CHAPTER 19 SYSTEMS: ENVIRONMENTAL CONTROL AND LIFE SUPPORT SYSTEM—SUPPORTING THE HUMAN ELEMENT OF THE ISS 346 annunciate a fire and sound the alarms throughout the ISS and on the ground in Mission Control. In addition to the smoke detectors picking up the event, if the crew sees or smells smoke, they can manually trigger an alarm via the caution and warning panel (see Chapter 5). When an alarm is annunciated, one of the first responses is for the software to turn off all fans and close the IMVs to help stifle the fire and prevent smoke from being transferred to other modules. If a fire is detected by the smoke detectors, the crew will need to quickly fight the fire. For a fire detected inside a rack, the crew can remove power to that rack instantly by throwing a switch called the Rack Power Switch. Astronauts will then use a long rod attached to the CSA-CP to measure the smoke within the rack for a period of time. If the CSA-CP readings hold steady or decrease, the fire is declared to be out. Readings that continue to increase means the fire is still ongoing and needs to be extinguished. In this case, the crew will use a Portable Fire Extinguisher (PFE)—i.e., an orange tank that contains about 2.7 kg (6 lbs) of CO 2 —and a long thin nozzle pushed through one of the small holes in the front of the rack to put out the fire. See Figure 11. By emptying the PFE into the rack, O 2 is displaced by CO 2 , thereby depriving the fire of a critical component needed to burn. Figure 11. PFE with rack attachment nozzle (left) and open cabin nozzle (right). A wide nozzle that is installed on the PFE allows the crew to extinguish the fire in the event of visible flames inside the cabin. Smoke in the cabin can be dangerous to breathe therefore, crew members will also don a Portable Breathing Apparatus (PBA) or a respirator (Figure 12). The small PBA tanks hold approximately 7 to 15 minutes of O 2 (depending on how well the mask fits to the individual’s face as well as the personal respiration rate of the crew member) however, the hose can be attached to an O 2 port within the USOS and can pull O 2 from the O 2 tanks on the airlock, if additional time is needed. Since the time for a PBA is so short, and because O 2 is also introduced locally near the fire, use of the respirator is preferable. Once the fire is extinguished, the flight control team in Mission Control assesses the recovery to clean the air. If few combustion by-products were created, they can be dissipated throughout the entire ISS volume and cleaned up via the TCCS. If large amounts of the by-products were created, the crew would set up a fan attached to a various filters to clean up the smoke and by-products. CO 2 from the PFE can be cleaned using the CDRA if the CDRA is in the same or nearby module. If sensors such as the PCA detect a decrease in atmospheric pressure, it is likely that the hull has been breached and the vital atmosphere is leaking out. In this case, the computer systems will annunciate a rapid depressurization emergency alarm. Alternatively, if the crew members feel their ears pop, they can initiate a manual rapid depressurization using the caution and warning panel. The crew will then follow the emergency response discussed below to locate and isolate or repair the hole. As crew members will be losing their