Fortifikationsverket (FORTV) has expressed a desire to investigate the design, reliability, performance and cost of a sprinkler system for a typical underground fortification facility. Based on the cost and the benefit associated with a sprinkler system, a cost-benefit analysis was performed. In addition, water mist fire protection systems were studied. The installation cost analysis was based on two fictious facilities; a small facility with a net area of 1 000 m² and a large facility with a 5 000 m² net area.

The estimated installation cost for a traditional sprinkler system in the smaller type facility is about SEK 1,3 million and about SEK 3,3 million for the larger type facility. The installation cost for a high-pressure water mist system is higher than that of a traditional sprinkler system for the smaller type facility but comparable for the larger type facility. A low‑pressure water mist system seems to be the least expensive option for both types of facilities. This is probably because the system, unlike a traditional sprinkler system, requires smaller pipe sizes, smaller water pumps and a smaller water tank and unlike a high-pressure system uses normal steel pipes and less expensive centrifugal pumps.

The cost-benefit analysis for the fictitious type facilities shows that a sprinkler system is cost-effective, especially for the larger type facility. But it should be noted that the uncertainty in the data base is quite large, which means that the trends in the result can be used for further analysis, but that the actual values ​​of the benefit ratio should be viewed with some caution. The sprinkler system mainly has an effect to reduce the property loss. The expected benefit for personal injury is around one percent of the total benefit of the sprinkler system. This is because the risk of fatality and injuries in the event of a fire is small, as people can usually put themselves in safety. The reduction in property loss was assumed to be 75%, and an assumed lowered benefit of sprinklers (50% and 25% property loss reduction, respectively) leads to a lower benefit ratio but for the large type facility the benefit ratio is still above 1,0. The benefit of sprinklers also decreases if the assumed fire frequency is reduced. However, for the larger type plant, the calculation shows that there is still a benefit, even if the assumed fire frequency is halved. The same applies if the cost of replacement of expensive equipment is assumed to be half as high.