When the timer or buzzer goes off in a microwave, the microwaves stop being generated. However, there may still be some residual microwave energy bouncing around inside the microwave cavity. Opening the door immediately after the timer goes off does not pose any significant safety risk, as modern microwave ovens are designed with safety mechanisms that turn off the magnetron (the component that generates microwaves) when the door is opened.
The reason some people suggest waiting a few seconds before opening the microwave door is mainly to allow the steam and heat to dissipate slightly. This is particularly relevant when heating liquids or food with high moisture content, as opening the door right away could cause a burst of steam to escape, which may lead to burns or scalding.
To ensure your safety when opening the microwave door:
Wait a few seconds: If you've heated liquids or high-moisture food, it's generally a good idea to wait a few seconds before opening the door to let the steam dissipate.
Open the door slowly: When you do open the door, do so slowly to allow any steam or hot air to escape gradually.
Use oven mitts or a towel: To further protect yourself, use oven mitts or a towel to handle hot containers or plates.
As a general rule, treat the microwave with caution, and follow the specific instructions and safety guidelines provided in your microwave's user manual. Additionally, avoid using microwave-safe containers with tight-fitting lids as they can trap steam and create pressure, which can be hazardous when the container is opened.