What atmospheric condition should be tested before entering a confined space, and what is the permissible oxygen concentration range for safe entry?

The atmospheric conditions that should be tested before entering a confined space are oxygen concentration, the presence of combustible gases or vapors, and the presence of toxic air contaminants. Of these, a critical parameter is oxygen concentration. The permissible oxygen concentration range for safe entry into a confined space is typically between 19.5% and 23.5% by volume. An oxygen concentration below 19.5% is considered oxygen-deficient, which can lead to asphyxiation. An oxygen concentration above 23.5% is considered oxygen-enriched, which creates a fire hazard. Combustible gases or vapors should be tested to ensure they are below the lower explosive limit (LEL) for the substance. Toxic air contaminants should be tested to ensure they are below the permissible exposure limit (PEL) established by regulatory agencies. These atmospheric tests are crucial to ensure that the confined space is safe for workers to enter.