Short Answer
The full title of FM DS 3-29 is Reliability of Fire Protection Water Supplies, and it aims to keep the water supply continuously available as designed. The data sheet ranks supply types in order of preference, lists the conditions that undermine reliability, and uses risk factors to define when a secondary supply should be considered.
Identity and Scope of the Data Sheet
The copy used here is dated October 2017, with an April 2021 interim revision, and runs to 5 pages (cover, PDF p.1). Under Section 1.0 Scope, the data sheet covers the minimum requirements for fire protection water supplies and the risk factors that determine when a higher level of reliability may be considered (DS 3-29, Section 1.0, PDF p.2). For the design, installation, maintenance and impairment management of the equipment itself, it refers to other FM data sheets.
The FM data sheets referenced in Section 4.1 are: 1-2 Earthquakes, 2-8 Earthquake Protection for Water-Based Fire Protection Systems, 2-81 Fire Protection System Inspection, Testing and Maintenance, 3-2 Water Tanks for Fire Protection, 3-7 Fire Protection Pumps and 3-10 Private Fire Service Mains and Connections (PDF p.3). On this site the tank side is covered in the DS 3-2 water tanks article and the pump side in the DS 3-7 fire pump field guide.
Definition of a Reliable Supply
Section 2.1.1.1 asks for two things: a reliable water supply for sprinkler systems, and that supply arranged, installed and maintained in line with FM data sheets and the equipment manufacturer's requirements. The same section adds an operating history requirement: the supply should have no history of repeated unplanned or unsupervised impairments (DS 3-29, Section 2.1.1.1, PDF p.2).
The Appendix A glossary separates two terms. An adequate water supply is one expected to provide enough volume, flow, pressure and duration to supply sprinklers and hoses according to FM data sheet requirements. A reliable water supply is one arranged, installed and maintained so that it will deliver water in line with the design parameters under normal conditions and under natural hazard conditions (PDF p.3-4). Adequacy is the result of a calculation; reliability is the result of arrangement and operation.
Order of Preference for Supply Types
Section 2.1.1.2 ranks typical water supplies in order of preference for reliability (PDF p.2).
| Rank | Supply type |
|---|---|
| 1 | Direct connection to a reliable public or industrial (private) main |
| 2 | Connection to a gravity (elevated) tank on site |
| 3 | Fire pump taking suction from a closed-top tank |
| 4 | Fire pump taking suction from a reliable public or industrial main |
| 5 | Fire pump taking suction from an open-top reservoir (pond, lake, river) |
| 6 | Fire pump taking suction from a break tank |
The logic of the list is simple: the more equipment in between, the higher the chance of failure. A main connection has no moving parts, while a pumped solution adds the pump, driver, controls and suction conditions to the chain. Pump selection itself is covered in the fire pump selection guide.
Eight Conditions That Undermine Reliability
Section 2.1.1.3 requires the water supply to be free of the following conditions (PDF p.2):
- A. Deterioration or seasonal fluctuation of the water source that reduces the available fire water below the demand
- B. Deterioration of equipment or materials through age or neglect
- C. Fire pumps that are unreliable because of their arrangement or condition
- D. Faulty installation or arrangement of equipment
- E. Use of fire protection equipment for purposes other than intended
- F. A history of impairments in the water supply system
- G. A history of delayed response to impairment conditions
- H. Exposure to unplanned outages from natural hazards (earthquake, wind, flood, freeze, brush fire, etc.)
Half of these eight items come from operation rather than hardware. What they look like on site is collected in inadequate water supply cases and closed valve failures.
When an Enhanced Water Supply Comes Up
Section 2.1.2 states plainly that the criteria in Section 2.1.1 are minimum criteria. Where there is an unwanted risk to property or operations and a higher level of reliability is desired, an enhanced water supply is considered (PDF p.2).
The data sheet's framing here is realistic: every water supply will at some point be out of service, either unexpectedly or for planned maintenance. Depending on the size and nature of the facility, even a short period without automatic protection can create an unacceptable risk (PDF p.3).
An enhanced supply is a supply that meets all of Section 2.1.1, backed up by a secondary supply. The order of preference is (Section 2.1.2, PDF p.3):
| Option | Definition |
|---|---|
| A | Two or more completely independent, physically separated supplies, each meeting the reliability and adequacy criteria, not subject to a common impairment |
| B | Two adequate supplies subject to a common impairment (example: one electric and one diesel pump taking suction from a common tank) |
| C | A single supply with redundancy within the system (example: an electric pump fed from the utility and from an emergency generator) |
| D | A secondary supply that is reliable but may not be fully adequate |
Risk Factors: Appendix C
Appendix C gives five risk factors for assessing whether enhanced reliability is needed, and states that the approach is not prescriptive: in some cases a single factor may be enough, in others more than one factor is needed (PDF p.4).
| Factor | Question asked | Section |
|---|---|---|
| Size and value | Is significant property value at risk? Would a fire spread through a single undivided building? | C.1.1, PDF p.4 |
| Business continuity | Would an uncontrolled fire have a serious business impact? Are rebuilding and equipment lead times long? | C.1.2, PDF p.4 |
| Occupancy | Does the occupancy have a history of frequent fires? Does the construction or occupancy feed rapid spread? | C.1.3, PDF p.4 |
| Arrangement and condition of the water supply | Are the mains very long, is the equipment old, is there a history of underground main breaks, is there an alternative feed? | C.1.4, PDF p.4 |
| Geographic location | Could infrastructure reliability and natural hazards such as earthquake, storm, freeze or flood take the supply out of service? | C.1.5, PDF p.5 |
The explanation in C.1.4 contains a practical detail: on a looped main fitted with suitable sectional valves, water can be routed around a leak, while damage to a single pipe from the source to the point of use can take protection out of service completely (PDF p.5). The example in C.1.5 follows the same logic: an electric pump fed by an overhead power line can be vulnerable to wind or ice storms.
