FM Global DS 8-34: Top-Loading ASRS and Crane-Based Pallet AS/RS

In a top-loading ASRS (TL-ASRS), containers are stacked one on top of another in vertically aligned columns beneath a metal grid, and robots travelling on top of the grid lift containers out and return them (DS 8-34 Section 3.1.2, Appendix A). The containers are almost always open-top and made of plastics such as HDPE or polypropylene. Because no forklifts are needed, there are no aisles between the arrays (3.1.2.1, Appendix A). Classic crane-based pallet warehouses are not covered by DS 8-34; the last section of this article explains which data sheet applies to them.

General Rules (Sections 2.3.1–2.3.4)

• Section by container type: FM Approved non-flame propagating containers 2.3.1, solid-walled containers 2.3.2 (small systems 2.3.2.2, ceilings up to 9.1 m 2.3.2.3, ceilings over 9.1 m 2.3.2.4), non-solid-walled containers 2.3.3, and non-solid-walled containers combined with FM Approved non-flame propagating containers 2.3.3.13. Open-top containers with gridded bottoms are outside the scope (1.0).
• Drainage: where possible, a curb at least 100 mm high around the array with floor drainage sized for both the ceiling sprinkler discharge and the expected hose stream application (2.3.2.1.5.1).
• Robots: as little exterior combustible material as possible, with any covers or trim made of noncombustible material (2.3.2.1.2.1).
• Robot holding areas: designated areas on the grid to which all robots move on detection; they must not be designated where a fire service access point has been established, and their storage columns must be kept free of combustibles (2.3.2.1.3).
• Detection: FM Approved very early warning fire detection at ceiling level per DS 5-48; under an unobstructed ceiling, detector spacing must not exceed 50% of the maximum listed in the Approval Guide. On activation the system alarms to a constantly attended location, sends the robots to the holding areas and deactivates the charging stations (2.3.2.1.4).

Ceiling Sprinkler Protection

• FM Approved non-flame propagating containers (2.3.1): where they are used throughout, the ceiling protection is designed, as a minimum, for the adjacent occupancies; where other containers are also present, design for the worst-case container (2.3.1.1, 2.3.1.2).
• Combustible solid-walled containers (2.3.2): wet, single-interlocked preaction or antifreeze systems; dry-pipe systems are not among the options (2.3.2.1.6.1). For ceilings up to 9.1 m (storage up to 6.1 m), Table 2.3.2.3.3.1 with a wet system only, a 950 L/min hose demand and a water supply of at least 2 hours; for ceilings over 9.1 m up to 13.7 m, Table 2.3.2.4.6.1 for storage up to 6.1 m and Table 2.3.2.4.6.2 for storage from 6.1 to 7.6 m, a 1,900 L/min hose demand and a water supply of at least 4 hours; a false ceiling beyond 13.7 m.
• Non-solid-walled containers (2.3.3): the array is divided into subdivisions by voids at least 1.2 m wide or by walls, with storage no higher than 7.6 m; wet or antifreeze systems only; minimum K14.0 (K200) quick-response pendent sprinklers for ceilings up to 12.2 m and at least 455 L/min from the most remote sprinkler; hose demand 1,900 L/min and a water supply of at least 4 hours.

Final Extinguishment and Fire Service Access

In a TL-ASRS the fire service has no direct access to the fire, so DS 8-34 includes a dedicated final extinguishment section for combustible containers (2.3.2.1.1, 2.3.2.3.1, 2.3.2.4):

• A pre-incident plan with the fire service covering access to the grid, where removed containers will go, where the robot holding areas are, and letting the ceiling sprinkler system operate for at least 2 hours or until the fire service confirms the fire is out (2.3.2.1.1).
• Clearly marked access points along the side walls, and consideration of limiting the distance from one end of the array to the other to 30 m (2.3.2.3.1.1–2.3.2.3.1.2, 2.3.2.4.2.2, 2.3.2.4.2.5).
• Mezzanines or platforms along the longer walls at or above grid level; a single platform suffices where the array is no more than 15 m wide. Where the array exceeds 30 m in both directions, solid-floored elevated mezzanines are needed (2.3.2.3.1.3, 2.3.2.4.2.1–2.3.2.4.2.3).
• Alternative: a wet ceiling system per Table 2.3.2.3.3.1 (storage up to 6.1 m, ceiling up to 9.1 m) with a water supply of at least 2 hours and a 950 L/min hose demand, in which case elevated mezzanines and fixed monitors are not called for (2.3.2.3).
• In addition, for ceilings over 9.1 m: fixed monitor nozzles no more than 30 m apart and within 15 m of the array corners, each delivering at least 760 L/min, guided by infrared cameras; and small hose stations delivering 190 L/min from each of the two most remote (2.3.2.4.3–2.3.2.4.5).

