Which of the following is not used as a scald prevention device?

The choice that is not used as a scald prevention device is the water heater thermostat. While a water heater thermostat is essential for regulating the water temperature in the heating tank, it does not directly prevent scalding at the point of use. Instead, it simply maintains the set temperature of the water, which can still be too hot, increasing the risk of scalding if not properly managed.

In contrast, pressure balancing valves, thermostatic mixing valves, and scald guards are all specifically designed to prevent scalding. Pressure balancing valves work by equalizing the pressure between hot and cold water supplies, ensuring that if one supply experiences a drop in pressure, the other does not dominate, thus preventing sudden hot water surges. Thermostatic mixing valves, on the other hand, blend hot and cold water to deliver a consistent and safe water temperature, effectively preventing overheating. Scald guards are devices that restrict the maximum temperature of water at the faucet to avoid burns. Together, these devices work to enhance safety and prevent incidents of scalding.