From block stacking to drive-in racking: separating the six storage configurations defined in EN 12845 and the ceiling and in-rack logic behind each, from a site perspective.
Starting a sprinkler revision at an e-commerce warehouse, the architectural drawings said "racking", the client said "we're putting in drive-in", and an earlier insurer's report carried the note "ST4 protection". Fitting three different configurations into one hydraulic calculation is impossible, because EN 12845 ties each storage type to a different protection regime. This article takes the ST1–ST6 classes one by one and summarises which decision to take when.
Where the standard covers it
EN 12845:2015+A1:2019 addresses this in three places: the definitions of the six configurations; the criteria for high-hazard storage protection by ceiling sprinklers alone; the criteria for intermediate in-rack sprinklers; a table of maximum block area, aisle width and perimeter clearance for each ST; and the provisions for sprinklers beneath solid shelving in ST5 and ST6. It is read together with the commodity categories (I–IV): the category constrains the product, the ST constrains the storage method.
The six configurations at a glance
ST1 Free standing / block stack ST2 Post pallet, single row
+--------+ +--------+ [P][P][P] ---- [P][P][P]
| GOODS | | GOODS | [P][P][P] 2.4m [P][P][P]
| BLOCK | | BLOCK | [P][P][P] ---- [P][P][P]
+--------+ +--------+ single row caged pallets
ST3 Post pallet, multiple row ST4 Palletised (beam) racking
[P][P][P][P][P] ---- |=|=|=| ---- |=|=|=|
[P][P][P][P][P] 2.4m |=|=|=| >1.2m |=|=|=|
[P][P][P][P][P] ---- |=|=|=| ---- |=|=|=|
adjacent cages, no internal aisle beam rack, intermediate levels
ST5 Solid shelf, w <= 1 m ST6 Solid shelf, 1 m < w <= 6 m
|--shelf--| ---- |------ shelf 1-6 m -------|
|--shelf--| 1.2m+ |------ shelf 1-6 m -------|
|--shelf--| ---- |------ shelf 1-6 m -------|
narrow solid or slatted shelving wide solid shelving, water-tight
ST1 — free standing / block stacking
Goods stacked directly on the floor on pallets, in cases, sacks or bulk bags. No racking; the stack stands on the strength of the goods themselves. Ceiling sprinklers can reach the heat effectively and no internal protection is needed. Block area is limited to 50 m² in ordinary hazard and 150 m² in high hazard, with 2.4 m of perimeter clearance mandatory. Reading the ST1 row, Category I can reach 5.3 m at 7.5 mm/min, while at 30 mm/min Category IV comes down to 4.4 m. In practice ST1 is the most comfortable configuration for sprinkler design.
ST2 — post pallet, single row
Framed post pallets arranged in single rows with at least 2.4 m of aisle between them. Although it looks like racking, there are no load-bearing uprights; the stack stands on the pallet frames. Ceiling protection again dominates. Block area is 50 m² in ordinary hazard, while in high hazard with aisles kept wider than 2.4 m the block area is unlimited. ST2 and ST4 share a row in the ceiling-only table: 4.7 m for Category I at 7.5 mm/min, and 4.4 m for Category IV at 30 mm/min.
ST3 — post pallet, multiple row
The multiple-row (double or more) version of ST2, with post pallets adjacent and no aisles between them. That makes it harder for ceiling water to reach the pallets in the interior, so ST3 is tightly limited to 50 m² in ordinary hazard and 150 m² in high hazard, with 2.4 m of perimeter clearance mandatory.
ST4 — palletised (beam) racking
Beam pallet racking with load-bearing uprights and horizontal beams — the backbone of European logistics. The rules draw fine distinctions:
- Aisle below 1.2 m: in-rack sprinklers mandatory, three racks counted in the hydraulics.
- Aisle 1.2–2.4 m: in-rack mandatory, two racks counted.
- Aisle 2.4 m or more: in-rack mandatory, one rack counted.
- High hazard protection is possible without in-rack, but once the clearance between ceiling deflector and goods exceeds 4 m, in-rack becomes mandatory.
For ST4: 4.7 m for Category I at 7.5 mm/min, 5.0 m for Category II at 12.5 mm/min, and 4.4 m for Category IV at 30 mm/min. Above those heights you move to the in-rack table.
ST5 — solid or slatted shelving, w ≤ 1 m
Back-to-back or single solid (water-tight) or slatted shelving with a total width no greater than 1 m. Here ceiling water cannot reach the internal levels; each shelf level needs its own water. Ordinary hazard allows a 50 m² block with aisles of 1.2 m or more. In high hazard without in-rack, 150 m² with aisles below 1.2 m; with in-rack and aisles of 1.2 m or more, the block area is unlimited.
For ST5 (s ≤ 1.0 m), one row of intermediate sprinklers is placed beneath every solid shelf level, at 2.8 m spacing.
ST6 — solid shelving, 1 m < w ≤ 6 m
The configuration the standard treats most cautiously. Wide solid shelving — retail gondolas, compact archive shelving, mid-store gondolas — is too closed for ceiling sprinklers to reach the goods. The standard recognises only one exception for ordinary hazard: a gondola of 1.2 m total width with a full-height central barrier. All other ST6 arrangements fall directly under high hazard protection.
ST6 is accepted only with high hazard protection plus in-rack sprinklers: 150 m² block, 1.2 m aisles, 2.4 m perimeter. For shelving:
- 1.0 m < s ≤ 3.0 m: one row of intermediate sprinklers at 2.8 m spacing.
- 3.0 m < s ≤ 6.0 m: two rows, at 2.8 m and 2.8 m.
Where in-rack sprinklers are physically impossible, full-height blind barriers of EN 13501-1 class A1 or A2 are installed longitudinally and transversely within each shelf.
