What risk is associated with pouring molten lead into a wet vertical joint?

Pouring molten lead into a wet vertical joint poses significant risks, primarily due to the interaction between the hot lead and the moisture present. When molten lead comes into contact with water, a rapid steam explosion can occur. This is because the extreme heat of the molten lead converts the water into steam almost instantly, leading to splattering. This splattering can not only create a hazardous situation for anyone nearby but also result in loss of material and compromised joint integrity.

The other aspects of the scenario involve considerations like solidification rates or joint sealing, but they do not capture the immediate physical danger posed by the reaction between the hot lead and the moisture. The risk of splattering is particularly critical to safety practices in plumbing and metalworking, as it underscores the need for proper dry conditions when working with molten metals.