Cold weather conditions require concrete floor placements to be completed in enclosed, heated conditions which can sometimes create a harmful buildup of both carbon monoxide and carbon dioxide fumes. These fumes are generated from a variety of sources, including direct fired/open flame (salamander type) heaters and other equipment operating within the building envelope. Carbon monoxide poisoning occurs from exposure to these gases in enclosed spaces, creating extreme hazards for all tradespeople. Adequate ventilation with fresh air must be provided to avoid this condition. Although the use of indirect fired (furnace type) heaters which use heat exchangers do not produce these gases, gas levels should be monitored at all times.
Freshly placed concrete must also be protected from carbon dioxide which can react with freshly placed concrete to produce a soft chalky surface through a chemical reaction process known as carbonization (production of calcium carbonate). There are no known threshold limits of carbon dioxide that can be monitored to avoid causing this problem.
Liquid phenolphthalein (available from some chemical suppliers and pharmacies) can be used to test the acidity of the concrete surface.
It is recommended that indirect fired vented heaters be used for concrete project — not direct fired heaters. All other gasoline/diesel/propane equipment other than concrete placing equipment should be minimized or shut off as well. Concrete trucks should be limited to three in the building at any one time.
Scrubbers (catalytic converters) attach to equipment to minimize carbon monoxide in the environment, converting carbon monoxide into carbon dioxide which hurts concrete. The use of scrubbers carries a cautionary note that damage to the fresh concrete may result through their use. Note: The field practice of directing engine exhaust through a hose into a drum of water does not remove any carbon monoxide or carbon dioxide gas emissions, but does remove the smell of the engine exhaust creating a dangerous working environment. Therefore, adequate ventilation must always be provided.