Crane-Based (Stacker Crane) Pallet AS/RS

DS 8-34 covers systems that handle small containers and trays. For pallet-based "rack structure ASRS", with bays sized for a single pallet load and pallets resting on roller conveyors or on supports perpendicular to the aisle, the protection guidelines are in FM DS 8-9 (DS 8-34 Appendix A). Ceiling and in-rack sprinkler selection for crane-served pallet warehouses therefore follows the rack storage provisions of DS 8-9; DS 8-34 contains no tables specific to them.

The loss history in DS 8-34 (Section 3.2) describes the collapse of a rack-supported ASRS at a non-FM-client location on 13 July 2002: reportedly caused by deficient welding and design of the rack framing, the domino-style collapse led to paper goods in the racks being ignited by the building's lighting system, and the building, reportedly ten storeys high and 10,685 m² in area, was completely lost. The case shows that rack anchorage and structural design (2.2.1.3) are part of the protection concept.

Quick Checklist

• System type identified: top-loading (DS 8-34 Section 2.3) or pallet-based rack structure ASRS (DS 8-9)
• Container type: FM Approved non-flame propagating, solid-walled or non-solid-walled; no gridded-bottom open containers
• Very early warning detection, robot holding areas and charging station shutdown defined
• Curbing and drainage around the array planned
• Ceiling sprinkler design from Table 2.3.2.3.3.1, 2.3.2.4.6.1 or 2.3.2.4.6.2 (2.3.3.10 for non-solid-walled containers); water supply duration of 2, 3 or 4 hours established
• Fire service access: access points, platforms or mezzanines, and monitors and cameras where needed
• Pre-incident plan prepared with the fire service

Frequently Asked Questions

Why is fire protection different for a top-loading ASRS?

Containers are stacked in columns with no aisles and the robots access them from above, so the fire service has no direct route to the fire. DS 8-34 therefore adds very early warning detection, robot holding areas and final extinguishment measures such as platforms, fixed monitors or extended sprinkler operation to the ceiling sprinkler tables (Section 2.3).

What do TL-ASRS robots do when a fire is detected?

The detection system alarms to a constantly attended location, sends the robots to designated robot holding areas and deactivates the charging stations (DS 8-34 2.3.2.1.4.4). Holding areas must not be designated where a fire service access point has been established, and their storage columns must be kept free of combustibles (2.3.2.1.3.2, 2.3.2.1.3.3).

Can a dry-pipe sprinkler system be used over a TL-ASRS?

It depends on the container. Where FM Approved non-flame propagating containers are used throughout, the ceiling protection follows the design for the adjacent occupancies (2.3.1.1). For solid-walled containers the options are wet, single-interlocked preaction and antifreeze systems (2.3.2.1.6.1); non-solid-walled containers are limited to wet or antifreeze systems (2.3.3.8.1), although a dry ceiling design is given where non-solid-walled containers are combined with FM Approved non-flame propagating containers in a checkerboard pattern (2.3.3.13.2, 2.3.3.13.3.3). For solid-walled containers under ceilings up to 9.1 m, the Table 2.3.2.3.3.1 designs require a wet system (2.3.2.3.2.1).

Are crane-based pallet warehouses protected under DS 8-34?

No. DS 8-34 covers ASRS handling small containers and trays. For pallet-based rack structure ASRS with bays sized for a single pallet load, DS 8-34 Appendix A refers to FM DS 8-9, and ceiling and in-rack sprinklers are selected under that data sheet's rack storage provisions.

How long must the water supply last for a TL-ASRS?

For solid-walled containers, at least 2 hours for ceilings up to 9.1 m (2.3.2.3.5.1) and at least 4 hours above (2.3.2.4.8.1). At least 4 hours for non-solid-walled containers (2.3.3.12.1), and at least 3 hours where non-solid-walled and FM Approved non-flame propagating containers are combined (2.3.3.13.5.1).

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