Confined spaces in construction include manholes, crawl spaces, tanks, vaults, pits, silos, and excavations deeper than 4 feet with limited access. Before entry: evaluate the space for hazards (atmospheric, engulfment, mechanical). Permit-required spaces need: written permit, atmospheric testing (O2 19.5-23.5%, LEL below 10%, toxic gas below PEL), continuous ventilation, trained attendant stationed outside, rescue team or retrieval system, communication between attendant and entrants. Non-permit spaces must be reclassified by competent person. Atmospheric testing order: oxygen first, then combustible gases, then toxic gases. Never trust your senses — many confined space atmospheres are immediately dangerous to life and health (IDLH) without detectable odor. Approximately 100 confined space fatalities per year in construction.