Building Systems - You May Know More Than You Think

What do you know about building systems? You may not realize how much you do know. Often times, the systems located in our own homes are great examples for understanding what we may find in a commercial structure.

Residential HVAC Unit

The first picture shown is a typical residential HVAC unit. There's a fan at the bottom, a heating section above the fan, and a cooling section above that. The fan pushes the air through the supply duct and the air is heated or cooled as needed. The fan also draws return air back to the unit where it is filtered and sent back through the system.

Conceptually, this is not really different than a commercial HVAC unit. It's just a much smaller scale, but there will be differences. The unit orientation may be different. The unit may be located on a roof and draw in outside air. Heating and cooling can be accomplished with hot or chilled water instead of electric, natural gas, or refrigeration.

The main intent of HVAC systems is to provide comfort. They may also offer some type of "environmental protection" to occupants or to a process. For example, they may use air pressurization to keep contaminants out of a pharmaceutical manufacturing area or contain biologics in a laboratory. A properly engineered system can also provide protection to firefighters and building occupants by controlling airflow to contain fires and preventing the transmission of smoke containing harmful contaminants. What happens if the system is not engineered, installed, or maintained correctly? A system failure can make a bad situation worse and lead to inefficient use of time on the fireground.

Firefighters should be able to recognize these units and understand how they operate in the event they need to get control of them. In a light commercial structure, this may not be a complicated task. In a more complicated installation, this may not be easy. The units may not be as easy to gain control of and shutting them down could create other issues or concerns. In these situations it is good to have a strong working relationship with building personnel that can help firefighters get control of the equipment and the situation. The units may even be controlled to provide smoke removal in lieu using fans and openings in the buildings.

Air Handling Unit © Wikipedia

If you understand the system in your home you can relate it to a larger system. If you don't understand the system, ask your service technician to explain it to you the next time they come out to do preventative maintenance. For larger more elaborate systems, have a working relationship with the facility to be able to understand and operate these units. We all know that if you can control the air, you can control the fire. The HVAC system can be your control point so it's important for firefighters to understand how the system operates and how to gain control of it.

Be Smart - Stay Safe!

Corrugated Stainless Steel Tubing (CSST) - Know What You're Dealing With

Corrugated stainless steel tubing (CSST) is not a new product and has been installed in natural gas systems for quite some time. Although I have always been familiar with it, I've never specified it on project that I have designed. It's primarily used in residential construction and doesn't suit the commercial projects that I work on. I was not aware of any issues with this tubing from the engineering side and was surprised when I became aware of the hazards associated with CSST from the firefighting side.

Brothers Gone Too Soon

Sadly, I became aware of the issues with CSST following two LODD's. Both tragedies took place in a neighboring state and one of the lives lost was known by firefighters that I know from training and/or social media. If you are not familiar with the circumstances around their final calls, I encourage you to honor their memory by reading the reports and educating yourself. Their stories prompted me to do some research as a designer and as a firefighter. I was quite surprised at what I learned.

For those that are not familiar with CSST, it is a flexible, thin wall tubing used to distribute natural gas or propane typically in residential occupancies. Most people associate CSST with yellow, corrugated tubing because that is probably what is most commonly found. The shape and color of the tubing can vary based on the age of the tubing and whether it is meant for distribution or as an appliance connector. It is preferred because it typically results in less joints that can leak and is easier to install than more traditional steel piping. However, it can be damaged easier and is more susceptible to failure from contact with electricity which is a serious liability to firefighters.

Newer versions have a black coating and are provided with arc shielding. The coating does has a flame and smoke spread rating. Although the newest versions are ANSI and Lighting Code rated, there are concerns that the testing is not sufficient because the tested ratings do not reach a high enough current level to match what is experienced in common lighting strikes. This is what has caused the most recent LODD's.

It does seem to be relatively safe if it’s installed properly, but that's the problem. It's only as good as it was installed and it can be installed by the weekend warrior. There is a difference between distribution tubing and appliance connectors which may not be understood. They are not the same and not meant for the same application. There may be improvements to be made in its construction and some companies are proactive. Gastite has been improving its product over the years to make it safer and even tries to work with the fire service to make a safer product. 

