What could be a direct effect of poor ventilation in confined spaces?

The correct choice highlights the significant risk associated with poor ventilation in confined spaces, where higher concentrations of toxic gases can accumulate. Confined spaces often have limited airflow, which means that any gases produced from processes occurring within, or gases that infiltrate from outside, are not effectively diluted or removed. This can lead to dangerous levels of harmful substances such as carbon monoxide, hydrogen sulfide, or other toxic fumes, which can pose serious health risks to anyone entering that space.

Inadequate ventilation also fails to replace oxygen that may be consumed in chemical reactions or by personnel working in the space. Consequently, the potential for higher concentrations of these toxic gases increases, creating an environment that can lead to acute health risks, unconsciousness, or even fatalities if proper safety measures are not implemented.

While options like increased light intensity or improved air quality would generally be beneficial effects, they do not align with the consequences of poor ventilation. Similarly, reduced visibility is often not a direct effect of poor ventilation itself, making the correct identification of toxic gas accumulation essential for safety in these environments.