FM Global DS 3-7 Fire Pumps: A Field Guide

On a European-owned logistics warehouse project, the third-party insurance survey arrives with an unexpected finding: the pump room sits inside the main building, separated only by one-hour construction, and is not even sprinkler protected. The project had been approved against BYKHY Article 93 and TS EN 12845, and the mechanical team had also laid out the pump room to NFPA 20. The surveyor cited FM Global DS 3-7 Section 2.2.1.2: the pump should be in a detached noncombustible building at least 15 m from the protected buildings; where that is not feasible it should be separated from the rest of the building by two-hour fire-rated construction, reduced to one hour only when the pump room and adjacent areas are sprinkler protected. The design was revised at significant cost. This article summarises DS 3-7 (April 2012, Interim Revision April 2025) in practical terms — the rules that make sure a fire pump is in the right place, with the right connections and the right control logic.

Pump Room Location and Construction

FM Global's strictest requirement concerns pump room separation, given at three levels:

• Preferred: a detached building of noncombustible construction at least 15 m from the protected building.
• Where a detached building is not feasible: locate the pump room away from fire and falling-debris exposure, provide an access door along an exterior wall, and separate the pump from all other areas by two-hour fire-rated construction.
• Sprinklered case: where the pump room and adjacent areas are sprinkler protected, the separation may be reduced to one hour.

The pump room may not be located within or attached to an unprotected building (2.2.1.2 D). Sprinklers are provided over engine-driven pumps (2.2.1.5). The pump room may not be used for storage — the most frequently violated clause on site, where material stacked in a corner produces an immediate non-conformance at survey.

Alarm Requirements

DS 3-7 requires the alarm set to report to a constantly attended location. For an electric pump, four alarms as a minimum:

• Pump (driver) running
• Loss of power
• Controller connected to an alternate power source (battery bank/generator, where applicable)
• Failure to start

For a diesel pump the four alarms reporting to the constantly attended location are: diesel driver running, loss of power (AC and/or DC), controller off/in manual/in test position, and failure to start. In addition, four visual or audible notifications are provided (2.2.1.12.1): overspeed, low oil pressure, high coolant temperature and engine failure. These four need not be monitored at a central location and may be combined into a single general pump trouble alarm. Alarm operation is verified at least annually, for example during the annual flow test (2.2.1.12.2).

Suction Piping — The Red Lines

Suction piping is the section most often rejected at survey. The key rules:

• Positive pressure (2.3.2.1): suction pressure must remain positive at all times over the whole flow range. Split case, end suction and in-line centrifugal pumps are not used where a static suction lift is required (2.4.1.1); where the water level is below the discharge flange a vertical shaft turbine pump is used (2.4.2.1).
• Friction limit (2.3.2.2): friction loss between the suction tank and the pump inlet must not exceed 0.4 bar (6 psi) at 150% of rated flow, including the equivalent lengths of elbows and fittings. This prevents inadequate NPSH so the pump does not cavitate even at low tank level.
• Eccentric reducer (2.3.2.3): where the suction pipe is larger than the pump suction flange, they are connected with an eccentric tapered reducer arranged so that no air pocket can form (Figures 2.3.2.3-1 and 2.3.2.3-2).
• Elbow clearance (2.3.2.4): on a horizontal split-case pump, no elbow or tee with its centreline plane parallel to the pump within 10 suction pipe diameters of the suction flange. Otherwise the inlet flow is asymmetric and the impeller is unbalanced.
• Velocity limit (2.3.2.5): velocity must not exceed 4.6 m/s (15 ft/s) at 150% of rated flow; with a common suction source all pumps are assumed to flow together. Per Table 2.3.2.5-1 this corresponds to 5,000 L/min in DN150, 8,860 L/min in DN200 and 13,850 L/min in DN250 pipe.
• Prohibited devices (2.3.2.7-2.3.2.9): nothing that could stop or restrict pump starting or discharge may be fitted in the suction piping, including backflow preventers; low suction pressure cut-off and regulating valves are not installed, and monitoring devices that raise an alarm are used instead. Backflow preventers are located on the discharge side whenever possible (2.3.2.8).

Discharge Piping and Relief Valves

• Avoid first (2.3.4.1): relief valves are avoided wherever proper system design allows, are not used to relieve excess pressure at low flows in normal operation, and are not used on pump and tank configurations.
• When a relief valve is required (2.3.4.2): if the net rated shutoff (churn) pressure plus the maximum static suction pressure could exceed the rated pressure of the system components, usually 12 bar (175 psi), a main relief valve is provided. On high-rise projects this is usually the case.
• Installation (2.3.4.3): an FM Approved relief valve is fitted between the pump and the discharge check valve so that it can be removed without disturbing the pipework. Its discharge is readily visible or easily detectable by the pump operator and is piped preferably outside the building or back to the suction tank, but never to the pump suction or supply piping. No shutoff valve is installed in the relief valve supply or discharge piping; sizes are in Table 2.3.4.3-1.
• PRV prohibition (2.3.5.1): pressure reducing valves are not installed on the pump suction or discharge. DS 3-7 also asks for high-rise systems to be designed so that pressure reducing valves are not needed; where unavoidable, FM Approved valves are installed per DS 3-11 (2.2.2.3).

