A large number of confined space fatalities are a result of hazardous atmospheres. Many of these fatalities occur because gas detectors were not used to test the atmosphere or if used hazards were missed or underestimated. If personnel understand confined space atmospheres, conduct risk assessment and follow correct testing procedures accidents can be avoided. Topics covered include: Atmosphere testing; Oxygen levels, flammability and toxicity; Lower explosive limit; Permissible exposure limits; Common testing problems and Testing procedures. 15 minutes.