Box manufacturer's certificates 2010

Here are some perspectives on Mullen vs. ECT in relation to certifying corrugated boxes.

Sterling Anthony, CPP
Sterling Anthony, CPP
In 1991, the edge crush test (ECT) became an alternative to the bursting strength test (a.k.a Mullen) as a declaration on box manufacturer's certificates (BMCs). Much has occurred during the almost two decades since, justifying a retrospective and a look ahead.

Mullen from the start

At the inception of carrier regulations requiring BMCs, Mullen (along with its associated basis weight) was the only permitted declaration that a corrugated box met construction requirements. First came Rule 41 (circa 1919) for rail carriers, followed by Item 222 (circa 1968) for truck carriers. Mullen measures the force (in pounds per square inch) required to burst the combined board, making it an intuitive, though indirect, measure of the box's ability to withstand rough handling. Since rough ride also was a concern, this article will use the term "rough conditions" to denote both. The convenient, somewhat forced association is that bursting strength is reflective of rough conditions encountered in the distribution channel.

Carriers published the aforementioned regulations to manage their liability under damage claims by shippers, the understanding being that a shipper's failure to comply with the regulations can invalidate damage claims. That's good business thinking, but why the emphasis on rough conditions? Back then, there was less mechanical-handling of cargo than there is today and manual-handling is rougher. In addition, transportation equipment didn't have the shock-dampening and suspension systems that are now commonplace.
 
That history only partially explains why Mullen lasted as long as it did as the only test permitted on BMCs, despite its indirectness as a measure. The rest of the explanation is mostly due to the stakeholder's deriving benefits from standardizing on Mullen. Carriers faced fewer claims, shippers suffered fewer damaged goods, and board/box-makers gained efficiencies from tooling for long runs of Mullen-grade board/boxes. An example of the comfort level developed with Mullen is the wide diversity of products shipped in what became an industry workhorse: 200 lb. test C-flute. Even so, successful results from the use of Mullen-grade board/boxes is not proof that the test directly relates to rough conditions.

ECT comes on board

A box that can withstand rough conditions, nonetheless, might fail under the compression of stacking. The consequences can range from damage to a single box to the collapse of an entire unitized load. Those recognitions were behind ECT's being incorporated into carrier regulations and appearing on BMCs.

ECT measures the force (in pounds per linear inch) required to crush a sample of board standing on an edge. The result is regarded as an indicator of the compression strength (the force that can be withstood momentarily before causing collapse) of a box made from the board; therefore, there is some indirectness, although not as much as with Mullen. Arguably, compression strength is not as relevant a measure as stacking strength (the force the box can withstand throughout its time in the distribution channel). The two measures are steeped in formulas and estimates, and even incorporate another measure (ring crush test), aspects that increase complexity and imprecision.
 
Despite such shortcomings, ECT has become the dominant method of declaration on BMCs. And it's not only because ECT addresses storage and warehousing more than Mullen does; rather, ECT provides cost-savings to the shipper. Unlike a Mullen certificate, an ECT one doesn't mandate that the corrugated board have "minimum combined weight facings," in other words, minimum basis weight (pounds per 1,000 sq. ft.). That allows the use of lighter-weight, less-costly board for ECT-graded boxes. Board/box- makers, in turn, can provide a specified ECT-grade from a variety of basis weights for facings and a variety of calipers for mediums, to meet their own profit objectives.
 
Separate and not equal

Mullen and ECT, as already noted, purport to measure separate properties of the box; hence, there is no equivalence between them, not in the way that inches can be converted to centimeters, for example. Such equivalency, however, is implied (if not explicitly asserted) by carrier regulations and board/box makers. The resulting overlaps in these supposed equivalencies are not unexpected, in that a specified Mullen rating is associated with more than one ECT rating.
 
The shipper, therefore, should never assume that a specified ECT-grade box automatically provides sufficient bursting strength or that a specified Mullen-grade box automatically provides sufficient stacking strength. Grade has no intrinsic meaning other than designating that the board was manufactured to give a specified rating on a specified test.
 
So, how does a shipper specify the designation that will appear on the BMC? The shippers with the easiest go of it are those whose distribution-channel model clearly favors a particular designation: parcel shipments favor Mullen; unitized, truck/boxcar-loads, shipped through a network of warehouses or distribution centers favor ECT. But most shipments fall in between those two models, thereby requiring more than modest protection from rough conditions and compression. This can be achieved when the box is built against a specification that calls for a particular Mullen rating, for example, even though the ECT rating will be printed on the BMC (and vice-versa). Knowing what the respective ratings should be may require a combination of experience, laboratory testing, test shipments, and supplier assistance. There is software available that performs analysis and calculations related to ECT, but the output is only as good as the input.

Throw in sustainability (of course)

Although cost-savings were initial drivers of the growth of ECT ratings on BMCs, the sustainability era has accelerated the trend and complicated matters, in the bargain. The increasing percentage of recycled fiber incorporated into box-making increases the difficulty of controlling the consistency of quality and performance. Two boxes with the same percent of recycled fiber won't necessarily yield identical test grades (whether Mullen or ECT), due to one's containing fibers that have been recycled more times, with each time having shortened and weakened the fibers.
 
And even if the smaller carbon footprint claimed by promoters of ECT-grade board/boxes is to be taken as gospel, box performance is the ultimate arbiter of sustainability. If the ECT box does not serve its intended function and allows its contents to be damaged beyond use, all of the resources that went into box and contents will have been wasted.

As a final mention, there are other trends and drivers that will affect box certification throughout the foreseeable future, not the least of which is globalization. Harmonization of regulations will be a formable task, especially given certain countries' practices of using in their boxboard indigenous materials that are quite different than materials used in the U.S. It's possible that the Mullen-ECT dichotomy might become a thing of the past. Then again, having to grapple with diametrically opposed scenarios is merely par for the course in the world of packaging.

Sterling Anthony is a consultant, specializing in the strategic use of marketing, logistics, and packaging.  His contact information is: 100 Renaissance Center-176, Detroit, MI 48243; 313-531-1875 office; 313-531-1972 fax; sterlinganthony1@sbcglobal.net.
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