Explain the three primary categories of atmospheric hazards found in confined spaces, and detail how they are detected and controlled to maintain a safe working environment.

The three primary categories of atmospheric hazards in confined spaces are oxygen deficiency, flammable gases and vapors, and toxic substances. Each presents unique risks and requires specific detection and control strategies to ensure a safe working environment. Oxygen deficiency refers to an insufficient concentration of oxygen in the air, typically below 19.5 percent. Normal air contains approximately 20.9% oxygen, which is necessary to sustain human life and cognitive function. Oxygen deficiency can occur due to a variety of reasons, such as displacement by other gases like nitrogen or carbon dioxide, or by chemical reactions like rusting or combustion within the space. The consequences can range from dizziness and increased heart rate to unconsciousness and death. For instance, a recently sealed storage tank may experience oxygen depletion as residual liquids oxidize or as microbes consume the oxygen within the space. Detection of oxygen deficiency is done using an oxygen sensor within a multi-gas meter, which is calibrated to give readings in percent of available oxygen. Readings below 19.5% trigger a warning and require immediate action. Control involves introducing fresh air through forced ventilation or the use of air-supplying respirators, which bring external air into the respirator so that the worker is not breathing the contaminated air. Workers will also be trained to never go into a confined space that has not been tested an....