Which construction type is most hazardous due to the use of plywood I-beams?

Which construction type is most hazardous due to the use of plywood I-beams?

• A. Type I
• B. Type II
• C. Type III
• D. Type V

Answer: (D)

Plywood I-beams are an engineered wood product used in light-frame construction, and they illustrate why Type V, all-wood or otherwise combustible construction, is the most hazardous in this context. In Type V buildings the structure relies on wood for major load-bearing components, and I-beams with plywood or OSB webs burn and spall more quickly than solid lumber. The web can burn away while the flanges stay hot, weakening the floor system and leading to a sudden collapse with little warning. There are also concealed voids inside these I-joists that allow fire to spread quietly, making detection and timely fire attack more difficult. All of this combines to create a high-risk scenario for interior operations. In contrast, noncombustible types (I and II) resist burning, and heavy timber (Type IV) has greater inherent fire resistance due to mass, so the extreme hazards associated with plywood I-beams are most pronounced in Type V construction.

Plywood I-beams are an engineered wood product used in light-frame construction, and they illustrate why Type V, all-wood or otherwise combustible construction, is the most hazardous in this context. In Type V buildings the structure relies on wood for major load-bearing components, and I-beams with plywood or OSB webs burn and spall more quickly than solid lumber. The web can burn away while the flanges stay hot, weakening the floor system and leading to a sudden collapse with little warning. There are also concealed voids inside these I-joists that allow fire to spread quietly, making detection and timely fire attack more difficult. All of this combines to create a high-risk scenario for interior operations. In contrast, noncombustible types (I and II) resist burning, and heavy timber (Type IV) has greater inherent fire resistance due to mass, so the extreme hazards associated with plywood I-beams are most pronounced in Type V construction.