With high quantities of flammable material within DL4 and the disastrous effects any fire could have on the atmosphere, the plant and animal life and the station’s structure itself, it is obvious that some method of fire prevention, monitoring and suppression must be implemented on the settlement.
Fire prevention will be catered for to a certain extent in the atmospheric composition (see Life Support). The terrestrial (sea level) pressure of the inert gases nitrogen and carbon dioxide, along with the 40% relative humidity level, help prevent the reaction of flammable materials with the atmospheric oxygen. Other aspects of prevention are fairly basic, such as, maintaining stringent temperature controls on any technologies capable of combustion (e.g. – producing heat, made of flammable materials, in contact with oxygen), and the positioning of industries, which involve any fire or explosion risk, in a segment of the settlement that is, once evacuated, easily vented into space (i.e. – central sphere). Also, for the purposes of fire prevention 10cm thick lunar synthesised silicon cellular panels will be used for house wall construction, while ceilings will be made from silicon fibreglass, an equally fire resistant material (ref. 37).
For the purposes of fire detection and monitoring there are basically five methods available: smoke detection; obscuration smoke detectors, scattering smoke detectors, condensation nuclei counter and ionisation smoke detectors, and flame detection. The decision on which method to choose was a difficult one as all systems provide suitable detection capabilities. Therefore a combination of two systems was chosen; firstly the relatively simple obscuration smoke detector, and secondly, a flame detector, monitoring a large section of the infrared band of the electromagnetic spectrum.
The obscuration smoke detector produces a beam of light from a laser diode that is transmitted directly to a receiver (photodiode). The simple process by which smoke is detected depends on the obscuration of the light beam by smoke particles. These detectors will be placed within the atmospheric monitoring and purification loops thus providing a constant airflow through the subsystem. These detectors were chosen for their relative simplicity as they could operate in emergency situations, requiring little power and practically no maintenance.
The infrared electromagnetic spectrum monitoring was chosen to facilitate fire detection in the more open human and plant habitats of the torus. These systems will require a high level of maintenance and are less capable of operating in the emergency situations that a fire could produce – especially as they will be more easily susceptible to fire damage due to their location. They do however provide the advantages of not requiring a flow of smoke reaching them before an alarm can be sounded and being capable of identifying, to a certain extent, the material being burnt and the temperature of the flames.
Once detected, a fire must be put out. This must be done in such a way as to balance the risk of the fire spreading with the risk of damaging the surrounding environment and equipment. Therefore, different methods will be used in different areas.
As mentioned earlier, those areas easily opened to space, once all humans have been evacuated, could be vented, providing that the fire was a serious enough threat to require such action. In other areas, where humans or plants live, suppression systems could be as simple as water, alternatives were ruled out due to their impact on the ecology. [The use of the suffocant, carbon dioxide, or the toxic (banned) halon could harm the residents and damage DaedalusaL4’s environment.]
Water will obviously be useless on electrical fires or on systems that could be damaged by water, therefore carbon dioxide, cryogenically stored as dry ice, could instead reduce the heat of the system and suffocate the fire. The use of pressurised carbon dioxide will provide the residents with time to evacuate the industrial/research areas to the human habitats (where water will be used as a suppressant). The excess carbon dioxide released into the atmosphere by this process could later be removed by carbon dioxide condensers and once again cryogenically stored.