How many layers can the ISO containers&offshore containers be stacked?

Whatever the container is used for, the key to workplace safety and preventing employee injury is correctly stacking. So how to safety stack ISO containers or DNV2.7-1 offshore containers and What is the maximum number of ISO shipping containers or the DNV2.7-1 offshore containers in a stack? 

• ISO Container stacking layers:
  ​Shipping ISO containers may be stacked up to nine layers.

• DNV 2.7-1 offshore containers module stacking layers: 

      For the offshore functional containers for living playing or working purpose, such as potable offshore              office, portable offshore lab package or offshore accommodation, we recommend a height of no more            than 2 units.
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      A height of three floors or more will require more modification work to ensure that the final build is                  structurally safe, as well as a wider range of administrative tasks, such as planning permission                      applications.

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