This article has been rewritten from the text of FM Global DS 8-9 (March 2010, Interim Revision April 2026); statements in the previous version such as "K115-K240 CMSA ceiling, K11.2 in-rack at 0.5-1 bar, one level every 3 m" are not in the data sheet and have been removed. Every value below is given with its DS 8-9 section, table or figure number.
1. What does "CMSA" mean in DS 8-9?
The revision history (Appendix B) explains that sprinklers are categorised as Suppression Mode (formerly ESFR), Control Mode Specific Application (formerly Large-Drop) and Control Mode Density Area (formerly Standard), but that the protection tables were reformatted by sprinkler type. In the current text every ceiling design sits in one table format: in Tables 2 to 11 the standard-response pendent (K11.2, K14.0, K19.6, K25.2), standard-response upright (K11.2, K16.8, K25.2) and 280 °F dry-system columns represent the "control mode" side, while the quick-response pendent and upright columns represent the "suppression mode" side. For example, Table 7 (Class 1-3, open-frame racks) gives, at a 9.0 m ceiling, standard-response pendent K11.2 18 @ 50 psi (3.5 bar), K14.0 18 @ 32 psi (2.2 bar), K19.6 9 @ 16 psi (1.1 bar) and K25.2 9 @ 10 psi (0.7 bar); in the same row quick-response pendent K25.2 reads 9 @ 20 psi (1.4 bar). The ceiling side is covered in the Storage sprinkler decision matrix; this article covers the in-rack side.
2. When are in-rack sprinklers needed? (Section 2.3.4.2, Figure 3)
Rack storage is protected either by a ceiling-only system or by a combination of ceiling and in-rack sprinklers (2.3.4.1). The need depends on commodity hazard, ceiling height, available water supply, the presence of solid shelves or open-top containers, and the width and location of flue spaces. The questions of Figure 3, in order:
- Does the rack arrangement qualify as open-frame per Section 2.2.3.2?
- Is there a ceiling-only option in the applicable table (Tables 7 to 11, 14a, 14b or 17b), and can the available water supply meet its flow and pressure demand?
- Will open-top containers be stored in the racks? (Are in-rack sprinklers recommended in Section 2.2.4?)
- Does the rack qualify as a rack with solid shelves greater than 64 ft² (6.0 m²)?
- Is the commodity Class 1-4 or cartoned plastics; does the storage height exceed 15 ft (4.5 m) or 10 ft (3.0 m); is the maximum ceiling over 30 ft (9.0 m)?
Every negative branch ends in "in-rack sprinklers will be needed". When they are needed, the six steps of Section 2.3.4.1.4 follow: horizontal arrangement (2.3.4.6), vertical increments (2.3.4.7), in-rack hydraulic design (2.3.4.8.1), ceiling design when supplemented by in-rack sprinklers (2.3.4.8.2), sprinklers per branch line for the ceiling system (Table 1) and hose demand and duration for the combined system (2.3.5).
3. Open-frame definition and flue spaces (Section 2.2.3.2)
Rack classes: single-row when the depth does not exceed 6 ft (1.8 m) and a minimum 4 ft (1.2 m) aisle separates it from adjacent racks; double-row when the depth exceeds 1.8 m but not 12 ft (3.7 m) with minimum 1.2 m aisles; otherwise multiple-row (2.2.3.2.1.1-3). Racks with grated, mesh or slatted shelves count as open-frame when the openings are at least 70 % of the shelf area and flue spaces are adequate; solid shelves not exceeding 20 ft² (1.9 m²) also count as open-frame (2.2.3.2.1.4-6). Rolled commodities are arranged so they cannot bulge into transverse flues (2.2.3.2.1.7). Racks not meeting these guidelines are treated as racks with solid shelves; the solid shelf dimension is defined by the surrounding flues: net 150 mm transverse flues (75 mm at rack uprights), net 75 mm longitudinal flues in double-row racks and net 150 mm longitudinal flues in multiple-row racks (2.2.3.2.1.9).
