowledge of the building such as location of utilities and the interior layout for the location of open elevator shafts, fire doors, and all available exits will help ensure the safety of your crews. Having contact information for maintenance staff or the owner readily available can help you as well if you don’t have floor plans on hand. You’ll also want to consider additional water sources as the use of aerials have the potential to quickly overpower the nearest hydrants depending on pressure available.
Unlike taxpayer fires, where we suggested the use of the smaller diameter hose due to low manpower and maneuverability; selecting the larger diameter hose may be the key to these fires. The likelihood of deploying more than one attack line is high as well, and closing the fire doors as mentioned above should be a priority. Two more reasons manpower is important. Because there are few walls throughout the large open space, fire spreads rapidly, and your stream may need to be able to reach from the stairwell to the far corner before conditions allow you to advance, yet another reason to choose the 2.5”. One benefit to the open space, is that there are few concealed spaces allowing hidden fire spread, which in theory should make finding the seat of the fire easier. While fires in these buildings are considered difficult to start due to the low surface-to-mass ratio, they expand quickly. It is important that you acknowledge your department’s limits, and understand that these fires can quickly overwhelm even a well staffed urban department’s resources. That fact, combined with response times, manpower, and collapse risks, may make defensive operations your only option.
Remember, a small fire in a big building is a big fire anywhere else. Manage your resources wisely and don’t be afraid to change tactics if you’re not seeing changes. Utilize the inherent construction features to your advantage. In theory, with a quick response and enough manpower, if you can get to the fire, you can put it out. That is, if you have enough water.
Citations
Due to the nature of how common trade knowledge, jargon, terminology and methods are passed down amongst the fire service much of the articles information can not be cited as a proprietary source to one particular piece of work, individual, group or otherwise.
Dunn V. Collapse of Burning Buildings: a Guide to Fireground Safety: 2nd Ed. 2nd. Ed.
Tulsa, OK: Pennwell; 2010.
Dunn, V. (2007). The strategy of firefighting.
Tulsa, OK: PennWell
Hill HJ. Failure Point: How to Determine Burning Building Stability.
PennWell Publishing Company; 2012.
NFPA 220: Standard on Types of Building Construction. (06.2018).