The bottom line is that fire departments need to be educated. CSST is not flawless, but it's critical that the correct material is used and installed correctly. Some of the newer products are better, but still need to be improved. Firefighters need to beware of legacy installations as they will be less safe than newer installations and materials. Home owners should be encouraged to update older systems that aren’t as safe as newer systems. Local authorities having jurisdiction should mandate that installers submit certifications with permits to show that they are qualified to the latest standards and are installing the latest material technologies. Making sure that installations and the materials used are the best possible to ensure firefighter safety is crucial.

Resources

•Lightning Fire Research Google Form

•CSST Info

Be Smart - Stay Safe!

The Importance of the 360 Size-Up

The importance of performing a 360 size up makes a huge difference in the operation of a structure. Keep in mind size up can be performed by simply walking around your first due area and checking out new construction. Let’s look at some simple factors I came across in a new residential community.

Picture #1

• Two story wood frame single family home

• Appears it could be balloon frame (although weird for new construction)

• Only one door is in plain sight

• Bottom window of the 1/2 corner is a bit raised appearing there may be a basement level or storage area below

Picture #2

• House is actually a three story residential

• Basement is designed to be fully furnished

• Basement level could possibly be used as an apartment (could cause a hazard if the stairway between the basement and first floor is illegally blocked for privacy)

• Two additional means of egress located off the first floor balcony on the #2 side and the basement level door

• From the rear it’s clear it’s not balloon frame

Again, just a few small factors to hit on. Do you notice anything else?

Beware The Red Label

Keep yours eyes open for red labels on electrical equipment and conduits as this is an indication of the presence of solar panels. This can present a hazard on the fire ground for a few reasons but one of the biggest is that the system probably won't be fully deenergized.

It took me a bit to find the solar panels where this picture was taken but I knew they were there because of the labels. It's a convenience store and the picture shows the equipment on the store building. The solar panels are located on the canopy over the gas pumps. I was caught off guard when the solar panels and associated equipment were not on the same structure. The way the canopy roof slopes, the solar panels are not visible from the store.

Let's say you're dispatched to a residential structure with a walk-out basement so there's 2 floors above grade in the front and 3 floors in the back. It's 0300 and you're doing a 360 in the dark. How close are you staying to the structure to evaluate it? You're probably not walking too far into the back yard. Will the rear roof be visible? What if the solar panels look like shingles? Are you going to know solar is there? Maybe, maybe not, but I bet you'd notice the red labels on the associated electrical equipment if you knew about them. Especially since the labels are to be reflective.

Now let's say the presence of solar power is not identified and you're working in the attic of a residential structure. The PV wiring is to be metal clad or run in rigid conduit. Again, it is supposed to be labeled so if you see this you need to report it to command and beware that you're operating around energized electrical lines/equipment. Even if the power has been shut-off, the solar panels and associated wiring will remain energized from the panels to the AC disconnect. It's also possible that the system can't be isolated from the public utility service and remain energized although this is a rare condition.

Once identified, the presence of solar power should be communicated on the radio so all those operating or responding know. Firefighters need to start isolation mitigation while understanding and confirming which parts are actually isolated. By the way, do you know that TAC sticks only work on AC power, not DC, so they won't be able to identify the "hot" side coming from the solar panels?

As always, preplanning is the key to success. Residential systems can be drastically different from commercial systems and residential systems can be drastically different from each other. Do a drill night reviewing a solar install with the home or business owner and the installer to get detailed info about the system. Hopefully you have some type of relationship with your local buildings/codes department to be made aware of these systems and gather valuable information. I'm a proponent of a placarding system to better identify the presence of solar upon arrival at an incident. Newer installations are a little more firefighter friendly as the equipment and codes are updated to improve these systems but legacy systems will present more challenges.

Solar generation systems can be complex and pose a significant hazard on the fireground. It's important for firefighters to be aware of solar generation systems in their first due, understand how they operate, and how to mitigate the associated hazards.

Originally posted at Building Firefighter Development - Beware The Red Label (buildingfirefighters.com)

Cloud Ceilings

Cloud ceilings are not new and have been around for a while. They are, however, becoming more common and more complex. I’ve noticed a trend over the last few years where clouds have increasingly become a regular part of the interior design and the architectural ceilings in spaces where aesthetics are important or it's a "community" space where occupants will gather on a regular basis. These ceilings are also taking many different shapes and sizes and come in a variety of materials. I have, on multiple occasions, had to design sprinkler protection around floating panels of ceiling tiles, sheet rock, open grid ceilings, fabric panels, wood slats, and geodesic patterns. Designing around these ceilings has always been a challenge but the NFPA is providing guidance with the last few versions of Chapter 13.

