Common Safety Orientation (CSO) Practice Test 2026 - Free CSO Practice Questions and Study Guide

The correct choice highlights the presence of PCBs, or polychlorinated biphenyls, in oils used in older electrical transformers. PCBs were widely utilized in various industrial applications due to their chemical stability and insulating properties, particularly in electrical equipment such as transformers and capacitors. This makes the oils in these transformers a significant concern for environmental health, as PCBs can leach into the environment and pose serious risks to human health and ecosystems.

The other materials listed do not typically contain PCBs. For example, plastic insulation is often made from materials like PVC or polyethylene, which do not have the same chemical characteristics as PCBs. Wood composites are primarily made from wood fibers and adhesive substances, usually lacking PCBs. Glass products, being inorganic, would not contain organic compounds like PCBs. Therefore, the association of PCBs with oils in older electrical transformers is the most accurate reflection of where these harmful substances may be found.