Many fatal inhalational accidents occurring during construction typically involving confined spaces and structures that confine the atmosphere continue to defy identification. Very little information is available, principally from accident summaries and government reports. Increasingly, these identify CO2 (carbon dioxide) as a probable cause. This article discusses situations identified in accident summaries and worldwide databases. CO2 lacks an odor and other means of identification without the use of monitoring instruments. Emissions typically involve exhaust gases; aerobic and anaerobic respiration in microbiological systems in wastewater and landfills; geological deposits capable of chemical reaction to produce CO2; and unintended discharge from pressurized systems. Emissions can occur continuously or abruptly subject to the type of system and conditions involved. Anaerobic systems that behave as shear-thinning, pseudoplastic, non-Newtonian fluids emit abruptly on the application of a shear force. A lethal concentration can develop almost instantaneously. Upon cessation of the stress, the ambient condition restores rapidly. Chemical and physical processes provide reservoirs for the storage of gas. Very limited methods are available for the prevention of these accidents because of the infrequency and unpredictability of the emission. Preventive measures include mandatory atmospheric monitoring and ventilation at all times, where hazardous conditions can develop, and sometimes the use of high-level respiratory protection.
