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.