The height to depth ratio of your pallet racks could be putting you at risk.
With the weak economy, the temptation to buy used or uncertified pallet racks can become a safety, operational, or liability danger if warehouse owners and managers aren’t careful. In warehouse, distribution, and retail settings where selective rack is used, for instance, the height to depth rack ratio in low seismic areas must meet Rack Manufacturers Institute (RMI) specification to prevent pallet rack damage and tipping safety hazards.
“The RMI specification, which the International Building Code (IBC) references for the design of steel storage rack, must be met or permitting can be delayed, but not everyone may know about it,” says Anne Russell, senior structural engineer at Steel King, designer and manufacturer of warehouse storage rack, pallet rack and material handling products. “This is particularly common when dealing in used rack or smaller warehouse operations. The risk of rack tipping increases where fork trucks operate or when racks are loaded improperly.”
As a prime example, Russell points to American National Standards Institute (ANSI) code MH-16.1 2008, which is the RMI specification for the design, testing, and utilization of industrial steel storage racks.
“If a vendor is RMI-compliant or offers a calculation package for the permit process, the rack is automatically designed to spec,” says Russell. “But that’s not always the case.”
While avoiding the overloading at the top of pallet racks and installing more robust base plates can help to minimize the risk of a pallet rack tipping, it’s not always enough.
For warehouse owners and managers who may be uncertain whether their pallet rack or storage rack meets RMI specs for height to depth rack ratio in low seismic areas—which may put them at risk of a pallet rack tipping—Russell offers some guidelines:
When taking into account the height to depth ratio of the rack, the height would be the dimension to the top loaded shelf level and not necessarily the height of the upright, unless the top loaded beam level is at the top of the rack. For instance, if the upright height is 300", but the top loaded shelf level is 284 inches and the upright depth is 48 inches, the height to depth ratio would be 284/48 (5.9 to 1). This is acceptable (less than 6 to 1 as specified in the RMI code) so no special action may be required.
However, if the height to depth ratio is between 6 to 1 and 8 to 1, either oversized base plates or the use of row spacers in back-to-back configurations will be needed.
If any selective pallet rack in low seismic areas has a height to depth rack ratio larger than 8 to 1, it will, more than likely, require row spacers or cross-aisle ties.
“Whether redoing warehouse rack design or putting in new rack, warehouse owners and managers want to be certain they aren’t being penny wise and pound foolish by neglecting some important but not always well known codes,” says Russell. “Meeting RMI storage rack specs for height to depth rack ratio in low seismic areas is one such instance that can help prevent pallet rack damage and tipping safety hazards. For these and other important guidelines, it’s important to work with a trusted RMI-certified vendor.”
Del Williams is a technical writer based in Torrance, California.