## 1 Introduction  
Mining plays a vital role in the economic and social development of many countries, and their sustainable development helps to enhance workers' occupational safety and health (OSH), promotes the participation of diverse communities, and fosters sustainable mining practices [1]. The economic impact of mining can be measured in terms of employment and income generation, considering that small-scale mining provides income to about 13 million workers and their families worldwide [2]. Mining is one of the most critical sectors for Colombia's economic development. The mining sector contributed 5.4% of the country's Gross Domestic Product (GDP) for the first trimester of 2019. Colombia is one of the largest coal exporters in the world [3], with proven reserves of 0.5% of the world's total [4], which will allow it to remain one of the leading world producers during the next 183 years [5]. It is also the second-largest producer of emerals in the world, after Zambia [6], so mining has become one of the economic alternatives in the rural sector in Colombia, which results in support of a high percentage of families and constitutes one of the essential industrial lines in the country. However, underground mining is a dangerous job. Between 2005 and 2019, there were 1316 mining emergencies in Colombia, with a balance of 1476 fatalities [7]. The causes range from falls (collapses) to other incidents, including the operation of heavy machinery and accidents involving explosions. These emergencies are associated with using explosives, coal dust, and/or the concentration of explosive gases. In this context, and recognizing the high number of fatalities in developing countries, the challenge invites us to create and adapt technological solutions to mitigate these OSH risks from prevention and alerts in the case of accidents. One of the most promising avenues to achieve this goal is the implementation of Industrial Internet of Things (IIoT) systems in underground mining environments. These systems, composed of wireless sensor networks, have the potential to continuously monitor environmental conditions, such as the concentration of explosive gases, and provide early warnings to prevent accidents. However, an open issue in this scenario is how to adopt these technologies for deployment and their cost, which can be an obstacle, particularly in small-scale mining operations. Therefore, this study focuses on developing a methodology for the efficient deployment of Wireless Sensor Networks (WSNs) in underground mines aimed at early detection of hazardous gases and mitigation of explosion risks. At the same time, it focuses on cost efficiency, seeking to create an accessible and low-cost IIoT system that can be implemented in large mining operations and smaller mines with limited resources. Many technologies can be used to improve the miners' safety, combining wireless and wired technologies. WSNs were designed to communicate with sensors by generating a cooperative network between nodes to measure and control various variables. They are characterized by using sensor nodes capable of processing data that work collaboratively. WSNs play a vital role in the IIoT, increasing the awareness of specific environments and linking physical and virtual objects, using WSNs to connect the sensor nodes. The IIoT applies Internet of Things (IoT) technology in industrial environments. In the IIoT context, sensors and devices collect real-time data regarding production processes, equipment, supply chain, and energy consumption. These data are analyzed to make decisions, predict maintenance, and optimize production. According to the taxonomy proposed by [PERSON] et al. [8], the industry sectors that use the IIoT are the energy sector, water, sewerage, transport, telecommunications, agriculture, mining, manufacturing, and retail. All are considered critical infrastructure for the development of the economy, except the retail sector.