Construction Site Work Thru Facility Preplanning & Construction Evaluation

The Indian River Volunteer Fire Company continues to monitor and evaluate types of building construction in order to obtain knowledge of the building trends and patterns within our immediate fire district. However, this is primarily beneficial for incident pre-planning in case of an actual incident at one of these locations.

Indian River’s Safety Officer Steven R. Hawkins attended a renowned construction site to participate in a walk-thru evaluation process to identify the type and nature of construction materials being utilized in order to fully highlight and document the operational concerns of the fire service.

These concerns continue to be with buildings and structures that contain lightweight wood truss and/or I-beam construction that are susceptible to collapse from fire exposure in a very short amount of time.

Lightweight wooden truss construction

Lightweight wooden truss construction is being used more and more with new construction because it offers construction companies and builders cost savings, easier access to run utilities and ventilation, and can support a weight load equivalent to a solid structural member under normal conditions.

Lightweight truss construction consists of top and bottom members that run parallel. These are referred to as chords and are made of wood. These chords are cross-connected for support by wood that forms a web like pattern. All wood usually consists of 2x4's or 2x3's. The wood members are connected together with a fastener made of stamped sheet metal containing spikes ("gusset plates").

Unlike conventional construction, lightweight wood truss construction does not obtain its strength from the size of the materials used but rather from compression and tension of the materials used in its construction. The top chord is supported by load bearing walls. It acts as a bridge between these walls. With this being under a load, the top chord is being placed under compression while the bottom unsupported chord provides tension.

Most wooden truss systems use metal gusset plates to fasten the top and bottom chords to the webbing, but some are just finger-jointed together with glue.

Lightweight I-beam construction

Lightweight construction is generally considered to be either wood frame or steel building materials, where the roof and/or floor supporting systems are constructed of lightweight prefabricated materials. Also used extensively in today's wood-frame construction are wooden I-beams. These typically consist of particle board and dimension lumber less than 2x4 inches to form the I-beam shape, and are often finger jointed and glued together to create longer length beams.

Wooden I-beams are notorious for rapid fire spread and early catastrophic failure in as little as four minutes of fire involvement. The particle board is often breached by flex ductwork or other utility penetrations, which further weakens the system. It’s cheaper and faster for the builder to construct, and this method of construction is likely to continue in existence.

In any case, lightweight wooden truss and I-beam systems under fire conditions, regardless whether the lightweight construction is of wood or metal design, can quickly and catastrophically fail with no warning causing significant injury or death to firefighting responders.

The Indian River Volunteer Fire Company works with the Office of the State Fire Marshal for building construction plan reviews and tenders commentary on a regular basis.

Additional information regarding lightweight truss construction can be viewed at the following websites:

http://www.cdc.gov/niosh/docs/2005-132

http://www.cdc.gov/niosh/docs/2005-132/pdfs/2005-132.pdf