What is missing is a drain tube. A TPRV is usually toward the top of a tank, so it has a lot of potential of scalding someone or causing property damage if it goes off. To help prevent this most manufacturers require the installation of a drain tube. It is a simple drain tube = that is usually made of copper or other heat resistant material.
These tubes should be installed within six inches of the floor to prevent splashing of the hot water that comes out. These tubes are cheap and easy to install, so be sure that your water heater and/or boiler has one.