What is the appropriate action after the head riser is removed?

The appropriate action after the head riser is removed is to cover the base risers with a blanket. This action is necessary to help retain heat in the welded area and to protect the weld from environmental factors such as wind or moisture, which could potentially affect the quality and integrity of the weld.

Covering the base risers assists in stabilizing the temperature of the weld pool during the cooling process, reducing the risk of cracking or weakening in the joint. It ensures that the thermal conditions remain conducive for a strong and durable bond.

In contrast, continuing with welding immediately would not be advisable as it may disrupt the cooling process or create uneven heating. Allowing the rail temperature to drop is not ideal; maintaining warmth around the weld area is critical. Removing all equipment from the area, while it may seem sensible for safety, does not address the immediate need to protect the weld that is crucial during the cooling phase. Thus, covering the base risers is the most responsible and effective course of action to ensure the quality of the thermite weld.