Which of the following is NOT a characteristic of a firewall?

A firewall is primarily designed to prevent the spread of fire between different sections of a building. One important characteristic is its ability to restrain the spread of fire, effectively providing a barrier to protect lives and property. Additionally, firewalls can separate different areas of a building, creating distinct compartments that help contain fires should they occur.

While it is true that many firewalls are made of concrete due to its fire-resistant properties, this is not a strict requirement. Firewalls can also be constructed from other materials, provided they meet specific fire-rating criteria. Therefore, saying that a firewall is "always built with concrete" is inaccurate, as there are various materials that can serve that purpose effectively. Thus, the statement about the exclusive use of concrete is the characteristic that stands out as not being universally applicable to firewalls.