Historically, the issue was whether or not you had to sprinkler above and below the cloud ceiling. The ceiling was considered an obstruction and guidance was found in the code sections dealing with obstructions that were either less than or greater than 18" from the face of the deflector. Some instances may have required applying the open grid ceiling section as well. In 2016, the NFPA began to address cloud ceilings in Chapter 13 and then again made further, more beneficial, updates in 2019. Cloud ceilings became defined and the rules for determining when the space above the cloud can be considered a concealed space were provided. These sections determine when sprinklers are only required at the cloud ceiling level, and not above the cloud. Basically, the code provides guidance to determine whether or not the cloud is a sufficient heat collector to initiate sprinkler head operation. This decision is based on the size of the cloud, the size of the gaps around adjacent clouds, and the height of the ceiling. There are additional factors such as sprinkler types and construction materials that play into the decision matrix. The NFPA has even provided some suggestions with respect to seismic concerns. Depending on how the cloud is supported and secured to the structure above, you may need to provide some flexibility in your piping system by utilizing elements such as flexible sprinkler drops in order to accommodate the shifting of the clouds in a seismic event.

A sprinkler designer has many challenges and factors to consider when designing around cloud ceilings. The bottom line is that the design must be code compliant to ensure optimum life safety for the building arguments. There are other factors that must be considered such as aesthetics, constructability, and cost. A designer can't just design a system with sprinklers above and below the cloud ceiling instead of doing the work to interpret the code. It's not the correct design and it drives up the cost for the owner. Working with the architect can also be a struggle. They spend time developing a unique design element of the building and the fire protection designer wants to put an ugly sprinkler head right in the middle of it! Both sides have to work together to find a resolution that not only works but is aesthetically pleasing as well. Although this isn't a fire protection designer's priority, it's providing a quality design that keeps clients coming back.

As firefighters, we need to pay attention when we find ceilings like these. We all know the importance of air movement in an active fire and recognizing the flow path is critical to firefighter tactics and safety. These ceilings may mask heat or smoke and delay the identification of the flow path resulting in us working below heated air or smoke (unburned fuel). It is important to know how the clouds are suspended. Are the clouds hung from rods/cables or are they secured to a rigid structure attached to the deck above? The clouds could move around when hit with a hose stream making your attack difficult or could possibly become a hazard if they fall. They could carry significant weight or become an obstacle when advancing the hose line. The clouds may even be an illusion. For example, in the picture on the right, is that a cloud ceiling or are the doors attached to a sheetrock ceiling that has been painted black?

The bottom line is that success starts early. We need to get into buildings and find out what's in them. When we find an atypical element like a cloud ceiling, we have to investigate to find out why it's there, and how it can impact our tactics and safety. Then we must share this info with our crews. Keep your eyes open, ask questions, and talk. Don’t wait until you're involved in a fire event to figure this out.

Be Smart - Stay Safe!

Building Firefighter Development (buildingfirefighters.com)

About the Author
E.J. Henninger has been designing building systems for more than 20 years. He is currently a Senior Engineering Operations Manager working with a team to deliver plumbing and fire protection designs for a wide range of projects. He has also been a volunteer firefighter for more than 10 years and is currently the captain at a rural Fire & Rescue Company with an active role in the training program. E.J. actively supports the fight against cancer through the International Association of Fire Chiefs and his annual Firefighter Relay Challenge. He is happily married to his beautiful wife of 25 years and has three wonderful sons.

Masonry Walls & Tie-Rods

Understanding building construction is integral for all firefighters however, knowing and identifying aspects of building construction and how it plays part in the buildings overall makeup is even more vital. Looking at a brick wall to some, is well just a brick wall. To others, looking at a brick wall is much more. So what is it? A brick wall or is this wall telling a story?

 The brick wall to firefighters is in fact telling a story. In fact, these walls are known as masonry walls and in this case for our discussion, "load bearing" masonry walls. The construction of these walls began in the 1700s and ended around the mid-1900s. These walls built with stones, bricks, cement blocks or concrete blocks were designed to carry the weight that is transferred from the roof top to the buildings foundation. 

