Single-wall metal pipes should not pass through which of the following?

Single-wall metal pipes should not pass through concealed spaces or unoccupied attics due to the significant fire hazard they pose. These pipes can become extremely hot during operation, and if they are placed in areas that are not easily accessible, such as concealed spaces or attics, there is an increased risk of igniting nearby combustible materials.

In concealed spaces, it can be challenging to monitor the temperature, and any heat buildup could go unnoticed, leading to potential structural damage or fire. The safety regulations dictate that any flue or venting systems that could present a hazard must be easily accessible for inspection and maintenance, ensuring that they do not compromise the safety of the building. Therefore, the placement of single-wall metal pipes is restricted within these areas to minimize risks and adhere to safety standards.