What the Loss History Says
Section 3.1 gives two figures based on FM client loss history (PDF p.3):
- About 80% of sprinkler system failures result from inadequate valve supervision, impairment management, and inadequate testing and maintenance.
- A further 16% is attributed to the sprinkler system being shut off prematurely during the fire.
The same section adds that facilities with adequate sprinkler protection and a single, properly designed, installed, maintained and tested water supply have almost no history of uncontrolled fire loss. FM therefore recommends a single adequate and reliable water supply; additional considerations such as facility size, business continuity, occupancy, supply arrangement and geographic location can create a need for higher reliability and redundancy.
For the engineer the meaning of these two figures is clear: before adding a second pump, close the gaps in valve supervision and maintenance of the first supply. The testing and maintenance side is detailed in the DS 2-81 article.
Field Note
The emphasis of DS 3-29 and habits on site often pull in opposite directions. The discussion usually starts with "should we add a second pump", while the data sheet's own loss data ties the great majority of failures to valve supervision, impairment management and lack of maintenance (Section 3.1, PDF p.3). A second pump does not open a valve that was left closed.
The second point is items F and G of Section 2.1.1.3: a history of impairments and a history of delayed response weigh as much, in the data sheet's view, as hardware defects. The reliability of a water supply is therefore not a document but a recorded history. A facility that keeps no records of valve closures and response times cannot defend these items, even if its hardware is flawless.
Checklist
- Which of the six options in Section 2.1.1.2 the existing supply is has been recorded in writing
- The eight conditions A to H in Section 2.1.1.3 have been checked one by one and the findings recorded
- Valve supervision, impairment management and response times are being recorded
- Natural hazard exposure (earthquake, freeze, storm, flood) has been assessed specifically for the supply
- Whether the distribution main is looped or a single line, and whether sectional valves exist, has been established
- The five risk factors of Appendix C have been answered separately for the project
- If an enhanced supply is needed, it has been chosen in the A-D order of Section 2.1.2 and the risk of a common impairment questioned
- The relevant FM data sheets (3-2, 3-7, 3-10) have been applied separately for the tank, pump and underground main
Frequently Asked Questions
What is a reliable water supply under FM DS 3-29?
Under DS 3-29 Section 2.1.1.1, a reliable water supply is one arranged, installed and maintained in line with FM data sheets and the equipment manufacturer's requirements, with no history of repeated unplanned or unsupervised impairments in its operation.
What is the order of preference between water supply types?
DS 3-29 Section 2.1.1.2 ranks six options: 1) direct connection to a reliable public or industrial main, 2) a gravity (elevated) tank on site, 3) a fire pump taking suction from a closed-top tank, 4) a pump taking suction from a reliable main, 5) a pump taking suction from an open-top reservoir, 6) a pump taking suction from a break tank.
Is a single water supply enough?
According to DS 3-29 Section 3.1, yes: facilities with adequate sprinkler protection and a single adequate and reliable supply that is properly designed, installed, maintained and tested have almost no history of uncontrolled fire loss. FM therefore recommends a single adequate and reliable supply; the need for an enhanced supply is assessed with risk factors.
Why do sprinkler systems fail?
According to the FM client loss history in DS 3-29 Section 3.1, about 80% of sprinkler system failures result from inadequate valve supervision, impairment management, and inadequate testing and maintenance. A further 16% is attributed to the system being shut off prematurely during the fire.
References
- FM Property Loss Prevention Data Sheet 3-29, Reliability of Fire Protection Water Supplies, October 2017, Interim Revision April 2021. Sections used: Section 1.0 (PDF p.2), 2.1.1.1-2.1.1.3 (p.2), 2.1.2 (p.2-3), 3.1 (p.3), 4.1 (p.3), Appendix A (p.3-4), Appendix C.1.1-C.1.5 (p.4-5).
- FM Global, Property Loss Prevention Data Sheets: https://www.fmglobal.com/research-and-resources/fm-global-data-sheets
- selvi.org, FM Global DS 3-2: Water Tanks for Fire Protection
- selvi.org, FM Global DS 3-7: Fire Pumps Field Guide
- selvi.org, DS 2-81: Inspection, Testing and Maintenance
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Download MEP Calc on the App StoreFM Property Loss Prevention Data Sheet 3-29, Reliability of Fire Protection Water Supplies, October 2017, Interim Revision April 2021; clause and page references are listed under References. General information only: the current edition governs, and design must be carried out by a qualified engineer.