21 Confined Spaces I. Atmospheric Testing Atmospheric testing is required for the evaluation of hazards during initial classification and upon each subsequent entry into a confined space.At aminimum, the spacemust be tested for oxygen, combustible gases and vapors, and toxic gases and vapors. These items can be tested individually (oxygen first, combustibles, then toxics) or they can be tested simultaneously. All testing must be recorded on either the Confined Spaces Inventory or on the Verification and Monitoring Record on the back of the Confined Spaces Entry Plan . Testing for atmospheric hazards must be conducted prior to entry into all confined spaces to determine if acceptable entry conditions exist. The atmosphere must be tested at various levels in the confined space. Atmospheric hazards may be found at different levels, depending on the contaminants present and the conditions of the space. During entry into the space, monitoring must be conducted either continuously or periodically (at least every 15 minutes) to ensure that acceptable entry conditions are maintained. Continuous atmospheric testing must be used when the risk of the development of hazardous atmospheres is high. If the monitoring instrument goes into alarm or fails to operate at any time during entry, the entry must be stopped and Entrants removed from the space. Monitoring equipment must bemaintained according tomanufacturers' specifications to ensure proper operation during confined space testing and entry. Instrument calibration to known gas concentrations must be conducted prior to instrument use in a confined space entry, to ensure equipment operation is within acceptable ranges. Proper atmospheric testing will be one of the most important subjects covered in employee training. Employees must become familiar with the performance and limitations of their particular monitoring equipment. EH&S can assist departments with the proper selection and usage of personal monitoring equipment for confined spaces testing and entry.