Forensics

Rack Collapses

Efficient utilisation of storage space is increasingly effected by the installation of storage racking systems. Goods are packed onto standard pallets that are lifted into modularised slots many tiers high. Although the designs of these systems are superficially similar, there is significant differences in the fine detail that give rise to structural problems that either exist at the outset or develop in service. The designs are now so fine-tuned that if a section fails, the collapse can carry through to involve the whole of the installation. We have seen rack collapses that involve as many as 1100 pallet positions.

Rack designs can be considered in two categories, as follows.

Selective Racking

Collapse of selective racking system in Malaysia

This configuration places all loads on an aisle and is the most commonly used in industry as it provides efficient use of space, yet it allows immediate access to everything in storage. The rack consists of vertical columns (frames) which support horizontal load-supporting members (beams). The front and rear column sections are tied together by horizontal braces.

Drive-in/thru Racks

Collapse of drive-through racking system in Thailand

This design has bays three or more loads deep. To allow a forklift or other device access to the loads, instead of the pallets straddling load beams front-to-rear, parallel to the aisle; they straddle load beams (support rails) left-to-right, perpendicular to the aisle. These systems offer a highly efficient method of storing large quantities of similar loads by allowing the forklift driver to enter the rack system and place the load on structural rails. A drive-thru rack is merely a drive-in rack that is accessible from both sides of the rack.

Failure Analysis

Collapse of drive-through racking system in Indonesia

Each design of rack has its inherent strengths and weaknesses. The weaknesses will be exacerbated by poor maintenance and methods of usage. We have investigated rack collapses in Malaysia, Indonesia and Thailand, including selective, drive-in and drive-thru racking designs. Rack collapses are best investigated at site, before the collapsed sections are removed. Our engineers are available to attend accident sites.

Collapse of drive-in racking system in Indonesia
Collapse of drive-in racking system in Malaysia
Snapshot sequence of rack collapse as captured by CCTV
1. Forklift reversing into bay 2. Rack begins to collapse. Note startled looks from workers
3. Rack continues to collapse. Workers begin to move 4. Rack has collapsed. Workers at a safe distance. Forklift driver was not seriously injured