Sensitivity analysis of the spinal load model used in the draft standard ISO 2631-5

In the 1990’s, Seidel et al. applied a biomechanical approach to develop a new method to assess the health effects caused by WBV on seated drivers. Their works were based on the assumption that intervertebral pressure may cause damage to the lumbar spine and thus lead to low back pain. As the measurement of intervertebral pressure is too invasive, a finite element model developed by Wölfel GmbH was used as an alternative to calculate transfer functions describing the relationship between vehicle accelerations and intervertebral pressures. These transfer functions were finally coupled to a risk model and integrated in a risk assessment software application. This assessment method is currently being discussed in the framework of a draft standard for ISO-2631-5. The INRS has investigated the responses of the risk assessment software to various input conditions (acceleration input signals, anthropometrical driver parameters and seated postures). Particular attention was paid to responses to Gaussian random accelerations. An alternative but equivalent method of calculating the vibration dose used in the risk assessment software is presented. This alternative method, whose theoretical backgrounds were first published by Cartwright in 1956, is limited to Gaussian signals. However it has the significant advantage of being able to calculate the vibration dose value without requiring an automatic peak detection algorithm.