Since the beginning of the well-drilling activities of oil and gas industry, in the 19th century, these activities have presented specific risks that, over the course of their evolution to the present day, have greatly increased their potential to cause harm to people, the environment, and corporate sustainability. Stimulated by the world’s energy needs, especially in developed and growing countries, the technology used by the O&G industry has evolved significantly, not only to increase production and profit levels, but also to reduce the risks of these activities, using reliable automation and other barriers to worker protection. However, despite all this investment, accidents such as the Deepwater Horizon, in 2010, and Odebrecht NS-32, in 2017, shown that there are still gaps in this process of evolution of protection systems, especially those used in highly complex systems such as offshore oil rigs. In addition, inevitably, the technological contribution implemented in offshore drilling systems increases their complexity and, consequently, also increases the complexity of the relationship between workers, systems, machines, and environment, definitively characterizing oil rigs as complex socio-technical systems. Keeping that in mind, a FRAM model was developed to understand the levels of complexity and show the relevant human factors that are critical for the safe operations of these workplaces, considering the natural and variability that emerges from these labour scenarios. Some functions of the FRAM model built presented significant variability, as function “Perform drilling operations”, where the most significant variabilities were observed in its 10 outputs, causing a large resonance within the model, once their couplings, mostly in their control aspects, can vary in terms of time and precision.