Which of the following best defines a hazardous atmosphere?

A hazardous atmosphere is best defined as a space that can cause immediate injury or death. This encompasses a variety of situations where the air is contaminated with harmful substances such as toxic gases, vapors, or insufficient oxygen levels. In such environments, the risk is acute, meaning that exposure can lead to instant dangerous outcomes for workers present, emphasizing the critical need for proper training, detection systems, and safety measures.

The other options highlight conditions that do not adequately capture what constitutes a hazardous atmosphere. For instance, a space devoid of harmful chemicals does not pose a risk to health, while an atmosphere that is exclusively oxygen-rich might be safe when it doesn't exhibit any other hazardous factors. Lastly, an area with only physical hazards does not address atmospheric quality, which is essential when determining the presence of potential dangers in the environment. Thus, recognizing that a hazardous atmosphere can lead to immediate threats provides a clearer understanding of safety requirements in such settings.