**1. Introduction**

Radon is a colorless, odorless, and tasteless inert gas. It can only be detected or measured with the help of special detectors. It can travel through cracks of the bedrock, soil, and through groundwater. In underground mines or underground structures, high concentrations of radon may be detected in the absence of adequate ventilation. In underground mines with uranium-bearing mineralization, radium 226 (radium's most stable isotope) is a natural source of radiation. Other isotopes of radon, such as radon 220 and radon 219, also exist naturally; however, because of the small amount and short lifetime, other isotopes are of less concern. Radium 226 decays into radon 222, which in turn decays into its short-lived radioactive daughters in the mine atmosphere. The uranium decay chain can be summarized as shown in **Figure 1**.

Until the late 1970s, radon and its daughter products were of concern only at uranium mines. A study conducted by Daniels and Schubauer in 2017 shows that the radon exposure varied widely among several working populations, most of whom were employed in industries unrelated to the uranium fuel cycle. With the recent advancement of scientific knowledge, there has been more interest and attention to the hazards in non-uranium mines, underground structures, and residential buildings. In the absence of control measures, occupational exposures outside the uranium fuel cycle (e.g., tourist cave workers, waterworks employees) can exceed those found in most uranium workers [1].

Dehnret [2] reported high radon concentrations in old underground workings in Germany and protective steps taken for miners' safety. Sahu et al. [3] reported

the sources of radon, its emanation rate, and measurement techniques, particularly for underground uranium mines. Hu et al. [4] highlighted radon and radon progeny problems in Chinese uranium mines. In the United States, radon has been listed as the second major cause of lung cancer after tobacco [5]. A study of underground miners shows that 40% of lung cancer deaths may be due to radon progeny exposure [6]. MSHA has regulations for radon concentration in underground mines and sampling procedures depending on the concentration.

Considering the short half-life and the high radiation dose of radon gas and its daughter products, its mitigation in the underground environment becomes very important. In the absence of mitigation techniques, both the uranium and nonuranium mines (with uranium mineralization in the orebody) pose a serious threat to the personnel working in the underground environment.

Ventilation plays a significant role by supplying fresh air and removing the contaminated air from the working areas, thereby minimizing the radon concentrations in the mine environment. In addition, an appropriate mining method and welldesigned mining sequence can also help control radon gas in the mine atmosphere [4]. In this chapter, the different radon mitigation methods that are specific to the underground mining operations are discussed.