Mobile racking and drive-in: the standard's grey zone
Mobile racking (palletised racking on rails) and drive-in or drive-through racking do not receive their own ST code. Field practice:
- Mobile racking: treated as a variant of ST4. Aisles close as the racks move, so the hydraulic calculation assumes the worst case — all aisles closed, three racks counted for in-rack. A pump-to-rack interlock is recommended, sending the racks to a separated position when the system activates. The standard flags this as a risk requiring specific study, and most insurers direct it to their own data sheets.
- Drive-in and drive-through: aisle-free configurations where forklifts enter the racking. Ceiling sprinklers cannot reach the goods; it resembles ST3 but the height is usually 6–9 m. Because EN 12845 does not define it directly, the project generally proceeds through joint in-rack design with the rack manufacturer plus a commodity category selection. NFPA 13 is far more explicit here, defining specific sprinkler arrangements for drive-in racking. On European projects, the insurer's report is decisive.
A single decision table
| ST | Description | Typical protection | OH block (m²) | HH block (m²) |
|---|---|---|---|---|
| ST1 | Free standing / block stacking | Ceiling only is sufficient | 50 | 150 |
| ST2 | Post pallet, single row (≥ 2.4 m aisle) | Ceiling only; unlimited in high hazard | 50 | Unlimited |
| ST3 | Post pallet, multiple row | Ceiling, with in-rack recommended in high hazard | 50 | 150 |
| ST4 | Palletised (beam) racking | In-rack by aisle width and height | 50 | Unlimited |
| ST5 | Solid shelving, w ≤ 1 m | One in-rack row beneath every solid level | 50 | 150 / unlimited |
| ST6 | Solid shelving, 1 m < w ≤ 6 m | High hazard plus in-rack only (or barriers) | — | 150 |
The errors most often made on site
- "Drive-in racking is ST4 too". Beam racking and drive-in are not the same category; drive-in is an aisle-free variant not directly covered by the standard, and it requires a specific study.
- Treating ST1 as unlimited area. ST1 is limited to a 50 m² block in ordinary hazard, and dividing the block area in a multi-level e-commerce warehouse needs a 2.4 m clear aisle.
- Ceiling sprinklers only over ST5 and ST6 shelving. A design without sprinklers beneath solid shelving will not be approved, and insurers will not accept it.
- A static hydraulic calculation for mobile racking. When the aisles close in motion, the number of effective racks changes; without a worst-case calculation, the pump falls short.
- Skipping the 4 m clearance provision. Once ceiling-to-goods clearance exceeds 4 m, either the density rises or in-rack sprinklers are added; without that, the ceiling-only table values are invalid.
Comparison with NFPA
NFPA 13 runs storage protection through a commodity class and storage method matrix. There is no direct equivalent to the ST codes, but the approximate mapping:
- ST1 ≈ palletised / solid-piled storage
- ST2 ≈ single-row rack
- ST3 ≈ double-row rack
- ST4 ≈ multiple-row rack (beam)
- ST5 ≈ solid shelf rack (narrow)
- ST6 ≈ solid shelf rack (wide) — NFPA is equally aggressive here, requiring sprinklers beneath every level or barriers
On the NFPA side, ESFR solutions without in-rack protection are far more common. EN 12845 handles ESFR separately in EN 12845-2:2024, partly removing the storage height limits. But ST6 solid shelving stays closed even with ESFR; internal protection remains indispensable.
Turkish context
BYKHY permits sprinkler design to TS EN 12845 or NFPA 13. The configurations most often seen in Turkish logistics warehouses are ST1 (food warehouse block stacking), ST4 (e-commerce beam racking) and ST5/ST6 (retail store and pharmacy gondolas). Insurers ask "which ST under EN 12845?" from the first day of the project; the hydraulic calculation firms up only when the client answers. Changing the ST late in design means rewriting the pump, the tank volume and the pipework from scratch.
Frequently asked questions
What is the difference between ST1 and ST3?
ST1 is free block stacking on pallets, with no racking. ST3 arranges framed post pallets in multiple adjacent rows. Both are limited to 50 m² blocks in ordinary hazard and 150 m² in high hazard, with 2.4 m of perimeter clearance.
When are in-rack sprinklers mandatory in ST4?
Once the clearance between the ceiling deflector and the top of storage exceeds 4 m, either the density rises (+2.5 mm/min for the first metre, +1 mm/min thereafter, minimum K115) or in-rack levels are added. Exceeding the ceiling-only height limits also brings in-rack in.
Why is ST6 treated so restrictively?
Because solid or slatted shelving between 1 m and 6 m wide prevents ceiling water reaching the goods. EN 12845 accepts ST6 only under high hazard protection with in-rack sprinklers, or with full-height class A1/A2 barriers where in-rack is impossible.
Which ST category covers mobile racking?
None specifically; it is treated as a variant of ST4. Because aisles open and close in motion, the hydraulic calculation must assume the worst case with all aisles closed, and a rack interlock is generally added.
How do NFPA storage classes map onto the ST codes?
There is no exact mapping. NFPA commodity class constrains the product while the ST code constrains the storage method. Roughly: ST1 is palletised or solid-piled, ST2 and ST3 single and double-row rack, ST4 multiple-row rack, ST5 and ST6 solid shelf rack.
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Download MEP Calc on the App StoreBS EN 12845:2015+A1:2019 Fixed firefighting systems — Automatic sprinkler systems. EN 12845-2:2024 (CMSA & ESFR sprinkler systems). NFPA 13 Standard for the Installation of Sprinkler Systems. Turkish Regulation on Fire Protection of Buildings (BYKHY). FM Global Property Loss Prevention Data Sheet 2-0.