1. Sisinni, E., Saifullah, A., Han, S., Jennehag, U., & Gidlund, M. (2018). Industrial Internet of Things: Challenges, and Research Opportunities. IEEE Transactions on Industrial Informatics, 14(11), 4723-4734. In Section II-A, "Requirements and Challenges," the paper explicitly states: "IIoT devices are often deployed in harsh environments, which may be characterized by extreme temperature, humidity, vibration, noise, and the presence of corrosive materials." (p. 4724). DOI: 10.1109/TII.2018.2852491
2. Cisco. (2020). Cisco Validated Design: Industrial IoT (IIoT) Networking and Data Management. In the chapter "Solution Design," the section "IT and OT Convergence Challenges" contrasts office-grade IT equipment with industrial-grade OT/IIoT equipment, emphasizing that industrial devices must be "hardened" or "ruggedized" to withstand the physical conditions of the factory floor, including wide temperature ranges, shock, and vibration.
3. Boyes, H., Hallaq, B., Cunningham, J., & Watson, T. (2018). The industrial internet of things (IIoT): An analysis framework. Computers in Industry, 101, 1-12. In Section 3.2, "Context," the authors highlight the environmental differences: "The context is the physical environment in which the ‘things’ are located... For example, a sensor on a North Sea oil rig will be in a very different context to one in a climate-controlled laboratory." This directly supports the idea that the operational environment dictates the physical characteristics of IIoT devices. DOI: 10.1016/j.compind.2018.04.015