Which of the following is a critical safety factor when working in confined spaces?

Ventilation is a critical safety factor when working in confined spaces because it ensures that fresh air is supplied and that potentially harmful gases, vapors, or dust are removed from the area. In confined spaces, the risk of a hazardous atmosphere is significantly higher due to limited airflow, which can lead to oxygen deficiency or the accumulation of toxic substances. Adequate ventilation helps to maintain a safe environment by preventing these dangerous conditions, making it vital for the safety of workers.

While temperature control, noise level, and lighting are also important considerations in confined space work, they do not directly address the immediate life-threatening hazards associated with the air quality and breathing conditions. Therefore, ventilation stands out as the most critical factor in ensuring a safe working environment.