Pump Sizing and Selection

The governing DS 3-7 rule is that the pump must deliver at least 65% of rated pressure at 150% of rated flow (Section 2.4). So a pump rated 5,000 L/min at 10 bar must still produce at least 6.5 bar at 7,500 L/min. The 140% limit on churn pressure is not in DS 3-7; it comes from BYKHY Article 93 (see below). DS 3-7 sizes the pump to Qmax: one 100% Qmax pump or three 50% Qmax pumps, with up to 140% of rated flow usable with a single pump and up to 110% with multiple pumps (2.4.6).

• Split case, end suction and in-line centrifugal: not used where a static suction lift is required (2.4.1.1). An air release valve of at least 12.7 mm discharging to atmosphere is provided, except on end suction pumps with top discharge and vertically mounted split case pumps, which vent naturally (2.4.1.2).
• Vertical shaft turbine: used where the water level lies below the discharge flange or the supply pressure is insufficient to feed the pump suction (2.4.2.1) — typical for wells, reservoirs and wet pits. Water below the minimum submergence is not counted in the supply duration (2.4.2.3).
• Positive displacement: used for pumping water (water mist), foam concentrates or additives; liquid viscosity is considered in selection (2.4.3.1).

Mechanical seals (2.4.5) are used only on pumps specifically FM Approved for mechanical shaft seals, and only where all of the following apply: the suction water is clean and no water source is an open body of water (retention pond, lake or river); suction pressure is positive at all flows; a spare split seal set is kept on site; and the pump is tested weekly.

Controllers, Sequence Starting and Weekly Testing

An FM Approved fire pump controller is mandatory. The key control rules:

• Automatic start, manual stop (2.4.7.2-2.4.7.3, 2.4.10.1): the pump starts automatically on pressure or flow but is stopped manually. Whenever it starts, appropriate personnel attend the pump house, confirm the set is running correctly and that the start cause has cleared and any fire emergency is resolved before stopping it. Any run-period timer is defeated by the method in the controller manual, not by setting it to zero.
• Jockey pump required: a jockey pump makes up normal leakage and small pressure drops. The fire pump may never serve as pressure maintenance, or it wears out through repeated short runs.
• Sequence starting: where two or more pumps operate in parallel, simultaneous starting is prevented. If one pump fails to start, the next is not prevented from starting, so redundancy survives a failure.
• Weekly test: where the controller has an automatic weekly test feature, it may not run unattended. A technician is present in the pump room, watches the test data and can intervene.

Practical Differences From NFPA 20

• Equipment approval: NFPA 20 accepts listed components; DS 3-7 accepts only FM Approved pump, driver, controller and relief valve.
• Pump room separation: under NFPA 20 (2025) Table 4.14.1.1.2, one-hour construction applies only when the pump room and the exposing building are fully sprinklered, two hours when the building is not sprinklered (50 ft (15.3 m) separation being the alternative in both cases), and high-rise buildings need two hours or 50 ft (15.3 m) (4.14.1.1.1); where a detached building is not feasible FM requires two hours, or one hour when the pump room and adjacent areas are sprinklered.
• Separation distance: NFPA 20 (2025) gives 50 ft (15.3 m) as the alternative to fire-rated separation and for outdoor pump units (Table 4.14.1.1.2, 4.14.1.2.1); FM prefers a detached building at least 15 m away.
• Test regime: under FM DS 2-81 Table 2.9.1.1, diesel pumps are started in automatic mode and churned weekly, electric pumps monthly, with an annual performance test. The Appendix C comparison in DS 2-81 shows NFPA 25 also calling for weekly diesel and weekly/monthly electric churn runs and an annual performance test. DS 3-7 adds that an automatic weekly test timer is never relied on without attendance (2.4.9.1).
• Variable speed pumps: NFPA 20 permits them under defined conditions; DS 3-7 Section 2.4.16 accepts only FM Approved variable speed electric fire pump controllers and calls for a main relief valve where the uncontrolled net churn pressure plus maximum static suction pressure can exceed 16 bar (232 psi).

