No, it is not safe to put metal objects, including mason jar lids, in the microwave, even if there are no visible sparks. Microwaving metal can lead to a variety of hazards and cause damage to the microwave oven.
When metal is placed inside the microwave, it acts as a conductor of electricity. This can cause electrical currents to flow through the metal, leading to the following potential hazards:
Fire and sparks: While you might not always see visible sparks, the electrical currents can still generate heat and sparks within the metal. This can lead to a fire hazard and may cause damage to the interior of the microwave.
Damage to the microwave: The sparks and heat generated by the metal can damage the microwave's internal components, such as the magnetron (which produces microwaves) and the microwave's cavity.
Potential explosions: Some metal objects, like mason jar lids, can act as antennas, concentrating the electrical energy and causing rapid and uneven heating. This concentrated heating can lead to steam buildup inside the jar, which might result in an explosion when the jar is opened.
Radiation leakage: Placing metal inside the microwave can also interfere with the electromagnetic waves, potentially leading to radiation leakage, which is a serious safety hazard.
To ensure safe microwave use, it's crucial to avoid putting any metal objects inside the microwave. Always use microwave-safe containers, such as glass, ceramic, or microwave-safe plastics, and follow the manufacturer's guidelines and instructions provided with the microwave oven. If you suspect that your microwave has been damaged due to metal use or any other reason, it should be inspected and repaired by a qualified technician before using it again.