| Rack type | Adequate flue space options | Source |
|---|---|---|
| Single-row | Net 75 mm transverse flues at most every 1.4 m (Figure 2a); or net 150 mm transverse flues every 2.7 m (Figure 2b); with misaligned flues, vertically aligned net 150 mm flues every 1.4 m (Figure 2c) | 2.2.3.2.2.2 |
| Double-row | Net 75 mm longitudinal + net 75 mm transverse flues every 1.4 m (Figure 2d); or 75 mm longitudinal + 150 mm transverse flues every 2.7 m (Figure 2e); longitudinal flue under 75 mm: aligned 150 mm transverse flues every 1.5 m (Figure 2f); misaligned transverse flues: 75 mm longitudinal + aligned 150 mm transverse flues every 1.4 m (Figure 2g) | 2.2.3.2.3.2 |
| Multiple-row | Net 150 mm longitudinal flues every 1.5 m + net 150 mm transverse flues every 1.5 m (Figure 2h); or depth limited to 20 ft (6.1 m) by minimum 8 ft (2.4 m) aisles with 150 mm transverse flues every 1.5 m (Figure 2i) | 2.2.3.2.4.2 |
Where double-row and multiple-row racks are protected by in-rack sprinklers, flue spaces are not required for the tier directly above the sprinklers (2.2.3.2.3.4, 2.2.3.2.4.4).
4. In-rack sprinkler selection and position (Sections 2.3.4.3-2.3.4.5)
- Product: FM Approved in-rack sprinklers listed in the Approval Guide under "Storage Sprinklers (In-Racks)" (2.3.4.1.1).
- Temperature and response: 160 °F (70 °C) and quick-response for all in-rack installations (2.3.4.3.1-2).
- K-factor: minimum K8.0 (K115) when the design flow exceeds 30 gpm (115 L/min) (2.3.4.3.3).
- Water shields: when 2 levels are in the design; not needed where horizontal barriers or solid shelves block water from above (2.3.4.1.2-3).
- System type: wet, dry, preaction or refrigerated area; grid piping only for wet (2.3.4.4). Maximum water delivery time for a dry-type in-rack system is 60 s to the most remote sprinkler (2.3.4.8.1.4).
- Position: all in-rack sprinklers within the rack structure (2.3.4.5.1); face sprinklers no more than 18 in (450 mm) horizontally from the rack face (2.3.4.5.2). In a single-row rack within 300 mm of a wall, sprinklers may be outside the rack, within 150 mm of the structure and not more than 75 mm offset from the transverse flue intersection they protect (2.3.4.5.3-4). Sprinklers are not placed directly behind rack uprights (2.3.4.5.5).
- Vertical position: at each level the deflector is at least 6 in (150 mm) above the top of storage and at or just below the bottom of the fully loaded horizontal support; where 150 mm cannot be provided, additional sprinklers are needed in single- and double-row racks (2.3.4.5.6).
- Mechanical protection: piping and sprinklers are arranged to avoid material-handling damage; a double horizontal support at the rack face and a single one in the longitudinal flue is one method (2.3.4.5.8, Figure 4).
5. Horizontal arrangements: IRAS(EO) and IRAS(E) (Section 2.3.4.6)
There are two basic arrangements: IRAS(EO), sprinklers at every other transverse flue intersection between pallet loads; IRAS(E), sprinklers at every transverse flue intersection (2.3.4.6.1.1). Which one is acceptable depends on rack type, commodity, open-top containers, maximum ceiling height, whether the 150 mm vertical clearance is provided and whether horizontal barriers are installed (2.3.4.6.1.2); the decision comes from the flowcharts in Figure 5 (single-row ≤ 0.9 m), 5a (single-row > 0.9 m), 6 (double-row ≤ 2.7 m), 6a (double-row > 2.7 m) and 7 (multiple-row). The figures show pallet loads as nominal 20 ft² (2.0 m²) squares.
- Where IRAS(EO) is acceptable but the distance between every other transverse flue exceeds 10 ft (3.0 m), sprinklers are installed in every flue and, if needed, between flues so that the spacing does not exceed 3.0 m; where it is under 4 ft (1.2 m), no more than 2 transverse flues are left between sprinklers (2.3.4.6.4-5).
