Why hot water scald risk depends on both temperature and contact time, and where the tension with hygiene sits.
Hot water safety has a built-in tension, and Level 2 expects you to understand it: water must be kept hot enough to be hygienic but delivered cool enough not to scald. The key idea is that scalding depends on temperature and time together.
A scald is a burn from hot liquid, and how badly it injures depends both on how hot the water is and on how long it stays against the skin. Hotter water needs only a very short contact to cause a serious scald, while slightly cooler water takes much longer to do the same harm.
That time-and-temperature link is why a few degrees matter so much. Water that feels only a little hotter can cut the safe contact time sharply, which is dangerous for those who cannot move away quickly, such as young children, older people and anyone with reduced sensation or mobility.
At the same time, stored hot water has to be kept hot enough to control bacteria such as Legionella, and that storage temperature can be hotter than is safe to deliver straight to a bath or basin. So the system is deliberately run hot in store.
The resolution is to store hot and blend down. The water is stored and distributed hot for hygiene, then mixed with cold at or near vulnerable outlets, typically by a thermostatic mixing valve, to bring the delivered temperature down to a safe level, especially at baths where the risk of a long immersion is highest.
For revision, hold the two ideas together: keep stored water hot enough for hygiene, but protect people at the outlet by limiting the delivered temperature, since it is the combination of temperature and contact time that injures. Confirm safe delivery temperatures and where they apply against the current guidance.