On behalf of and in cooperation with NAM, the University of Twente (UT) has carried out an investigation into the compression forces on the lumbar verte-bral column at the level L5-S1 during drops with a 8-metre long Free-Fall Lifeboat, used for the training of offshore personnel.

The following questions were posed:

  • What is the effect of two different seat positions at a drop height of 15.5 m:

    • where a seat is reclined at 15° and facing the stern of the boat?

    • where a seat is reclined at 75° and facing the bow of the boat?

  • What is the effect of different drop heights (5, 10, 15.5 and 20 m)?

In addition,it was requested that the permissibility of the calculated com-pression forces be estimated.

Using the 3-D computer man model TADAPS, approximate calculations have been made of the compression forces for the various situations.

From the results, it can be concluded that there is a substantially lower maximum compression force for the seat reclined at 75° than for that reclined at 15°.

Evaluating the results, using the NIOSH standard and a safety factor of 1.25 for the model approximation, the following conclusions can be made:

  • The seat reclined at 15° remains below the permissible limit at a drop height of 10 m;

  • The seat reclined at 75° remains below the permissible limit at a drop height of 15.5 m.

It is recommended that seats reclined at 75°, facing forwards, be used for the Free-Fall Lifeboat under investigation. Furthermore, the training drop height, based on the NIOSH standard, should be 15 m.

Higher 'drops' are only permissible, under emergency conditions.

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