- Where IRAS(E) is acceptable but the flue spacing exceeds 8 ft (2.4 m), additional sprinklers keep the spacing at or below 2.4 m; where it is under 2 ft (0.6 m), no more than 1 flue is left between sprinklers (2.3.4.6.6-7).
- With solid shelves, sprinklers are positioned as close to the shelf openings as possible (2.3.4.6.8).
- Horizontal barriers generally reduce the number of sprinklers per level but not the number of levels (2.3.4.6.1.5). Barriers are minimum 22 ga (0.7 mm) sheet metal or 3/8 in (10 mm) plywood, spanning aisle face to aisle face and upright to upright; a maximum 75 mm gap is acceptable at the uprights (2.3.4.6.1.6). Sprinklers installed with barriers need not be positioned relative to transverse flues unless the 150 mm clearance is missing or open-top containers are present (2.3.4.6.10.1). Loads may extend at most 75 mm beyond the barrier edge; beyond that, an arrangement with face sprinklers is used (2.3.4.6.10.2-3).
6. Vertical increments (Section 2.3.4.7, Figure 15)
| Condition | In-rack vertical increment |
|---|---|
| Open-top containers | Per Section 2.2.4 |
| Solid shelves > 64 ft² (6.0 m²) | Below every such shelf; maximum 10 ft (3.0 m) of storage above the top level |
| Solid shelves > 20 ft² (2.0 m²) | Not exceeding 15 ft (4.5 m) where the highest hazard is below cartoned plastics; otherwise 10 ft (3.0 m) |
| Open-frame, highest hazard below Class 3 | Not exceeding 25 ft (7.5 m) |
| Open-frame, below cartoned unexpanded plastics | Not exceeding 20 ft (6.0 m) |
| Open-frame, below cartoned expanded plastics | Not exceeding 15 ft (4.5 m) |
| Open-frame, uncartoned plastics | Not exceeding 10 ft (3.0 m) |
The increments apply to levels below the top of storage as well as to any level installed above it (2.3.4.7.2). Where the first tier rests on a horizontal support rather than the floor, the distance may be measured from the underside of the first-tier pallet load (2.3.4.7.3).
7. Hydraulic design: Table 12 and Table 13 (Section 2.3.4.8)
| Commodity | Storage above top IRAS level | Installed IRAS levels | Sprinklers in design | Minimum flow per sprinkler |
|---|---|---|---|---|
| Class 1-3 | ≤ 10 ft (3.0 m) | 1 | 6 | 22 gpm (85 L/min) |
| 2 or more | 10 (5 on 2 levels) | |||
| Class 4 and plastics | ≤ 10 ft (3.0 m) | 1 | 8 | 30 gpm (115 L/min) |
| 2 or more | 14 (7 on 2 levels) |
Minimum operating pressure 7 psi (0.5 bar) (2.3.4.8.1.3); the in-rack demand is hydraulically balanced with the ceiling demand at the point of connection (2.3.4.8.1.2). The ceiling system is designed from Table 13, which states, by commodity, IRAS arrangement (EO/E), storage height above the top IRAS level (1.5 or 3.0 m) and clearance between the top of storage and the ceiling, which protection table (7, 8 or 10) and which ceiling height row to use. Examples: Class 1-3, IRAS(EO), 1.5 m of storage above the top level and 1.5 m clearance → Table 7, 10 ft (3.0 m) row; clearance up to 6.0 m → Table 7, 20 ft (6.0 m) row. Class 4 and cartoned plastics use the 10, 15 or 20 ft rows of Table 8; uncartoned plastics the 15-20 ft rows of Table 8 or 10. Where the clearance exceeds 6.0 m, Section 2.3.3.7.3 applies. With horizontal barriers or sprinklers under solid shelves, the IRAS(E) row is used (2.3.4.8.2.2).
8. Special applications (Section 2.3.6)
- In-rack sprinklers only in the longitudinal flue (2.3.6.3): Class 1-4 and cartoned plastics, wet pipe, open-frame, double-row depth ≤ 2.7 m, at every transverse flue intersection (Figures 11/12), vertical increments not exceeding 12 ft (3.6 m), storage above the top level ≤ 3.0 m; in-rack design per Table 12, ceiling per Table 13, hose per Table 14. Alternative: quick-response sprinklers at every other intersection, staggered vertically, with all intersections protected at increments not exceeding 24 ft (7.2 m).