 Ever notice the stars or other subtle designs on masonry walls which are spaced strategically on the wall mainly in rows? These are commonly referred to as "reinforcing stars" or "anchor plates".

 Here are some reasons for the use of this "décor" on masonry walls. 

1. Building Stabilization. These were added to buildings during the late 19th century and early 20th century, these were used to connect and support tie rods in order to stabilize the building.

2. Visibility. Not all of these plates are visible from the street. Sometimes, these plates are hidden behind facades or not retrofitted to the walls leaving the exposed tie rods or cables nestled between the brick and mortar. In these instances, take note during pre plan and during the initial fire ground size up.

3. Fire Conditions and Collapse. These rods are known to fail under most fire conditions causing a collapse of the structure or parts of the structure.

4. Structural Integrity. Not all of these tie rods and plates were retrofitted as the building aged. In some instances, these tie rods and plates were installed during the construction of the building to give the building added integrity. 

So a brick wall isn't just a brick wall, it has many components such as the 1 we just spoke about. Take time during your next pre plan and identify these plates on the structures should you have any in your jurisdiction. Understand and be comfortable with identifying key indicators in building construction. Keep in mind the role plates and tie rods play in possible building collapse should they fail under fire conditions. Remember a brick wall isn't just a brick wall, it's telling a story of what's behind it. 

Until next time; work hard, stay safe & live inspired.

Parapet Walls

Throughout our history in the fire service and since its inception to building construction, parapet walls have injured and killed several firefighters. Many departments respond to buildings with these walls on daily basis and some departments don’t ever encounter these but there’s no such thing as “never” in the fire service.

So with that, what are parapet walls?

For starters, parapet walls are those that extend above the roof level giving the illusion to street viewers that the building is taller than it actually is and could range from inches to several feet above the roof level. Despite its decorative appearance the wall provides protection to the building from the elements as well. Although they are commonly known as an extended wall above the roof level, they serve multiple purposes for the building itself and we will list a few of them for you and then explain each.
1.    Fire Protection
2.    Improve wind-up lift resistance. 
3.    Vapor pressure relief for older masonry buildings
4.    Scupper drains

Fire Protection
Extending the wall above the roof level, these walls prevent fire spread from going up the exterior of a building which would almost immediately ignite any and all roofing membrane. 

Wind-up lift resistance
When wind blows against a building, it produces vortices at the roof edges causing these forces to lift the roof edge and peel back the roofing system. By having a parapet wall in place, this will help prevent any elevated wind pressure from compromising the roof edge.

Vapor Pressure Relief
Older masonry buildings that have a parapet wall also provide vapor pressure relief. Water, as we know cannot pass through the roofing membrane so the vapor pressure relief was designed to have water find its way to the roof edge and exit through back side of the parapet. Usually these are finished with permeable clay bricks. 

Scuppers
Scupper drains are openings in the side walls of an open-air structure, found at the bottom of a parapet wall. They are used to allow rain or other liquids to flow off the side of the structure instead of pooling within the walls or possible collapsing the roof. 

Notice 2 scuppers at the foot of the parapet wall. 

Hazards with parapet walls
During fire operations parapets are prone to failure. Mostly, these walls are exposed to all elements and could possibly fall into disrepair but with regular maintenance of a structure these walls should be checked and maintained as need be. Many of these walls are supported by an horizontal steel I-beam that runs the length of the front of the structure. The hazard that comes along with this is, should fire reach the cockloft, this steel beam can be exposed to high heat and thus expand causing the wall to potentially fail. There is really no one way that these walls will fail. They could fall as one piece or they could crumble and fall in pieces. 

Changing occupancies in the structure is another potential hazard with parapets. The reason behind this is the new owner or renter’s signage that is placed over the existing parapet. Some signs are anchored through the wall itself while others can be mounted from around and over the existing parapet. Either way these add to the load of the wall and increasing its fail potential should it be put under stress in fire or collapse conditions. 

What do look out for and how to work with these walls
When working on a structure with a parapet, here are some tips to keep in mind:

1.    Set up a collapse zone and monitor the walls for signs of cracking or bowing and notify the IC immediately. Keep in mind that these walls could collapse at any given time even after the fire has been under control. 
2.    Check or exposures throughout the interior and exterior making sure no fire as reached the cockloft putting extra stress on the parapet. 
3.    When setting up an aerial device, look for scuppers to determine the height of the parapet with relationship to the scuppers. If you don’t think you can make the roof due it the walls height, try and look for a secondary means on to the roof. Don’t take a chance trying to jump up and grab the ladder from the roof.
4.    Before stepping on to the roof from the ladder, sound the roof with your tool. Usually a 6 foot hook of any kind will work best. 
5.    Lastly, never assume during fire operations that the parapet was engineered to take the weight and forces of the additional dead and live loads being added to the structure. 

