## 1 Introduction  
Extensive effort is needed to achieve the ambitious climate goals set by the Paris agreement. Biomass is a considerable renewable energy source, which fulfilled approx. 19% of heating needs and almost 3% of electricity needs in 2019, in the EU [1]. However, biomass processing generates particles, the accumulation of which could be considered an important hazard at various stages of bio-based supply chains [2; 3; 4]. Due to the possible loss of life and high cost due to such explosions, a cautious approach is adopted, and significant emphasis is put on prevention aspects, focusing on the elimination of potential explosion hazards both in biomass processing and utilization facilities [5; 6]. With increasing interest in novel processes for the valorization of biomass [7; 8], the necessity of investigations focused on process safety, as well as on the characteristics of the valorized biomass with respect to its subsequent utilization, is evident. Torrefaction, also known as mild pyrolysis [9; 10], is one of the processes that offer important benefits in usingvalorized biomass as a sustainable solid fuel [11; 12]. It offers important advantages across the whole bioenergy value, improving solid fuel properties [13; 14; 15] and offering advantages for various energy conversion processes, such as combustion [16; 17; 18] or gasification [19; 20; 21]. The influence is multifaceted. Firstly, torrefraction has an enhancing influence on the reactivity of biomass, which has been confirmed by many studies [22; 23; 24; 25]. Secondly, torrefraction improves grindability and makes biomass more brittle [26; 27; 28]. This is important since particle size distribution has an immense influence on the behavior of solid fuels during combustion [29; 30; 31]. Moreover, torrefraction is capable of removing some part of chlorine from biomass [32], followed by the formation of chloromethane [33]. This has a positive influence in terms of the formation of deposits in boilers [34], and the diminishing influence of torrefraction on the formation of deposits has been confirmed empirically for the combustion of torrefied Palm Kernel Shells in small-scale boilers [35]. A number of published works confirmed the feasibility of using torrefied biomass to decrease the carbon footprint of thermal power plants by co-firing torrefied biomass with coal at ratios much higher in comparison to untreated biomass [36; 37]. However, not much is known about the process safety of torrefied biomass, thus creating potential business uncertainties for large-scale users, such as power plants, where explosions are related to significant human and financial losses. [PERSON] et al. [38] investigated the influence of torrefraction on selected parameters of dust explosivity of wheat and willow, reporting a slight increase in (dp/dt)max and K\({}_{\text{STmax}}\) due to torrefraction. [PERSON] et al. [39] also characterized the explosion reactivity of torrefied spruce. [PERSON], [PERSON], and [PERSON] [40] reported the explosivity properties of dusts from torrefied biomass pellets and measured flame front velocity using an in-house developed method. Flame speeds have been compared for coal and biomass by various sources [41; 42; 43]. Due to the reported increase in the biomass explosion parameters caused by torrefraction, it seems sensible to determine if coarse particles, typically not considered hazardous in the case of raw biomass, should be treated as a potential risk for torrefied materials. Moreover, a good understanding of combustion behaviour and knowledge of laminar burning velocity is critical in terms of the design of burners, as well as assessment of consequences of fuel change for existing burners, whether that be a transition from coal to torrefied biomass (also known as biocal) or transition from untreated biomass to biocool.