## 3 Case Study 1  
### Case Study Context and Goal of the Analysis  
The first case study concerned the analysis of the accident that occurred in 1997 in an Italian hospital and consisted in a fire in a hyperbaric oxygen therapy (HBOT) room (or chamber). This accident caused the death of ten patients and one nurse, who were in the HBOT when the fire broke out [58]. A multi-place HBOT room can provide oxygen therapy treatment to two or more people at the same time. For this purpose, each patient inside the room uses a mask or a hood for breathing, and a nurse or a technician is usually in the room during the treatment to assist patients. This type of device allows patients to breathe oxygen at a pressure higher than the atmospheric pressure, and it is used for the treatment or prevention of several diseases [59]. The presence of high-pressure oxygen and its augmented percentage represents a serious hazard of fire, explosion, or implosion, which has led to numerous accidents worldwide [56; 60]. Nowadays, to prevent the occurrence of these types of accidents, international regulations and technical standards establish strict safety requirements for both manufacturers and users [8; 61]. In particular, as far as operational safety is concerned, several basic rules must be observed during the use of the device, such as avoiding the presence of volatile or flammable liquids in the chamber; avoiding the presence of combustible lubricants; keeping the oxygen concentration below 23%, etc. [62]. Furthermore, the continuous monitoring of the chamber is requested during its use, as well as the periodic maintenance of fire suppression systems [63]. For this purpose, specific training of the hospital personnel in charge of using the device is foreseen, as well as providing information to patients [64]. At the time of the accident in Milan, most current safety requirements were not issued yet. However, procedures on the proper use and maintenance of the equipment were in use at the hospital, as well as constructive safety requirements for the device manufacturer. As emerged from the investigations carried out following the accident, a gas-operated hand warmer introduced into the chamber by a 77-year-old female patient was the probable trigger, and it is likely that the chamber was pressurized with oxygen rather than air, as an explosive fire would not occur in a chamber pressurized with air. The increase in the oxygen percentage was caused by the use of hoods that were modified by the hospital personnel to make them easier to wear: in detail, two zips in the latex collar were added, causing a significant oxygen leakage from the zips and the collar itself. Thus, in the chamber, the percentage of oxygen was much higher (27%) than the requested level (23%). Moreover, the fire suppression system of the chamber was found to be not functioning, as the water tank of the fire extinguishing system was empty and the shutter of the water delivery pipe was found closed, as was the valve of the compressed air cylinder used as propellant (although the fire tank was prepared for the installation of the level gauge, this had never been installed). Hence, due to the failure of the extinguishing system, the fire was extinguished only due to the exhaustion of the oxygen present inside the chamber: it was found that some people in the chamber survived for at least a minute after the fire broke out. They could have been saved if the fire suppression system had been working. Although police investigations and the subsequent trial provided a detailed technical analysis of the accident, a proper accident analysis method was not used, missing a systemic perspective on the elements and events that were analyzed independently. With this goal in mind, to achieve a more comprehensive understanding of the accident, a FRAM model was developed, starting from the analysis of the correct functioning of the HBOT room considering the safety requirements and procedures in force when the accident occurred.