Until next time; work hard, stay safe and live inspired.  

About the Author

NICHOLAS J. HIGGINS is a firefighter with 15 years in the fire service all within departments in Piscataway, NJ. Nick has held the ranks of Lieutenant and Captain as well as being a township elected District Fire Commissioner for 1 term (3 years) in Piscataway, NJ. He is also a NJ State certified level 2 fire instructor. He holds a B.S. in Accounting from Kean University working in Corporate Taxation and is the founder/contributor of the Firehouse Tribune website.

Window Bars & the Set of Irons

Mostly found in urban areas but not uncommon in suburban or rural areas are window bars. These bars are common to private dwellings and often found on basement and first floor windows for security reasons.  

These bars present a multitude of problems for firefighters responding to calls at these locations. 

1. Delay in access to inside the structure.

2. Difficult to perform VEIS (Vent. Enter. Isolate. Search) 

3. Reduces means of egress for firefighters and victim removal should a window need to be used. 

Window bars have the tendency to turn room and content fires into multiple alarm fires and have created havoc for access to victims or down firefighters for reasons mentioned above; so for that reason lets discuss how to remove them quickly and efficiently using the set of irons. 

On type 3 brick buildings the bars are held in by expandable anchors. Holes are first drilled into the brick and the anchors are used to hold the bars in place around the window.

For wood frame structures (type 5) lag screws are usually used to hold the bars in place. 

For either structure, use the set of irons (axe & halligan) and destroy the screws and anchors holding the bars in place by forcing them with the adz end of the halligan driving the halligan with the butt (non blade side) of the axe. 

Should the fastening points be unattainable, split the frame using the halligan and pry the gate from the opening using the fork side of the halligan. 

If the bars are set into the brick, mortar or concrete use a sledge or any type of mauling tool and smash the area encasing the bars into the wall and pry the bars away from the window. Should it be out of reach, hooks are another tool we can use for prying away as well.

Don't let obstacles get in the way of protecting life and property. This was a couple ways we can gain entry to a building should we only have hand tools available to us. Relying heavily on gas and hydraulic tools can be costly and some times cause more damage than it's worth. The more efficient we are using hand tools the quicker we can get to work and get the job done. 

Until next time; work hard, stay safe and live inspired. 

About the Author

NICHOLAS J. HIGGINS is a firefighter with 15 years in the service all within departments in Piscataway, NJ. Nick has held the ranks of Lieutenant and Captain as well as being a township elected District Fire Commissioner for 1 term (3 years) in Piscataway, NJ. He is also a NJ State certified level 2 fire instructor. He holds a B.S. in Accounting from Kean University working in Corporate Taxation and is the founder/contributor of the Firehouse Tribune website.

Bulkhead Doors

Some stairs in a bulkhead doors are sloped greater than normal sloped stairways thus causing increasing issues for crews to make entry due to its steeper incline should entry be warranted through such doors. On the other hand, these doors make great use for ventilation sources for below grade fires due to its easier and for the most part safer access when fighting below grade fires. They can be found in both resident and commercial structures.

Until next time; work hard, stay safe and live inspired. 

About the Author

NICHOLAS J. HIGGINS is a firefighter with 15 years in the service all within departments in Piscataway, NJ. Nick has held the ranks of Lieutenant and Captain as well as being a township elected District Fire Commissioner for 1 term (3 years) in Piscataway, NJ. He is also a NJ State certified level 2 fire instructor. He holds a B.S. in Accounting from Kean University working in Corporate Taxation and is the founder/contributor of the Firehouse Tribune website.

All About Truss, Part 3

In the first 2 parts of this series, we spoke about what truss is and explained different type of roof truss systems. In this part we will discuss the dangers of truss construction on the fire ground and how it affects firefighters today a long with ways it has harmed us over the years.

In order to understand the dangers behind these systems, let’s first look at how these systems have affected the fire service. Over the last 40 some years the fire service has seen multiple tragic truss collapses that has forever changed the fire service and how it looks a not just building construction but its advancements in understanding truss construction. 

