Ionizing radiation members, to comply with a European Directive. The FAA has a recommended limit of 1 mSv total for a pregnancy, and no more than 0.5 mSv per month. Information originally based on "Fundamentals of Aerospace Medicine" published in 2008. Hazardous levels of ionizing radiation are signified by the trefoil sign on a yellow background. These are usually posted at the boundary of a radiation controlled area or in any place where radiation levels are significantly above background due to human intervention. The red ionizing radiation warning symbol (ISO 21482) was launched in 2007, and is intended for IAEA Category 1,
Non-ionizing radiation the gases in the atmosphere, particularly oxygen. The remaining ultraviolet radiation from the Sun causes molecular damage (for example, sunburn) by photochemical and free-radical-producing means. Different biological effects are observed for different types of non-ionizing radiation. A difficulty is that there is no controversy that the upper frequencies of non-ionizing radiation near these energies (much of the spectrum of UV light and some visible light) is capable of non-thermal biological damage, similar to ionizing radiation. Health debate therefore centers on the non-thermal effects of radiation of much lower frequencies (microwave, millimeter and radiowave radiation). The International Agency for Research on