Modern propellants contain solvents. These will outgas if not kept at a regulated temperature and lose their properties. The temperature depends on the type of propellant used. Outgassing of solvents is of concern for two reasons:
- Diminished solvent concentrations increase the burning rate of the powder, which would at least change the anticipated projectile velocity and possibly generate dangerous chamber pressure when guns are fired.
- Outgassed solvents (typically ethers and alcohols) may create flammable or explosive atmospheres when powder canisters are opened.
Another advantage of refrigerating magazines is to extend the useful life of smokeless powder. Nitrocellulose smokeless powder spontaneously decomposes with the production of oxides of nitrogen which react with moisture to form acids which accelerate further decomposition. The rate of decomposition was considered acceptable at temperatures below 20 degrees Celsius, but accelerated dangerously when temperatures exceeded 35 degrees Celsius. Spontaneous combustion of decomposing powder was blamed for loss of the battleships Jena in 1907 and Liberte in 1911.
Initial velocity of projectiles varies directly with powder temperature. Maintaining a uniform powder temperature simplifies ballistic computations and reduces dispersion of salvos fired from different magazines.
Finally, a low temperature magazine is safer because it increases the amount of thermal energy required to initiate combustion. A heated shell fragment or other potential ignition source may lose enough energy in elevating the temperature of magazine walls, air and canisters to drop its temperature below the ignition point.
- 5 February 2000