The first incident of truss construction that claimed the lives of firefighters was in 1968 at the Yingling Chevrolet in Wichita, KS. Within six minutes of arrival on scene the bowstring truss roof failed taking the lives of 5 firefighters.

The second incident occurred at a bowling alley fire in Cliffside Park, NJ in 1968. This was where five firefighters loss their lives when the truss roof collapsed, causing an exterior wall to be pushed out and trap the firefighters under the debris. 

The third incident occurred at the Hackensack Ford Dealership in Hackensack, NJ in 1988. This was where the bowstring truss roof collapsed and the resulting debris buried and killed five firefighters.

Since this incident, the State of New Jersey Uniform Code developed a system of adding 12” x 6” reflective truss shaped plaque on the street side of all truss built structures (commercial and planned residential developments). On the signs will appear if the floor and/or roof contains truss construction. An “F” would identify floor, an “R” would identify roof and an “R/F” would identify both roof and floor. 

The most recent incidents were the Sofa Super Store fire in Charleston, SC in 2007 that claimed the lives of 9 firefighters operating inside the structure and the 2012 theater fire in Abbotsford, WI that claimed the life of one firefighter operating inside the structure when the bowstring truss roof collapsed.

So where were the warning signs of these tragic truss roof collapses?? 

Well, there weren’t any and let us now discuss the dangers of truss construction on the fire ground.

Truss systems of any design have the same characteristics. They all use the least amount of material in order to achieve the greatest strength for long spans. They have smaller cross-sections and use considerably less mass than a solid beam of wood of the same strength which results in less inherent fire resistance and can cause early failure in fires. Should truss fail at any single connection, it can cause the failure of the entire system and should either the top or bottom chord fail, the entire system has the potential to fail. 

Loose gusset plates or metal tooth plate connectors (MPC) on the bottom chord can lead to tensile forces (tensile strength is a measurement of the force required to pull something such as rope, wire, or a structural beam to the point where it breaks) that will pull the truss apart. A plate that is loose or is lost from the top chord will cause any attached web members to the top chord to pull away. Both of these situations will greatly reduce the load capacity of the truss and may even cause the system to collapse. 

Any alterations to an individual truss or the building itself can alter the load capacity and integrity of the system. Trusses are often at times cut or altered to accommodate plumbing, wiring, vent ducts and other fixtures added to the building. Truss systems are designed to support the roof above. By added weight to the system this can drastically compromise the load-carrying capacity of the truss system. Sometimes buildings add suspended ceilings to their areas to cover up the exposed truss thus overstressing the truss. Other ways the truss can be overstressed is by adding air conditioning units, ventilation systems or any other loads within or above the roof that the system was not designed to bear.

Things to consider when working on truss construction.

1.    Pre-incident planning during the construction phases. This is your initial size up.
2.    Note the type of truss system that is being built, type of building construction and materials used.
3.    Ensure there is an initial size up (360 degrees of structure) and risk assessment of the incident before any and all interior and roof operations begin.
4.    Use a thermal imaging camera as part of the size up operation to assist in locating fires in concealed spaces. If done outside, do a 360 degree walk around the structure or use multiple firefighters to assist.
5.    Continually size up the structure during the incident paying close attention to the structure and the roof conditions until the fire is under control and all manpower is accounted for. 
6.    ALWAYS have Rapid Intervention ready should an emergency occur to a firefighter(s) inside.
7.    If trusses are exposed due to fire conditions, all firefighters working under or above should be evacuated and should go to defensive attack mode and expect for an imminent collapse.
8.    The IC should establish a collapse zone outside the structure. Truss collapses can push out on the walls and cause secondary exterior wall collapses. A collapse zone should be equal to 1 ½ times the full height of the structure, although can be greater based on the situation at hand and allowance for scattering debris.
9.    If at all possible, avoid cutting the truss chords when cutting holes for ventilation.
10.    Avoid roofs areas containing added dead loads.
11.    Have multiple means of egress at all times when inside the structure or working on the roof.
12.    During fire operations, immediately open ceilings and other concealed spaces when fire is suspected in truss systems. Be aware of a possible flashover or backdraft when doing so and make sure to have a charged hoseline ready for protection.
There you have it. Types of truss construction and their components, how it has affected the fire service, its dangers and how to stay safe while working on the fire ground with truss construction.

