For dilution of a concentrated acid, we should add:

When diluting a concentrated acid with water, heat is gradually released and readily absorbed by the larger volume of water. Conversely, when water is added to concentrated acid, a significant amount of heat is rapidly generated. This sudden heat production can cause some of the water to turn into steam explosively, potentially splashing the acid onto skin or clothing and causing acid burns. Additionally, the excessive heating may lead to the glass container breaking.