What is a key factor in determining whether an atmosphere is hazardous in confined spaces?

The presence of flammable vapors or toxic gases is indeed a key factor in determining whether an atmosphere is hazardous in confined spaces. Confined spaces often have limited ventilation, which can lead to the accumulation of harmful substances. When flammable materials or toxic gases are present, they create a significant risk for workers, as they can lead to fires, explosions, or serious health issues. Therefore, identifying and evaluating the types and concentrations of gases and vapors in a confined space is essential for ensuring safety and compliance with regulations.

Other factors like the number of workers, temperature, and duration of entry can influence conditions in a confined space, but they do not directly determine the atmospheric hazards present. Focusing on the specific contaminants and their properties addresses the immediate risks that may compromise worker safety.