Read the cooking instructions on the package

Puncture cooking pouches and foods that have tight skins to release steam as they cook. Never use a brown paper bag for popping popcorn. It can catch fire. These product emission limits are defined for the purpose of compliance testing, not specifically exposure protection. The International Commission on Non Ionizing Radiation Protection (ICNIRP) has published guidelines on exposure limits for the whole EMF part of the spectrum. Exposure guidelines in the microwave range are set at a level that prevents any known adverse health effect. Exposure limits for workers and for the general public are set well below levels where any hazardous heating occurs from microwave exposure.