Sprinkler systems connected directly to water supply networks
The project Water sprinkler systems – capacity tests and public water supply networks, funded by the Swedish Fire Sprinkler Association, FM Global Fire Provision Grant and the International Fire Sprinkler Organisation, was concluded in April 2016. The project investigated why some local authorities have prohibited connecting sprinkler systems directly to water supply networks, what risks such connections may pose to drinking water quality, and how trade association recommendations, guidelines, and standards can be improved to minimise these risks.
Since 2013, automatic water sprinkler systems are required in hospitals and other care facilities in Sweden where people might need assistance to evacuate in case of fire. For various forms of means-tested housing, domestic sprinkler systems are required. In addition, sprinkler systems are often incorporated as part of fire safety engineering to allow a more flexible design compared to using pre-accepted solutions in the building code. The water for sprinkler systems can be supplied directly from the municipal water supply network, with or without sprinkler pumps, depending on the available levels of pressure and flow. The alternative to a direct connection is to have sprinkler pumps and separate water tank with the capacity necessary to supply all of the water needed. A ban on direct connections in some municipalities in Sweden has led to that this is the only viable option in some areas. This solution, however, comes with increased costs for installation and, more particularly, maintenance, as pumps require testing on a weekly basis. The extra costs incurred for a means-tested housing facility, where a domestic sprinkler system is required, are estimated to be a 1 million SEK one-time fee for installation, and 25-100,000 SEK per year for maintenance. As the thousands of means-tested housing facilities in Sweden are often run by local authorities, a total ban on the direct connection of sprinkler systems would constitute a suboptimal use of our tax revenue.
Problems and misunderstandings
The bans that have been put in place are partially based on real problems that require solutions, and partially on misunderstandings that need to be straightened out. The most common misunderstandings are:
- Sprinkler pumps draw so much water from the network that a negative pressure is created, meaning that contaminated water can be sucked back into the water supply network.
- Sprinkler water contains poisonous foam additives.
- In case of fire, all sprinkler heads in the building are activated at the same time, and the water flow rate is just as high as during capacity testing.
It is possible for a negative pressure to be created in the water supply network, but only by a very powerful pumping system that has not been designed, installed, or undergone final testing according to the current standard, which states that the supplying line should have a pressure of least 0.5 bar at a flow rate of 120% of the dimensioned flow. In addition, many sprinkler systems, particularly domestic sprinklers as these require relatively low flow rates, can be installed without a pump. These systems are unable to create a negative pressure, regardless of flow rate.
Foam additives are used in very few sprinkler systems, primarily in industrial operations. All other systems are conventional ones that use only water. Prohibiting the direct connection of sprinkler systems which use foam may be a reasonable course of action, but to prohibit conventional systems based on the mere possibility of systems using foam is not.
Water flow rates rarely reach the levels that occur during capacity testing when actually extinguishing fires. During most fires, between one and four sprinklers are activated, and these either extinguish the fire altogether or limit its spread so that no more sprinklers are activated. In some high-risk environments, ‘deluge systems’ might be installed, which are designed with open sprinkler nozzles so that entire sections can be activated simultaneously. Just as with foam sprinkler systems, however, these only comprise a tiny portion of all sprinkler systems.
The most frequently occurring, real problems that need to be solved are:
- Pipes being of large dimensions and having low flows and poor circulation can lead to microbial growth and thus problems with drinking water quality. Local authorities are therefore unwilling to limit their options for the future by allowing the connection of sprinkler systems, as this may lead to later difficulties in terms of reducing pipe dimensions so as to solve such problems.
- When annual capacity testing is performed so as to verify the supply volume of the water source, it is sometimes undertaken with such high flow rates that encrustations in the pipes are dislodged. Although testing continues until clean water reaches the sprinkler facility, there is a risk that discoloured water has already reached other users, causing complaints and extra work for water supply and sewerage companies.
- Planning for capacity tests and attending testing requires substantial personnel resources on the part of larger local authorities, which means that daily operations and planned maintenance work can suffer as a result.
Aside from these problems, it can also be the case that the existing water supply network does not have sufficient capacity to supply the needs of a sprinkler system. Even though some administrative sections of a city may have plenty of water, the supply capacity may be far lower in more remote areas, and in these cases a separate water tank is necessary.
Responsibilities and obligations
The Swedish Public Water Services Act is clear as regards the obligation of water supply and sewerage companies to provide a water supply to sprinkler systems – there is no such obligation. If it is technically possible to facilitate this without causing inconvenience, it is something that should be done; at the same time, however, water supply and sewerage companies can claim that the need has been provided for if the installation of a separate
water tank with a sprinkler pump has been permitted. As a result, even though it is less than ideal from the perspective of government spending to prohibit the direct connection of sprinkler systems, water supply and sewerage companies have the legal right to do so. Thus, the sprinkler industry must find solutions that minimise the risk of inconvenience, ensure that imposed limitations are adhered to, and be prepared to waive some of its demands. The alternative is that more local authorities will impose a ban, and that more systems with their own water tanks and pumps will have to be installed in the future.
Limited capacity tests
Several years ago, the Gothenburg Recycling and Water and Sewage administrations found a pragmatic middle way that allows the direct connection of sprinkler systems while simultaneously minimising inconveniences. This involves limiting capacity tests, so that the maximum flow rate in pipes is set to 1.3 m/s. The implementation of this system has shown that this flow rate limitation is able to prevent the occurrence of polluted water in pipes during capacity testing, while still allowing direct connection of sprinkler systems. The full flow rate is permitted during delivery inspection, but is again limited immediately afterwards. Where water pipe dimensions are sufficiently large the full flow rate is allowed; otherwise, it is limited. This policy is commonly employed by many Norwegian local authorities as well, and Norwegian studies show that limited capacity tests in combination with hydraulic calculations provide results that correspond well to full-scale capacity tests.
Suggestions for a solution
Among other things, the Water sprinkler systems project suggests that the following technical and organisational measures be implemented so as to minimise the risk of inconvenience during the direct connection of sprinkler systems:
- Limited capacity tests are to be allowed following an assessment undertaken by the Authority having jurisdiction in consultation with the water supply and sewerage company.
- The interval for capacity testing may be extended to up to five years if it is deemed that the reliability of the water source is good, e.g. for a connection to a water main to which several sprinkler systems are connected and where at least one test is performed each year.
- For connection to pipes that are fed from a ring main, capacity tests are allowed for without shutting of the water supply from either side.
- A smaller test tank for the circulation of water is allowed as an alternative for the testing of sprinkler pumps for those parts of systems in which testing at the full flow rate is not allowed.
- A water gauge with a pre-set maximum flow rate should be installed parallel to the regular water meter to ensure that the maximum flows that the water supply and sewerage companies have decided are not exceeded.
Some may argue that these suggestions are a step in the wrong direction, that they will negatively affect the reliability of the water source due to the fact that full-scale capacity tests are not performed. The alternative, however, is for the trend of prohibitions and limitations to spread to additional local authorities, with the end result that the only remaining possibility is water supply from separate water tanks. To relax the standards to which capacity tests are held, however, will mean that the possibilities for direct connection will increase, with the alternative possibility of using separate water tanks remain where necessary.
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