A Recurring Surprise at Survey

A common pattern on industrial sites: a diesel fire pump is installed to a design accepted by the local authority under BYKHY and also checked against NFPA 20. Months later a customer supplier audit or an insurer survey reports that the installation does not comply with DS 3-7, typically for three reasons:

• The pump room is unsprinklered, with only one-hour separation where FM requires two
• A backflow preventer sits in the suction line, which FM prohibits — it belongs on the discharge
• Only the running alarm reports to the attended location; the loss of power, controller off/manual/test and failure to start alarms that FM requires are missing

The remedy is straightforward but disruptive: sprinklers added over the pump room, the backflow preventer relocated, and the alarm panel connected to the building management system. Taking DS 3-7 as the baseline at design stage would have covered all three at a fraction of the cost.

When FM Compliance Is Required in Practice

The Turkish fire regulation (BYKHY) sets fire pump performance rules itself in Article 93: churn (zero-flow) head at most 140% of rated head, head at 150% of rated flow not below 65% of rated head, use for system demands up to 130% of rated flow, and a standby pump of equal capacity where a single pump is used. Under Article 96(5) the pump arrangement feeding the sprinklers is also part of the TS EN 12845 design. The regulation does not reference NFPA 20 or FM data sheets; these apply as an added layer that must still meet its minimum requirements. FM compliance becomes binding through other routes:

• European-owned logistics warehouses operating to a group standard
• Industrial facilities inside an international insurance portfolio
• Automotive and electronics plants subject to OEM supplier audit
• Data centres pursuing certification, where FM compliance is expected alongside

The practical advice is to ask the question explicitly at design stage: will FM compliance be required? Even if the insurer has not been selected, the owner may move the portfolio within a few years, and designing FM compliant from the start avoids a costly retrofit later.

Quick Checklist

• Pump room detached at 15 m, or separated by two-hour construction (one hour if the pump room and adjacent areas are sprinklered)
• No storage in the pump room; sprinklers above engine-driven pumps
• Four alarms reporting to a constantly attended location for both electric and diesel pumps, plus four local notifications on diesel pumps (overspeed, oil pressure, coolant temperature, engine failure)
• Positive suction pressure with friction below 0.4 bar at 150% flow
• Eccentric reducer, elbows/tees at least 10 diameters from a split-case pump, velocity at 150% flow not above 4.6 m/s
• No backflow preventer, cut-off or regulating valve on the suction side
• Relief valve where required, FM Approved, not returned to suction
• Pump curve: at least 65% pressure at 150% flow (DS 3-7); no more than 140% at churn (BYKHY Article 93)
• Automatic start, manual stop, with a separate jockey pump
• Sequence starting for parallel pumps
• Weekly test never run unattended
• All components FM Approved

Frequently Asked Questions

Why does FM require a detached pump room or two-hour separation?

Because the pump must survive the fire it is there to fight. A pump room inside the protected building, separated by one hour and unsprinklered, can be lost early in an incident, taking the water supply with it. A detached building at 15 m, or two-hour separation (one hour where the pump room and adjacent areas are sprinklered), keeps the pump available for the duration.

Why is a backflow preventer prohibited on the pump suction?

Anything on the suction side that can restrict flow threatens the pump's ability to start and run at full demand, and a backflow preventer adds significant friction loss exactly where NPSH margin is scarce. Where one is required for water authority reasons, it goes on the discharge side instead.

Why an eccentric rather than a concentric reducer at the suction?

A concentric reducer creates a high point at the top of the pipe where air collects, and that air pocket is drawn into the pump when it starts, causing loss of prime. DS 3-7 therefore requires an eccentric tapered reducer arranged so that no air pocket forms (2.3.2.3); in practice this means the flat side up.

Why must the fire pump be stopped manually?

So that someone confirms the emergency is genuinely over before the water supply is removed. An automatic stop at churn pressure can shut the pump down while the fire is still developing, and it also causes repeated short-cycle running that wears the pump. DS 3-7 therefore arranges the controller for manual stopping and has any run-period timer defeated (2.4.7.3, 2.4.10.1).

What does the 150% at 65% rule actually mean?

It defines the required shape of the pump curve. DS 3-7 Section 2.4 requires at least 65% of rated pressure at 150% of rated flow; the limit of 140% at churn comes from BYKHY Article 93, not from DS 3-7. This guarantees the pump still delivers useful pressure if actual fire demand exceeds the design figure, rather than collapsing off the end of its curve.

How does FM DS 3-7 differ most from NFPA 20 in practice?

Equipment approval and pump room separation. FM accepts only FM Approved pumps, drivers, controllers and relief valves, where NFPA accepts listed components. And FM requires a detached building or two-hour separation (one hour if the pump room and adjacent areas are sprinklered), where NFPA 20 (2025) accepts one hour only when the pump room and the exposing building are fully sprinklered (Table 4.14.1.1.2). Those two differences account for most of the findings raised at survey.

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