Safety Trained Supervisor in Construction (STSC) Practice Exam 2026 - Free STSC Practice Questions and Study Guide

When monitoring indicates 15% oxygen in a confined space, the appropriate action is to evacuate because the space is considered oxygen deficient. Normal atmospheric air contains approximately 20.9% oxygen. An oxygen level of 19.5% or higher is considered safe for breathing, while levels below 19.5% can pose serious health risks. An oxygen level of 15% can lead to symptoms such as increased heart rate, shortness of breath, and impaired judgment, which could endanger workers’ health and safety.

Evacuating the confined space ensures that workers are removed from a potentially hazardous environment, thereby preventing accidents and health-related incidents that could arise from low oxygen levels. After evacuation, it is essential for trained personnel to assess the situation and ensure that proper ventilation or other safety measures are implemented before allowing any return to the space.