Appendix: Calculating The Amount of Water Required To Suppress A Fire in A Closed Volume
In the case of a closed volume, it is easy to compute the amount of water needed. The oxygen (O2) in air (21%) is necessary for combustion. Whatever the amount of fuel available (wood, paper, cloth), combustion will stop when the air becomes "thin", i.e. when it contains less than 15% oxygen. If additional air cannot enter, we can calculate:
- The amount of water required to make the atmosphere inert, i.e., to prevent the pyrolysis gases to burn—this is the "volume computation"
- The amount of water required to cool the smoke, the atmosphere—this is the "thermal computation"
These computations are only valid when considering a diffused spray that penetrates the entire volume. This is not possible in the case of a high ceiling: the spray is short and does not reach the upper layers of air. Consequently the computations are not valid for large volumes such as barns or warehouses: a warehouse of 1,000 m² (1,200 square yards) and 10 m high (33 ft) represents 10,000 m3. In practice, such large volumes are unlikely to be airtight anyway.
Read more about this topic: Fire Fighting
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