## 1 Introduction
It is important to highlight the main contributions and key differences in comparison to existing WBAN surveys. Among them, some well cited survey papers such as [5,6], were published a few years ago, and presented general overviews on WBAN requirements and design challenges for medical related applications, from the physical (PHY), medium access control (MAC) and networking layer points of view. More recently, [PERSON] _et al._[7] surveyed medical and non-medical applications considering the latest development in the different layers, with special emphasis on routing and security. An interesting comparative analysis of existing radio technologies was explored in [8] to better understand the corresponding requirements of WBAN applications. Furthermore, it also presented specific issues concerning channel modeling, energy consumption, and coexistence. However, the scope of the applications covered by all these surveys is limited to closed-system with almost no Body-to-Body (or Inter-WBANs) interactions. These general-purpose or medical WBANs solutions are very different from rescue and critical based applications, discussed in this paper, in terms of both design requirements and constraints. First, mobile workforces are generally deployed in harsh or disaster environments and require effective communication, coordination, and monitoring capabilities. Second, during practical cases of deployment existing infrastructure might be absent, damaged or overloaded and mobile workforces might face various uncertainties and hazards, and finally, sensitive and/or real-time information should  
Figure 1: Overview of On-Body, Off-Body and Body-to-Body Communications. still be transmitted from the deployed mobile workforces teams to external command centers to ensure timely and effective decision making. In this context, the resulting Wearable WBAN systems for safety and life critical applications should be autonomous, self-organizing, large scale, robust to external interferences, energy efficient, secure, and support various data types and rates. Moreover, these systems should enable cooperative (or collaborative), reliable and real-time communications while providing various quality of services (QoS) and security levels. To the best of our knowledge, this survey paper is the first to address rescue and critical based applications in which wearable technologies based systems (_i.e._, WBANs) are exploited. In typical WBAN research studies, health-care and monitoring of patients is considered as the main application. In contrast, this work explores the use of wearable WBAN technologies for rescue, mission-critical and worker safety applications. The detailed requirements and architectures of these applications are provided first, and the limitations of existing research and development in this context are highlighted. Moreover, the relevant key features of the newly published IEEE 802.15.6 WBAN standard [9] are investigated, along with a recent overview on WBAN research in order to help researchers and developers rapidly understand the key requirements and design challenges of such applications. Finally, a case study (worker safety and protection) is discussed as one of the potential applications from the open research issues and challenges points-of-view. The rest of this paper is organized as follows: after this Introduction, WBANs for life and safety critical applications are presented in Section 2, which includes key technologies, detailed specific applications and requirements, and finally the limitations of the existing solutions with regards to the given applications are discussed. The key enabling IEEE 802.15.6 standard and its important features such as physical layer details, medium access mechanisms, coexistence, and security, are explored in Section 3. A recent and detailed state-of-the-art on the WBAN communication stack, including PHY, MAC and networking layers, is provided in Section 4.