**The Hidden Dangers of Confined Spaces: Understanding the Risks for Welders**

The correct answer is "All of the above." Permit required confined spaces are particularly hazardous for welders due to several factors: - **Toxic or flammable substances:** These spaces often contain or have previously contained dangerous chemicals that can be harmful if inhaled or ignited. - **Oxygen level changes:** The atmosphere within a confined space can fluctuate, leading to potential oxygen deficiency (asphyxiation) or the presence of toxic gases. - **Physical hazards:** These spaces might have limited means of entry or exit, increasing the risk of being trapped, and could also contain potential fire, electrical, or mechanical hazards. Given these combined risks, stringent safety protocols and permits are essential for anyone working in these environments.