Construction Concerns: Pressure

Article and photos by Greg Havel

The chemicals used in pressure-treating lumber, including fire-retardant chemicals, are corrosive to bare steel. The joist hangers used in construction with both sawn lumber and manufactured joists are usually galvanized (zinc-coated). Photos 1 and 2 show galvanized steel joist hangers supporting nontreated lumber joists. Until recently, the zinc coating on the steel joist hangers prevented corrosion by the most common wood preservative, chromated copper arsenate (CCA), and by some fire-retardant chemicals (usually boron- or borax-based). Stainless steel joist hangers are available for contact with more corrosive treated lumber.

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Although CCA in the concentration used in wood preservatives is not as toxic to humans as some other arsenic compounds, it is released from burning wood and may react chemically at the temperatures in free-burning fires to form other more toxic compounds. These toxic arsenic compounds are in addition to the soup of chemicals present in smoke at every fire: water vapor, carbon dioxide, carbon monoxide, cyanides, acids, unburned hydrocarbons, ash particles, and the residue of whatever the fire burned in addition to its primary fuel. This should be another argument in favor of the use of self-contained breath apparatus at all fires; the gross decontamination of turnouts and SCBA after use at a fire, before any parts are removed; and the frequent laundering of turnouts.

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Gregory Havel is a member of the Town of Burlington (WI) Fire Department; retired deputy chief and training officer; and a 30-year veteran of the fire service. He is a Wisconsin-certified fire instructor II, fire officer II, and fire inspector; an adjunct instructor in fire service programs at Gateway Technical College; and safety director for Scherrer Construction Co., Inc. Havel has a bachelor's degree from St. Norbert College; has more than 30 years of experience in facilities management and building construction; and has presented classes at FDIC.