Until next time; work hard, stay safe and live inspired.  

About the Author

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NICHOLAS J. HIGGINS is a firefighter with 14 years of service all within departments in Piscataway, NJ. Nick has held the ranks of Lieutenant and Captain as well as being a township elected District Fire Commissioner for 1 term (3 years) in Piscataway, NJ. He is also a NJ State certified level 2 fire instructor. He holds a B.S. in Accounting from Kean University working in Corporate Taxation and is the founder/contributor of the Firehouse Tribune website.

All About Truss, Part 2

In the first part of our mini blog series on truss, we spoke about the 2 basic types of roof truss; Pitched Chord Truss and Parallel Chord Truss. In this part, we will discuss a few other types of roof truss; King Post, Queen Post, Gambrel and Bowstring Truss. So let’s now talk about some truss.

King Post Truss

This is the simplest form of truss construction due to the minimal number of truss members in the system (individual lengths of either wood or metal). It consists of 2 diagonal members that meet at the apex (otherwise known as the peak, tip, or top) of the truss. One horizontal beam serves to tie the bottom end of the diagonal members together and the king post connects the apex the horizontal beam below. In roof truss construction the diagonal members are known as rafters and the horizontal members are known as a ceiling joist.

The king post truss system is limited to how far up it can extend (maximum of 30 feet) and is unsuitable for longer spans. If a larger system is in fact needed, additional diagonal members would be needed to make multiple truss systems. This system was often used in the Medieval, Gothic Revival and Queen Anne Architecture and was originated in the 13th century and commonly used in the 15th century. Today the king post truss system can be found in European churches, barns and bridges.

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                                                                      King Post Truss

Queen Post Truss

The queen post is a tension member in a truss designed system to expand longer openings than a king post truss can. As we know a king post truss uses one central supporting post (king post), while the queen post truss uses two. Although it is a tension member and not a compression member, the posts are still commonly referred to as posts. The queen post truss system is used when a larger span is needed to be covered (30-45 feet and possibly up to 60 feet). This system transfers the weight load of the roof to the eave posts, which allow for a clean open space that requires no internal posts that could affect the design of the building. This type of system provides exceptional structural support and can be combined with other types of roof truss systems. 

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Gambrel Truss

Gambrel Truss is one of the earliest types of roof construction in American architecture. The earliest documented use was in the 1600’s. Gambrel truss, often confused with Hipped Roof, is commonly referred to as “Dutch Colonial” giving the roof a barn like appearance and is often found in Colonial style architecture which makes frequent use of the Gambrel Truss system. This system is a symmetrical, doubled-sided roof with a double slope on each side. The lower slope is known as a steep and has an almost vertical angle. The Gambrel system allows for a maximum amount of storage space in the attic area and do not require interior walls or support posts. Most pitched roofs have sharply angled walls that make for much of the space unusable, except when using the Gambrel Truss system. This is due to the pitch break being in the Gambrel roof itself and allowing for more interior space to be used because of the slope of the ceiling. This allows for more space directly under the roof to be used as living space.

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                                                                        Gambrel Truss

Bowstring Truss

The name of this system is directly related to the look of the truss system. The shape resembles an archery bow, thus how it gets its name. Bowstring Truss was first used for arched truss bridges, which is often confused as tied-arched bridges and are great for spanning large distances. There are many different variations in the arrangement of the members connecting the nodes of the upper arc with those of the lower chord. In some instances, the lower sections go up at a slightly steeper angle than the other sections of the truss, which allow for easier water run-off. In some cases, a roof may be built over the top of an already existing bowstring truss roof. If this has occurred, the ridge at the top of the roof may not have a ridge cap. A ridge cap normally runs along the length of the roof, covering the seam where the materials forming each side of the roof join at the very top of the roof. Since this system is arched, there is no point at the top where the two sets of roofing materials meet.

Bowstring truss was a very popular structural system in the early 20th century, especially in America. Today, large wooden bowstring truss systems are popping up all over. They are refurbished and left exposed as former industrial spaces are being reconstructed for other purposes. Because of this, it is allowing for new uses in the construction industry such as skylights being added to the roof between each truss system. Bowstring trusses are found almost everywhere today, from warehouses and bowling alleys to even coffee shops and modern offices but as in all truss systems, should one fail, they all fail.

