Sometimes Say Never

Vertical ventilation has no place on open web steel-bar joist roofs

Recently, I was asked to review a training program developed by a colleague of mine from a department in another section of the country. Most of the information I reviewed was very good and covered such subjects as ladders, RIT, search and roof tactics—a lot of truck company operations.

While reading through the material, I came upon a slide on the proper way to ventilate an open web steel bar joist roof. I don’t like to use the word “never” in the fire service, but this is one of the times when I must. Although we all agree that ventilation is necessary when an interior attack is employed, and roof venting at commercial buildings usually affects the outcome of the fire, there comes a time when construction must be factored into the risk-vs.-benefit analysis.

We cut roofs to provide the escape of fire, heat, smoke and gases, allowing the engine company to operate in less-punishing conditions while advancing the line. In tightly sealed buildings, vertical roof ventilation will prevent backdraft of the structure, which in turn could cause collapse. But in buildings with open web steel-bar joist construction, opening the roof can actually increase the chances of collapse, and is a highly dangerous operation that shouldn’t be part of any department’s SOPs.

Truss & Fire Resistance
In newer construction, many of the support systems used for commercial building roofs are made of open web steel bar joists. These joists are spaced further apart than standard wood joists, sometimes up to 60 feet. Spacing of the joists will vary depending on the strength of the joists and the type of roofing materials used. The most common roof deck is corrugated steel, and the joists are usually spaced 4–6 feet apart.

The danger of these systems is that they can be weakened by fire and heat. Fire resistance is a function of mass of the material. These trusses are lightweight and made from thin steel, so they have very little inherent fire resistance. Fire ratings in these roof systems depend upon the ceiling finish and the finished roofing.

A truss is composed of a top and bottom chord and center web members that hold it together. When any part of the truss fails, the entire truss assembly is subject to failure. During a fire in a building with this type of roof construction, changes are happening that you probably cannot control. The steel is being attacked by fire.

When Steel Fails
Steel starts to rapidly lose its strength at 1,000 degrees F. This temperature is easily obtained in a normal dwelling-and-contents fire, and in a commercial structure, these temperatures will be reached very rapidly.

When steel absorbs heat at a rapid rate, it begins to expand, twist and bend—in essence, it starts to fail. Unprotected open web steel joists are vulnerable to collapse and will fail 5–10 minutes after exposure to elevated temperatures.

Incident commanders must be aware of this scenario when operating at fires in buildings with this type of roofing system installed. Units could be committed to an interior operation with a drop ceiling system in place without realizing there may be a heavy fire condition in the ceiling above their heads and the roof area. Upon entering the structure, remove one of the tiles above or poke a hole through the ceiling to detect the presence of fire. Caution: Removing a tile or poking a hole adds air to the area, which could cause a backdraft and the entire ceiling could be blown down on top of operating units. An abundance of flammable stock in the occupancy will accelerate the amount of heat generated and rapidly heat the steel joists.

Correct Roof Operations
Roof operations in structures with this type of roofing system must focus on the safety of the firefighters. Many fires in these occupancies occur after business hours and the civilian life hazard is significantly reduced. The firefighters, however, face a significant life hazard.

Roofs of fire buildings with this open web steel bar joist should not be cut. Vertical ventilation in these structures should be limited to the removal of skylights if present. After venting roof-level skylights, members must immediately evacuate the roof.

Why do we not cut the roofs in this type of construction? There’s a high chance of early failure of the roof, resulting in a collapse. Another reason: Members using saws to ventilate may inadvertently cut into the top chord of the truss, further weakening it, or they might make a coffin cut between widely spaced joists and fall into the weakened hole due to a lack of support underneath. These roofs are not designed to carry the weight of firefighters and their equipment.

Conclusion
To identify these types of structures in your response area, you should make notations during building inspection and pass this information throughout your department. When new construction of these buildings is taking place in your response area, get out there and inspect them, and develop pre-fire plans. If you notice these buildings in areas that you don’t respond to, notify the fire companies in that area. Use these buildings for company and multi-unit drills so members become familiar with them.

So here is one of those rare situations when you can use the word “never” when discussing firefighting. The above are recommendations that will no doubt make the brothers and sisters safer and possibly prevent serious injury or death.

Chief Fred LaFemina is a 23-year veteran of the New York City Fire Department (FDNY), presently serving as a battalion commander for Rescue Operations Battalion #1. He has been with Special Operations for more than 19 years and is the task force leader for New York’s Task Force 1 Urban Search and Rescue team. He is also the operations chief on the USAR IST White Team. LaFemina has written many articles on fire operations and technical rescue and lectures throughout the country. He is a technical editor of FireRescue.