49 C.F.R. § 178.1055 – Stacking test.

(a) General. The stacking test must be conducted for the qualification of all Flexible Bulk Containers design types.
(b) Special preparation for the stacking test. All Flexible Bulk Containers design types must be loaded to their maximum permissible gross mass.
(c) Test method.
1. (1) All Flexible Bulk Containers must be placed on their base on level, hard ground and subjected to a uniformly distributed superimposed test load that is four times the design type maximum gross weight for a period of at least twenty-four hours.
2. (2) For all Flexible Bulk Containers, the load must be applied by one of the following methods:
  1. (i) Four Flexible Bulk Containers of the same type loaded to their maximum permissible gross mass and stacked on the test Flexible Bulk Container;
  2. (ii) The calculated superimposed test load weight loaded on either a flat plate or a reproduction of the base of the Flexible Bulk Container, which is stacked on the test Flexible Bulk Container.
(d) Criteria for passing the test. There may be no deterioration that renders the Flexible Bulk Container unsafe for transportation and no loss of contents during the test or after removal of the test load.