FM Global DS 8-9 is the heart of warehouse sprinkler design. Commodity class (from DS 8-1) plus storage height plus rack configuration determine the design route: ceiling-only for low-piled Class 1 and 2, CMSA with in-rack sprinklers for intermediate cases, and ESFR for high storage. This is the practical summary of a long and detailed data sheet.
The Design Flow
- Establish the commodity class using DS 8-1
- Measure the storage height, current and projected five years ahead
- Identify the rack type: palletised, single row, double row or multi-row rack
- Establish the ceiling height
- Select the design route from the DS 8-9 tables
- Carry out the hydraulic calculation, water demand and tank sizing
Storage Height and Design Selection
| Storage height | Class 1–2 | Class 3–4 | Plastics |
|---|---|---|---|
| Up to 3.7 m | Ceiling-only | Ceiling-only | Ceiling-only or CMSA |
| 3.7–7.6 m | Ceiling-only or CMSA | CMSA or ESFR | CMSA with in-rack, or ESFR |
| 7.6–12.2 m | CMSA or ESFR | ESFR with in-rack | ESFR with in-rack at every level |
| Above 12.2 m | ESFR | ESFR with in-rack | ESFR, in-rack and fire wall zoning |
ESFR Design
- K-factor: K200 up to 7.6 m, K360 up to 10.7 m, K480 up to 13.7 m storage
- Pressure: 3.5 to 5.2 bar depending on the K-factor
- Operating count: 12 sprinklers
- Roof slope: essentially flat; ESFR is very sensitive to slope
- Roof venting: not compatible with ESFR
- Duration: 60 minutes
CMSA Design
- K-factor: K115 to K240
- Pressure: 2 to 4 bar
- Operating count: 15 to 30 sprinklers
- Roof slope: considerably more tolerant than ESFR
- Duration: 60 to 90 minutes
In-Rack Sprinklers
- Required for multi-row racking and high storage
- Horizontal and vertical spacing taken from the DS 8-9 tables
- Flue space of at least 150 mm limits vertical fire spread
- K11.2 is the typical in-rack head, at low operating pressure
- Maintenance is difficult, so ESFR is preferred where the building allows it
Flue Space Management
- Transverse flue: across the rack, at least 150 mm
- Longitudinal flue: between back-to-back rows, at least 75 to 100 mm
- Are they clear? This is the most common site violation — cartons overhang the rack edge and close the flue. Annual photographic records are the practical control
Quick Checklist
- Commodity class established per DS 8-1
- Storage height with a five year projection
- Rack type and ceiling height documented
- Design route selected from the DS 8-9 tables
- Flue space minimums maintained
- In-rack spacing correct where required
- Hydraulic calculation and tank capacity completed
Frequently Asked Questions
How do I decide between ceiling-only, CMSA and ESFR?
The decision follows commodity class and storage height together. Low-piled Class 1 and 2 can be ceiling-only. Intermediate storage of Class 3 and 4 moves to CMSA or ESFR. Above roughly 7.6 m, and for plastics at almost any height, ESFR with in-rack sprinklers becomes the route. The DS 8-9 tables give the specific combination.
Why does storage height matter more than floor area?
Because a warehouse fire grows vertically through the flue spaces, not across the floor. Doubling the stack height changes the fire dynamics fundamentally, whereas doubling the floor area simply repeats the same design. That is why storage height, not building size, governs sprinkler selection and water demand.
What is flue space and why does it fail so often?
Flue spaces are the vertical channels within and between racks that let water down into the array and hot gases up to the ceiling heads. They fail because cartons overhang the rack edge during normal operation. A fully compliant design can then be ineffective, which is why annual photographic surveys form part of the protection.
Why avoid in-rack sprinklers where possible?
In-rack pipework is exposed to forklift damage, hard to inspect, and adds a continuing maintenance burden for the life of the building. Where the roof geometry allows ESFR as a ceiling-only solution, that is generally the lower total cost of ownership even if the ceiling heads themselves are more expensive.
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Download MEP Calc on the App StoreFM Global Property Loss Prevention Data Sheet DS 8-9 (Storage of Class 1, 2, 3, 4 and Plastic Commodities), design tables; DS 8-1 (Commodity Classification); NFPA 13 storage chapters.