- Longitudinal sprinklers plus horizontal barriers (2.3.6.4): up to uncartoned unexpanded plastics; longitudinal sprinkler spacing not exceeding 5 ft (1.5 m), vertical 3.6 m; barriers above the lowest level and at every other level.
- Single in-rack level with K200 or larger quick-response pendent ceiling sprinklers, ceilings up to 13.5 m (2.3.6.5): the in-rack level within one-half to two-thirds of the storage height, minimum 60 gpm (230 L/min) from the most remote 8 sprinklers; ceiling design from the 40 ft (12.0 m) row; for uncartoned unexpanded plastics K14.0 12 @ 90 psi (6.2 bar), K16.8 12 @ 63 psi (4.3 bar).
- Alternative in-rack designs (2.3.6.6): wet pipe; standard-coverage, quick-response, pendent Storage (ceiling) sprinklers minimum K22.4 (K320), K14.0 (K200) where the flow is ≤ 380 L/min; horizontal spacing 27 in (700 mm) to 4.5 ft (1.4 m); vertical increments 30 ft (9.0 m) for cartoned expanded and uncartoned plastics, 40 ft (12 m) for Class 1-4 and cartoned unexpanded plastics; design per Table 15 (4-5 in single-row, 6 in double- and multiple-row; for uncartoned expanded plastics plus 4 in the adjacent rack where the aisle is under 2.4 m) and Table 16 (9.0 m vertical installation: Class 1-4 and cartoned unexpanded K14.0 at 65 gpm / 250 L/min; cartoned expanded K14.0 at 100 gpm / 380 L/min; uncartoned plastics K22.4 at 120 gpm / 455 L/min; 12 m vertical: K22.4 at 455 L/min); hose 950 L/min, duration 60 min; in-rack and ceiling systems designed independently, no balancing. For the ceiling design the top in-rack level is treated as the floor (Figure 22).
- K25.2EC pendent in-rack sprinklers with horizontal barriers (2.3.6.8): Class 1-4 and cartoned unexpanded plastics, closed-top containers, wet pipe; linear spacing 2.1-2.5 m, area 4.6-6.3 m²; vertical distance not exceeding 9.0 m; deflector not more than 175 mm below the barrier and at least 225 mm above the top of storage; 160 gpm (605 L/min) from the most remote sprinkler; 3-8 sprinklers per Table 17a; no balancing with the ceiling where overhang is ≤ 75 mm.
- Scheme 8-9A (2.3.4.9): a dedicated rack for small amounts of high-challenge commodities, horizontal barriers (maximum 12 ft / 3.6 m apart in open-frame racks, every level with solid shelves) and quick-response in-rack sprinklers; the protection extends one pallet load beyond the high-challenge area or a vertical barrier separates it.
The retrofit design for uncartoned plastics in Section 2.3.6.7 (minimum K22.4 quick-response pendent face sprinklers, 455 L/min, Table 17) is described in the plastic storage article.
Field note: the three most common in-rack non-conformities concern flue spaces: transverse flues closed by carton overhang, longitudinal flues shrinking below 75 mm, and sprinklers hidden behind uprights. DS 8-9 defines all of them by dimension (2.2.3.2, 2.3.4.5.5) and asks for a physical means to keep flues open where they cannot be maintained (2.2.3.2.1.7). The loss history section (3.2) calls in-rack sprinklers used with ceiling sprinklers "overwhelmingly successful"; failures always come from installation deficiencies: inadequate water supply, closed valves, obstructed piping, missing sprinklers.
