Fire protection in ammunition storage spaces on board naval craft: An evaluation of the water application rate

Ammunition storage spaces on naval vessels are commonly fitted with drencher systems that are designed to prevent ordnance reaching a temperature where it might explode due to fast or slow “cook‐off”. Many of these systems are traditional low pressure water spray systems that are required by the Naval Ship Code and class requirements to deliver water at a rate of between 24 ℓ/m2/min and 32 ℓ/m2/min. The origin of this requirement is not entirely clear. The high flow rates are a burden on system design and rapid flooding of the magazines decreases the stability of the ship due to free surface effects. The objective of this study was to evaluate the necessity of high flow rates. In addition, the feasibility of reducing them using a lower flow rate drencher system –if necessary in conjunction with a low pressure water mist system– was investigated. The experiments involved exposure of an instrumented steel tube, representing ordnance, to a diesel pool fire located beneath or beside it. The temperature of the tube was monitored prior to, during and after activation of the fire suppression to ensure that it did not exceed a threshold temperature of 200°C. Flow rates from the drencher system were varied and at lower flows the WMS was activated. For the fire scenarios studied, the results indicated that a flow rate of 32 ℓ/m2/min exceeded that required to keep the temperature of the ordnance below 200 oC. At an application rate of 10 ℓ/m² per minute, the installed drencher system suppressed the fire and the kept the temperature of the ordnance below the threshold. A dual system of drencher combined with water mist system was effective at comparable flow rates. The fire however, although controlled, was not fully extinguished in all cases. This study is part of a trilateral research project between Canada, The Netherlands and Sweden designated FiST. Results contribute to defining the way ahead in the process of evaluation of national requirements for fixed fire fighting systems for magazines.