Noncombustible Construction
Article and photos by William Shouldis
In Part 1, “The Struggle for Safety,” we discussed an objective path from plan review to emergency response that is designed to improve the decision-making process for first responders. An awareness of building construction types is the cornerstone for responding to fires, floods, or any situation that requires entry into a potentially unstable structure.
This column will examine framing systems with fire protection features that are included during the construction phase. By understanding how buildings are built, code officials and first responders can properly prepare for the future.
Fire-resistive construction (Type I) includes protected structural elements and is the most fire-resistive category of all building construction. Noncombustible fire-rated materials are coated or encased for protection against normal fire conditions. Key structural elements are commonly encased in concrete or fire-rated drywall, or sprayed with a fire-rated material so that the framing materials are not immediately exposed to any direct flame impingement. The protective materials used in this category will not ignite, burn, support combustion, or release flammable vapors when subject to predictable heat conditions. Data collected from concrete or steel skeleton-framed buildings with properly applied fire-resistive materials have shown that Type I structures can withstand complete devastation of the contents under fire conditions and still remain structurally sound.
The weakness of Type I construction is that smoke and flames may spread from floor to floor. If so equipped, central air conditioning may penetrate all parts of these buildings, allowing fumes and toxic gases to be circulated by the heating, ventilation, and air conditioning (HVAC) system or travel in ducts that do not have properly maintained self-closing dampers. This is a condition known as a “sick building,” which may result in a hazardous material or medical emergency.
(1) Fire Resistive: Key structural elements are commonly encased in concrete or fire-rated dry wall, or sprayed with a fire-rated material so that the framing materials are not immediately exposed to any direct flame impingement. Click to enlarge
A major problem under fire conditions is auto-exposure resulting from fire lapping out the windows and up the side of the structure and entering the floors above through windows. Also, fire can extend to the floors above through the perimeter where the outer wall of the building attaches to the floor. Newer Type I buildings are designed with curtain walls that create a space between the steel frame and the outer prefabricated wall. This space that is created is called a safing gap. In the older Type I construction buildings, this space was often filled with loose insulation that over time failed to properly seal this area to prevent fire extension. Today’s codes are quite specific on the proper method and materials required to protect this space. This opening still may be compromised during repairs and renovations occurring after the building is occupied.
Other operational challenges for firefighters in Type I construction might include wide-open floor areas, poke-through construction that negate firestops, and the generation of high heat levels with limited ventilation points.
Noncombustible/Limited combustible construction (Type II) features building materials that will not directly contribute to the development of fire or any flame spread. This type of building has few fire-resistive qualities and is susceptible to early failure, yet is very popular in industrial and commercial facilities because of the reduced construction costs. The height of exterior bearing wall, which is normally only one or two stories, is of a noncombustible or limited-combustible material. The structural framework is made of steel that is bolted, riveted, or welded in place and can be configured into many shapes. Typically, walls are made from metal or concrete block. Large area, single-story prefabricated metal-clad buildings are becoming more popular.
(2) Noncombustible/Limited combustible: Command decisions must be based on the conditions encountered. The safety of everyone operating at an emergency is an awesome responsibility of Command. Interior positions and roof operations can be very dangerous. If time permits, skylights should be removed and responders must monitor any cracks in the bearing walls. Click to enlarge
The metal deck roof can be flat or peaked. The flat roof is often constructed and supported with a steel bar joists. A peaked roof is often supported on a metal framed truss consisting of small-dimensional angle iron and a roof surface of corrugated metal. The Type II building can be seriously compromised by using combustible material during the construction or renovation phase. This includes the installation of wood paneling in an office area or decorative flammable wall covering. Automatic sprinklers should be used to protect combustible or valuable contents. The strength of this construction is its load-carrying capacity and its ability to span long areas with or without columns. However, unprotected steel will expand as it is heated and begins to lose strength at 1,100°F; at 1,500°F, it will not even support its own weight. As steel warms up during a fire, it can twist and distort. As a result of this movement, supported structural members can drop or a wall may be pushed to the point of collapse.
Although the structural elements do not add fuel to the fire; they are unprotected under serious fire conditions and likely to fail. Responders must be aware of the potential for early collapse and clearly establish collapse zones based on the height of the structure.
William Shouldis retired as deputy chief of the Philadelphia (PA) Fire Department, where he served in line and staff positions for more than 34 years. His assignments included working directly for the chief on labor relation and accountability issues and serving as field commander for one-half of the city, department safety officer, director of training, and hazardous material task force leader. He is an instructor at the Graduate School at St. Joseph’s University in Philadelphia (PA), the National Fire Academy, and the Emergency Management Institute. He has a master’s degree in public. He can be contacted via e-mail at WShouldis@gmail.com.
Subjects: Building construction for firefighters, fireground decision-making.