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In the next part of this series, we will discuss the dangers associated with truss construction on the fire ground.

Until next time; work hard, stay safe and live inspired.  

About the Author

NICHOLAS J. HIGGINS is a firefighter with 14 years of service all within departments in Piscataway, NJ. Nick has held the ranks of Lieutenant and Captain as well as being a township elected District Fire Commissioner for 1 term (3 years) in Piscataway, NJ. He is also a NJ State certified level 2 fire instructor. He holds a B.S. in Accounting from Kean University working in Corporate Taxation and is the founder/contributor of the Firehouse Tribune website.

All About Truss, Part 1

As we all know, building construction has changed drastically over the last 20-25 years especially with the evolution of the increasingly popular use of lightweight construction and its engineered structural components. The reason for its popularity is simple; the load carrying capacity increases in these structures and its cost efficient.

Originally in this post, I said this has changed over the last 20-25 but in reality the changes started to have an impact on the fire service around 50-65 years ago with the development of the first part of the structural component, floor and roof truss construction which were both and to an extent are today held together with glue.

So let’s start off with the basic types wood truss construction.

Trusses are easily identifiable by their triangular framework of multiple structural elements. This is what distinguishes them from other structural products. Due to their structural efficiency this element is a cost-effective solutions for many structures we see all over the world today (bridges & buildings). When talking about residential construction, wood truss held together but metal plates are the primary type used and are fabricated from 2x4 or 2x6 dimension lumber. Any trusses built from larger dimension lumber is usually found in custom built homes and due to the popularity of these type of homes today, this is fairly common in newer suburban developments.   

Roof Truss

In roof truss construction the three sides of the triangle are known as “chords” and the pieces connecting the top and bottom chords together are known as the “webs”. The “connectors” that join the chords and webs in the modern truss system together are usually done by metal-toothed plates and is most common in truss roof assembly. In truss roof assembly or otherwise known as pitch chord truss, the top chord is sloped and the bottom chord is typically horizontal because it will directly support the ceiling.

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                                                                     Pitch Chord Truss

Another type of truss found in roof truss assembly is parallel chord truss but this is normally found to form floor assemblies. In this type of truss assembly, the top and bottom chords run parallel with the top chord in compression and the bottom chord in tension.

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                                                                   Parallel Chord Truss

 In both parallel and pitched chord trusses metal tooth plate connectors (MPC) are used extensively to join the chords and webs together. These connectors are multi-tooth plated and are embedded into the wood fibers using a hydraulic press.

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                                                                    Multi Tooth Plates

 So how do these trusses carry a load?

As we all know from high school geometry, a simple triangle is stable in nature and all 3 sides are equal. Meaning, any force applied to it will be transferred around all three sides with limited movement or change of shape. As previously mentioned, the top chord is in compression and the bottom is under tension when the system is under what is known as gravity loads (i.e. live loads). Live loads are not to be confused with the assembly itself.

Redistributing the load

The performance of wood truss construction, whether exposed to outside forces such as hurricanes, earthquakes or fire can be attributable to 2 factors.

Structural redundancy & load redistribution across the floor or roof

This is found within each truss. When one truss member fails, the load it is carrying will redistribute itself to the remaining truss members. Also, should one of the truss lose its strength or stiffness, the entire assembly – floor or roof – will redistribute the loads through sheathing and/or bracing to the adjacent trusses.

When a single member of a truss is cut, the structural integrity is in fact compromised. However, this alone will not normally cause a catastrophic collapse. In most cases the truss will still carry the most of the normal load that has been originally applied. The cut member of the truss however, will cause a glaring defect that will need inspection. When looking at a total collapse of the system, this is dependent on many factors. These factors will include the amount of the load, span of the truss, & roof and floor integrity all under fire conditions or not.

In the next part of this multi-part series, we will discuss other types of more advanced wood truss construction.

Until next time; work hard, stay safe and live inspired.  

About the Author

NICHOLAS J. HIGGINS is a firefighter with 14 years of service all within departments in Piscataway, NJ. Nick has held the ranks of Lieutenant and Captain as well as being a township elected District Fire Commissioner for 1 term (3 years) in Piscataway, NJ. He is also a NJ State certified level 2 fire instructor. He holds a B.S. in Accounting from Kean University working in Corporate Taxation and is the founder/contributor of the Firehouse Tribune website.