Quick checklist
- Rack type (single/double/multiple-row) and open-frame conditions (70 % open shelves, solid shelves ≤ 1.9 m², flue spaces) documented
- Figure 3 worked through; if in-rack sprinklers are needed, the six steps of 2.3.4.1.4 applied in order
- In-rack sprinklers FM Approved, 70 °C, quick-response; minimum K115 above 115 L/min; water shields for two levels
- Face sprinklers ≤ 450 mm, deflector ≥ 150 mm above the top of storage, not behind uprights
- IRAS(EO)/IRAS(E) from the applicable flowchart; 3.0 / 2.4 m maximum spacing rules met
- Vertical increments per Figure 15 (7.5 / 6.0 / 4.5 / 3.0 m); ≤ 3.0 m of storage above the top level
- In-rack design per Table 12 (6/10 or 8/14 sprinklers, 85 or 115 L/min), minimum 0.5 bar
- Ceiling design from the table and row selected by Table 13; hydraulic balance at the connection
- Hose demand and duration per Table 14; 60 s water delivery for dry in-rack systems
- Horizontal barriers, if any: 0.7 mm sheet / 10 mm plywood, ≤ 75 mm gap at uprights, load overhang ≤ 75 mm
Frequently Asked Questions
When does FM DS 8-9 require in-rack sprinklers?
Per Section 2.3.4.2 and Figure 3 the need depends on commodity hazard, ceiling height, available water supply, solid shelves or open-top containers, and flue spaces. The main questions: are the racks open-frame, is there a ceiling-only option in the tables and can the water supply meet it, are open-top containers present, do solid shelves exceed 6.0 m², does storage exceed 3.0 m or 4.5 m.
Which K-factor and temperature rating are used for in-rack sprinklers?
Section 2.3.4.3: 160 °F (70 °C), quick-response FM Approved in-rack sprinklers; minimum K8.0 (K115) when the design flow exceeds 115 L/min. Water shields when two levels are in the design; not needed with horizontal barriers or solid shelves.
How many sprinklers and what flow are used in the in-rack hydraulic design?
Table 12: Class 1-3, 6 sprinklers for one level or 10 (5 on 2 levels) for two or more, 85 L/min; Class 4 and plastics, 8 or 14 sprinklers (7 on 2 levels), 115 L/min. Storage above the top level does not exceed 3.0 m, minimum pressure 0.5 bar, hydraulic balance with the ceiling.
What is the maximum vertical distance between in-rack sprinkler levels?
Figure 15: with solid shelves over 6.0 m², below every shelf and 3.0 m of storage above the top. In open-frame racks by hazard: 7.5 m (below Class 3), 6.0 m (below cartoned unexpanded plastics), 4.5 m (below cartoned expanded plastics), 3.0 m (uncartoned plastics). With solid shelves over 2.0 m², 4.5 or 3.0 m.
What are the minimum flue space dimensions?
Section 2.2.3.2: single-row racks 75 mm transverse flues every 1.4 m or 150 mm every 2.7 m; double-row racks 75 mm longitudinal + 75 mm transverse every 1.4 m or 150 mm transverse every 2.7 m, and 150 mm transverse every 1.5 m where the longitudinal flue is under 75 mm; multiple-row racks 150 mm longitudinal and transverse flues every 1.5 m. No flue is required for the tier directly above in-rack sprinklers.
References
- FM Global Property Loss Prevention Data Sheet 8-9, Storage of Class 1, 2, 3, 4 and Plastic Commodities, March 2010, Interim Revision April 2026: Section 2.2.3 and Figures 2a-2i (p.10-22), 2.2.4 (p.23-26), 2.3.4.1-2.3.4.5 and Figures 3-4 (p.41-43), 2.3.4.6 and Figures 5-14 (p.44-55), 2.3.4.7 and Figure 15 (p.55-56), 2.3.4.8 and Tables 12-13 (p.57-58), 2.3.4.9 (p.58), 2.3.5 and Table 14 (p.62-63), 2.3.6.3-2.3.6.6 and Tables 15-16 (p.66-71), 2.3.6.8 and Table 17a (p.76-79), 3.2 and Table 18 (p.80), Appendix B (p.99)
- FM Global data sheets: fmglobal.com
Values are transcribed from the FM Global data sheet above with section, table and figure numbers. This article is for general information; the design must be based on the FM Approval listing of the selected product and the current data sheet text, carried out by a qualified engineer and accepted by the insurer.