CMSA Design Criteria in Detail

In CMSA design, matching the commodity and storage arrangement to the product listing matters more than anything else. K-factor selection, 15–30 operating sprinklers, in-rack hydraulic balance, pressure management — step by step. Where ESFR cannot be used, CMSA is what saves the project.

At a tyre distribution warehouse, CMSA K200 was selected because a 12 % roof slope ruled ESFR out. The design described the commodity as "tyres stacked on tread, 6 m". The manufacturer's listing, however, read "tyres, palletized, ≤ 6 m" — that is, on pallets. On site the tyres were stacked directly, without pallets. The insurer recorded a specific-application mismatch, and the heads had to be replaced with a product listed for "tyres, columnar, ≤ 6 m", with a two-week delay. A product listing has to describe the storage geometry exactly as built.

Ten-step CMSA design flow

1. Establish storage height and commodity classification
2. Confirm why ESFR is unsuitable (roof > 5 %, large skylights, obstructions)
3. Match commodity and storage arrangement to the manufacturer's listing
4. Select the K-factor (K115–K240 depending on commodity)
5. Determine the number of design sprinklers (15–30)
6. Set the pressure, 2–4 bar, from the product listing
7. Coordinate in-rack protection where storage exceeds 6 m
8. Calculate water demand for 60–90 min
9. Produce the hydraulic report
10. Obtain insurer approval

Commodity, K-factor and design sprinkler table

Commodity	Storage height	K-factor	Pressure	Design heads
Tyres, columnar	≤ 6 m	K160	3.5 bar	20
Tyres, palletized	≤ 6 m	K160	3.0 bar	15
Paper rolls on end	≤ 8 m	K200	3.0 bar	15
Paper rolls on side	≤ 6 m	K160	2.4 bar	15
Class III cartons	≤ 7.6 m	K160	2.4 bar	15
Group A plastics, palletized	≤ 6 m	K200	3.5 bar	20
Mixed plastics	≤ 6 m	K240	3.5 bar	30
Idle timber pallets	≤ 6 m	K160	3.0 bar	15

Worked water demand example

Tyres stored columnar, K160, 3.5 bar, 20 design heads:

• Per sprinkler: Q = K × √P = 160 × √3.5 ≈ 299 L/min
• 20 sprinklers: 20 × 299 = 5980 L/min
• In-rack, 6 heads at K80 and 2 bar: 6 × 80 × 1.41 ≈ 677 L/min
• Total: 5980 + 677 = 6657 L/min
• Duration: 90 min
• Water volume: 6657 × 90 ≈ 599 000 L, i.e. about 600 m³
• Tank: 600 m³ plus margin, so around 660 m³
• Pump pressure: 3.5 + 2 (friction) + 1.2 (static) + 0.5 (margin) = 7.2 bar

In-rack coordination

Storage height	In-rack levels	Horizontal spacing
≤ 6 m	None (ceiling only)	—
6–9 m	1 (at about 3 m)	3 m
9–12 m	2 (at about 3 m and 6 m)	3 m
12–15 m	3 (at about 3 m, 6 m and 9 m)	2.4 m

Hydraulic balance: ceiling plus in-rack

• Ceiling pressure is the highest in the system
• In-rack pressure must sit below the ceiling pressure
• Calculate as parallel branches — the ceiling branch and the in-rack branch
• Total flow: 20 ceiling heads plus the six worst-case in-rack heads
• Use hydraulic software to balance the two parametrically
• The insurer's report must identify the critical point

Field error — in-rack hydraulics left out of the calculation

A paper warehouse was designed with CMSA at ceiling plus in-rack heads, but the hydraulic analysis covered only the ceiling branch. During commissioning water reached the in-rack heads at 0.8 bar against a requirement of 2 bar. The main had to be increased from DN150 to DN200 and a separate feed branch added. Ceiling plus in-rack always demands a parallel-branch calculation.

Checking the listing

• The commodity is named explicitly (tyres, paper rolls and so on)
• The storage geometry is stated (palletized, columnar, on side)
• The storage height limit is given
• K-factor and pressure are specified
• The number of design sprinklers is stated
• Roof slope limit is given
• Skylight limit is given
• Obstruction tolerance is stated

Turkish regulation and local practice

BYKHY contains no CMSA-specific provision; the EN 12845-2 or NFPA 13 reference is sufficient. Turkish tyre and paper manufacturers commonly use CMSA, frequently with foam-water. When procuring listed heads, products carrying both FM Approval and EN certification are preferred; domestic insurers generally accept EN certification alone.

Quick check list

• The ten-step design flow was followed.
• The reason ESFR is unsuitable is stated in writing.
• Commodity and storage geometry match the listing.
• K-factor and design head count match the table.
• In-rack hydraulics calculated as a parallel branch.
• Ceiling pressure exceeds in-rack pressure.
• Hydraulic report ready for the insurer.
• Foam-water system listed, where used.

Frequently Asked Questions

What decides the CMSA K-factor?

The commodity and its storage geometry, taken from the manufacturer's listing — not the storage height alone. Typical values run K115 to K240, with 2–4 bar operating pressure.

How many sprinklers are assumed to operate in a CMSA design?

Between 15 and 30, depending on the commodity. Class III cartons and paper rolls are typically 15; Group A plastics and columnar tyres are typically 20; mixed plastics can reach 30.

Does storage geometry really have to match the listing?

Yes, exactly. A listing for tyres "palletized" does not cover tyres stacked columnar. This mismatch is one of the most common reasons an insurer rejects a CMSA installation.

Must in-rack heads be calculated separately?

Yes — as a parallel hydraulic branch. Calculating only the ceiling branch is a recurring error that surfaces at commissioning, when in-rack pressure falls well short.

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